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   40884篇
  免费   445篇
  国内免费   351篇
安全科学   1321篇
废物处理   1735篇
环保管理   5591篇
综合类   7350篇
基础理论   10335篇
环境理论   15篇
污染及防治   10121篇
评价与监测   2593篇
社会与环境   2371篇
灾害及防治   248篇
  2022年   323篇
  2021年   386篇
  2020年   238篇
  2019年   318篇
  2018年   567篇
  2017年   580篇
  2016年   881篇
  2015年   711篇
  2014年   1030篇
  2013年   3265篇
  2012年   1278篇
  2011年   1738篇
  2010年   1398篇
  2009年   1506篇
  2008年   1778篇
  2007年   1737篇
  2006年   1579篇
  2005年   1342篇
  2004年   1338篇
  2003年   1293篇
  2002年   1208篇
  2001年   1469篇
  2000年   1016篇
  1999年   660篇
  1998年   485篇
  1997年   500篇
  1996年   550篇
  1995年   606篇
  1994年   550篇
  1993年   487篇
  1992年   516篇
  1991年   506篇
  1990年   486篇
  1989年   486篇
  1988年   425篇
  1987年   367篇
  1986年   360篇
  1985年   378篇
  1984年   386篇
  1983年   374篇
  1982年   402篇
  1981年   359篇
  1980年   297篇
  1979年   305篇
  1978年   281篇
  1977年   240篇
  1976年   235篇
  1974年   247篇
  1973年   271篇
  1972年   246篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
401.
402.
The modern consumer is very much interested in healthy food. The reason is that a special group of consumers is focusing more and more attention on health and nutrition problems. Further, there is increased emphasis on education in food science at universities as well as polytechnics. For some years worldwide dietary goals are published with the intention to reduce nutrition-based sickness. For the first time in our nutrition report 1988, clear proposals for optimal nutrition were formulated.  相似文献   
403.
404.
Upper limb reduction was diagnosed by ultrasound scan at 17 weeks after chorion villus sampling at 9 weeks' gestation. Pregnancy was terminated and necropsy confirmed limb reduction in an otherwise normal fetus. The relationship of limb reduction to amniotic band syndrome is discussed.  相似文献   
405.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  相似文献   
406.
407.
The excellent technical assistance of H. Führer and I. Leib is appreciated. Part of the work was supported by the Bundesministerium für Forschung und Technologie, the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and from the Leitz and Hoechst companies. This paper is part of the M. D. thesis of Ch.L.  相似文献   
408.
409.
Consensus on the evolutionary position of turtles within the amniote phylogeny has eluded evolutionary biologists for more than a century. This phylogenetic problem has remained unsolved partly because turtles have such a unique morphology that only few characters can be used to link them with any other group of amniotes. Among the many alternative hypotheses that have been postulated to explain the origin and phylogenetic relationships of turtles, a general agreement among paleontologists emerged in favoring the placement of turtles as the only living survivors of the anapsid reptiles (those that lack temporal fenestrae in the skull). However, recent morphological and molecular studies have radically changed our view of amniote phylogenetic relationships, and evidence is accumulating that supports the diapsid affinities of turtles. Molecular studies favor archosaurs (crocodiles and birds) as the living sister group of turtles, whereas morphological studies support lepidosaurs (tuatara, lizards, and snakes) as the closest living relatives of turtles. Accepting these hypotheses implies that turtles cannot be viewed any longer as primitive reptiles, and that they might have lost the temporal holes in the skull secondarily rather than never having had them.  相似文献   
410.
 The Australian buprestid beetle Merimna atrata (Coleoptera: Buprestidae) approaches forest fires because its larvae develop in freshly burnt wood. So far nothing is known about possible sensory systems enabling the beetles to detect fires and to cope with the thermal environment close to the flames. We found that M. atrata has two pairs of infrared (IR) organs on the ventrolateral sides of the abdomen. Each IR organ consists of a specialized IR-absorbing area which is innervated by one thermosensitive multipolar neuron. The primary dendritic branches ramify into more than 800 closely packed terminal endings which contain a large number of mitochondria. We called the special morphology of the dendritic region a terminal dendritic mass. The type of IR receptor found in M. atrata is unique in insects and can best be compared with the IR organs of boid snakes. Received: 14 August 2000 / Accepted in revised form: 18 October 2000  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