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1.
Geobiology is a new discipline on the crossing interface between earth science and life science,and aims to understand the interaction and co-evolution between organisms and environments.On the basis of the latest international achievements,the new data presented in the Beijing geobiology forum sponsored by Chinese Academy of Sciences in 2013,and the papers in this special issue,here we present an overview of the progress and perspectives on three important frontiers,including geobiology of the critical periods in Earth history,geomicrobes and their responses and feedbacks to global environmental changes,and geobiology in extreme environments.Knowledge is greatly improved about the close relationship of some significant biotic events such as origin,radiation,extinction,and recovery of organisms with the deep Earth processes and the resultant environmental processes among oceans,land,and atmosphere in the critical periods,although the specific dynamics of the co-evolution between ancient life and paleoenvironments is still largely unknown.A variety of geomicrobial functional groups were found to respond sensitively to paleoenvironmental changes,which enable the establishment of proxies for paleoenvironmental reconstruction,and to play active roles on the Earth environmental changes via elemental biogeochemical cycles and mineral bio-transformations,but to be deciphered are the mechanisms of these functional groups that change paleoenvironmental conditions.Microbes of potential geobiology significance were found and isolated from some extreme environments with their biological properties partly understood,but little is known about their geobiological functions to change Earth environments.The biotic processes to alter or modify the environments are thus proposed to be the very issue geobiology aims to decipher in the future.Geobiology will greatly extend the temporal and spatial scope of biotic research on Earth and beyond.It has great potential of application in the domains of resource exploration and global change.To achieve these aims needs coordinative multidisciplinary studies concerning geomicrobiology and related themes,database and modeling of biogeochemical cycles,typical geological environments,and coupling of biological,physical,and chemical processes.  相似文献   

2.
Results derived from the study of petrophysical properties and mineralogy of rocks, minerals, and model objects differing in formation conditions and composition are presented. Petromagnetic and paleomagnetic characteristics of rock samples are examined and modeling experiments on crystallization of ferromagnetic minerals are carried out in a wide region of pressures and temperatures. Minerals of rocks of different origins and ages (igneous and metamorphic rocks, xenoliths, and megacrystals) are studied, and the physicochemical conditions of their formation are reconstructed. Constraints are obtained on redox conditions of occurrence of rocks, the depth of magma chambers, and implications of secondary superimposed processes of metasomatism and metamorphism for variations in physical properties of Earth’s interior substance with depth. The structural factor is shown to be of great significance for the formation of magnetic properties of iron oxides. Using mineral geothermobarometry, the deep distributions of temperature and oxygen fugacity beneath volcanically active regions are estimated.  相似文献   

3.
地震层析成像中的不确定性   总被引：1，自引：0，他引：1  
地震层析成像已经是一种常用的探测地球内部三维波速结构的地球物理方法。这些深部地球结构信息是人们深入认识地球的重要依据,同时由于地表地质过程往往取决于深部动力过程,因此深部结构已经开始受到了地质学家们的广泛重视。但地震层析成像方法众多,所得到的参数和精度可能有所不同,这给非地震学专业的研究人员在使用层析成像结果的过程中造成了极大的不便。为了更好地实现地球物理,地球化学和地质等多学科交叉应用,本文系统分析了地震层析成像结果中可能存在的不确定性,同时提出了相应的建议以帮助地质学家们能够正确对待层析成像结果中的不确定性并合理利用地震层析成像结果。  相似文献   

4.
Using a fluorescence microscope and EPMA, abundant microbe ”bodies“ and clear microbic fluorescent microstructure are determined in the ferromanganese nodules recently collected from the East Pacific deep sea floor. The microbic fluorescent structure shows a close relation to the formation of the ferromanganese nodules. According to their morphological features, the microbes are classified into two types: one is named clumpy microbe, which takes a bar-shaped manganese mineral as a pillar and grows like fasciculate coral, resulting in irregular cauliflorate nodules with rough surfaces; the other is called filamentous microbe, which grows in very thin arcuate and/or concentric circular laminae composed of a microbe layer and a metal (manganese and iron)-rich layer, leading to potato-shaped nodules with relatively smooth surfaces. It also can be seen that the two types of microbes are intergrown together, resulting in nodules complicated in compositions and shapes.  相似文献   

