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   18873篇
  免费   191篇
  国内免费   133篇
安全科学   481篇
废物处理   716篇
环保管理   2258篇
综合类   5491篇
基础理论   4027篇
环境理论   7篇
污染及防治   4480篇
评价与监测   988篇
社会与环境   664篇
灾害及防治   85篇
  2022年   151篇
  2018年   244篇
  2017年   241篇
  2016年   356篇
  2015年   258篇
  2014年   380篇
  2013年   1294篇
  2012年   445篇
  2011年   633篇
  2010年   565篇
  2009年   643篇
  2008年   672篇
  2007年   686篇
  2006年   620篇
  2005年   510篇
  2004年   549篇
  2003年   506篇
  2002年   472篇
  2001年   638篇
  2000年   448篇
  1999年   300篇
  1998年   222篇
  1997年   203篇
  1996年   212篇
  1995年   246篇
  1994年   261篇
  1993年   215篇
  1992年   234篇
  1991年   239篇
  1990年   262篇
  1989年   239篇
  1988年   191篇
  1987年   187篇
  1986年   191篇
  1985年   189篇
  1984年   204篇
  1983年   196篇
  1982年   207篇
  1981年   216篇
  1980年   172篇
  1979年   185篇
  1978年   152篇
  1977年   143篇
  1974年   147篇
  1973年   146篇
  1968年   156篇
  1967年   184篇
  1966年   154篇
  1965年   148篇
  1964年   151篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
561.
The fetal heart rate (FHR) was continuously monitored during 42 umbilical vessel punctures performed at the placental insertion of the cord in 24 diagnostic fetoscopies in which pure fetal blood was obtained. In only one patient did a deceleration first appear during puncture and aspiration of fetal blood. In two patients decelerations preceded fetoscopy and in two others they began during the fetoscopy but before puncture of an umbilical vessel. In 19 patients, the FHR did not change at all during the procedure. Fetal haemorrhage after sampling was either absent or minimal. Six pregnancies were terminated because a positive diagnosis had been made and 18 healthy babies were born. Umbilical cords were examined after 7 terminations of pregnancy and after 6 deliveries. In the former group the puncture could just be seen with the naked eye and the needle track was demonstrated histologically in 6. No traces of the puncture or other abnormalities were found in the cords after delivery. Fetal blood sampling from umbilical cord vessels, particularly at the placental insertion of the cord, is the technique of choice since pure fetal blood can be obtained without increasing the risk of fetoscopy.  相似文献   
562.
True microcephaly can be diagnosed at an early stage of gestation by serial measurements of fetal head growth as demonstrated by this case report in which the diagnosis of genetic microcephaly was made but termination refused. True microcephaly was evident at birth.  相似文献   
563.
564.
565.
566.
567.
568.
Environmental managers at U.S. Department of Defense (DoD) installations overseas are faced with the challenge of managing contaminated sites at these installations with little information on the extent of contamination or the risk posed by the site. In this regard, DoD managers overseas encounter a situation quite similar to the situation faced by decision makers in the U.S. who are managing brownfields. Innovative site characterization and risk-based decision-making methods, which are currently being developed for expeditious application at brownfield sites in the U.S., may also be appropriate for application at overseas DoD sites. In this paper, the analytic hierarchy process (AHP) is used by DoD decision makers to evaluate and rank innovative site characterization technologies and risk-based decision-making and management methods, for use at installations in Korea. Results indicate that for sites with high potential risk the decision makers preferred site characterization technologies that produce data of high quality and a method that can be used to establish credible risk-based remediation goals. This study provides a framework for applying characterization technologies and risk management to poorly characterized contaminated sites in developing countries, where resources for remedial actions may be limited.  相似文献   
569.
吉林省的风能潜力(英文)   总被引:2,自引:0,他引:2  
近两年我国电力突然短缺,已经引起政府的高度重视。由于我国风电发展的紧迫性和风电发展的潜力,特别是国际上正在如火如荼地开发风电的情景,中国- 奥地利政府间双边合作计划将风电评估列入2001~2003 年度合作计划,论文是该计划的成果之一。以我国吉林省为研究对象,采用广泛使用的风机选址算法和空间分布诊断程序( WAsP和ZAWIMOD2),运用数字地形图和遥感资料获得的土地利用图,进而得到数字化的表面粗糙度,再对吉林省的风能潜力进行估算。完成了近1km2 分辨率的距地面60m高度的风速和风能密度计算,并制作了它们的分布图。这是我国第一次在较大区域上估算距地面60m 高度的风速和风能密度,其方法对我国风电资源的评估有重要的借鉴作用。结果显示最有效的风能资源在吉林省的中西部地区,而南部和东部的高风资源区位于山脊和山顶,对风能的开发有一定的限制。  相似文献   
570.
This study provides data on the incidence of fetal trisomies 21, 18, and 13 at 9–14 weeks' gestation in women aged 35–45 years and estimates of maternal age-specific risks in women aged 20–45 years. Our data from 5814 singleton pregnancies undergoing first-trimester karyotyping for the sole indication of maternal age ⩾ 35 years were combined with those from two previous reports and the incidence of the trisomies was calculated from a total of 15 793 pregnancies. Comparison of incidences at 9–14 weeks' gestation with published data at 15–20 weeks' gestation and in livebirths demonstrated that at birth the maternal age-specific incidence of trisomy 21 is 33 per cent lower than at 15–20 weeks' gestation and 54 per cent lower than at 9–14 weeks' gestation. Furthermore, the relative frequency of trisomies 18 and 13 decreases from 30 per cent at 9–14 weeks to 22 per cent at 15–20 weeks and 14 per cent at birth.  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