全文获取类型
收费全文 | 334篇 |
免费 | 3篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 28篇 |
地球物理 | 48篇 |
地质学 | 136篇 |
海洋学 | 6篇 |
天文学 | 101篇 |
自然地理 | 6篇 |
出版年
2021年 | 5篇 |
2020年 | 6篇 |
2016年 | 4篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 3篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1948年 | 3篇 |
1938年 | 4篇 |
1937年 | 7篇 |
1936年 | 4篇 |
1935年 | 3篇 |
1934年 | 3篇 |
1933年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有337条查询结果,搜索用时 31 毫秒
101.
P. Richter Aj. Fox N. Ben Bekhti M. T. Murphy D. Bomans S. Frank 《Astronomische Nachrichten》2014,335(1):92-98
In this article we discuss the importance of high‐resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi‐phase nature of the CGM in low‐redshift galaxies. High‐precision absorption‐line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi‐wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm‐hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ 6374.5 Å and [Fe XIV] λ 5302.9 Å absorption in optical QSO spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
102.
L Richter P CosteV.V Gromov H KochanR Nadalini T.C NgS Pinna H.-E RichterK.L Yung 《Planetary and Space Science》2002,50(9):903-913
For planetary landing missions, the capability to acquire samples of soil and rock is of high importance whenever complex analyses (e.g. isotopic studies) on these materials are to be carried out, or when samples are to be returned to Earth. Not only surface samples are of relevance, but in recent concepts at least for Mars landing missions also subsurface samples are required. Subsurface material on Mars is believed to have been protected from the inferred oxidants at the immediate surface while also being protected from the UV influx. Therefore, there is considerable hope that in subsurface soil samples on Mars, at least organic matter delivered by meteorites may be detected, and possibly also relics of earlier simple microbial life on the planet. Likewise, samples from the inside of Martian surface rocks promise to have been protected from weathering and for the same reason they are important for organic chemistry studies. In this paper, an overview is given of the development and science of two different subsurface sampling devices for the Beagle 2 lander of ESA's Mars Express mission, being a “Mole” subsurface soil sampler and a small rock coring and sampling mechanism. Besides their sampling function, both the Mole and the Corer/Grinder will provide data on physical properties of Martian soils and rock, respectively, through the way they interact with the sampled materials. Details of the Mole and Corer/Grinder design are presented, along with results of recent tests with prototypes in the laboratory on physically analogous sample materials. 相似文献
103.
J. Götze M. Plötze Th. Götte R. D. Neuser D. K. Richter 《Mineralogy and Petrology》2002,76(3-4):195-212
Summary ?Sheet silicates of the serpentine–kaolin-group (serpentine, kaolinite, dickite, nacrite, halloysite), the talc–pyrophyllite-group
(talc, pyrophyllite), the smectite-group (montmorillonite), and illite (as a mineral of the mica-group) were investigated
to obtain information concerning their cathodoluminescence behaviour. The study included analyses by cathodoluminescence (CL
microscopy and spectroscopy), electron paramagnetic resonance (EPR), X-Ray diffraction (XRD), scanning electron microscopy
(SEM) and trace element analysis.
In general, all dioctahedral clay minerals exhibit a visible CL. Kaolinite, dickite, nacrite and pyrophyllite have a characteristic
deep blue CL, whereas halloysite emission is in the greenish-blue region. On the contrary, the trioctahedral minerals (serpentine,
talc) and illite do not show visible CL.
The characteristic blue CL is caused by an intense emission band around 400 nm (double peak with two maxima at 375 and 410 nm).
EPR measurements indicate that this blue emission can be related to radiation induced defect centres (RID), which occur as
electron holes trapped on apical oxygens (Si–O centre) or located at the Al–O–Al group (Al substituting Si in the tetrahedron).
Additional CL emission bands were detected at 580 nm in halloysite and kaolinite, and between 700 and 800 nm in kaolinite,
dickite, nacrite and pyrophyllite.
Time-resolved spectral CL measurements show typical luminescence kinetics for the different clay minerals, which enable differentiation
between the various dioctahedral minerals (e.g. kaolinite and dickite), even in thin section.
Received December 3, 2001; revised version accepted February 27, 2002 相似文献
104.
Gert Richter 《GeoJournal》1994,32(2):173-178
105.
