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   41096篇
  免费   447篇
  国内免费   326篇
安全科学   1216篇
废物处理   1488篇
环保管理   5719篇
综合类   6521篇
基础理论   11649篇
环境理论   25篇
污染及防治   10619篇
评价与监测   2477篇
社会与环境   1881篇
灾害及防治   274篇
  2022年   263篇
  2021年   276篇
  2019年   324篇
  2018年   561篇
  2017年   552篇
  2016年   827篇
  2015年   668篇
  2014年   944篇
  2013年   3106篇
  2012年   1170篇
  2011年   1711篇
  2010年   1417篇
  2009年   1413篇
  2008年   1726篇
  2007年   1811篇
  2006年   1668篇
  2005年   1358篇
  2004年   1358篇
  2003年   1291篇
  2002年   1262篇
  2001年   1662篇
  2000年   1163篇
  1999年   736篇
  1998年   595篇
  1997年   583篇
  1996年   592篇
  1995年   656篇
  1994年   629篇
  1993年   536篇
  1992年   565篇
  1991年   530篇
  1990年   551篇
  1989年   575篇
  1988年   479篇
  1987年   424篇
  1986年   389篇
  1985年   424篇
  1984年   431篇
  1983年   459篇
  1982年   453篇
  1981年   405篇
  1980年   343篇
  1979年   378篇
  1978年   324篇
  1977年   274篇
  1976年   260篇
  1975年   268篇
  1974年   257篇
  1973年   246篇
  1972年   293篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
881.
Mosaic trisomy 9 was detected in an amniotic fluid cell culture from a 40-year-old woman evaluated because of advanced maternal age. After counselling, parents elected to terminate the pregnancy. On autopsy the fetus was found to have hydrocephalus and a single kidney. The diagnosis of trisomy 9 mosaicism was confirmed in cultured skin fibroblasts. This is the third reported case of trisomy 9 mosaicism diagnosed prenatally.  相似文献   
882.
Panorpa vulgaris   has become a model insect for testing theories of sexual selection. This contribution summarizes that which has been learned in recent years and presents new data that clearly show that the mating system of P. vulgaris is not simply a resource-defense polygyny, as has previously been thought. In P. vulgaris neither the pattern in food exploitation nor the ratio of variance in the lifetime reproductive success of the two sexes is in accordance with that expected in resource defense polygynous mating systems. Lifetime mating duration is the most important proximate determinant of male fitness. Males employing alternative mating tactics obtain copulations of varying duration in relation to the following sequence: saliva secretion  1  food offering  1  no gift. The number of salivary masses which males provide to females during their lifetime is significantly correlated with the lifetime condition index. The condition index depends on the fighting prowess of males and their ability to find food items. Thus saliva secretion of Panorpa is considered a Zahavian handicap, which can serve as an honest quality indicator used by mating females. Our results confirm four main predictions of the indicator model of the theory of sexual selection: (a) the indicator signals high ecological quality of its bearer, (b) the indicator value increases with phenotypic quality, (c) the indicator value is positively correlated with the genetic quality affecting offspring fitness in a natural selection context, and (d) the quality indicator is more costly for low- than for high-quality individuals. The evolutionary consequences of the mating pattern and the sperm competition mechanism in P. vulgaris are discussed in the context the way in which sexual selection creates and maintains sperm mixing and the evolution of a promiscuous mating system.  相似文献   
883.
884.
885.
Serum PAPP-A measurements taken from 254 women in the first trimester are reported. Eleven chromosomal abnormalities were detected. The mean serum PAPP-A levels in cases of Down syndrome were 0.44 MOM at 9 weeks gestation, 0.15 MOM at 10 weeks, and 0.29 MOM at 11 weeks. The PAPP-A level at 10 weeks was below those of pregnancies which aborted spontaneously. At 11 weeks, the pregnancies with Down syndrome recorded the lowest PAPP-A levels at that gestation. On this small sample, offering chorionic villus sampling to women with singleton pregnancies and a PAPP-A level below 0.3 MOM (approximately 6.5 per cent of this at-risk group) would have detected all the Down syndrome fetuses at 10 weeks and 50 per cent at 11 weeks without selecting those cases destined to abort. This suggests that serum PAPP-A should continue to be investigated as a potential first-trimester screening test for Down syndrome.  相似文献   
886.
A case of spontaneous abortion after transcervical CVS is presented. Despite no evidence of bacteria in the vagina and cervix prior to sampling and the prophylactic use of Metronidazole, pathological evidence of chorioamnionitis was found. The implications of this are discussed.  相似文献   
887.
888.
889.
890.
Non-aqueous electrolyte solutions are nowadays intensively studied owing to their unique properties for their application in various electrochemical devices and procedures. Important advances have already been made in high-energy primary batteries, wet capacitors, electroplating, phase-transfer catalysis and electro-organic synthesis; advances are expected in further fields such as high-energy secondary batteries, non-emissive displays, solar cells, thin-film procedures and coating. A survey is given both for successful recent applications and expectations.  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