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   74033篇
  免费   1470篇
  国内免费   674篇
测绘学   1799篇
大气科学   5328篇
地球物理   14954篇
地质学   26576篇
海洋学   6363篇
天文学   16685篇
综合类   230篇
自然地理   4242篇
  2022年   407篇
  2021年   704篇
  2020年   807篇
  2019年   857篇
  2018年   2208篇
  2017年   2086篇
  2016年   2380篇
  2015年   1432篇
  2014年   2286篇
  2013年   3844篇
  2012年   2437篇
  2011年   3253篇
  2010年   2667篇
  2009年   3557篇
  2008年   3334篇
  2007年   3098篇
  2006年   2933篇
  2005年   2769篇
  2004年   2818篇
  2003年   2481篇
  2002年   1978篇
  2001年   1818篇
  2000年   1726篇
  1999年   1387篇
  1998年   1474篇
  1997年   1392篇
  1996年   1105篇
  1995年   1147篇
  1994年   963篇
  1993年   877篇
  1992年   853篇
  1991年   761篇
  1990年   858篇
  1989年   719篇
  1988年   653篇
  1987年   816篇
  1986年   663篇
  1985年   854篇
  1984年   921篇
  1983年   864篇
  1982年   832篇
  1981年   704篇
  1980年   652篇
  1979年   597篇
  1978年   597篇
  1977年   547篇
  1976年   531篇
  1975年   496篇
  1974年   502篇
  1973年   465篇
排序方式: 共有10000条查询结果,搜索用时 15 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