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   7456篇
  免费   43篇
  国内免费   30篇
安全科学   181篇
废物处理   428篇
环保管理   563篇
综合类   1061篇
基础理论   1780篇
环境理论   2篇
污染及防治   2041篇
评价与监测   595篇
社会与环境   847篇
灾害及防治   31篇
  2023年   62篇
  2022年   129篇
  2021年   116篇
  2020年   53篇
  2019年   77篇
  2018年   135篇
  2017年   159篇
  2016年   218篇
  2015年   134篇
  2014年   255篇
  2013年   612篇
  2012年   293篇
  2011年   394篇
  2010年   302篇
  2009年   277篇
  2008年   384篇
  2007年   381篇
  2006年   336篇
  2005年   285篇
  2004年   238篇
  2003年   257篇
  2002年   223篇
  2001年   288篇
  2000年   175篇
  1999年   117篇
  1998年   47篇
  1997年   66篇
  1996年   60篇
  1995年   70篇
  1994年   72篇
  1993年   69篇
  1992年   61篇
  1991年   66篇
  1990年   74篇
  1989年   55篇
  1988年   61篇
  1987年   56篇
  1986年   55篇
  1985年   41篇
  1984年   47篇
  1983年   50篇
  1982年   49篇
  1980年   30篇
  1979年   33篇
  1978年   29篇
  1976年   30篇
  1974年   32篇
  1973年   30篇
  1964年   28篇
  1958年   32篇
排序方式: 共有7529条查询结果,搜索用时 31 毫秒
101.
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   
102.
103.
Circulating placental [human chorionic gonadotrophin (hCG), Schwangerschafts protein 1 (SP1), pregnancy-associated plasma protein A (PAPP-A), decidual (pregnancy protein) 12 (PP12), and fetal alphafetoprotein (AFP)] proteins were measured immediately before and within 1 h in 18 women undergoing diagnostic chorionic villus sampling (CVS) in the first trimester. An elevation of serum AFP levels was consistently seen, while fluctuations in excess of 10 per cent of the pre-CVS levels of SP1 and PP12 were seen in the majority of patients. Fluctuations in hCG and PAPP-A were consistently less than 10 per cent of pre-CVS values. Post-CVS changes in levels were not apparently associated with any feature of the technique, the pregnancy, or its outcome (one missed abortion). As feto-maternal haemorrhage is a common event, anti-D should be offered to rhesus-negative women undergoing CVS. In the prediction of subsequent miscarriage, only hCG and PAPP-A measurements should be considered.  相似文献   
104.
105.
106.
107.
108.
109.
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   
110.
Duodenal stenosis associated with oesophageal atresia was diagnosed by ultrasound at 12 weeks' gestation. The diagnosis was made by recognition of a double bubble sign which was more pronounced when a vaginal transducer was used. Post-abortion autopsy confirmed the diagnosis. Oesophageal and duodenal obstruction in this case had no effect on the amount of amniotic fluid or the alpha-fetoprotein concentration since swallowing and subsequent utilization of amniotic fluid do not occur before 12 weeks of gestation.  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