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   115271篇
  免费   1547篇
  国内免费   1433篇
测绘学   3305篇
大气科学   7917篇
地球物理   21771篇
地质学   44695篇
海洋学   9342篇
天文学   22855篇
综合类   2356篇
自然地理   6010篇
  2022年   619篇
  2021年   1034篇
  2020年   1121篇
  2019年   1254篇
  2018年   7813篇
  2017年   6919篇
  2016年   5589篇
  2015年   1589篇
  2014年   2696篇
  2013年   4509篇
  2012年   4097篇
  2011年   7075篇
  2010年   6106篇
  2009年   7294篇
  2008年   6172篇
  2007年   6959篇
  2006年   3628篇
  2005年   2932篇
  2004年   2990篇
  2003年   2864篇
  2002年   2637篇
  2001年   2028篇
  2000年   2026篇
  1999年   1551篇
  1998年   1617篇
  1997年   1466篇
  1996年   1244篇
  1995年   1241篇
  1994年   1043篇
  1993年   1008篇
  1992年   929篇
  1991年   967篇
  1990年   933篇
  1989年   818篇
  1988年   752篇
  1987年   883篇
  1986年   774篇
  1985年   945篇
  1984年   1070篇
  1983年   1032篇
  1982年   950篇
  1981年   907篇
  1980年   812篇
  1979年   748篇
  1978年   727篇
  1977年   613篇
  1976年   623篇
  1975年   610篇
  1974年   584篇
  1973年   654篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin.  相似文献   
16.
17.
18.
Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years.  相似文献   
19.
The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996.  相似文献   
20.
Nowadays, the research works on landscape at fine scales using high-resolution images are uncommon.This research is based on the analysis of the combination of remote sensing data (1KONOS imagery acquired in 2002 and historical aerial photo taken in 1942). In the paper, the ecotopes in Qiujiadou and Xishao villages in Yixing City of Jiangsu Province in 1942 and 2002 were compared and landscape changes as well as the causes of the considerable changes were analyzed. It was found that the ecotope changes were at greater level in some aspects such as water surface and perennial vegetation coverage etc. This study at fine scale is globally significant for the rural areas, especially for the subsistence agricultural land, which occupies larger percentage in the earth. And it analyzes the structure of landscape based on a new landscape classification system--stratifications method.  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