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   53105篇
  免费   938篇
  国内免费   491篇
测绘学   1588篇
大气科学   3889篇
地球物理   11113篇
地质学   18030篇
海洋学   4636篇
天文学   11857篇
综合类   144篇
自然地理   3277篇
  2021年   451篇
  2020年   526篇
  2019年   603篇
  2018年   1243篇
  2017年   1157篇
  2016年   1516篇
  2015年   924篇
  2014年   1430篇
  2013年   2630篇
  2012年   1604篇
  2011年   2107篇
  2010年   1890篇
  2009年   2560篇
  2008年   2262篇
  2007年   2209篇
  2006年   2150篇
  2005年   1666篇
  2004年   1799篇
  2003年   1615篇
  2002年   1573篇
  2001年   1333篇
  2000年   1259篇
  1999年   1088篇
  1998年   1082篇
  1997年   1024篇
  1996年   851篇
  1995年   797篇
  1994年   765篇
  1993年   673篇
  1992年   606篇
  1991年   601篇
  1990年   590篇
  1989年   580篇
  1988年   524篇
  1987年   635篇
  1986年   565篇
  1985年   707篇
  1984年   841篇
  1983年   723篇
  1982年   682篇
  1981年   651篇
  1980年   549篇
  1979年   559篇
  1978年   576篇
  1977年   498篇
  1976年   446篇
  1975年   448篇
  1974年   405篇
  1973年   452篇
  1972年   308篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities.  相似文献   
92.
93.
Lithology and Mineral Resources - The chemical composition and Nd isotope systematics were obtained for mudrocks (mudstones) from sections of the Siberian hypostratotype of the Riphean and Vendian...  相似文献   
94.
Natural Resources Research - Exploration ventures in frontier areas have high risks. Before committing to them, firms prepare regional resource assessments to evaluate the potential payoffs. With...  相似文献   
95.
96.
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   
97.
98.
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   
99.
Relationships of mineralized microbiota with the content of polycyclic aromatic hydrocarbons in hydrothermal systems are considered. It has been established that the mineralized microbiota can serve as an indicator of hydrothermal hydrocarbon flows in present-day and ancient deposits.  相似文献   
100.
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   
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