全文获取类型
收费全文 | 749篇 |
免费 | 73篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 54篇 |
地球物理 | 252篇 |
地质学 | 229篇 |
海洋学 | 56篇 |
天文学 | 173篇 |
综合类 | 2篇 |
自然地理 | 33篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 11篇 |
2018年 | 38篇 |
2017年 | 42篇 |
2016年 | 39篇 |
2015年 | 35篇 |
2014年 | 44篇 |
2013年 | 32篇 |
2012年 | 36篇 |
2011年 | 45篇 |
2010年 | 46篇 |
2009年 | 49篇 |
2008年 | 32篇 |
2007年 | 41篇 |
2006年 | 21篇 |
2005年 | 17篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 23篇 |
2001年 | 22篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 13篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1989年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有822条查询结果,搜索用时 23 毫秒
31.
Sensitivity analysis of automatic landslide mapping: numerical experiments towards the best solution
The automatic detection of landslides after major events is a crucial issue for public agencies to support disaster response. Pixel-based approaches (PBAs) are widely used in the literature for various applications. However, the accuracy of PBAs in the case of automatic landslide mapping (ALM) is affected by several issues. In this study, we investigated the sensitivity of ALM using PBA through digital terrain models (DTMs). The analysis, carried out in a study area of Poland, consisted of the following steps: (1) testing the influence of selected DTM resolutions for ALM, (2) assessing the relevance of diverse landslide morphological indicators for ALM, and (3) assessing the sensitivity to landslide features for a selected size of moving window (kernel) calculations for ALM. Ultimately, we assessed the performance of three classification methods: maximum likelihood (ML), feed-forward neural network (FFNN), and support vector machine (SVM). This broad analysis, as combination of grid cell resolution, surface derivatives calculation, and performance classification methods, is the challenging aspect of the research. The results of almost 500 experimental tests provide valuable guidelines for experts performing ALM. The most important findings indicate that feature sensitivity in the case of kernel size increases with coarser DTM resolution; however, the peak of the optimal feature performance for the selected study area and landslide type was demonstrated for a resolution of 20 m. Another finding indicated that in combining a set of topographic variables, the optimal performance was acquired for a DTM resolution of 30 m and the support vector machine classification. Moreover, the best performance of the identification is represented for SVM classification. 相似文献
32.
Paolo?A.?SossiEmail author Julie?Prytulak Hugh?St.?C.?O’Neill 《Contributions to Mineralogy and Petrology》2018,173(4):27
Vanadium has multiple oxidation states in silicate melts and minerals, a property that also promotes fractionation of its isotopes. As a result, vanadium isotopes vary during magmatic differentiation, and can be powerful indicators of redox processes at high temperatures if their partitioning behaviour can be determined. To quantify the partitioning and isotope fractionation factor of V between magnetite and melt, piston cylinder experiments were performed in which magnetite and a hydrous, haplogranitic melt were equilibrated at 800 °C and 0.5 GPa over a range of oxygen fugacities (\({f_{{{\text{O}}_{\text{2}}}}}\)), bracketing those of terrestrial magmas. Magnetite is isotopically light with respect to the coexisting melt, a tendency ascribed to the VI-fold V3+ and V4+ in magnetite, and a mixture of IV- and VI-fold V5+ and V4+ in the melt. The magnitude of the fractionation factor systematically increases with increasing log\({f_{{{\text{O}}_{\text{2}}}}}\) relative to the Fayalite–Magnetite–Quartz buffer (FMQ), from ?51Vmag-gl = ? 0.63?±?0.09‰ at FMQ ? 1 to ? 0.92?±?0.11‰ (SD) at ≈?FMQ?+?5, reflecting constant V3+/V4+ in magnetite but increasing V5+/V4+ in the melt with increasing log\({f_{{{\text{O}}_{\text{2}}}}}\). These first mineral-melt measurements of V isotope fractionation factors underline the importance of both oxidation state and co-ordination environment in controlling isotopic fractionation. The fractionation factors determined experimentally are in excellent agreement with those needed to explain natural isotope variations in magmatic suites. Furthermore, these experiments provide a useful framework in which to interpret vanadium isotope variations in natural rocks and magnetites, and may be used as a potential fingerprint the redox state of the magma from which they crystallise. 相似文献
33.
