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   35201篇
  免费   398篇
  国内免费   477篇
安全科学   1096篇
废物处理   1710篇
环保管理   4602篇
综合类   5480篇
基础理论   9178篇
环境理论   8篇
污染及防治   8680篇
评价与监测   2531篇
社会与环境   2570篇
灾害及防治   221篇
  2023年   170篇
  2022年   360篇
  2021年   392篇
  2020年   242篇
  2019年   321篇
  2018年   529篇
  2017年   568篇
  2016年   857篇
  2015年   648篇
  2014年   1011篇
  2013年   2939篇
  2012年   1198篇
  2011年   1610篇
  2010年   1301篇
  2009年   1359篇
  2008年   1653篇
  2007年   1580篇
  2006年   1417篇
  2005年   1256篇
  2004年   1222篇
  2003年   1170篇
  2002年   1110篇
  2001年   1325篇
  2000年   924篇
  1999年   562篇
  1998年   421篇
  1997年   445篇
  1996年   479篇
  1995年   552篇
  1994年   460篇
  1993年   406篇
  1992年   439篇
  1991年   419篇
  1990年   385篇
  1989年   374篇
  1988年   341篇
  1987年   293篇
  1986年   284篇
  1985年   297篇
  1984年   314篇
  1983年   302篇
  1982年   312篇
  1981年   266篇
  1980年   204篇
  1979年   220篇
  1978年   188篇
  1977年   161篇
  1975年   165篇
  1973年   198篇
  1972年   183篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
521.
522.
523.
524.
An interdisciplinary approach based on high-resolution physical stratigraphy, biostratigraphy, organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic/carbonate Kimmeridgian/Tithonian deposits of the Boulonnais (north-western France). These rocks are the age-equivalents of some of the offshore marine source rocks of the North Sea and were deposited in an overall storm-dominated homoclinal ramp setting which may represent one of the most shore-proximal sediments of this age cropping out in north-western Europe. Comparison with data from the Yorkshire, Dorset, Lorraine and Aquitaine areas allows the discrimination of three major transgressive-regressive sediment packages with disconformities of interregional extent: (1) from the Baylei Zone to top Eudoxus Zone; (2) from the Autissiodorensis Zone to base Scitulus Zone; (3) from the upper Scitulus Zone to the Pectinatus Zone. The lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the Eudoxus Zone and the top of the Autissiodorensis Zone, formed by high-frequency relative sea-level variations during the periods of maximum transgression of the platform. The latter disconformity (the P1 nodule bed) reflects a major tectonically induced reorganization of the north-west European intrashelf sedimentary basin, characterized by a shift in both the location of the main depocentre and the sources of sediment production.  相似文献   
525.
XII Ecdysone Workshop July 22–26, 1996 Barcelona, Spain  相似文献   
526.
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   
527.
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   
528.
529.
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   
530.
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