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   72660篇
  免费   1513篇
  国内免费   655篇
测绘学   1917篇
大气科学   5166篇
地球物理   14651篇
地质学   25785篇
海洋学   6269篇
天文学   16597篇
综合类   228篇
自然地理   4215篇
  2022年   412篇
  2021年   723篇
  2020年   821篇
  2019年   864篇
  2018年   2010篇
  2017年   1847篇
  2016年   2361篇
  2015年   1437篇
  2014年   2294篇
  2013年   3908篇
  2012年   2401篇
  2011年   3227篇
  2010年   2703篇
  2009年   3589篇
  2008年   3321篇
  2007年   3103篇
  2006年   2929篇
  2005年   2384篇
  2004年   2300篇
  2003年   2139篇
  2002年   1957篇
  2001年   1826篇
  2000年   1736篇
  1999年   1394篇
  1998年   1498篇
  1997年   1401篇
  1996年   1111篇
  1995年   1157篇
  1994年   975篇
  1993年   879篇
  1992年   866篇
  1991年   767篇
  1990年   869篇
  1989年   725篇
  1988年   657篇
  1987年   817篇
  1986年   665篇
  1985年   862篇
  1984年   922篇
  1983年   871篇
  1982年   840篇
  1981年   712篇
  1980年   671篇
  1979年   608篇
  1978年   608篇
  1977年   554篇
  1976年   539篇
  1975年   500篇
  1974年   502篇
  1973年   467篇
排序方式: 共有10000条查询结果,搜索用时 947 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