Frank M. Richter Philip E. Janney Ruslan A. Mendybaev Andrew M. Davis Meenakshi Wadhwa 《Geochimica et cosmochimica acta》2007,71(22):5544-5564
Vacuum evaporation experiments with Type B CAI-like starting compositions were carried out at temperatures of 1600, 1700, 1800, and 1900 °C to determine the evaporation kinetics and evaporation coefficients of silicon and magnesium as a function of temperature as well as the kinetic isotope fractionation factor for magnesium. The vacuum evaporation kinetics of silicon and magnesium are well characterized by a relation of the form J = Joe−E/RT with Jo = 4.17 × 107 mol cm−2 s−1, E = 576 ± 36 kJ mol−1 for magnesium, Jo = 3.81 × 106 mol cm−2 s−1, E = 551 ± 63 kJ mol−1 for silicon. These rates only apply to evaporation into vacuum whereas the actual Type B CAIs were almost certainly surrounded by a finite pressure of a hydrogen-dominated gas. A more general formulation for the evaporation kinetics of silicon and magnesium from a Type B CAI-like liquid that applies equally to vacuum and conditions of finite hydrogen pressure involves combining our determinations of the evaporation coefficients for these elements as a function of temperature (γ = γ0e−E/RT with γ0 = 25.3, E = 92 ± 37 kJ mol−1 for γSi; γ0 = 143, E = 121 ± 53 kJ mol−1 for γMg) with a thermodynamic model for the saturation vapor pressures of Mg and SiO over the condensed phase. High-precision determinations of the magnesium isotopic composition of the evaporation residues from samples of different size and different evaporation temperature were made using a multicollector inductively coupled plasma mass spectrometer. The kinetic isotopic fractionation factors derived from this data set show that there is a distinct temperature effect, such that the isotopic fractionation for a given amount of magnesium evaporated is smaller at lower temperature. We did not find any significant change in the isotope fractionation factor related to sample size, which we interpret to mean that recondensation and finite chemical diffusion in the melt did not affect the isotopic fractionations. Extrapolating the magnesium kinetic isotope fractionations factors from the temperature range of our experiments to temperatures corresponding to partially molten Type B CAI compositions (1250-1400 °C) results in a value of αMg ≈ 0.991, which is significantly different from the commonly used value of . 相似文献
106.
Laurel Saito Bill Christian Jennifer Diffley Holly Richter Melissa M. Rohde Scott A. Morrison 《Ground water》2021,59(3):322-333
Groundwater is a critical resource not only for human communities but also for many terrestrial, riparian, and aquatic ecosystems and species. Yet groundwater planning and management decisions frequently ignore or inadequately address the needs of these natural systems. As a consequence, ecosystems dependent on groundwater have been threatened, degraded, or eliminated, especially in arid regions. There is growing acknowledgment that governmental protections for these ecological resources are necessary, but current legal, regulatory and voluntary provisions are often inadequate. Groundwater management premised on “safe yield,” which aims to balance human withdrawals with natural recharge rates, typically provides little to no consideration for water needed by ecosystems. Alternatively, the “sustainable yield” concept aims to integrate social, economic and environmental needs for groundwater, but the complexity of groundwater systems creates substantial uncertainty about the impact that current or future groundwater withdrawals will have on ecosystems. Regardless of the legal or regulatory framework, guidance is needed to help ensure environmental water needs will be met, especially in the face of pressure to increase human uses of groundwater resources. In this paper, we describe minimum provisions for planning, managing, and monitoring groundwater that collectively can lower the risk of harm to groundwater-dependent ecosystems and species, with a special emphasis on arid systems, where ecosystems and species may be especially reliant upon and sensitive to groundwater dynamics. 相似文献
107.
Wetlands are a key archive for paleoclimatic and archeological work, particularly in arid regions, as they provide a focus for human occupation and preserve environmental information. The sedimentary record from 'Ayn Qasiyya, a spring site on the edge of the Azraq Qa, provides a well-dated sequence through the last glacial–interglacial transition (LGIT) allowing environmental changes in the present-day Jordanian desert to be investigated robustly through this time period for the first time. Results show that the wettest period at the site preceded the last glacial maximum, which itself was characterised by marsh formation and a significant Early Epipaleolithic occupation. A sedimentary hiatus between 16 and 10.5 ka suggests a period of drought in the region although seasonal rains and surface waters still allowed seasonal occupation of the Azraq region. Archeological evidence suggests that conditions had improved by the Late Epipaleolithic, about the time of the North Atlantic Younger Dryas. The changes between wet and dry conditions at the site show similarities to patterns in the eastern Mediterranean and in Arabia suggesting the Jordan interior was influenced by changes in both these regions through the LGIT climatic transition. 相似文献
108.
