全文获取类型
收费全文 | 2950篇 |
免费 | 658篇 |
国内免费 | 804篇 |
专业分类
测绘学 | 354篇 |
大气科学 | 463篇 |
地球物理 | 711篇 |
地质学 | 1703篇 |
海洋学 | 412篇 |
天文学 | 131篇 |
综合类 | 290篇 |
自然地理 | 348篇 |
出版年
2024年 | 16篇 |
2023年 | 75篇 |
2022年 | 167篇 |
2021年 | 220篇 |
2020年 | 165篇 |
2019年 | 194篇 |
2018年 | 171篇 |
2017年 | 178篇 |
2016年 | 202篇 |
2015年 | 175篇 |
2014年 | 206篇 |
2013年 | 197篇 |
2012年 | 215篇 |
2011年 | 207篇 |
2010年 | 215篇 |
2009年 | 198篇 |
2008年 | 160篇 |
2007年 | 142篇 |
2006年 | 115篇 |
2005年 | 81篇 |
2004年 | 73篇 |
2003年 | 71篇 |
2002年 | 133篇 |
2001年 | 127篇 |
2000年 | 115篇 |
1999年 | 104篇 |
1998年 | 63篇 |
1997年 | 70篇 |
1996年 | 59篇 |
1995年 | 44篇 |
1994年 | 49篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 37篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1958年 | 6篇 |
排序方式: 共有4412条查询结果,搜索用时 15 毫秒
981.
Xiang Rong Li Tiegang Yang Zuosheng Yan Jun Cao Qiyuan College of Marine Geosciences Ocean University of China 《海洋学报(英文版)》2003,(1)
Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b 相似文献
982.
本文首次对苏皖北部地区上元古界中已有K-Ar同位素年龄出现的分散及“倒置”现象的原因作了探讨,指出大多数K-Ar年龄由多种因素造成Ar丢失,从而导致不同程度的偏新。因此,这些年龄数据不能代表本区晚元古代沉积岩的真实年龄。作者根据近几年新获得的一些Rb-Sr全岩等时线年龄数据及地壳波浪运动中表现出来的周期性特征,讨论了建立“徐淮系”的可能性及必要性。作者认为,“徐淮系”可以填补青白口系与震旦系之间至少150Ma的沉积缺失。 相似文献
983.
Xinqi Yu Zongxiu Wang Xiang Zhou Weifeng Xiao Xinpeng Yang 《International Journal of Earth Sciences》2016,105(5):1637-1661
984.
Zhang ZhiJian Wang ZhaoDe Joseph Holden Xu XinHua Wang Hang Ruan JingHua Xu Xin 《水文研究》2012,26(1):15-26
Global warming poses a great threat to wetland ecological stability and water quality improvement. In this paper, we sampled six types of wetlands representing different kinds of land utilisation around the TaiHu Lake Basin in southeast China. An outdoor computerized microcosm was set up in May 2008 to simulate climate scenarios of ambient temperature (control) and a warmed ambient temperature (+5 °C) using a novel minute‐scale daily and seasonal temperature manipulation technology. The 18‐month incubation indicated that warming impaired the ecological sink of sediment (fixing P from porewater) while strengthening the role of the ecological source, moreover, the rate of P release from sediment into porewater (19–113% for total phosphorus) was much stronger than from top sediment into overlying water. Warming enhanced the activity of neutral and alkaline phosphatases for P‐deficient wetland sediments and neutral phosphatases for P‐rich sediments, at the 14th month of incubation. A significant increase in total phospholipid fatty acids (PLFAs) occurred under warming in sediments with relatively low levels of PLFAs, but bacterial abundance in the sediment biomass tended to decrease (18%) along with an increase (4·5%) of the fungi‐to‐bacteria ratio. The variations of carbon consumption and availability indicated by measured dissolved organic carbon in sediment may have contributed to P release from sediments to water. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
985.
