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   44273篇
  免费   534篇
  国内免费   308篇
测绘学   1060篇
大气科学   2892篇
地球物理   8860篇
地质学   15317篇
海洋学   3763篇
天文学   10961篇
综合类   97篇
自然地理   2165篇
  2021年   409篇
  2020年   452篇
  2019年   453篇
  2018年   1048篇
  2017年   950篇
  2016年   1171篇
  2015年   650篇
  2014年   1140篇
  2013年   2180篇
  2012年   1293篇
  2011年   1731篇
  2010年   1540篇
  2009年   2180篇
  2008年   1800篇
  2007年   1816篇
  2006年   1694篇
  2005年   1277篇
  2004年   1275篇
  2003年   1184篇
  2002年   1135篇
  2001年   1014篇
  2000年   963篇
  1999年   844篇
  1998年   859篇
  1997年   829篇
  1996年   699篇
  1995年   713篇
  1994年   634篇
  1993年   542篇
  1992年   504篇
  1991年   517篇
  1990年   592篇
  1989年   509篇
  1988年   465篇
  1987年   594篇
  1986年   496篇
  1985年   616篇
  1984年   701篇
  1983年   662篇
  1982年   580篇
  1981年   607篇
  1980年   505篇
  1979年   478篇
  1978年   482篇
  1977年   436篇
  1976年   423篇
  1975年   419篇
  1974年   400篇
  1973年   428篇
  1971年   263篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
72.
73.
74.
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   
75.
76.
77.
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   
78.
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   
79.
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   
80.
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