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   44463篇
  免费   555篇
  国内免费   308篇
测绘学   1053篇
大气科学   2931篇
地球物理   8876篇
地质学   15383篇
海洋学   3784篇
天文学   10991篇
综合类   100篇
自然地理   2208篇
  2021年   413篇
  2020年   455篇
  2019年   462篇
  2018年   1064篇
  2017年   958篇
  2016年   1173篇
  2015年   669篇
  2014年   1148篇
  2013年   2207篇
  2012年   1291篇
  2011年   1759篇
  2010年   1563篇
  2009年   2195篇
  2008年   1806篇
  2007年   1821篇
  2006年   1700篇
  2005年   1278篇
  2004年   1276篇
  2003年   1197篇
  2002年   1151篇
  2001年   1024篇
  2000年   981篇
  1999年   834篇
  1998年   857篇
  1997年   831篇
  1996年   705篇
  1995年   717篇
  1994年   630篇
  1993年   544篇
  1992年   512篇
  1991年   516篇
  1990年   588篇
  1989年   507篇
  1988年   460篇
  1987年   589篇
  1986年   488篇
  1985年   619篇
  1984年   702篇
  1983年   667篇
  1982年   579篇
  1981年   614篇
  1980年   505篇
  1979年   477篇
  1978年   484篇
  1977年   444篇
  1976年   423篇
  1975年   420篇
  1974年   402篇
  1973年   427篇
  1971年   263篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
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   
76.
Data of hydrological and hydrochemical observations conducted in August 2000 at Lake Seliger and its major tributaries are presented. The analyzed characteristics included: O2, H2S, CH4, microelements; mineral and organic compounds of P and N, ionic composition components (HCO3 , Cl, Na+, K+, dry residue, pH; color index, electrical conductivity. Bottom sediment samples were analyzed for microelement concentrations, CH4, oil hydrocarbons. The influence of the basin on the ecological state of the lake was assessed, and tendencies in the evolution of its ecosystem are analyzed. It is shown that the ecological conditions of the lake has not changed significantly since 1960–1991, however, nutrient concentrations in the lake water was found to increase.  相似文献   
77.
78.
79.
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   
80.
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   
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