A preliminary investigation of the geomorphological evolution of the small delta of the Argentina river (Riviera di Ponente, Italy) shows that it has largely been affected by anthropic processes. Erosion is undermining land and structural developments not only in the delta, but also along the nearby shores and a thorough knowledge of them seems necessary prior to management applications. In fact, processes affecting the evolution of the investigated area could well be regarded as a good example of the evolution of many other deltaic areas in the Northern Mediterranean. 相似文献
34.
35.
Angela Marinoni Paolo Laj Pierre Alexandre Deveau Federica Marino Grazia Ghermandi Fabien Aulagnier Hlne Cachier 《Atmospheric Research》2005,74(1-4):565-580
The physical and chemical properties of aerosol particles were investigated at Plan d'Aups, one of the ESCOMPTE sites located in the St. Baume mountain area (700 m a.s.l.), 50 km east of Marseilles (France). The site is ideally located for assessing the vertical and horizontal extent of the pollution plume from the Marseilles–Berre area.Our study showed that polluted air masses from the Marseilles–Berre area are advected to Plan d'Aups in the early afternoon. Average daily concentration of particles reaches up to 40 μg m−3 while 1-h average particle number concentration is greater than 30,000 cm−3. Most of the particle mass is composed of SO42− and organic carbon (OC). The chemical properties of the particles revealed that an additional source, possibly from the industrial area of Gardanne, contributes to the aerosol mass. This last source is characterised by significant emissions of elements, such as Zn, V, Al and Si.In addition to transport, we found that gas-to-particle conversion takes place at the interface between the free troposphere and the boundary layer. We estimated that on average, 30% of the particle number is accounted for by direct nucleation. This is potentially a major aerosol source to the free troposphere. 相似文献
36.
The Otranto–Leuca coastal tract is marked by the presence of numerous sea caves placed close to present sea level. They are located generally at the back of a shore platform covered by a sequence of breccia deposits, marine sediments and speleothems. At Grotta di Masseria dell'Orte, marine cemented sands rest on a narrow shore platform at about 6.2 m above mean sea level and are covered by speleothems older than 185 ka. At Grotta del Diavolo, which is mostly filled by breccia deposits, three beach levels have been detected at about 3.0, 3.5 and 5.9 m above msl. They are either covered by or overlie speleothems that yield an U/Th age of 340, 78 ka and between 170.3 and 146.5, respectively. Geomorphological evidence and radiometric ages indicate that the area after a period of uplift has been tectonically stable since the last part of the Middle Pleistocene so that marine landforms close to the present shoreline underwent a polycyclic evolution. The sedimentary fills of sea caves formed during Middle-Late Pleistocene glacial stages, when arid or semiarid conditions promoted the removal of regolith and the development of thick breccia deposits. During Marine Isotope Stages (MIS) 9.3, 5.5 and 5.1, cave sediments were partially eroded whereas beach layers and related speleothems developed. These are, in fact, the only marine isotope stages marked by a sea level position which in this Mediterranean region was either close to, or slightly higher than, the present one. 相似文献
37.
38.
Wolfram Wobrock Andrea I. Flossmann Marie Monier Jean-Marc Pichon Laurent Cortez Jean-Franois Fournol Alfons Schwarzenbck Stephan Mertes Jost Heintzenberg Paolo Laj Giordano Orsi Loretta Ricci Sandro Fuzzi Harry Ten Brink Piet Jongejan Ren Otjes 《Atmospheric Research》2001,58(4):7907
The second field campaign of the Cloud Ice Mountain Experiment (CIME) project took place in February 1998 on the mountain Puy de Dôme in the centre of France. The content of residual aerosol particles, of H2O2 and NH3 in cloud droplets was evaluated by evaporating the drops larger than 5 μm in a Counterflow Virtual Impactor (CVI) and by measuring the residual particle concentration and the released gas content. The same trace species were studied behind a round jet impactor for the complementary interstitial aerosol particles smaller than 5 μm diameter. In a second step of experiments, the ambient supercooled cloud was converted to a mixed phase cloud by seeding the cloud with ice particles by the gas release from pressurised gas bottles. A comparison between the physical and chemical characteristics of liquid drops and ice particles allows a study of the fate of the trace constituents during the presence of ice crystals in the cloud.In the present paper, an overview is given of the CIME 98 experiment and the instrumentation deployed. The meteorological situation during the experiment was analysed with the help of a cloud scale model. The microphysics processes and the behaviour of the scavenged aerosol particles before and during seeding are analysed with the detailed microphysical model ExMix. The simulation results agreed well with the observations and confirmed the assumption that the Bergeron–Findeisen process was dominating during seeding and was influencing the partitioning of aerosol particles between drops and ice crystals. The results of the CIME 98 experiment give an insight on microphysical changes, redistribution of aerosol particles and cloud chemistry during the Bergeron–Findeisen process when acting also in natural clouds. 相似文献
39.
