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   4472篇
  免费   42篇
  国内免费   30篇
安全科学   97篇
废物处理   283篇
环保管理   365篇
综合类   514篇
基础理论   910篇
环境理论   6篇
污染及防治   1625篇
评价与监测   420篇
社会与环境   296篇
灾害及防治   28篇
  2023年   56篇
  2022年   134篇
  2021年   180篇
  2020年   86篇
  2019年   83篇
  2018年   167篇
  2017年   174篇
  2016年   256篇
  2015年   133篇
  2014年   258篇
  2013年   428篇
  2012年   314篇
  2011年   335篇
  2010年   243篇
  2009年   182篇
  2008年   240篇
  2007年   274篇
  2006年   190篇
  2005年   159篇
  2004年   127篇
  2003年   101篇
  2002年   104篇
  2001年   57篇
  2000年   52篇
  1999年   31篇
  1998年   20篇
  1997年   12篇
  1996年   11篇
  1995年   20篇
  1994年   11篇
  1993年   5篇
  1992年   9篇
  1991年   5篇
  1990年   8篇
  1988年   4篇
  1986年   3篇
  1982年   2篇
  1980年   2篇
  1978年   2篇
  1970年   2篇
  1967年   5篇
  1966年   4篇
  1965年   2篇
  1964年   5篇
  1962年   3篇
  1959年   4篇
  1958年   16篇
  1957年   5篇
  1956年   2篇
  1955年   2篇
排序方式: 共有4544条查询结果,搜索用时 15 毫秒
21.
22.
23.
We studied the Noel KempffMercado Climate Action Project (NKMCAP),Bolivia, to assess whether forestprotection carbon (C) projects cansignificantly benefit local people. Wehypothesized that forest protection canonly securely deliver C if significantstakeholders are meaningfully andtransparently involved, traditional orcustomary rights are recognized and theirloss compensated for, and there are directlinkages between conservation anddevelopment objective. Our researchfocused on 53 members of the communities ofFlorida, Porvenir and Piso Firme and 36secondary stakeholders. In each of thevillages we held half-day meetings withcommunity leaders, complemented bysemi-structured one-hour interviews with 5,10, and 7 families, representing 20%, 10%and 8% of each community. The long-termimpact of the NKMCAP on the localcommunities may well be positive. However,in the short run, certain sections of thelocal communities are financially poorer. Forest protection projects clearly have thepotential to sequester C, protectbiodiversity and simultaneously contributeto sustainable rural development, but ifthey really are to improve rurallivelihoods, they must be designed andimplemented carefully and participatively.  相似文献   
24.
Hybridization between Aegilops geniculata, A. biuncialis and bread wheat Triticum aestivum has been evaluated during two seasons under simulated field conditions to estimate the field hybridization rate under Central Spain conditions. The mean frequencies of hybridization between A. biuncialis and A. geniculata with wheat were 0.34% and 0.31%, respectively. Data from 10 hybrid plants for each combination showed that hybrids can be partially fertile by backcrossing with wheat parent, with percent averages of 3.17 grains/spikelets for A. biuncialis × wheat hybrids and 2.87 grains/spikelets for A. geniculata × wheat hybrids. Self-pollination, although at very low rates, was also possible in hybrids. The potential risks associated with natural hybridization in the context of transgenic wheat cultivation are discussed.  相似文献   
25.
Pregnancies with fetal trisomy 21 have been associated with low amniotic fluid alpha-fetoprotein levels (AFAFP). This observation led to the suggestion that low AFAFP levels be used as a criterion for completion of a chromosomal analysis in patients who are not otherwise at increased risk for a fetal chromosome abnormality and in whom karyotyping might not have been completed for economic reasons. In order to assess the usefulness of such criteria, we reviewed the AFAFP levels of 90 cases of fetal trisomy 21, 23 cases of trisomy 18, and 10 cases of trisomy 13. These were compared with 2400 control samples with normal chromosome constitution. AFAFP levels were generally lower in pregnancies with trisomy 21, showing a median value of 0·72 MoM. However, 40 per cent of the trisomy 21 samples had AFAFP values greater than 0·8 MoM and 20 per cent were over 1·0 MoM. These data imply that over 50 per cent of Down syndrome cases might have been missed using a cut-off level of 0·70 MoM for completion of chromosome analysis. Using a higher cut-off level will leave only a small percentage of samples unkaryotyped. The distribution of AFP levels in trisomy 13 and 18 is no different from controls; we therefore believe that fetal karyotyping should be completed in every amniotic fluid sample obtained.  相似文献   
26.
27.
28.
29.
An analysis of the impacts on Mexican energy demand and associated carbon dioxide (CO2) emissions in the year 2005 due to efficient lighting in the commercial and residential sectors and cogeneration in the industrial sector is presented. Estimation of CO2 abatement costs and an incremental cost curve for CO2 mitigation options are considered. These technologies are cost effective opportunities, and together are projected to reduce CO2 emissions in 2005 by nearly 13 percent. Implementation of efficient lighting is already part of the demand side management (DSM) programs of the Mexican state-owned utility. However, there are important barriers that may hinder the implementation of large scale cogeneration plants.  相似文献   
30.
生物膜填料塔处理浓度有机废气的工业应用试验研究   总被引:2,自引:0,他引:2  
工业应用试验研究表明,生物膜填料塔处理工业有机废气是可行的,当运行条件控制适当时,净化效率可保持在90%以上,能够实现达标排放,这一成果填补了我国环保工业技术领域的空白,工程技术上接近现阶段国外的技术研究水平。  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