5.
Determining Earth’s structure is a fundamental goal of Earth science, and geophysical methods play a prominent role in investigating Earth’s interior. Geochemical, cosmochemical, and petrological analyses of terrestrial samples and meteoritic material provide equally important insights. Complementary information comes from high-pressure mineral physics and chemistry, i.e., use of sophisticated experimental techniques and numerical methods that are capable of attaining or simulating physical properties at very high pressures and temperatures, thereby allowing recovered samples from Earth’s crust and mantle to be analyzed in the laboratory or simulated computationally at the conditions that prevail in Earth’s mantle and core. This is particularly important given that the vast bulk of Earth’s interior is geochemically unsampled. This paper describes a quantitative approach that combines data and results from mineral physics, petrological analyses of mantle minerals, and geophysical inverse calculations, in order to map geophysical data directly for mantle composition (major element chemistry and water content) and thermal state. We illustrate the methodology by inverting a set of long-period electromagnetic response functions beneath six geomagnetic stations that cover a range of geological settings for major element chemistry, water content, and thermal state of the mantle. The results indicate that interior structure and constitution of the mantle can be well-retrieved given a specific set of measurements describing (1) the conductivity of mantle minerals, (2) the partitioning behavior of water between major upper mantle and transition-zone minerals, and (3) the ability of nominally anhydrous minerals to store water in their crystal structures. Specifically, upper mantle water contents determined here bracket the ranges obtained from analyses of natural samples, whereas transition-zone water concentration is an order-of-magnitude greater than that of the upper mantle and appears to vary laterally underneath the investigated locations.  相似文献   

6.
Carbonates capping Neoproterozoic glacial deposits contain peculiar sedimentological features and geochemical anomalies ascribed to extraordinary environmental conditions in the snowball Earth aftermath. It is commonly assumed that post-snowball climate dominated by CO2 partial pressures several hundred times greater than modern levels, would be characterized by extreme temperatures, a vigorous hydrological cycle, and associated high continental weathering rates. However, the climate in the aftermath of a global glaciation has never been rigorously modelled. Here, we use a hierarchy of numerical models, from an atmospheric general circulation model to a mechanistic model describing continental weathering processes, to explore characteristics of the Earth system during the supergreenhouse climate following a snowball glaciation. These models suggest that the hydrological cycle intensifies only moderately in response to the elevated greenhouse. Indeed, constraints imposed by the surface energy budget sharply limit global mean evaporation once the temperature has warmed sufficiently that the evaporation approaches the total absorbed solar radiation. Even at 400 times the present day pressure of atmospheric CO2, continental runoff is only 1.2 times the modern runoff. Under these conditions and accounting for the grinding of the continental surface by the ice sheet during the snowball event, the simulated maximum discharge of dissolved elements from continental weathering into the ocean is approximately 10 times greater than the modern flux. Consequently, it takes millions of years for the silicate weathering cycle to reduce post-snowball CO2 levels to background Neoproterozoic levels. Regarding the origin of the cap dolostones, we show that continental weathering alone does not supply enough cations during the snowball melting phase to account for their observed volume.  相似文献   

7.
Microbes have been widely reported in the deep subseafloor environment. Still it is difficult to detect a global chemical signature of bacterial activity in the oceanic crust. We carried out experiments up to 355 days exposing very young oceanic basalts to anaerobe sulfate reducing organisms in an in-vitro marine environment. The Natural Remanent Magnetization of samples was monitored during the whole duration of experiments and within this time frame the most magnetized sub-samples lost up to 30% of their original signal. Scanning electron microscope observations show cycling of iron from the titanomagnetites to iron sulfide phases. Our results suggest that microbes can have a major and fast impact on the magnetization of young oceanic basalts and could contribute to a global signal as the central anomaly magnetic high seen along ridges axis.  相似文献   

8.
Melting temperatures of the silicate fraction of the Allende CV3 meteorite, at upper mantle pressures, are several hundred degrees lower than that of fertile peridotite xenoliths or ‘pyrolite’. If the Earth accreted from material similar to chondrites, then deep mantle melting could have occurred with a relatively modest heat budget. It is concluded that initial chemical composition is an important variable in realistic magma ocean models.  相似文献   

