全文获取类型
收费全文 | 93198篇 |
免费 | 1225篇 |
国内免费 | 1132篇 |
专业分类
安全科学 | 3790篇 |
废物处理 | 3443篇 |
环保管理 | 14156篇 |
综合类 | 21371篇 |
基础理论 | 26664篇 |
环境理论 | 73篇 |
污染及防治 | 16093篇 |
评价与监测 | 5592篇 |
社会与环境 | 3829篇 |
灾害及防治 | 544篇 |
出版年
2022年 | 832篇 |
2021年 | 819篇 |
2020年 | 649篇 |
2019年 | 867篇 |
2018年 | 1175篇 |
2017年 | 1223篇 |
2016年 | 2223篇 |
2015年 | 1847篇 |
2014年 | 2607篇 |
2013年 | 9284篇 |
2012年 | 2277篇 |
2011年 | 2592篇 |
2010年 | 3337篇 |
2009年 | 3465篇 |
2008年 | 2175篇 |
2007年 | 2016篇 |
2006年 | 2430篇 |
2005年 | 2390篇 |
2004年 | 2707篇 |
2003年 | 2575篇 |
2002年 | 2095篇 |
2001年 | 2553篇 |
2000年 | 2112篇 |
1999年 | 1604篇 |
1998年 | 1396篇 |
1997年 | 1384篇 |
1996年 | 1498篇 |
1995年 | 1590篇 |
1994年 | 1507篇 |
1993年 | 1333篇 |
1992年 | 1344篇 |
1991年 | 1314篇 |
1990年 | 1270篇 |
1989年 | 1213篇 |
1988年 | 1072篇 |
1987年 | 988篇 |
1986年 | 1000篇 |
1985年 | 1074篇 |
1984年 | 1160篇 |
1983年 | 1169篇 |
1982年 | 1177篇 |
1981年 | 1096篇 |
1980年 | 947篇 |
1979年 | 936篇 |
1978年 | 820篇 |
1977年 | 713篇 |
1976年 | 643篇 |
1974年 | 619篇 |
1973年 | 646篇 |
1972年 | 643篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
751.
Two patients referred for evaluation of very high maternal serum alpha-fetoprotein (10–20 multiples of the median) were carrying triploid fetuses with placentas showing features of partial hydatidiform mole. The diagnosis of fetal triploidy should be considered when there is a very high maternal serum alpha-fetoprotein and no ultrasound evidence of open neural tube defect, ventral wall defect, or any other explanation. Therefore, chromosomal analysis of amniotic fluid cells in such cases is essential. 相似文献
752.
753.
Chorionic villus sampling: Improved method for preparation of karyotypes after short-term incubation
A method for the isolation and trypsin-Giemsa banding of metaphases obtained after short-term incubation (48 h) of cytotrophoblast cells from chorionic villus sample is described. A new slide-making instrument, developed expressly to enhance the spreading of chromosomes from metaphases released from small tissue pieces, is responsible for the increase yield of analysable metaphases in this protocol. 相似文献
754.
755.
756.
The Science of Nature - 相似文献
757.
Gulzar Kassam Andrew T. L. Chen Marshall F. Goldberg Suzanne Trusler Godfrey P. Oakley Jr. 《黑龙江环境通报》1984,4(3):213-216
Although prenatal genetic diagnosis can usually provide prospective parents with information as to whether their fetus is affected with certain genetic conditions, the presence of twins and the uncertainty about the phenotype of some chromosome variations pose a major dilemma and make genetic counselling very difficult. Here, a case report of an unusual chromosome aberration (pericentric inversion of chromosome no. 17) in a twin pregnancy which was originally suspected to be monoamniotic but later proved to have two sacs was presented. 相似文献
758.
759.
760.
Social insects use complex chemical communication systems to govern many aspects of their life. We studied chemical changes in Dufours gland secretions associated with ovary development in several genotypes of honeybees. We found that C28–C38 esters were associated only with cavity nesting honeybee queens, while the alcohol eicosenol was associated only with their non-laying workers. In contrast, both egg-laying anarchistic workers and all parasitic Cape workers from queenright colonies showed the typical queen pattern (i.e. esters present and eicosenol absent), while egg-laying wild-type and anarchistic workers in queenless colonies showed an intermediate pattern, producing both esters and eicosenol but at intermediate levels. Furthermore, neither esters nor eicosenol were found in aerial nesting honeybee species. Both esters and eicosenol are biosynthetically similar compounds since both are recognizable products of fatty acid biosynthesis. Therefore, we propose that in honeybees the biosynthesis of esters and eicosenol in the Dufours gland is caste-regulated and this pathway has been conserved over evolutionary time. 相似文献