全文获取类型
收费全文 | 82731篇 |
免费 | 28134篇 |
国内免费 | 53657篇 |
专业分类
测绘学 | 12476篇 |
大气科学 | 25851篇 |
地球物理 | 20418篇 |
地质学 | 62803篇 |
海洋学 | 23131篇 |
天文学 | 1507篇 |
综合类 | 8150篇 |
自然地理 | 10186篇 |
出版年
2024年 | 608篇 |
2023年 | 1548篇 |
2022年 | 3796篇 |
2021年 | 4728篇 |
2020年 | 4783篇 |
2019年 | 7899篇 |
2018年 | 7523篇 |
2017年 | 7142篇 |
2016年 | 7054篇 |
2015年 | 7469篇 |
2014年 | 6942篇 |
2013年 | 8232篇 |
2012年 | 8673篇 |
2011年 | 8644篇 |
2010年 | 8571篇 |
2009年 | 7689篇 |
2008年 | 7276篇 |
2007年 | 6994篇 |
2006年 | 6457篇 |
2005年 | 5661篇 |
2004年 | 5059篇 |
2003年 | 3990篇 |
2002年 | 3789篇 |
2001年 | 3423篇 |
2000年 | 2911篇 |
1999年 | 2148篇 |
1998年 | 1886篇 |
1997年 | 1879篇 |
1996年 | 1506篇 |
1995年 | 1391篇 |
1994年 | 1238篇 |
1993年 | 1214篇 |
1992年 | 1052篇 |
1991年 | 774篇 |
1990年 | 758篇 |
1989年 | 596篇 |
1988年 | 510篇 |
1987年 | 398篇 |
1986年 | 327篇 |
1985年 | 251篇 |
1984年 | 293篇 |
1983年 | 171篇 |
1982年 | 213篇 |
1981年 | 154篇 |
1980年 | 110篇 |
1979年 | 130篇 |
1978年 | 57篇 |
1977年 | 50篇 |
1971年 | 54篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
61.
62.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献
63.
介绍了自动高精度测距系统。该系统能以5×10-7的测距精度测定多个观测点的形变,可作为跨断层动态连续观测的新仪器。 相似文献
64.
Ren Tinawi Marc Sarrazin Andr Filiatrault 《Soil Dynamics and Earthquake Engineering》1993,12(8):469-477
The 1990 edition of the National Building Code of Canada (Associate Committee of the National Building Code, National Research Council, Ottawa, 1990) makes a clear distinction between eastern and western Canada in terms of seismic acceleration and velocity zones. While it is well established that ground motions can be amplified significantly through loose clay deposits, no results are available that take into consideration the typical high frequency content of ground motions in eastern Canada. This paper develops ground amplification curves for clays having depths between 10 and 70 m excited by typical eastern Canadian ground motions scaled to two different values of peak horizontal accelerations. Simplified free-field spectral design curves, which could be used by structural designers, are proposed. The curves show that maximum spectral accelerations occur for structural periods between 0.2 and 0.5 s. In addition, soil depth does not appear to be an important parameter controlling the response of typical clay deposits in eastern Canada. 相似文献
65.
Based on the Intensive Field Campaign(IFC-1)data of Boreal Ecosystem-Atmosphere Study(BOREAS).a three-dimensional meso-β scale model is used to simulate the effect of boreal forests onthe lower atmosphere.A fine horizontal resolution of 2 km×2 km is used in order to distinguish thevegetative heterogeneity in the boreal region.A total of 20×25 grid points cover the entire sub-modeling area in BOREAS' South Study Area(SSA).The ecosystem types and their coverage ineach grid square are extracted from the North American Land Cover Characteristics Data Base(NALCCD)generated by the U.S.Geographical Survey(USGS)and the University of Nebraska-Lincoln(UNL).The topography of the study area is taken from the Digital Elevation Map(DEM)of USGS.The model outputs include the components of the energy balance budget within the canopyand at the ground.the turbulence parameters in the atmospheric boundary layer and the wind.temperature and humidity profiles extending up to a height of 1500 m.In addition to the fine timeand spatial step,the unique feature of the present model is the incorporation of both dynamic andbiological effects of the Boreal forest into the model parameterization scheme.The model resultscompare favorably with BOREAS' IFC-1 data in 1994 when the forest was in the luxuriant growingperiod. 相似文献
66.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
67.
68.
Yi-Zhong Fan Zi-Gao Dai Yong-Feng Huang Tan Lu Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2002,2(5):449-453
The optical flash accompanying GRB 990123 is believed to be powered by the reverse shock of a thin shell. With the best-fit physical parameters for GRB 990123 and the assumption that the parameters in the optical flash are the same as in the afterglow, we show that: 1) the shell is thick rather than thin, and we have provided the light curve for the thick shell case which coincides with the observation; 2) the theoretical peak flux of the optical flash accounts for only 3×10~-4 of the observed. In order to remove this discrepancy, the physical parameters, the electron energy and magnetic ratios, εe and εB, should be 0.61 and 0.39, which are very different from their values for the late afterglow. 相似文献
69.
70.
BIAN Jian-min LIN Nian-feng TANG Jie College of Environment Resources Jilin University Changchun Jilin China 《东北亚地学研究》2005,(Z1)
Desertification is an environmental issue in the world. The salt-alkalization desertification land area formed by both primary and secondary salt-alkalization has extended in a large scale, which has become a significant eco-environmental problem. Based on the characteristics of eco-environment and the situation of desertification in western Songnen plain, this paper reports the analyzes of its formation in background and cause. An early warning system on the salt-alkalization desertification is established and the GIS technology is used to abstract the information of desertification evaluation index. Supported by the integrated technology of the GIS and ANN, the orientation and quantitative result of desertification are gained, which is helpful to the eco-environment protection and resource development in western Songnen Plain. 相似文献