9.
The base of Earth's critical zone (CZ) is commonly shielded from study by many meters of overlying rock and regolith. Though deep CZ processes may seem far removed from the surface, they are vital in shaping it, preparing rock for infusion into the biosphere and breaking Earth materials down for transport across landscapes. This special issue highlights outstanding challenges and recent advances of deep CZ research in a series of articles that we introduce here in the context of relevant literature dating back to the 1500s. Building on several contributions to the special issue, we highlight four exciting new hypotheses about factors that drive deep CZ weathering and thus influence the evolution of life‐sustaining CZ architecture. These hypotheses have emerged from recently developed process‐based models of subsurface phenomena including: fracturing related to subsurface stress fields; weathering related to drainage of bedrock under hydraulic head gradients; rock damage from frost cracking due to subsurface temperature gradients; and mineral reactions with reactive fluids in subsurface chemical potential gradients. The models predict distinct patterns of subsurface weathering and CZ thickness that can be compared with observations from drilling, sampling and geophysical imaging. We synthesize the four hypotheses into an overarching conceptual model of fracturing and weathering that occurs as Earth materials are exhumed to the surface across subsurface gradients in stress, hydraulic head, temperature, and chemical potential. We conclude with a call for a coordinated measurement campaign designed to comprehensively test the four hypotheses across a range of climatic, tectonic and geologic conditions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
Experiments [T. Irifune (1994) Nature 370, 131–133; E. Ito et al. (1998) Geophys. Res. Lett. 25, 821–824; A. Kubo, M. Akaogi (2000) Phys. Earth Planet. Int. 121, 85–102] indicate that (Mg,Fe)SiO3 perovskite, commonly believed to be the most abundant mineral in the Earth, is the preferred host phase of Al2O3 in the Earth’s lower mantle. Aiming to better understand the effects of Al2O3 on the thermoelastic properties of the lower mantle, we use atomistic models to examine the chemistry and elasticity of solid solutions within the MgSiO3(perovskite)–Al2O3(corundum)–MgO(periclase) mineral assemblage under conditions pertinent to the lower mantle: low Al cation concentrations, P=25–100 GPa, and T=1000–2000 K. We assess the relative stabilities of two likely substitution mechanisms of Al into MgSiO3 perovskite in terms of reactions involving MgSiO3, MgO, and Al2O3, in a manner similar to the 0 Kelvin calculations of Brodholt [J.P. Brodholt (2000) Nature 407, 620–622] and Yamamoto et al. [T. Yamamoto et al. (2003) Earth Planet. Sci. Lett. 206, 617–625]. We determine the equilibrium composition of the assemblage by examining the chemical potentials of the Al2O3 and MgO components in solid solution with MgSiO3, as functions of concentration. We find that charge coupled substitution dominates at lower mantle pressures and temperatures. Oxygen vacancy-forming substitution accounts for 3–4% of Al substitution at shallow lower mantle conditions, and less than 1% in the deep mantle. For these two pressure regimes, the corresponding adiabatic bulk moduli of aluminous perovskite are 2% and 1% lower than that of pure MgSiO3 perovskite.  相似文献   

11.
The carbon cycle between the deep Earth and the atmosphere(i.e., the deep carbon cycle) can significantly affect the global climate on both long and short time scales. Although carbon in the deep Earth can be released to the atmosphere in many ways, plate subduction is the only pathway for the return of carbon from the surface to the deep Earth. Owing to diversity in the forms of carbon and the special physicochemical property of carbonates, the behavior of carbon and carbonates in subduction zones significantly affects the products of subduction processes, the oxygen fugacity in subduction zones, and the activation and migration of elements during the crust-mantle interaction. Therefore, the carbon cycle in subduction zones plays an important role in maintaining a habitable climate by regulating the atmospheric CO_2 concentration, which significantly affects the global climate, and in causing fundamental changes in the physical and chemical properties of the mantle that result in a heterogeneous mantle. In this study, we review and discuss previous studies and scientific problems regarding the carbon cycle in subduction zones from four aspects: observation and tracing of the carbon cycle, migration and variation of carbon during subduction,carbon flux, and the effect of the carbon cycle.  相似文献   

