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   41043篇
  免费   416篇
  国内免费   576篇
安全科学   1237篇
废物处理   1855篇
环保管理   4905篇
综合类   7648篇
基础理论   10457篇
环境理论   24篇
污染及防治   10510篇
评价与监测   2851篇
社会与环境   2301篇
灾害及防治   247篇
  2022年   409篇
  2021年   398篇
  2020年   301篇
  2019年   367篇
  2018年   638篇
  2017年   642篇
  2016年   964篇
  2015年   742篇
  2014年   1165篇
  2013年   3157篇
  2012年   1396篇
  2011年   1874篇
  2010年   1508篇
  2009年   1563篇
  2008年   1830篇
  2007年   1888篇
  2006年   1655篇
  2005年   1443篇
  2004年   1319篇
  2003年   1399篇
  2002年   1253篇
  2001年   1636篇
  2000年   1114篇
  1999年   705篇
  1998年   461篇
  1997年   472篇
  1996年   479篇
  1995年   557篇
  1994年   575篇
  1993年   443篇
  1992年   484篇
  1991年   469篇
  1990年   505篇
  1989年   451篇
  1988年   420篇
  1987年   341篇
  1986年   323篇
  1985年   341篇
  1984年   360篇
  1983年   346篇
  1982年   329篇
  1981年   311篇
  1980年   250篇
  1979年   271篇
  1978年   264篇
  1976年   189篇
  1975年   198篇
  1974年   204篇
  1972年   203篇
  1971年   200篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Stormwater runoff is now a major contributor to the pollution of coastal waters in the United States. Public agencies are responding by requiring stormwater monitoring to satisfy the National Pollutant Discharge Elimination System stormwater permit. However, studies to understand the utility of the current programs or to improve their usefulness have not yet been performed. In this paper, we evaluate the land-use-based program, the industrial stormwater permit program, and beach water-quality monitoring in the County of Los Angeles, California, to determine if the results will be helpful to planners and regulators in abating stormwater pollution. The utility of the program has been assessed based on the programs' ability to accurately estimate the emissions for different classes of land use. The land-use program appears successful, while the industrial monitoring program does not. Beach water-quality monitoring suffers from a lack of real-time monitoring techniques. We also provide suggested improvements, such as sampling method and time, and parameter selection.  相似文献   
102.
103.
104.
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   
105.
106.
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   
107.
108.
109.
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   
110.
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