全文获取类型
收费全文 | 884篇 |
免费 | 34篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 121篇 |
地球物理 | 191篇 |
地质学 | 369篇 |
海洋学 | 30篇 |
天文学 | 191篇 |
综合类 | 4篇 |
自然地理 | 25篇 |
出版年
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 28篇 |
2014年 | 28篇 |
2013年 | 44篇 |
2012年 | 41篇 |
2011年 | 42篇 |
2010年 | 34篇 |
2009年 | 40篇 |
2008年 | 48篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 31篇 |
2003年 | 24篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1972年 | 6篇 |
1960年 | 4篇 |
排序方式: 共有939条查询结果,搜索用时 15 毫秒
781.
Pedro Oyhant?abal Siegfried Siegesmund Klaus Wemmer 《International Journal of Earth Sciences》2011,100(2-3):201-220
A review of the lithostratigraphic units in the Río de la Plata Craton and of new and previously published geochronological, isotopic and geophysical data is presented. Sm?CNd TDM model ages between 2.6 and 2.2?Ga characterize the Piedra Alta Terrane of this craton. Crystallization ages between 2.2 and 2.1?Ga for the metamorphic protoliths and 2.1?C2.0?Ga for the post-orogenic granitoids indicate juvenile crust, followed by a short period of crustal recycling. Cratonization of this terrane occurred during the late Paleoproterozoic. Younger overprinting is not observed, suggesting it had a thick and strong lithosphere in the Neoproterozoic. A similar scenario is indicated for the Tandilia Belt of Argentina. Sm?CNd TDM model ages for the Nico Pérez Terrane show two main events of crustal growth (3.0?C2.6?and 2.3?C1.6?Ga). The crystallization ages on zircon ranges between 3.1 and 0.57?Ga, which is evidence for long-lived crustal reworking. The age for cratonization is still uncertain. In the Taquarembó Block, which is considered the prolongation of the Nico Pérez Terrane in southern Brazil, a similar scenario can be observed. These differences together with contrasting geophysical signatures support the redefinition of the Río de la Plata Craton comprising only the Piedra Alta Terrane and the Tandilia Belt. The Sarandí del Yí Shear Zone is regarded as the eastern margin of this Craton. 相似文献
782.
Ming‐Yue Hu Xing‐Tao Fan Brigitte Stoll Dmitry Kuzmin Ying Liu Yongsheng Liu Weidong Sun Guang Wang Xiu‐Chun Zhan Klaus Peter Jochum 《Geostandards and Geoanalytical Research》2011,35(2):235-251
Four silicate glasses were prepared by the fusion of about 1 kg powder each of a basalt, syenite, soil and andesite to provide reference materials of natural composition for microanalytical work. These glasses are referred to as ‘Chinese Geological Standard Glasses’ (CGSG) ‐1, ‐2, ‐4 and ‐5. Micro and bulk analyses indicated that the glasses are well homogenised with respect to major and trace elements. Some siderophile/chalcophile elements (e.g., Sn, Pt, Pb) may be heterogeneously distributed in CGSG‐5. This paper provides the first analytical data for the CGSG reference glasses using a variety of analytical techniques (wet chemistry, XRF, EPMA, ICP‐AES, ICP‐MS, LA‐ICP‐MS) performed in nine laboratories. Most data agree within uncertainty limits of the analytical techniques used. Discrepancies in the data for some siderophile/chalcophile elements exist, mainly because of possible heterogeneities of these elements in the glasses and/or analytical problems. From the analytical data, preliminary reference and information values for fifty‐five elements were calculated. The analytical uncertainties [2 relative standard error (RSE)] were estimated to be between about 1% and 20%. 相似文献
783.
