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   7285篇
  免费   101篇
  国内免费   195篇
安全科学   206篇
废物处理   409篇
环保管理   636篇
综合类   1251篇
基础理论   1571篇
环境理论   5篇
污染及防治   2281篇
评价与监测   656篇
社会与环境   513篇
灾害及防治   53篇
  2023年   77篇
  2022年   249篇
  2021年   234篇
  2020年   148篇
  2019年   147篇
  2018年   247篇
  2017年   257篇
  2016年   363篇
  2015年   226篇
  2014年   358篇
  2013年   592篇
  2012年   389篇
  2011年   518篇
  2010年   328篇
  2009年   322篇
  2008年   384篇
  2007年   371篇
  2006年   283篇
  2005年   296篇
  2004年   290篇
  2003年   255篇
  2002年   209篇
  2001年   173篇
  2000年   102篇
  1999年   74篇
  1998年   37篇
  1997年   43篇
  1996年   32篇
  1995年   57篇
  1994年   44篇
  1993年   28篇
  1992年   28篇
  1991年   34篇
  1990年   30篇
  1989年   25篇
  1988年   21篇
  1987年   15篇
  1986年   12篇
  1985年   14篇
  1984年   12篇
  1983年   19篇
  1982年   9篇
  1981年   10篇
  1979年   11篇
  1964年   15篇
  1963年   11篇
  1962年   12篇
  1960年   8篇
  1958年   16篇
  1957年   8篇
排序方式: 共有7581条查询结果,搜索用时 31 毫秒
61.
The Science of Nature - Because of the sudden rise in primary-energy costs and the rapid inflation of plants which are used for the conversion of primary to secondary energy, the storage of energy,...  相似文献   
62.
The observation that thyroid disease is frequent in mothers of children with Down syndrome (DS) has suggested that maternal thyroid antibodies could be a factor predisposing to trisomy 21 in their offspring. In this study, the incidences of thyroglobulin (Tg) and thyroid peroxidase (TPO) antibodies were analysed with a sensitive solid-phase immunosorbent radioassay in sera from 29 mothers giving birth to children with trisomy 21 and 87 control mothers. The serum samples were collected at delivery. There was no statistical difference regarding the proportion of thyroid antibodies (against Tg and/or TPO) in the two groups. Thyroid antibodies were detected in 6/29 (20.7 per cent) of the DS mothers and in 23/87 (26.4 per cent) of the control mothers. Among the women with thyroid antibodies, 4/6 (66.7 per cent) of the DS mothers and 12/23 (52 per cent) of the control mothers had antibodies against both Tg and TPO. There was no increase in the relative risk of having a child with DS if the titre of either Tg or TPO antibodies or both were positive, i.e. ≥ 1/5. The results indicate that the presence of thyroid antibodies in the serum of a pregnant woman has no prognostic value for the birth of an infant with DS.  相似文献   
63.
We examine carbon (C) reference and mitigation scenarios for the Mexicanforest sector between the year 2000 and 2030. Estimates are presentedseparately for the period 2008–2012.Future C emissions and capture are estimated using a simulation modelthat: a) allocates the country land use/land cover classes among differentfuture uses and categories using demand-based scenarios for forestryproducts; b) estimates the total C densities associated to each land usecategory, and c) determines the net carbon implications of the process ofland use/cover change according to the different scenarios.The options analyzed include both afforestation/reforestation, such ascommercial, bionenergy and restoration plantations, and agroforestrysystems, and forest conservation, through the sustainable management ofnative forests and forest protection.The total mitigation potential, estimated as the difference between the totallong-term carbon stock in the reference and the mitigation scenario reaches300 × 106 Mg C in the year 2012 and increases to 1,382 × 106 Mg C in 2030. The average net sequestration in the 30 year period is 46 × 106 Mg C yr-1, or 12.5 × 106 Mg C yr-1 within the period 2008 to 2012. The costs of selected mitigation options range from 0.7–3.5 Mg C-1 to 35 Mg C-1. Some options are cost effective.  相似文献   
64.
我们曾经将压电陶瓷粉体复合到传统的吸声降噪材料与阻尼减振材料中 ,制作出了性能更好的新型吸声降噪材料和新型阻尼减振材料 ;而且还发现废品压电陶瓷的粉体与正品压电陶瓷的粉体具有相同的功效[1~4 ] ,分析了它们同样发挥压电效应的原因。  相似文献   
65.
66.
67.
Anticardiolipin antibodies were measured in 60 pregnant women with acute parvovirus B19 infection. Test results for eight (13.3 per cent) women were positive for anticardiolipin antibody. Six of these eight women became negative later, yielding a prevalence of anticardiolipin antibodies of 3.3 per cent (2/60) 6 months after acute parvovirus B19 infection. Anticardiolipin antibody positivity was not associated with an increased risk of abortion, fetal death, or maternal complications. This study suggests that there is an elevated frequency of anticardiolipin antibodies in pregnant women with acute parvovirus B19, probably representing an epiphenomenon. However, this is not associated with an adverse maternal or perinatal outcome.  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