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   54086篇
  免费   1279篇
  国内免费   5725篇
安全科学   2348篇
废物处理   2298篇
环保管理   6671篇
综合类   16452篇
基础理论   12960篇
环境理论   27篇
污染及防治   14557篇
评价与监测   2823篇
社会与环境   2038篇
灾害及防治   916篇
  2023年   387篇
  2022年   982篇
  2021年   931篇
  2020年   747篇
  2019年   756篇
  2018年   1070篇
  2017年   1172篇
  2016年   1350篇
  2015年   1467篇
  2014年   2066篇
  2013年   4419篇
  2012年   2402篇
  2011年   2924篇
  2010年   2388篇
  2009年   2436篇
  2008年   2761篇
  2007年   2617篇
  2006年   2457篇
  2005年   1849篇
  2004年   1674篇
  2003年   1703篇
  2002年   1618篇
  2001年   1857篇
  2000年   1479篇
  1999年   1074篇
  1998年   829篇
  1997年   856篇
  1996年   855篇
  1995年   807篇
  1994年   739篇
  1993年   649篇
  1992年   664篇
  1991年   568篇
  1990年   582篇
  1989年   564篇
  1988年   485篇
  1987年   431篇
  1986年   399篇
  1985年   431篇
  1984年   401篇
  1983年   438篇
  1982年   443篇
  1981年   397篇
  1980年   354篇
  1979年   373篇
  1978年   336篇
  1977年   284篇
  1976年   300篇
  1974年   282篇
  1972年   288篇
排序方式: 共有10000条查询结果,搜索用时 742 毫秒
831.
辛基酚的体内类雌激素活性评价   总被引:5,自引:0,他引:5  
利用体内大鼠子宫增重试验检测辛基酚(OP)的类雌激素活性,并对其观测终点及影响因素进行了初步研究。结果显示,OP经大鼠体内染毒,可引起大鼠子宫湿重、子宫内皮细胞厚度、子宫腺数量明显增加,具有明显的类雌激素活性。三条染毒途径检测敏感度腹腔染毒>经皮下染毒>经灌胃染毒。  相似文献   
832.
833.
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   
834.
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   
835.
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   
836.
Congenital nephrosis is an autosomal recessive disorder requiring neonatal renal transplant for survival. The postnatal diagnosis rests upon the electron microscopic evaluation of the epithelial foot processes and basal membrane of the glomeruli. The prenatal diagnosis can be suspected in the presence of a positive family history with an amniotic fluid (AF) alpha-fetoprotein level greater than 5 standard deviations (SD) above the population mean accompanied by a negative AF acetylcholinesterase, absent haemoglobin F, and an unremarkable fetal sonographic examination. We reviewed our series of seven cases of congenital nephrosis fulfilling the above criteria; four cases had negative family histories, and in two cases the diagnosis of congenital nephrosis was further supported by the presence of elevated AF albumin concentrations. We conclude that (1) the prenatal diagnosis of congenital nephrosis is feasible in a low-risk population, and (2) an elevated AF albumin concentration may represent an additional marker for the diagnosis of congenital nephrosis, even though false-negative results have been reported.  相似文献   
837.
838.
839.
840.
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