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   69158篇
  免费   735篇
  国内免费   345篇
测绘学   1406篇
大气科学   4523篇
地球物理   13175篇
地质学   24728篇
海洋学   6347篇
天文学   16084篇
综合类   201篇
自然地理   3774篇
  2022年   503篇
  2021年   902篇
  2020年   958篇
  2019年   1047篇
  2018年   2074篇
  2017年   1884篇
  2016年   2190篇
  2015年   1107篇
  2014年   2108篇
  2013年   3628篇
  2012年   2339篇
  2011年   2968篇
  2010年   2719篇
  2009年   3439篇
  2008年   2973篇
  2007年   3052篇
  2006年   2855篇
  2005年   2012篇
  2004年   1959篇
  2003年   1836篇
  2002年   1833篇
  2001年   1604篇
  2000年   1571篇
  1999年   1258篇
  1998年   1257篇
  1997年   1162篇
  1996年   986篇
  1995年   1028篇
  1994年   825篇
  1993年   807篇
  1992年   730篇
  1991年   787篇
  1990年   732篇
  1989年   636篇
  1988年   589篇
  1987年   706篇
  1986年   626篇
  1985年   750篇
  1984年   853篇
  1983年   826篇
  1982年   742篇
  1981年   706篇
  1980年   631篇
  1979年   592篇
  1978年   597篇
  1977年   500篇
  1976年   511篇
  1975年   507篇
  1974年   466篇
  1973年   522篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
212.
 Stokes' formula from 1849 is still the basis for the gravimetric determination of the geoid. The modification of the formula, originating with Molodensky, aims at reducing the truncation error outside a spherical cap of integration. This goal is still prevalent among various modifications. In contrast to these approaches, some least-squares types of modification that aim at reducing the truncation error, as well as the error stemming from the potential coefficients, are demonstrated. The least-squares estimators are provided in the two cases that (1) Stokes' kernel is a priori modified (e.g. according to Molodensky's approach) and (2) Stokes' kernel is optimally modified to minimize the global mean square error. Meissl-type modifications are also studied. In addition, the use of a higher than second-degree reference field versus the original (Pizzetti-type) reference field is discussed, and it is concluded that the former choice of reference field implies increased computer labour to achieve the same result as with the original reference field. Received: 14 December 1998 / Accepted: 4 October 1999  相似文献   
213.
The Lower Cretaceous Fortress Mountain Formation occupies a spatial and temporal niche between syntectonic deposits at the Brooks Range orogenic front and post‐tectonic strata in the Colville foreland basin. The formation includes basin‐floor fan, marine‐slope and fan‐delta facies that define a clinoform depositional profile. Texture and composition of clasts in the formation suggest progressive burial of a tectonic wedge‐front that included older turbidites and mélange. These new interpretations, based entirely on outcrop study, suggest that the Fortress Mountain Formation spans the boundary between orogenic wedge and foredeep, with proximal strata onlapping the tectonic wedge‐front and distal strata downlapping the floor of the foreland basin. Our reconstruction suggests that clinoform amplitude reflects the structural relief generated by tectonic wedge development and load‐induced flexural subsidence of the foreland basin.  相似文献   
214.
215.
The studies carried out throughout the world have indicated that there are differences between environmental attitudes and environmentally responsible behaviors of undergraduate students. In what ways the environmental attitudes and behaviors of the students who will protect and manage the resources of the country in the future have changed is an important issue? This study was aimed at determining the environmental attitudes and environmentally responsible behaviors of the undergraduate students of Abant Ýzzet Baysal University toward environmental issues. In addition, the effects of the faculty in which the students are enrolled, locality and gender on the determined environmental attitudes and environmentally responsible behaviors of the students were investigated. The data were gathered from 507 students in 2005. To explain the environmental attitudes and environmentally responsible behaviors of undergraduate students toward environmental issues, factor analysis was used with Varimax Rotation method. To determine the changes of the environmental attitudes and environmentally responsible behaviors of the students with regard to the faculty, locality and gender, one-way analysis of variance was used. According to the results, students highly support the environmental attitudes and highly participate only in consumerism behaviors. Finally, it was determined if faculty and gender had an effect on the environmental attitudes and behaviors of the students.  相似文献   
216.
217.
Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.  相似文献   
218.
219.
Fildes Peninsula, in King George Island, Antarctica, has a great concentration of international facilities, and it has clearly been affected by human activities. The objective of this 5-year study was ...  相似文献   
220.
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