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91.
92.
93.
We have measured the rotation rate of short-lived solar filaments as a function of their latitude. The resulting rotation curve appears to be somewhat flatter than the corresponding curve for long-lived filaments. 相似文献
94.
Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions 总被引:19,自引:0,他引:19
Larry D. Hinzman Neil D. Bettez W. Robert Bolton F. Stuart Chapin Mark B. Dyurgerov Chris L. Fastie Brad Griffith Robert D. Hollister Allen Hope Henry P. Huntington Anne M. Jensen Gensuo J. Jia Torre Jorgenson Douglas L. Kane David R. Klein Gary Kofinas Amanda H. Lynch Andrea H. Lloyd A. David McGuire Frederick E. Nelson Walter C. Oechel Thomas E. Osterkamp Charles H. Racine Vladimir E. Romanovsky Robert S. Stone Douglas A. Stow Matthew Sturm Craig E. Tweedie George L. Vourlitis Marilyn D. Walker Donald A. Walker Patrick J. Webber Jeffrey M. Welker Kevin S. Winker Kenji Yoshikawa 《Climatic change》2005,72(3):251-298
The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems
are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems
are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system
and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the
Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions
are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing
point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being
affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to
isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system
has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental
time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing
efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental
manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and
modeling. 相似文献
95.
Linda A. Kirstein Chris J. Hawkesworth Frances G. Garland 《Contributions to Mineralogy and Petrology》2001,142(3):309-322
In the environment of felsic magma generation associated with continental flood basalt (CFB) provinces there is a close association between magma composition, phenocryst assemblage, temperature and eruption mechanism. In this paper we propose that by examining the chemical composition and, in particular the high field strength element (Zr and Nb) contents of the high silica rocks, we can identify those that contained halogen-rich volatiles and which degassed at different levels (deep versus shallow). The degassing depth has a direct influence on the type of eruption, with shallow degassing promoting explosive rather than effusive behaviour and consequentially the former is more likely to give rise to ignimbrites. Thus, we can infer likely eruption mechanisms, as high concentrations of F and Cl dramatically decrease magma viscosities and should favour deep degassing and hence promote lava effusion rather than explosive pyroclastic eruption. This hypothesis is tested by constraining the other possible variables which have an effect on the mode of eruption, and by examining the nature and composition of melt and fluid inclusions in quartz from CFB-associated felsic volcanic rocks. 相似文献
96.
A novel cryogenic sampling method combining the matrix isolation technique with FTIR spectroscopy has been developed for atmospheric trace gas analysis. It is applicable to a wide range of molecules with detection limits typically in the 10–50 ppt range. The method is described along with some measurements of N2O, CFCl3, CF2Cl2, OCS, CS2, SO2 and PAN from samples collected at ground level and from an aircraft between 9 and 14 km. 相似文献
97.
Frances J. Hein 《Natural Resources Research》2006,15(2):67-84
As conventional oil and gas reservoirs become depleted other unconventional energy sources have to be recovered and produced.
Four of the major unconventional resources that are strategic for North American interests are heavy oil, oil sands, oil shales,
and coal-bed methane. Recent interest and activity in Canada’s vast oil sands are progressing rapidly as soaring oil prices
are fueling a ‘gold rush’ in oil sands development in Alberta. This interest is evident by the record-number of oil sands
and heavy oil presentations at Energy Minerals Division (EMD)-sponsored sessions at the 2004 and 2005 Annual Conventions of
the American Association of Petroleum Geologists (AAPG), held in Dallas, TX and Calgary, AB. 相似文献
98.
The soft uppermost sediments in lakes and wetlands contain important records of past environmental change. Although the technology
for coring these sediments is relatively well established, there has been a continuing effort to improve the design of equipment
that can provide the precise volumetric samples required for high-resolution dating and elemental analysis. Soft-sediment
cores are usually sectioned near a coring site under a wide range of field conditions creating a challenge for both field
crews and equipment. A new field extruder was therefore designed to simplify the process of fine-sectioning these cores in
the field while improving volumetric-sampling accuracy. The new extruder is relatively light, stable, and easy to use, but
sufficiently strong to extrude long continuous cores of stiff sediment if required. The key features of this extruder minimize
sampling errors by enabling an operator to automate the measurement and extrusion of a pre-determined volume of sediment.
The extruder was successfully field tested on a variety of sediment types in a large wetland from southern Florida, USA and
proved easy to master by even inexperienced field crews. 相似文献
99.
100.
William C. Thayer Daniel A. Griffith Gary L. Diamond 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):461-471
Despite the dust cleanup and indoor air testing program led by the U.S. Environmental Protection Agency (EPA) and offered
to all residents of Lower Manhattan (south of Canal Street), concern remains about local chemical residues from the collapse
of the World Trade Center (WTC) buildings. Data on post-cleanup indoor airborne asbestos concentration, available from EPA
Region 2, were analyzed to assess the possibility that the WTC site is the source of geographically concentrated rare post-cleanup
exceedances of the health-based standard for asbestos. Recognizing that these rare exceedances may be attributable to sources
other than the WTC disaster, and that these sources are very likely to exhibit geographic patterns, the data were analyzed
using a spatial filter specification of the auto-Poisson probability model. Our analysis shows that ignoring geographic patterns
latent in these exceedances affects the empirical probability of exceeding the health-based standards for airborne asbestos.
We did not find any statistically-significant geographic pattern in the exceedance events that would indicate the WTC site
as the source of the post-cleanup exceedances. Apparent geographic patterns may be due to the geographic variability in sampling
intensity. Our analysis indicates the Residential Dust Cleanup Program lead by EPA Region 2 has been effective at reducing
the concentration of air-borne asbestos in indoor air to below the health-based benchmark. 相似文献