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   19761篇
  免费   195篇
  国内免费   175篇
安全科学   552篇
废物处理   800篇
环保管理   2652篇
综合类   2729篇
基础理论   5207篇
环境理论   7篇
污染及防治   5805篇
评价与监测   1293篇
社会与环境   958篇
灾害及防治   128篇
  2022年   167篇
  2021年   196篇
  2020年   120篇
  2019年   166篇
  2018年   338篇
  2017年   325篇
  2016年   519篇
  2015年   404篇
  2014年   596篇
  2013年   1669篇
  2012年   704篇
  2011年   916篇
  2010年   688篇
  2009年   790篇
  2008年   927篇
  2007年   974篇
  2006年   838篇
  2005年   685篇
  2004年   717篇
  2003年   652篇
  2002年   645篇
  2001年   778篇
  2000年   573篇
  1999年   318篇
  1998年   238篇
  1997年   227篇
  1996年   273篇
  1995年   274篇
  1994年   260篇
  1993年   234篇
  1992年   210篇
  1991年   192篇
  1990年   211篇
  1989年   192篇
  1988年   185篇
  1987年   173篇
  1986年   149篇
  1985年   149篇
  1984年   179篇
  1983年   177篇
  1982年   169篇
  1981年   171篇
  1980年   142篇
  1979年   159篇
  1978年   108篇
  1977年   103篇
  1976年   90篇
  1975年   95篇
  1973年   93篇
  1972年   100篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
222.
223.
224.
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   
225.
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   
226.
1977~1998年间,在苏格兰西部的艾尔萨克雷格对收集到的塘鹅蛋中的多氯联苯(PCB)同类物进行了回顾性分析.对一些年份所收集的塘鹅蛋中每年选择8~10个对其PCB同类物浓度范围分别进行了分析.所有的同类物在几年之内浓度都降在低,但不同的同类物降解速率不同.  相似文献   
227.
228.
229.
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   
230.
This study explores if assay of cancer antigen 125 (CA 125) in maternal serum might aid the detection of Down's syndrome in the second trimester of pregnancy. CA 125 levels were determined retrospectively in stored maternal serum samples from ten Down's syndrome pregnancies and 78 controls matched for gestational and maternal age. In addition, second-trimester amniotic fluid samples from nine Down's syndrome and 109 unaffected pregnancies were analysed for CA 125. Maternal serum CA 125 values for Down's syndrome pregnancies were lower, with the median being 0.72 multiples of the unaffected population median. The medians for affected and unaffected pregnancies did not differ significantly and there was a considerable overlap in the range of values of cases and controls. The distribution of amniotic fluid CA 125 levels for Down's syndrome pregnancies resembled that for controls. From our present results, we could not find an association between Down's syndrome and second-trimester maternal serum or amniotic fluid CA 125 levels.  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