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   47649篇
  免费   486篇
  国内免费   430篇
安全科学   1442篇
废物处理   2250篇
环保管理   5875篇
综合类   8034篇
基础理论   12223篇
环境理论   17篇
污染及防治   11952篇
评价与监测   3443篇
社会与环境   3034篇
灾害及防治   295篇
  2023年   226篇
  2022年   460篇
  2021年   495篇
  2020年   312篇
  2019年   402篇
  2018年   715篇
  2017年   731篇
  2016年   1156篇
  2015年   833篇
  2014年   1283篇
  2013年   3849篇
  2012年   1578篇
  2011年   2019篇
  2010年   1740篇
  2009年   1796篇
  2008年   2105篇
  2007年   2163篇
  2006年   1893篇
  2005年   1653篇
  2004年   1611篇
  2003年   1571篇
  2002年   1449篇
  2001年   1795篇
  2000年   1275篇
  1999年   845篇
  1998年   621篇
  1997年   615篇
  1996年   650篇
  1995年   697篇
  1994年   620篇
  1993年   543篇
  1992年   554篇
  1991年   530篇
  1990年   511篇
  1989年   519篇
  1988年   469篇
  1987年   374篇
  1986年   355篇
  1985年   375篇
  1984年   405篇
  1983年   388篇
  1982年   438篇
  1981年   346篇
  1980年   280篇
  1979年   325篇
  1978年   281篇
  1977年   238篇
  1976年   227篇
  1975年   221篇
  1973年   259篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
741.
742.
Unemployment effects of climate policy   总被引:1,自引:0,他引:1  
This paper models the unemployment effects of restrictions on greenhouse gas emissions, embodying two of the most significant types of short-term economic imperfections that generate unemployment: sectoral rigidities in labor mobility and sectoral rigidities in wage adjustments. A labor policy is also analyzed that would reduce the direct negative economic effects of the emissions restrictions.The politics of limiting greenhouse gas emissions are often dominated by relatively short-term considerations. Yet the current economic modeling of emissions limitations does not embody economic features that are likely to be particularly important in the short term, in particular, the politically sensitive unemployment rate. Moreover, only a few of these studies also consider policies that would offset the negative direct economic effects of emissions restrictions. For plausible estimates of the parameters, the model shows that, with the labor market imperfections, if there were no offsetting policies, the reductions in GNP in the U.S. in the first 10 years after emissions restrictions were imposed would be as much as 4%. However, if there were two policies, instead of just one: a counteracting labor market policy, as well as the emissions restrictions, the negative direct economic effects could be completely eliminated.  相似文献   
743.
XII Ecdysone Workshop July 22–26, 1996 Barcelona, Spain  相似文献   
744.
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   
745.
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed.  相似文献   
746.
747.
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   
748.
An integrated approach was developed to determine the critical levels of air pollution for ecological standard setting based on the unified index of biological response, by taking into account the effects of all pollution components simultaneously. An empirical model of plant productivity was taken as the dose response model for gaseous pollutant effect on the productivity of trees and the annual productivity of plants was used as the above mentioned index. The CO2 increase in the lower atmosphere was considered to potentially increase plant productivity and NO2 was estimated as neutral while being dangerous for plants as a chemical precursor of ozone or as a source of acidification. The maximum permissible chronic O3 and SO2 levels for trees were estimated and it was found that O3 is much more phytotoxic, as compared to SO2 , with a rather narrow range of permissible levels (27-33 ppb) which complicates its monitoring and control.  相似文献   
749.
750.
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