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   52753篇
  免费   579篇
  国内免费   677篇
安全科学   1570篇
废物处理   2162篇
环保管理   6789篇
综合类   10242篇
基础理论   13555篇
环境理论   30篇
污染及防治   13412篇
评价与监测   3263篇
社会与环境   2646篇
灾害及防治   340篇
  2022年   482篇
  2021年   488篇
  2020年   363篇
  2019年   458篇
  2018年   774篇
  2017年   757篇
  2016年   1179篇
  2015年   868篇
  2014年   1314篇
  2013年   4084篇
  2012年   1624篇
  2011年   2203篇
  2010年   1786篇
  2009年   1873篇
  2008年   2249篇
  2007年   2330篇
  2006年   2036篇
  2005年   1660篇
  2004年   1651篇
  2003年   1703篇
  2002年   1538篇
  2001年   1984篇
  2000年   1398篇
  1999年   898篇
  1998年   646篇
  1997年   623篇
  1996年   648篇
  1995年   728篇
  1994年   746篇
  1993年   633篇
  1992年   666篇
  1991年   636篇
  1990年   700篇
  1989年   645篇
  1988年   542篇
  1987年   508篇
  1986年   441篇
  1985年   490篇
  1984年   514篇
  1983年   509篇
  1982年   496篇
  1981年   463篇
  1980年   399篇
  1979年   418篇
  1978年   374篇
  1977年   317篇
  1975年   299篇
  1974年   311篇
  1973年   300篇
  1972年   335篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
131.
132.
133.
The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6-7 and 26-27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.  相似文献   
134.
135.
Spilt notochord syndrome is an extremely rare form of spinal dysraphism characterized by a complete cleft of the spine and a persistent communication between endoderm and ectoderm. A variant of split notochord syndrome was diagnosed in a 25-week-old fetus showing a prolapsed congenital colostomy and a spinal cystic lesion. The final diagnosis included protruding colon segment, imperforate anus with a rectourethral fistula and lipomyelomeningocele. The ultrasound features of the condition and the post-natal management are discussed. The neonate was successfully treated with a posterior sagittal anorectoplasty, while the lipomyelomeningocele was resected at a later stage. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
136.
137.
One of the most difficult tasks in conservation biology is identifying populations subject to stress before such stress has a detrimental impact on the population, thus allowing conservation and remedial action to be undertaken. Measuring fitness (fecundity, survival, etc.) changes directly is often difficult, expensive, or impractical. The ability of an organism to buffer its development against disturbances (developmental stability) is often considered an integral component of an individual's fitness. Data are presented from a number of studies that establish a clear relationship between developmental stability and fitness in response to both genetic and environmental stress. Consequently, I suggest that developmental stability may be used as a surrogate for more direct fitness estimation for use in conservation biology and biomonitoring programs and that is has widespread application as an early warning system for monitoring the effect of genetic and environmental stresses on natural populations.  相似文献   
138.
139.
140.
Haque CE  Zaman MQ 《Disasters》1989,13(4):300-314
As a deltaic plain, Bangladesh annually experiences riverbank erosion hazard due to sudden and rapid channel shifting, particularly in the major floodplain areas of the country. Consequently, valuable cultivable land is lost; also village settlements, markets and towns are destroyed, displacing tens of thousands of people. This paper examines the magnitude of river channel migration and encroachment on land, and the nature of human adjustment systems in the Brahmaputra–Jamuna floodplain, by investigating aspects of the social and cultural dynamics of resettlement of the displaced people. Some policy measures are recommended to improve the ability of the people in the floodplain to cope with these hazards.  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