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   71156篇
  免费   1405篇
  国内免费   649篇
测绘学   1723篇
大气科学   5044篇
地球物理   14275篇
地质学   25281篇
海洋学   6184篇
天文学   16350篇
综合类   210篇
自然地理   4143篇
  2022年   398篇
  2021年   697篇
  2020年   778篇
  2019年   830篇
  2018年   1900篇
  2017年   1768篇
  2016年   2241篇
  2015年   1321篇
  2014年   2190篇
  2013年   3779篇
  2012年   2289篇
  2011年   3132篇
  2010年   2623篇
  2009年   3528篇
  2008年   3265篇
  2007年   3054篇
  2006年   2883篇
  2005年   2367篇
  2004年   2254篇
  2003年   2114篇
  2002年   1932篇
  2001年   1805篇
  2000年   1719篇
  1999年   1378篇
  1998年   1468篇
  1997年   1389篇
  1996年   1098篇
  1995年   1143篇
  1994年   964篇
  1993年   879篇
  1992年   851篇
  1991年   760篇
  1990年   856篇
  1989年   718篇
  1988年   653篇
  1987年   816篇
  1986年   665篇
  1985年   857篇
  1984年   920篇
  1983年   865篇
  1982年   834篇
  1981年   708篇
  1980年   664篇
  1979年   606篇
  1978年   604篇
  1977年   552篇
  1976年   540篇
  1975年   499篇
  1974年   507篇
  1973年   469篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
31.
32.
33.
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   
34.
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   
35.
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   
36.
37.
38.
39.
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   
40.
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