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   2132篇
  免费   17篇
  国内免费   4篇
安全科学   51篇
废物处理   149篇
环保管理   135篇
综合类   253篇
基础理论   453篇
环境理论   1篇
污染及防治   744篇
评价与监测   210篇
社会与环境   154篇
灾害及防治   3篇
  2023年   23篇
  2022年   56篇
  2021年   58篇
  2020年   25篇
  2019年   36篇
  2018年   64篇
  2017年   72篇
  2016年   112篇
  2015年   67篇
  2014年   113篇
  2013年   212篇
  2012年   129篇
  2011年   163篇
  2010年   91篇
  2009年   63篇
  2008年   141篇
  2007年   147篇
  2006年   106篇
  2005年   86篇
  2004年   56篇
  2003年   48篇
  2002年   56篇
  2001年   36篇
  2000年   19篇
  1999年   18篇
  1998年   6篇
  1997年   8篇
  1996年   6篇
  1995年   12篇
  1994年   7篇
  1993年   11篇
  1992年   3篇
  1991年   6篇
  1990年   10篇
  1989年   3篇
  1988年   6篇
  1983年   3篇
  1975年   2篇
  1967年   4篇
  1966年   2篇
  1964年   8篇
  1963年   7篇
  1962年   7篇
  1960年   5篇
  1959年   2篇
  1958年   8篇
  1957年   3篇
  1956年   4篇
  1955年   2篇
  1943年   2篇
排序方式: 共有2153条查询结果,搜索用时 656 毫秒
11.
12.
13.
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   
14.
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   
15.
16.
17.
18.
A dicentric X chromosome was found in a female fetus during cytogenetic studies performed on amniotic cells. Blood samples from the parents showed normal karyotypes and the pregnancy was terminated. The mechanism for the formation of this ‘de novo’ rearrangement is discussed.  相似文献   
19.
Fluid from pleural effusion (n=2) and cystic hygroma (n=7) was obtained from eight fetuses, between 13 and 32 weeks of pregnancy at the time when a conventional prenatal diagnosis procedure was carried out. As these fluids contain lymphocytes, they were processed like peripheral blood. A karyotype was obtained in 4 days in both cases of pleural effusion and in four out of seven samples of cystic hygroma. An abnormal karyotype was detected in three of the four samples of cystic hygroma: two trisomies 21 and a monosomy X. Different parameters were evaluated in order to predict the feasibility of obtaining a cytogenetic diagnosis. Our data showed that if the amount of fluid obtained was ⩾4 ml and the initial lymphocyte count (ILC) was >0.2 × 106 cells/ml, a cytogenetic diagnosis was possible from an initial concentration of cultured lymphocytes )ICCL) of >0.06 × 106 cells/ml.  相似文献   
20.
As part of the Environmental Monitoring and Assessment Programin 1991, the field efficacy of six research indicators wasexamined in the estuarine systems of the Gulf of Mexico. Theutility of these indicators was tested by examining thoseresponses at both ends of multiple environmental gradients;namely, under minimally impacted conditions (reference) andheavily impacted conditions (by hypoxia, industrialdischarges, agricultural runoff). In addition, the geographiceffects of location (east and west of the Mississippi River)were examined. Numbers and frequencies of pathologies,abundance of splenic macrophage aggregates, and vertebralabnormalities showed response patterns that suggest widerfield testing along full gradients rather than simply theextremes of the gradient are warranted. Selected bloodproteins showed some promise but logistical constraints inestuarine environments may limit its utility. Concentrationsof selected organic compounds in bile showed no differences inthis study between references and contaminated sites.Molecular bioindicators are discussed with regard to theirpotential utility as indicators of ecosystem conditions. Ofthese potential indicators, the use of vitellogenin assays asa measure of reproductive impairment and frequency of shelldisease in selected crustaceans as an indicator ofimmunological aberrations deserve further examination.  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