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   46073篇
  免费   611篇
  国内免费   324篇
测绘学   1127篇
大气科学   3085篇
地球物理   9195篇
地质学   15880篇
海洋学   3963篇
天文学   11281篇
综合类   100篇
自然地理   2377篇
  2021年   434篇
  2020年   478篇
  2019年   498篇
  2018年   1095篇
  2017年   994篇
  2016年   1235篇
  2015年   711篇
  2014年   1181篇
  2013年   2316篇
  2012年   1364篇
  2011年   1826篇
  2010年   1591篇
  2009年   2267篇
  2008年   1902篇
  2007年   1905篇
  2006年   1782篇
  2005年   1320篇
  2004年   1347篇
  2003年   1267篇
  2002年   1198篇
  2001年   1066篇
  2000年   1010篇
  1999年   875篇
  1998年   882篇
  1997年   846篇
  1996年   715篇
  1995年   727篇
  1994年   649篇
  1993年   564篇
  1992年   526篇
  1991年   523篇
  1990年   611篇
  1989年   522篇
  1988年   471篇
  1987年   603篇
  1986年   497篇
  1985年   646篇
  1984年   723篇
  1983年   681篇
  1982年   588篇
  1981年   627篇
  1980年   515篇
  1979年   497篇
  1978年   500篇
  1977年   456篇
  1976年   436篇
  1975年   433篇
  1974年   416篇
  1973年   442篇
  1971年   272篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
This paper goes some way towards redressing the lack of geographical literature on charity through exploring the geography of the British domestic charitable sector. The size and geography of the third sector is outlined, followed by an analysis of how almshouses can be understood as inherently geographical and deeply embedded in local social networks of inclusion as well as exclusion.  相似文献   
85.
Studies evaluating the reproductive pattern of Mytilus edulis L. were conducted in western and eastern Iceland at two sites at about the same latitude but with different temperature regimes. Mussels were sampled once or sometimes twice a month during two years in Breidifjördur, western Iceland and one year at Mjoifjördur, eastern Iceland. Gonad development was monitored by microscopic observation of thin sections of the gonads. The initiation of gonad development was observed in January in Breidifjördur while in Mjoifjördur some of the animals started developing gonads in October, a month before spawning was over in the population. Spawning started in late June or July, peaked in August and continued until November at both sites. Nutrient reserve stores seemed to be limited and used for initiation of gonad development in winter but were not sufficient for maturation of the gonads. The main growth of the gonads occured in spring in conjunction with phytoplankton blooming and renewal of food resources.  相似文献   
86.
A zoobenthos submodel is included in an ecosystem model. The new model is used to assess the role of zoobenthos in the phosphorus exchange at the water–bed interface, in particular, the phosphorus cycle in the water body ecosystem is described more accurately. The calculated zoobenthos distribution over the bed of a lake can be used in modeling the lake ichthyocenoses.  相似文献   
87.
88.
The present contribution is the second of four parts. It considers the precision and correlation of the least-squares estimators of the carrier phase ambiguities. It is shown how the precision and correlation of the double-differenced ambiguities as well as of the widelane ambiguities are effected by the observation weights, by the number of satellites tracked, by the number of observation epochs used, and by the change over time of the relative receiver-satellite geometry. Also the ability of the widelane transformation to decorrelate and to improve the precision is investigated. Received: 16 July 1996 / Accepted: 14 November 1996  相似文献   
89.
90.
Pre-weighed blocks of a Jurassic Limestone were exposed on the ground surface in the coastal Namib Desert for a period of 2 years. The environment is both salty and foggy. Some of the blocks suffered extensive disintegration, and laboratory analyses (including geochemistry, XRD and SEM) indicate that the weathered samples have a high halite (sodium chloride) content. Cycles of wetting and drying associated with the frequent fog events of the area cause cycles of halite crystallization. Rocks exposed at the surface absorb salts from the surrounding desert surface and then disintegrate, contributing to planation of the landscape.  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