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   11204篇
  免费   170篇
  国内免费   268篇
安全科学   391篇
废物处理   566篇
环保管理   1576篇
综合类   1706篇
基础理论   2743篇
环境理论   4篇
污染及防治   2678篇
评价与监测   834篇
社会与环境   1057篇
灾害及防治   87篇
  2023年   73篇
  2022年   155篇
  2021年   131篇
  2020年   94篇
  2019年   128篇
  2018年   209篇
  2017年   216篇
  2016年   303篇
  2015年   242篇
  2014年   348篇
  2013年   987篇
  2012年   401篇
  2011年   551篇
  2010年   447篇
  2009年   486篇
  2008年   538篇
  2007年   563篇
  2006年   477篇
  2005年   408篇
  2004年   388篇
  2003年   409篇
  2002年   365篇
  2001年   413篇
  2000年   293篇
  1999年   166篇
  1998年   137篇
  1997年   129篇
  1996年   151篇
  1995年   163篇
  1994年   138篇
  1993年   125篇
  1992年   118篇
  1991年   121篇
  1990年   101篇
  1989年   89篇
  1988年   92篇
  1987年   99篇
  1986年   71篇
  1985年   85篇
  1984年   84篇
  1983年   81篇
  1982年   84篇
  1981年   92篇
  1980年   68篇
  1979年   61篇
  1978年   48篇
  1977年   49篇
  1974年   44篇
  1973年   50篇
  1972年   56篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
151.
 Two main types of joints occur in the damselfly wing: mobile and immobile. Some longitudinal veins (RP2, RP3&4, and MP) are elastically joined with cross veins, whereas other longitudinal veins (IR1+, IR2+, MA+, CuA'+) are firmly joined with cross veins. In this study we mapped the distribution of serial elastic elements in the wing. The occurrence of resilin, a rubberlike protein, in mobile joints suggests that the automatic twisting mechanism of the leading edge by aerodynamic force works not by flexibility but by the elasticity of these joints. First, it should result in elastic energy storage in the distal areas of the wing. Second, serial elastic elements of wing presumably act as dampers of an aerodynamic force, which are responsible for gradual twisting of the leading edge. Received: 16 March 1999 / Accepted in revised form: 26 August 1999  相似文献   
152.
Citrullinaemia was presumed to be excluded in a fetus at risk by the direct assay of argininosuccinate synthetase in chorionic villi. The diagnosis was confirmed after amniocentesis by normal argininosuccinate synthetase activity in the cultured amniotic fluid cells and by a normal citrulline concentration in the amniotic fluid. The prediction of a normal fetus was confirmed at term by the birth of a non-citrullinaemic boy.  相似文献   
153.
Works in the natural sciences are provided with comparatively less copyright protection than literary works. Nevertheless, this protection is important- for scientists. However, more recently, modern methods and techniques of information and documentation, such as reprography, microfilm archives, electronic data storage and retrieval, and data transmission have questioned the justification and effectiveness, even in principle, of this protection. A more detailed analysis demonstrates that this involves not so much a crisis of copyright law as a crisis of the entire field of scientific information.  相似文献   
154.
155.
156.
157.
158.
159.
160.
An interdisciplinary approach based on high-resolution physical stratigraphy, biostratigraphy, organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic/carbonate Kimmeridgian/Tithonian deposits of the Boulonnais (north-western France). These rocks are the age-equivalents of some of the offshore marine source rocks of the North Sea and were deposited in an overall storm-dominated homoclinal ramp setting which may represent one of the most shore-proximal sediments of this age cropping out in north-western Europe. Comparison with data from the Yorkshire, Dorset, Lorraine and Aquitaine areas allows the discrimination of three major transgressive-regressive sediment packages with disconformities of interregional extent: (1) from the Baylei Zone to top Eudoxus Zone; (2) from the Autissiodorensis Zone to base Scitulus Zone; (3) from the upper Scitulus Zone to the Pectinatus Zone. The lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the Eudoxus Zone and the top of the Autissiodorensis Zone, formed by high-frequency relative sea-level variations during the periods of maximum transgression of the platform. The latter disconformity (the P1 nodule bed) reflects a major tectonically induced reorganization of the north-west European intrashelf sedimentary basin, characterized by a shift in both the location of the main depocentre and the sources of sediment production.  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