12.
《Journal of Geodynamics》2010,49(3-5):126-131
It is well known, that high resolution borehole tiltmeters are able to observe deformations, caused by hydrological variations. The quantitative coherence is often unexplained, especially if the sources of deformation can be based on both natural as well as man-made hydrological variations. Since 1999 tilt observations have been taken at the Geodynamic Observatory Moxa in Thuringia/Germany. In two 50 m and one 100 m deep boreholes the ASKANIA tiltmeters are installed. The high quality of the recorded tilt data can be proved by the analysis of well known geodynamic signals like the tides of the solid Earth and the free modes of the Earth. Here we focus on investigations of induced tilt signals caused by pore pressure changes due to precipitation and/or ground water level changes and, in addition, on man-made induced pore pressure variations. The correlation of natural ground water level changes with the observed tilt data can be shown by different events of precipitation and snow melting. However, also the load effect of a big truck yields a small elastic deformation which is clearly detectable in the ground water level recording. The correlated tilt effect is discussed regarding changes of the tilt amplitude and the orientation of the induced pendulum tip movement during the load phase.  相似文献   

13.
Understanding the effects of hydrological processes on solute dynamics is critical to interpret biogeochemical processes. Water chemistry and isotopic compositions of surface water (δ18Ow and δDw) were investigated in rivers from Southwest China to study the effects of hydrological variability on biogeochemical processes. The inverse relationship between deuterium excess (d-excess) and δ18Ow could be ascribed to non-equilibrium fractionation processes, and the slope of the Local River Water Line was much lower than the Local Meteoric Water Line, suggesting the post-precipitation evaporation pattern. The evaporation fraction (1–f) was estimated by the d-excess method, varying from 0.01 to 0.18. (1–f), was a function of water temperature and drainage mean elevation, indicating that evaporation easily occurs at high temperatures in low-elevation regions. The hydrological processes co-varied with solute dynamics in the river network, and fluid transit time and temperature were likely responsible for the co-variations. Also, we found that hydrological processes played an important role in solute dynamics through shifting the geochemical processes (e.g., enrichment, water-rock reaction, photosynthesis, and secondary mineral precipitation). This study highlights that biogeochemical processes co-vary with hydrological processes, and we suggest that investigating hydrological processes can help to understand biogeochemical processes.  相似文献   

14.
This paper examines groundwater hydrochemical characteristics during mixing between thermal and non-thermal groundwater in low-to-medium temperature geothermal fields. A case study is made of Daying and Qicun geothermal fields in the Xinzhou basin of Shanxi province, China. The two geothermal fields have similar flow patterns, with recharge sourced from precipitation in mountain areas heated through a deep cycle, before flowing into overlying Quaternary porous aquifers via fractures. Hydrochemical features of 60 ground- and surface water samples were examined in the context of hydrogeologic information. The average temperatures of the deep geothermal reservoirs are estimated to be 125 °C in Daying field, and 159 °C in Qicun field, based on Na–K–Mg geothermometry, while slightly lower estimates are obtained using silica geothermometers. Hydrochemical features of thermal water are distinct from cold water. Thermal groundwater is mainly Cl·SO4–Na type, with high TDS, while non-thermal groundwater is mostly HCO3–Ca·Mg and HCO3–Ca type in the Daying and Qicun regions, respectively. Hydrogeochemical processes are characterized by analyzing ion ratios in various waters. Higher contents of some minor elements in thermal waters, such as F, Si, B and Sr, are probably derived from extended water–rock interaction, and these elements can be regarded as indicators of flow paths and residence times. Mixing ratios between cold and thermal waters were estimated with Cl, Na, and B concentrations, using a mass balance approach. Mixing between ascending thermal waters and overlying cold waters is extensive. The proportion of water in the Quaternary aquifer derived from a deep thermal source is lower in Daying geothermal field than in Qicun field (5.3–7.3% vs. 6.3–49.3%). Mixing between thermal and non-thermal groundwater has been accelerated by groundwater exploitation practices and is enhanced near faults. Shallow groundwater composition has also been affected by irrigation with low-temperature thermal water.  相似文献   