Constantine C.C. Tsang John R. Spencer Emmanuel Lellouch Miguel A. López-Valverde Matthew J. Richter Thomas K. Greathouse 《Icarus》2012,217(1):277-296
We present an analysis of 19 μm spectra of Io’s SO2 atmosphere from the TEXES mid-infrared high spectral resolution spectrograph on NASA’s Infrared Telescope Facility, incorporating new data taken between January 2005 and June 2010 and a re-analysis of earlier data taken from November 2001 to January 2004. This is the longest set of contiguous observations of Io’s atmosphere using the same instrument and technique thus far. We have fitted all 16 detected blended absorption lines of the ν2 SO2 vibrational band to retrieve the subsolar values of SO2 column abundance and the gas kinetic temperature. By incorporating an existing model of Io’s surface temperatures and atmosphere, we retrieve sub-solar column densities from the disk-integrated data. Spectra from all years are best fit by atmospheric temperatures <150 K. Best-fit gas kinetic temperatures on the anti-Jupiter hemisphere, where SO2 gas abundance is highest, are low and stable, with a mean of 108 (±18) K. The sub-solar SO2 column density between longitudes of 90–220° varies from a low of 0.61 (±0.145) × 10?17 cm?2, near aphelion in 2004, to a high of 1.51 (±0.215) × 1017 cm?2 in 2010 when Jupiter was approaching its early 2011 perihelion. No correlation in the gas temperature was seen with the increasing SO2 column densities outside the errors.Assuming that any volcanic component of the atmosphere is constant with time, the correlation of increasing SO2 abundance with decreasing heliocentric distance provides good evidence that the atmosphere is at least partially supported by frost sublimation. The SO2 frost thermal inertias and albedos that fit the variation in atmospheric density best are between 150–1250 W m?2 s?1/2 K?1 and 0.613–0.425 respectively. Photometric evidence favors albedos near the upper end of this range, corresponding to thermal inertias near the lower end. This relatively low frost thermal inertia produces larger amplitude seasonal variations than are observed, which in turn implies a substantial additional volcanic atmospheric component to moderate the amplitude of the seasonal variations of the total atmosphere on the anti-Jupiter hemisphere. The seasonal thermal inertia we measure is unique both because it refers exclusively to the SO2 frost surface component, and also because it refers to relatively deep subsurface layers (few meters) due to the timescales of many years, while previous studies have determined thermal inertias at shallower levels (few centimeters), relevant for timescales of ~2 h (eclipse) or ~2 days (diurnal curves). 相似文献
109.
Raffaella Meffe Gudrun Massmann Claus Kohfahl Thomas Taute Doreen Richter Uwe Dünnbier Asaf Pekdeger 《Environmental Earth Sciences》2012,65(3):861-870
The groundwater downstream of a former sewage irrigation farm in Berlin is contaminated with ammonium (NH4
+) and para-toluenesulfonamide (p-TSA), besides other anthropogenic pollutants. In the field, in situ removal of NH4
+ by gaseous oxygen (O2) and air injection is currently being tested. A laboratory column experiment using aquifer material and groundwater from
the site was performed to determine whether this remediation technology is also feasible to reduce high p-TSA concentrations in the anoxic groundwater. First, the column was operated under anoxic conditions. Later, compressed air
was introduced into the system to simulate oxic conditions. Samples were collected from the column outlet before and after
the addition of compressed air. The experiment revealed that whereas p-TSA was not removed under anoxic conditions, it was almost fully eliminated under oxic conditions. Results were modelled
using a transient one-dimensional solute transport model. The degradation rate constants for p-TSA increased from 2.8E−06 to 7.5E−05 s–1 as a result of microbial adaption to the change of redox conditions. Results show that O2 injection into an anoxic aquifer is a successful strategy for p-TSA remediation. 相似文献
110.
Despite the abundance of large wood (LW) river studies there is still a lack of understanding of LW transport dynamics on large low gradient rivers. This study used 290 radio frequency identification tagged (RFID) LW and 54 metal (aluminum) tagged LW, to quantify the percent of in‐channel LW that moves per year and what variables play a role in LW transport dynamics. Aluminum tags were installed and monitored on LW in‐transit during the rising limb of a flood, the mean distance traveled by those pieces during the week was 13.3 river kilometers (km) with a maximum distance of 72 km. RFID tagged LW moved a mean of 11.9 km/yr with a maximum observed at 101.1 km/yr. Approximately 41% of LW low on the bank moves per year. The high rate of transport and distance traveled is likely due to the lack of interaction between LW floating in the channel and the channel boundaries, caused primarily by the width of the channel relative to length of the LW. Approximately 80% of the RFID tags moved past a fixed reader during the highest 20% of river stage per year. LW transport and logjam dynamics are complicated at high flows as pieces form temporary jams that continually expand and contract. Unlike most other studies, key members that create a logjam were defined more by stability than jam size or channel/hydrologic conditions. Finally, using an existing geomorphic database for the river, and data from this study, we were able to develop a comprehensive LW budget showing that 5% of the in‐channel LW population turns over each year (input from mass wasting and fluvial erosion equals burial, decomposition, and export out of system) and another 16% of the population moving within the system. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. 相似文献