全文获取类型
收费全文 | 41157篇 |
免费 | 19244篇 |
国内免费 | 43758篇 |
专业分类
测绘学 | 3252篇 |
大气科学 | 22653篇 |
地球物理 | 14166篇 |
地质学 | 37842篇 |
海洋学 | 16691篇 |
天文学 | 1298篇 |
综合类 | 5201篇 |
自然地理 | 3056篇 |
出版年
2024年 | 155篇 |
2023年 | 368篇 |
2022年 | 807篇 |
2021年 | 1115篇 |
2020年 | 2211篇 |
2019年 | 5681篇 |
2018年 | 5942篇 |
2017年 | 5624篇 |
2016年 | 5801篇 |
2015年 | 5096篇 |
2014年 | 4627篇 |
2013年 | 5228篇 |
2012年 | 4857篇 |
2011年 | 4680篇 |
2010年 | 4548篇 |
2009年 | 4008篇 |
2008年 | 3243篇 |
2007年 | 3222篇 |
2006年 | 2815篇 |
2005年 | 2743篇 |
2004年 | 2963篇 |
2003年 | 2695篇 |
2002年 | 2417篇 |
2001年 | 2253篇 |
2000年 | 1917篇 |
1999年 | 2111篇 |
1998年 | 2068篇 |
1997年 | 2064篇 |
1996年 | 1716篇 |
1995年 | 1593篇 |
1994年 | 1432篇 |
1993年 | 1367篇 |
1992年 | 1148篇 |
1991年 | 850篇 |
1990年 | 800篇 |
1989年 | 692篇 |
1988年 | 589篇 |
1987年 | 424篇 |
1986年 | 366篇 |
1985年 | 278篇 |
1984年 | 307篇 |
1983年 | 178篇 |
1982年 | 213篇 |
1981年 | 160篇 |
1980年 | 119篇 |
1979年 | 111篇 |
1978年 | 53篇 |
1977年 | 44篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
徐江 《地球信息科学学报》1996,(1):21-25
本文阐述了地理信息系统在环境地球化学中的应用,提出建立区域环境地球化学空间信息系统的方法、功能及组成,并以红枫湖区域环境地球化学空间信息系统为例,作了分析。 相似文献
72.
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
73.
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
74.
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
75.
76.
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
77.
78.
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
79.
To seek nonlinear solutions of force-free magnetic fields, some symmetries or approximations are usually invoked. We consider magnetic fields lying on coordinate surfaces of an orthogonal curvilinear coordinate system. We conclude that only fields on parallel planes or spherical shells can be expressed in the form provided by Low in 1980s. These force-free fields are stable against small perturbations with rigid boundaries. Fields on cylindrical shells are also considered. 相似文献
80.
秦岭凤太矿田层控铅锌(铜)矿床的金属物质、硫和成矿溶液主要来自深部基底的岩石,属海底喷流—沉积成因矿床。从这一理论认识出发可进一步分析控矿地质条件及今后在该区有效地寻找同类矿床。 相似文献