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   18012篇
  免费   187篇
  国内免费   161篇
安全科学   512篇
废物处理   745篇
环保管理   2501篇
综合类   2438篇
基础理论   4810篇
环境理论   4篇
污染及防治   5224篇
评价与监测   1164篇
社会与环境   838篇
灾害及防治   124篇
  2022年   124篇
  2021年   155篇
  2020年   99篇
  2019年   141篇
  2018年   246篇
  2017年   243篇
  2016年   404篇
  2015年   339篇
  2014年   506篇
  2013年   1537篇
  2012年   594篇
  2011年   772篇
  2010年   605篇
  2009年   712篇
  2008年   819篇
  2007年   873篇
  2006年   758篇
  2005年   635篇
  2004年   659篇
  2003年   613篇
  2002年   611篇
  2001年   754篇
  2000年   559篇
  1999年   309篇
  1998年   233篇
  1997年   220篇
  1996年   268篇
  1995年   265篇
  1994年   253篇
  1993年   228篇
  1992年   205篇
  1991年   185篇
  1990年   206篇
  1989年   189篇
  1988年   180篇
  1987年   171篇
  1986年   148篇
  1985年   146篇
  1984年   176篇
  1983年   174篇
  1982年   166篇
  1981年   168篇
  1980年   137篇
  1979年   159篇
  1978年   108篇
  1977年   100篇
  1976年   88篇
  1975年   95篇
  1973年   92篇
  1972年   99篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Disturbance plays an important role in structuring marine ecosystems, and there is a need to understand how conservation practices, such as the designation of Marine Protected Areas (MPAs), facilitate postdisturbance recovery. We evaluated the association of MPAs, herbivorous fish biomass, substrate type, postdisturbance coral cover, and change in macroalgal cover with coral recovery on the fringing reefs of the inner Seychelle islands, where coral mortality after a 1998 bleaching event was extensive. We visually estimated benthic cover and fish biomass at 9 sites in MPAs where fishing is banned and at 12 sites where fishing is permitted in 1994, 2005, 2008, and 2011. We used analysis of variance to examine spatial and temporal variations in coral cover and generalized additive models to identify relations between coral recovery and the aforementioned factors that may promote recovery. Coral recovery occurred on all substrate types, but it was highly variable among sites and times. Between 2005 and 2011 the increase in coral cover averaged 1%/year across 21 sites, and the maximum increase was 4%/year. However, mean coral cover across the study area (14%) remained at half of 1994 levels (28%). Sites within MPAs had faster rates of coral recovery than sites in fished areas only where cover of macroalgae was low and had not increased over time. In MPAs where macroalgae cover expanded since 1998 there was no recovery. Where coral was recovering on granite reefs there was a shift in relative prevalence of colony life‐form from branching to encrusting species. This simplification of reef structure may affect associated reef fauna even if predisturbance levels of coral cover are attained. Efecto de la Expansión de Macroalgas y Áreas Marinas Protegidas sobre la Recuperación de Coral Después de una Perturbación Climática  相似文献   
942.
Magnetic resonance imaging (MRI) appears to be increasingly used, in addition to standard ultrasonography for the diagnosis of abnormalities in utero. Previous studies have recently drawn attention to the technical refinement of MRI to visualize the fetal bones and muscles. Beyond commonly used T2-weighted MRI, echoplanar, thick-slab T2-weighted and dynamic sequences, and three-dimensional MRI techniques, are about to provide new imaging insights into the normal and the pathological musculoskeletal system of the fetus. This review emphasizes the potential significance of MRI in the visualization of the fetal musculoskeletal system. © 2012 John Wiley & Sons, Ltd.  相似文献   
943.
944.
945.
946.
947.
948.
Risk factors for driving into flooded roads   总被引:2,自引:0,他引:2  
Motor vehicle-related deaths account for more than half of all flood fatalities in the United States, but to date, very little is known about the risk factors associated with why people drive into flooded roads. Using data from survey questionnaires administered in Denver, CO, and Austin, TX, this paper suggests that people who do not take warnings seriously are more likely to drive through flooded roads, as are people aged 18–35, and those that do not know that motor vehicles are involved in more than half of all flood fatalities. In Denver, people who have not experienced a flood previously and those who do not know they live in flood-prone areas are also more likely to drive into flooded roads.  相似文献   
949.
950.
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