The Solar TErrestrial RElations Observatory (STEREO) requires powerful tools for the three-dimensional (3D) reconstruction of the solar corona. Here we test such a program
with data from SOHO and TRACE. By taking advantage of solar rotation, a newly developed stereoscopy tool for the reconstruction
of coronal loops is applied to the solar active region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic reconstruction
is composed of three steps. First, we identify loop structures in two TRACE images observed from two vantage viewpoints approximately
17 degrees apart, which corresponds to observations made about 30 hours apart. In the second step, we extrapolate the magnetic
field in the corona with the linear force-free field model from the photospheric line-of-sight SOHO/MDI data. Finally, combining
the extrapolated field lines and one-dimensional loop curves from two different viewpoints, we obtain the 3D loop structures
with the magnetic stereoscopy tool. We demonstrate that by including the magnetic modeling this tool is more powerful than
pure geometrical stereoscopy, especially in resolving the ambiguities generated by classical stereoscopy. This work will be
applied to the STEREO mission in the near future. 相似文献
986.
This study is to combine a coastal high-resolution (2′×2′) two-way coupled wave-tide-surge numerical model (including 3 main physical mechanisms) with a material transport/diffusion model for understanding the law of material transport/diffusion. Results show that the law of material trans- port/diffusion driven by background current field simulated by the coupled wave-tide-surge model is dif- ferent from that simulated by pure tide-surge, and more different from traditional ones driven by tidal current. The coupled background current should be taken into account for the simulation. 相似文献
987.
Scenarios of land cover in China 总被引:3,自引:0,他引:3
A method for surface modeling of land cover change (SMLC) is developed on the basis of establishing transition probability matrixes between land cover types and HLZ types. SMLC is used to simulate land cover scenarios of China for the years 2039, 2069 and 2099, for which HLZ scenarios are first simulated in terms of HadCM3 climatic scenarios that are downscaled in zonal model of spatial climate change in China. This paper also analyzes spatial distribution of land cover types, area change and mean center shift of each land cover type, ecotope diversity, and patch connectivity under the land cover scenarios. The results show that cultivated land would decrease and woodland would expand greatly with climatic change, which coincides with consequences expected by implementation of Grain-for-Green policy. Nival area would shrink, and desertification area would expand at a comparatively slow rate in future 100 years. Climate change would generally cause less ecotope diversity and more patch connectivity. Ecosystems in China would have a pattern of beneficial cycle after efficient ecological conservation and restoration. However, if human activities would exceed regulation capacity of ecosystems themselves, the ecosystems in China might deteriorate more seriously. 相似文献
988.
Ross N. Mitchell Thomas M. Gernon Adam Nordsvan Grant M. Cox Zheng‐Xiang Li Paul F. Hoffman 《地学学报》2019,31(4):381-389
Estimated at ~58 Ma in duration, the Sturtian snowball Earth (ca. 717–659 Ma) is one of the longest‐known glaciations in Earth history. Surprisingly few uncontroversial lines of evidence for glacial incisions associated with such a protracted event exist. We report here multiple lines of geological field evidence for deep but variable glacial erosion during the Sturtian glaciation. One incision, on the scale of several kilometres, represents the deepest incision documented for snowball Earth; another much more modest glacial valley, however, suggests an erosion rate similar to sluggish Quaternary glaciers. The heterogeneity in snowball glacial incisions reported here and elsewhere was likely influenced by actively extending horst‐and‐graben topography associated with the breakup of supercontinent Rodinia. 相似文献
989.
The shear behavior at the interface between the soil and a structure is investigated at the macroscale and particle‐scale levels using a 3‐dimensional discrete element method (DEM). The macroscopic mechanical properties and microscopic quantities affected by the normalized interface roughness and the loading parameters are analyzed. The macro‐response shows that the shear strength of the interface increases as the normalized roughness of the interface increases, and stress softening and dilatancy of the soil material are observed in the tests that feature rough interfaces. The particle‐scale analysis illustrates that a localized band characterized by intense shear deformation emerges from the contact plane and gradually expands as shearing progresses before stabilizing at the residual stress state. The thickness of the localized band is affected by the normalized roughness of the interface and the normal stress, which ranges between 4 and 5 times that of the median grain diameter. A thicker localized band is formed when the soil has a rough shearing interface. After the localized band appears, the granular material structuralizes into 2 regions: the interface zone and the upper zone. The mechanical behavior in the interface zone is representative of the interface according to the local average stress analysis. Certain microscopic quantities in the interface zone are analyzed, including the coordination number and the material fabric. Shear at the interface creates an anisotropic material fabric and leads to the rotation of the major principal stress. 相似文献
990.