首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   94513篇
  免费   2517篇
  国内免费   2305篇
测绘学   2710篇
大气科学   7707篇
地球物理   18439篇
地质学   36702篇
海洋学   8001篇
天文学   19420篇
综合类   952篇
自然地理   5404篇
  2022年   627篇
  2021年   965篇
  2020年   996篇
  2019年   1074篇
  2018年   4358篇
  2017年   4112篇
  2016年   3732篇
  2015年   1686篇
  2014年   2498篇
  2013年   4088篇
  2012年   3430篇
  2011年   5644篇
  2010年   4970篇
  2009年   5878篇
  2008年   5081篇
  2007年   5425篇
  2006年   3138篇
  2005年   2934篇
  2004年   2706篇
  2003年   2647篇
  2002年   2332篇
  2001年   2027篇
  2000年   1972篇
  1999年   1718篇
  1998年   1799篇
  1997年   1715篇
  1996年   1339篇
  1995年   1365篇
  1994年   1170篇
  1993年   1053篇
  1992年   986篇
  1991年   886篇
  1990年   933篇
  1989年   793篇
  1988年   729篇
  1987年   856篇
  1986年   707篇
  1985年   884篇
  1984年   954篇
  1983年   882篇
  1982年   853篇
  1981年   730篇
  1980年   691篇
  1979年   616篇
  1978年   605篇
  1977年   554篇
  1976年   543篇
  1975年   500篇
  1974年   507篇
  1973年   468篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples.  相似文献   
44.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem.  相似文献   
45.
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer.  相似文献   
46.
47.
48.
49.
The interaction of free convection with thermal radiation of the oscillatory flow past a vertical plate is studied. The Rosseland approximation is used to describe the radiative heat flux in the energy equation.  相似文献   
50.
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号