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   76433篇
  免费   1960篇
  国内免费   785篇
测绘学   1959篇
大气科学   5670篇
地球物理   16306篇
地质学   27337篇
海洋学   6504篇
天文学   16636篇
综合类   387篇
自然地理   4379篇
  2022年   403篇
  2021年   700篇
  2020年   785篇
  2019年   835篇
  2018年   2473篇
  2017年   2261篇
  2016年   2499篇
  2015年   1484篇
  2014年   2285篇
  2013年   3893篇
  2012年   2846篇
  2011年   3510篇
  2010年   2720篇
  2009年   3637篇
  2008年   3381篇
  2007年   3163篇
  2006年   3002篇
  2005年   3244篇
  2004年   3295篇
  2003年   2838篇
  2002年   2096篇
  2001年   1873篇
  2000年   1760篇
  1999年   1392篇
  1998年   1472篇
  1997年   1408篇
  1996年   1109篇
  1995年   1151篇
  1994年   965篇
  1993年   873篇
  1992年   853篇
  1991年   762篇
  1990年   845篇
  1989年   702篇
  1988年   633篇
  1987年   793篇
  1986年   647篇
  1985年   844篇
  1984年   905篇
  1983年   846篇
  1982年   813篇
  1981年   699篇
  1980年   653篇
  1979年   597篇
  1978年   598篇
  1977年   547篇
  1976年   533篇
  1975年   500篇
  1974年   502篇
  1973年   466篇
排序方式: 共有10000条查询结果,搜索用时 247 毫秒
61.
62.
The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990).  相似文献   
63.
64.
65.
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   
66.
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   
67.
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   
68.
69.
70.
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