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   45284篇
  免费   679篇
  国内免费   257篇
测绘学   802篇
大气科学   3617篇
地球物理   9137篇
地质学   17412篇
海洋学   3705篇
天文学   8912篇
综合类   93篇
自然地理   2542篇
  2021年   456篇
  2020年   528篇
  2019年   598篇
  2018年   1046篇
  2017年   1056篇
  2016年   1125篇
  2015年   615篇
  2014年   1078篇
  2013年   1978篇
  2012年   1250篇
  2011年   1719篇
  2010年   1517篇
  2009年   1884篇
  2008年   1702篇
  2007年   1736篇
  2006年   1649篇
  2005年   1135篇
  2004年   1138篇
  2003年   1174篇
  2002年   1045篇
  2001年   898篇
  2000年   835篇
  1999年   755篇
  1998年   767篇
  1997年   773篇
  1996年   678篇
  1995年   628篇
  1994年   560篇
  1993年   522篇
  1992年   560篇
  1991年   581篇
  1990年   584篇
  1989年   523篇
  1988年   508篇
  1987年   572篇
  1986年   552篇
  1985年   635篇
  1984年   710篇
  1983年   715篇
  1982年   691篇
  1981年   644篇
  1980年   578篇
  1979年   595篇
  1978年   527篇
  1977年   532篇
  1976年   467篇
  1975年   481篇
  1974年   462篇
  1973年   512篇
  1971年   359篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
René Rutten, Director of the Isaac Newton Group of Telescopes, sets the scene for future developments in international astronomy on La Palma.  相似文献   
52.
A recent article by Beer et al. (1974) in Marine Geology describes an in-situ suspended sediment sampling system which utilizes a pump/motor unit, filter holders, and a lead-acid battery power source. Two aspects of their article may be misleading: the use of certain filter material as X-ray diffraction mounts, and the technique by which an oil-filled battery case may be operated.  相似文献   
53.
The sodian stellerite (a zeolite) occurs as lustrous white or slightly pink, easily cleavable lamellae, filling cavities and fractures in an acid lava (andesite or rhyolite) in the cliff below S. Efisio Tower, near Capo Pula, Cagliari, Sardegna, Italy. The principal forms present are {010}, {011}, {111}. Single crystal photographs show an orthorhombic symmetry and Ammm (or Ammm) space group. An indexed X-ray diffraction powder pattern is provided. Unit cell dimensions, chemical formula, density, optical properties and thermal behaviour are given.  相似文献   
54.
The gradient (ordination) analysis was used to find the tendencies and the rate of changes in discrete parameters of the cycle of forest phytomasses accompanying a growing thermoarid climatic trend. The prognostic estimates of biotic regulation of the carbon cycle by forest biogeocenoses according to the HadCM3 (version A2) climatic scenarios, describing the most powerful coming global warming, are presented.  相似文献   
55.
The physical-synoptic principles of the automated method of summer precipitation forecasting introduced into operational prognostic practice in 2006 by the decree of the Central Methodical Commission of the Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) are presented. Beside that, improved modifications of this method, which are automatically updated, are shown. Validation of those updates based on observational data collected in 2004 has shown improvement of all major criteria of forecasts efficiency. The performed improvement is based on the more detailed quantitative realization of mechanism of various showers formation (including heavy rainfalls).  相似文献   
56.
Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.  相似文献   
57.
58.
This paper reports the results of the experimental determination of the coefficient of sorption of rare-earth elements and yttrium (REY) under conditions of acidic pH using several strains of heterotrophic bacteria (Microbacterium sp., Curtobacterium sp., Bacillus subtilis, Pseudomonas putida, and Bacillus pumilis) that are widespread in natural and technogenic waters of the Far East (Russia). Insignificant fractionation between heavy and light rare-earth elements, negative cerium and dysprosium anomalies, and a positive europium anomaly were revealed. The selectivity of REY biosorption by gram-positive and gram-negative bacteria, as well as inertia of the biosorption process under more acidic conditions of the medium, were shown.  相似文献   
59.
60.
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