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   43925篇
  免费   539篇
  国内免费   304篇
测绘学   1056篇
大气科学   2875篇
地球物理   8781篇
地质学   15202篇
海洋学   3757篇
天文学   10834篇
综合类   98篇
自然地理   2165篇
  2021年   409篇
  2020年   451篇
  2019年   456篇
  2018年   1051篇
  2017年   949篇
  2016年   1166篇
  2015年   646篇
  2014年   1137篇
  2013年   2174篇
  2012年   1280篇
  2011年   1729篇
  2010年   1536篇
  2009年   2170篇
  2008年   1796篇
  2007年   1811篇
  2006年   1681篇
  2005年   1259篇
  2004年   1258篇
  2003年   1177篇
  2002年   1122篇
  2001年   1012篇
  2000年   958篇
  1999年   828篇
  1998年   849篇
  1997年   816篇
  1996年   696篇
  1995年   704篇
  1994年   627篇
  1993年   537篇
  1992年   503篇
  1991年   509篇
  1990年   585篇
  1989年   500篇
  1988年   457篇
  1987年   585篇
  1986年   485篇
  1985年   611篇
  1984年   690篇
  1983年   657篇
  1982年   573篇
  1981年   605篇
  1980年   500篇
  1979年   472篇
  1978年   476篇
  1977年   434篇
  1976年   420篇
  1975年   417篇
  1974年   397篇
  1973年   426篇
  1971年   260篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
72.
The Cone-in-Cone Structure and Its Origin   总被引:1,自引:0,他引:1  
Morphostructural investigation of carbonate cone-in-cone formations allows to conclude that they belong to self-organizing (dissipative, according to I. Prigogine's terminology) systems of the geological past formed in a thermogradient field at the expense of energy of heat and mass transfer (Prigogine and Stengers, 1984). First, the fluid-convective metasomatic hypothesis unites and reconciles the most well-known hypotheses that previously seemed to be incompatible and transforms them to rather consistent particular cases of a more intricate multistage geological phenomenon. Second, it helps to identify the morphologically and genetically analogous noncarbonate structures that mimic biogenic ones. The probable indicative role of cone-in-cone structure in the mapping of fluid-conducting systems is a consequence of the proposed hypothesis.  相似文献   
73.
74.
75.
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   
76.
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   
77.
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   
78.
79.
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   
80.
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