Erosion of continental margins in the Western Mediterranean due to sea-level stagnancy during the Messinian Salinity Crisis 总被引:1,自引:1,他引:0
Janna Just Christian H��bscher Christian Betzler Thomas L��dmann Klaus Reicherter 《Geo-Marine Letters》2011,31(1):51-64
High-resolution multi-channel seismic data from continental slopes with minor sediment input off southwest Mallorca Island,
the Bay of Oran (Algeria) and the Alboran Ridge reveal evidence that the Messinian erosional surface is terraced at an almost
constant depth interval between 320 and 380 m below present-day sea level. It is proposed that these several hundred- to 2,000-m-wide
terraces were eroded contemporaneously and essentially at the same depth. Present-day differences in these depths result from
subsidence or uplift in the individual realms. The terraces are thought to have evolved during one or multiple periods of
sea-level stagnancy in the Western Mediterranean Basin. According to several published scenarios, a single or multiple periods
of relative sea-level stillstand occurred during the Messinian desiccation event, generally known as the Messinian Salinity
Crisis. Some authors suggest that the stagnancy started during the refilling phase of the Mediterranean basins. When the rising
sea level reached the height of the Sicily Sill, the water spilled over this swell into the eastern basin. The stagnancy persisted
until sea level in the eastern basin caught up with the western Mediterranean water level. Other authors assigned periods
of sea-level stagnancy to drawdown phases, when inflowing waters from the Atlantic kept the western sea level constant at
the depth of the Sicily Sill. Our findings corroborate all those Messinian sea-level reconstructions, forwarding that a single
or multiple sea-level stagnancies at the depth of the Sicily Sill lasted long enough to significantly erode the upper slope.
Our data also have implications for the ongoing debate of the palaeo-depth of the Sicily Sill. Since the Mallorcan plateau
experienced the least vertical movement, the observed terrace depth of 380 m there is inferred to be close to the Messinian
depth of this swell. 相似文献
784.
785.
Ingrid Raczek Brigitte Stoll Albrecht W. Hofmann Klaus Peter Jochum 《Geostandards and Geoanalytical Research》2001,25(1):77-86
Different batches of the new US Geological Survey (USGS) reference materials (RMs) BCR-2, BHVO-2, AGV-2, DTS-2 and GSP-2 and the original USGS RMs BCR-1, BHVO-1, AGV-1, DTS-1 and GSP-1 have been analysed by isotope dilution using thermal ionisation mass spectrometry (ID-TIMS) and by multi-ion counting spark source mass spectrometry (MIC-SSMS). The concentrations of K, Rb, Sr, Ba and the rare earth elements were determined with overall analytical uncertainties of better than 1% (ID-TIMS) and 3% (MIC-SSMS). The analyses of different aliquots and batches of BCR-2, BHVO-2, AGV-2 and GSP-2, respectively, agree within 1%, i.e. approximately the analytical uncertainties of the data. This indicates an homogeneous distribution of the trace elements in these RMs. Differences in element concentrations of up to 17% in different aliquots of the depleted RM DTS-2 are outside the analytical uncertainty of our data. They may be attributed to a slightly heterogeneous distribution of trace elements in this dunite sample. Our trace element data for BCR-2, BHVO-2, AGV-2 and GSP-2 agree within about 3% with preliminary reference values published by the USGS. They also agree within 1-6% with those of the original RMs BCR-1, BHVO-1, AGV-1 and GSP-1. Large compositional differences are found between DTS-2 and DTS-1, where the concentrations of K, Rb, Sr and the light REE differ by factors of 2 to 24. 相似文献
786.
We present an interdisciplinary study on data and modeling intercomparison, concerning the possible existence of a Tibetan ice sheet and its climatological implications during the ice age. In the ice sheet model the fields of ice flow and temperature are calculated, and a highly parameterized formulation of the yearly snow balance is used, defining the forcing at the surface of the ice sheet. The data set used, supplies the height of the equilibrium line of the glaciers (=ELA) and documents the maximum extension of the glaciated areas. With prescribed snow accumulation above the ELA and melting below, the model is integrated for 10 000 model years and the model glaciation is then compared with the data.The main results are: Provided the height of the glacial equilibrium line has been reconstructed correctly, a Tibetan ice sheet can be bult up within 10 000 model years, using moderate rates of precipitation (maximum snow fall: 100 mm/year). Comparison of data and model glaciation suggests an increase of precipitation from the NW to the E of Tibet and from the S to the NE, which reflects the presently observed pattern of the monsoon circulation. 相似文献
787.
Spatial variability of physical and chemical properties in Amazonian soils is evaluated on sites of natural rain forest and pastures of different age in the Amazon region. The sampling scheme was regionalized using transects of fifty points 3 m apart each. Variables analysed were: soil bulk density; resistance to penetration; soil water content; available water; pH and extractable ions such as Ca, K, Al, P and Zn. Geostatistical analyses show that most variables are space independent for the 3 m spacing used. Variances indicate a much lower variability of the measured properties in the forest as compared to pastures. 相似文献
788.
789.
790.