15.
《Advances in water resources》2007,30(6-7):1505-1527
The immense diversity of microbial life found in the vadose zone reflects the extremely heterogeneous and highly dynamic aquatic and chemical environments formed within soil pore spaces. The notion of planktonian free swimming microbes is unrealistic under most unsaturated conditions. Experimental and theoretical evidence suggests that surface attachment is the prevailing lifestyle, where bacterial colonies are embedded in biosynthesized extracellular polymeric substances (EPS). This strategy represents a successful adaptation to the variable and unpredictable hydration conditions near the earth surface. The EPS matrix serves as the interface with the environment; it enhances hydration and transport properties in the immediate vicinity of microbial cells, and dampens effects of highly transient fluctuations in water and nutrient fluxes. The primary effect of soil pore geometry and hydration status is on diffusion pathways to and away from stationary microbial colonies. Microbial dependency on diffusion processes occurs at all scales, but is particularly important at the colony scale. We illustrate the critical role of diffusion pathways with their complex spatial and temporal patterns in promoting coexistence and diversity. We review specific features and adaptations of microbial life to the particular conditions of terrestrial soil environments. The physical and related chemical conditions that shape microbial habitats and govern key processes in unsaturated soils are reviewed in a quantitative framework. Key physiological adaptations and biological responses to challenges presented by unsaturated conditions are discussed. Finally, we discuss potential impacts of microbial activity on properties and characteristics of the host porous medium. This review is an attempt to establish an interdisciplinary dialogue between hydrologists and microbiologists towards a quantitative integration of the role of hydrologic conditions on microbial activity and the role of microbiology in controlling macroscopic fluxes within this important compartment of the biosphere.  相似文献   

16.
This is the era of digital landscapes; the widespread availability of powerful sensing technologies has revolutionized the way it is possible to interrogate landscapes in order to understand the processes sculpting them. Vastly greater areas have now been acquired at ‘high resolution’: currently tens of metres globally to millimetric precision and accuracy locally. This permits geomorphic features to be visualized and analysed across the scales at which Earth‐surface processes operate. Especially exciting is the capturing of process dynamics in repeated surveying, which will only become more important with low‐cost accessible data generation through techniques such as Structure from Motion (SfM). But the key challenge remains; to interpret high resolution Digital Terrain Models (DTMs), particularly by extracting geomorphic features in robust and objective ways and then linking the observed features to the underlying physical processes. In response to the new data and challenges, recent years have seen improved processing of raw data into DTMs, development of data fusion techniques, novel quantitative analysis of topographic data, and innovative geomorphological mapping. The twelve papers collected in this volume sample this progress in interrogating Earth‐surface processes through the analysis of DTMs. They cover a wide range of disciplines and spatio‐temporal scales, from landslide prone landscapes, to agriculturally modified regions, to mountainous landscapes, and coastal zones. They all, however, showcase the quantitative exploitation of information contained in high‐resolution topographic data that we believe will underpin the improvement of our understanding of many elements of Earth‐surface processes. Most of the papers introduced here were first presented in a conference session at the European Geosciences Union General Assembly in 2011. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Scanning electron microscopy and instrumental neutron activation analyses of filtered suspended matter from the Atlantic Ocean show that particulate aluminium (Alp) is a sensitive measure of bottom derived or resuspended material. The proportion of Alp in suspended particulate matter (SPM) increases slightly between surface and intermediate depths but shows large and steady increases in deep waters with approach to the bottom.

Fep/Alp andMnp/Alp ratios are always higher than the crustal ratios throughout the water column. We show that the processes which can explain such enrichments are different for particulate matter in surface waters (scavenging, incorporation in biogenic particles) than for resuspended material (precipitation from interstitial waters on surficial sediments).

Close to the Mid-Atlantic Ridge, the bottom suspended matter exhibits higher Fep/Alp andMnp/Alp ratios than in abyssal plains. A ridge crest source must be invoked to explain the striking enrichment of Mnp. This source could also explain the enrichment of Fep, although primarily because the resuspended flux is small in that region, one cannot exclude the contribution of particles from the mid-water column.  相似文献   


