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   538篇
  免费   33篇
  国内免费   98篇
安全科学   65篇
环保管理   36篇
综合类   328篇
基础理论   164篇
环境理论   1篇
污染及防治   33篇
评价与监测   15篇
社会与环境   11篇
灾害及防治   16篇
  2023年   4篇
  2022年   12篇
  2021年   15篇
  2020年   10篇
  2019年   13篇
  2018年   12篇
  2017年   17篇
  2016年   17篇
  2015年   12篇
  2014年   15篇
  2013年   48篇
  2012年   17篇
  2011年   48篇
  2010年   21篇
  2009年   23篇
  2008年   24篇
  2007年   22篇
  2006年   35篇
  2005年   32篇
  2004年   31篇
  2003年   25篇
  2002年   23篇
  2001年   21篇
  2000年   7篇
  1999年   11篇
  1998年   11篇
  1997年   6篇
  1996年   7篇
  1995年   15篇
  1994年   18篇
  1993年   6篇
  1992年   11篇
  1991年   17篇
  1990年   5篇
  1989年   15篇
  1988年   11篇
  1987年   13篇
  1986年   3篇
  1985年   4篇
  1984年   2篇
  1983年   4篇
  1982年   2篇
  1981年   4篇
排序方式: 共有669条查询结果,搜索用时 31 毫秒
61.
62.
In order to accurately detect the fetal behavioural state, we simultaneously measured fetal heart rate and multiple fetal activities in 27 healthy pregnant women at 38 to 40 weeks of gestation. We ultrasonically identified gross body movements, breathing movements and micturition. Analysis of fetal heart rate allowed us to distinguish two different patterns of fetal behaviour: active and quiet phases. The frequency distribution of the analysed fetal events was significantly different in these two phases. These data suggest that a complete biophysical profile of the fetus is effective in differentiating behavioural states and may improve the predictive accuracy of fetal heart rate analysis alone.  相似文献   
63.
64.
65.
66.
Abstract: The effects of human activities in forests are often examined in the context of habitat conversion. Changes in habitat structure and composition are also associated with increases in the activity of people with vehicles and equipment, which results in increases in anthropogenic noise. Anthropogenic noise may reduce habitat quality for many species, particularly those that rely on acoustic signals for communication. We compared the density and occupancy rate of forest passerines close to versus far from noise‐generating compressor stations and noiseless well pads in the boreal forest of Alberta, Canada. Using distance‐based sampling, we found that areas near noiseless energy facilities had a total passerine density 1.5 times higher than areas near noise‐producing energy sites. The White‐throated Sparrow (Zonotrichia albicollis), Yellow‐rumped Warbler (Dendroica coronata), and Red‐eyed Vireo (Vireo olivaceus) were less dense in noisy areas. We used repeat sampling to estimate occupancy rate for 23 additional species. Seven had lower conditional or unconditional occupancy rates near noise‐generating facilities. One‐third of the species examined showed patterns that supported the hypothesis that abundance is influenced by anthropogenic noise. An additional 4 species responded negatively to edge effects. To mitigate existing noise impacts on birds would require approximately $175 million. The merits of such an effort relative to other reclamation actions are discussed. Nevertheless, given the $100 billion energy‐sector investment planned for the boreal forest in the next 10 years, including noise suppression technology at the outset of construction, makes noise mitigation a cost‐effective best‐management practice that might help conserve high‐quality habitat for boreal birds.  相似文献   
67.
Truncus arteriosus (TA) is a rare cardiac anomaly constituting less than 1% of all congenital heart defects. Its association with complete atrioventricular septal defect (AVSD) is extremely unusual and only 12 cases diagnosed postnatally or postmortem have been reported so far. We describe the first case of truncus arteriosus with AVSD to be diagnosed prenatally by fetal echocardiography. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
68.
69.
70.
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