Paolo Laj Andrea I. Flossmann Wolfram Wobrock Sandro Fuzzi Giordano Orsi Loretta Ricci Stephan Mertes Alfons Schwarzenbck Jost Heintzenberg Harry Ten Brink 《Atmospheric Research》2001,58(4):256
We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H2O2, NH3 and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H2O2 and NH3 are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H2O2 is driven by co-condensation with water vapour onto ice crystals while NH3 uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH4+ in the ice could explain this result. Finally, it appears that the H2O2–SO2 reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming. 相似文献
40.
A clinopyroxene geobarometer for basaltic systems based on crystal-structure modeling 总被引:9,自引:0,他引:9
Paolo Nimis 《Contributions to Mineralogy and Petrology》1995,121(2):115-125
The crystal chemical response of basalt clinopyroxene to increasing pressure was investigated by means of crystal-structure
simulation (a procedure that enables modeling of the structural parameters of a clinopyroxene of known chemistry without requiring
direct X-ray diffraction analysis) using available experimental chemical data. Pressure proved the main physical variable
governing clinopyroxene behavior in a magmatic environment. The general internal consistency of the simulation data permitted
construction of an empirical geobarometer based on the relationship of cell volume (Vc) vs M1-site volume (VM1). The straightforward
geobarometric formulation in the absence of direct X-ray analysis is:
P(kbar)=698.443+4.985⋅AlT−26.826⋅Fe2+
M1−3.764⋅Fe3+
+53.989⋅AlM1+3.948⋅Ti+14.651⋅Cr
−700.431⋅Ca−666.629⋅Na−682.848⋅MgM2−691.138⋅Fe2+
M2−688.384⋅Mn−6.267⋅(MgM2)2−4.144⋅(Fe2+
M2
where:
(Fe2+
M1⋅MgM2)/(Fe2+
M2⋅MgM1)=e**(0.238⋅R3++0.289⋅CNM−2.315), CNM=Ca+Na+Mn, and R3+=AlM1+Fe3++Ti+Cr,
with cations in atoms per formula unit. The geobarometer reproduces experimental pressures within ±2 kbar (=1σ; max. dev.
≤5 kbar; N=29) in the range 0–24 kbar and is applicable to near-liquidus C2/c clinopyroxenes crystallized from basaltic melts in the absence of garnet (excepting high-Al2O3 basalts). It is therefore suitable for many natural clinopyroxenes occurring as mega- or phenocrysts or forming well-preserved
cumulate pyroxenites. If the above restrictions are not wholly satisfied, the Vc vs VM1 plot can also be used qualitatively
to deduce the relative pressure conditions of clinopyroxenes forming from similar batches of magma. The structural simulation of experimental data
also provided insight into the influence of minor chemical changes of the parental magma on the crystal chemistry of clinopyroxene
at high pressure. Within the considered compositional space at given P-T, a
CaO and a
SiO2 in the melt have opposite effects on M2- and T-site cation populations. As a result, under similar physical conditions, clinopyroxenes
from higher-CaO or more undersaturated basalts have higher VM2, VT and Vc and lower VM1. For basalts with normal contents of Al2O3 (<18 wt %), variations of major elements in the melt do not reduce the accuracy of the geobarometer.
Received: 3 April 1994 / Accepted: 23 December 1995 相似文献