18.
We present here a new model of core formation which is based on the current understanding of planetary accretion and discuss its implications for the chemistry of the Earth's mantle and core. Formation of the Earth by hierarchical accretion of progressively larger bodies on a time scale much longer than that of solid body differentiation in the nebula indicates that a significant fraction of metal in the core could be inherited from preterrestrially differentiated planetesimals. An analysis of the segregation of this iron to form the core suggests that most of the metal settles to the core without interaction with silicates; only a small fraction of the metal chemically equilibrates at high temperatures and pressures with the silicates. The siderophile element abundances in the mantle are considered to be a consequence of a two-step equilibration with iron, once preterrestrially in the planetesimals at low temperatures and pressures, and later in the Earth at high temperatures and pressures. The highly siderophile elements such as Re, Au and the platinum group elements in the mantle are essentially excluded from silicates from the preterrestrial equilibration. We attribute the abundances of these elements in the mantle to the later equilibration in the Earth at substantially reduced metal-silicate partition coefficients (Dmet/sil), for which there is a considerable experimental evidence now. Mass balance considerations constrain the fraction of core metal involved in such an equilibration at approximately 0.3 – 0.5%. The model accounts for the levels and the near-chondritic ratios of the highly siderophile elements in the mantle. The mantle abundances of the less siderophile elements are largely determined by preterrestrial metal-silicate equilibrium and are not significantly affected by the second equilibration. The extreme depletion of sulfur and the lack of silicate melt-sulfide signature in the noble metal abundances in the mantle are natural consequences of this mode of core formation. Sulfur was added to the magma ocean during the high-T, high-P equilibration in the Earth, not extracted from it by sulfide segregation to the core. Except for Ni and Co, the overall siderophile abundances of the mantle can be well matched in this two-step equilibration model.

The mantle characteristics of Ni and Co are unique to the Earth and hence suggest a terrestrial process as the likely cause. One such process is the flotation and addition of olivine to the primitive upper mantle. In our model of core formation, neither the elemental and isotopic data of Re---Os, nor the low sulfur content of the mantle remains as an objection to the existence of a magma ocean and olivine flotation.

The small fraction of core metal that equilibrates with silicates at high T and P suggests that the light elements O, Si or H are unimportant in the core, leaving S (and possibly C) as prime candidates. Sulfur, as FeS associated with incoming iron metal, is directly sequestered to the core along with the bulk of the iron metal. It appears unlikely that other light elements can be added to the core after its formation. U and Th are excluded from the core but the model allows for entry of some K; however, the extent to which K serves as a heat source in the core remains uncertain.

The model is testable in two ways. One is by investigation of the metal-silicate partitioning at high temperatures and pressures under magma ocean conditions to determine if the (Dmet/sil) values are lowered to the levels required in the model. The other is by experiments to determine if a solvus closure between metal and silicate liquids occurs at high temperatures relevant to a magma ocean.  相似文献   


19.
Our understanding of Lake Vostok, the huge subglacial lake beneath the East Antarctic Ice Sheet, has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake. The north of the lake, where the overlying ice sheet is thickest, is characterized by subglacial melting, whereas freezing of lake water occurs in the south, resulting in ～210 m of ice accretion to the underside of the ice sheet. The accreted ice contains lower concentrations of the impurities normally found in glacier ice, suggesting a net transfer of material from meltwater into the lake. The small numbers of microbes found so far within the accreted ice have DNA profiles similar to those of contemporary surface microbes. Microbiologists expect, however, that Lake Vostok, and other subglacial lakes, will harbour unique species, particularly within the deeper waters and associated sediments. The extreme environments of subglacial lakes are characterized by high pressures, low temperatures, permanent darkness, limited nutrient availability, and oxygen concentrations that are derived from the ice that provides the meltwater. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

20.
Which rule of mixture is the best for predicting the overall elastic properties of polyphase rocks based on the elastic properties and volume fractions of their constituents? In order to address this question, we sintered forsterite-enstatite polycrystalline aggregates with a varied forsterite volume fraction (0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0). Elastic properties (shear, bulk, and Young's moduli) of these synthesized composites were measured as a function of pressure up to 3.0 GPa in a liquid-medium piston-cylinder apparatus using a high-precision ultrasonic interferometric technique. The experimental data can be much better described by the shear-lag model than by the commonly used simple models such as Voigt, Ruess and Hill averages, Hashin-Shtrikman bounds, Ravichandran bounds, Halpin-Tsai equations, and Paul's calculations. We attributed this to the fact that the elastic interaction and stress transfer between phases are neglected in all the models except for the shear-lag model. In particular, t  相似文献   

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