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   40764篇
  免费   445篇
  国内免费   322篇
安全科学   1174篇
废物处理   1473篇
环保管理   5660篇
综合类   6491篇
基础理论   11548篇
环境理论   24篇
污染及防治   10568篇
评价与监测   2451篇
社会与环境   1868篇
灾害及防治   274篇
  2022年   260篇
  2021年   278篇
  2019年   322篇
  2018年   556篇
  2017年   547篇
  2016年   816篇
  2015年   663篇
  2014年   942篇
  2013年   3077篇
  2012年   1154篇
  2011年   1694篇
  2010年   1400篇
  2009年   1401篇
  2008年   1710篇
  2007年   1794篇
  2006年   1642篇
  2005年   1348篇
  2004年   1350篇
  2003年   1280篇
  2002年   1246篇
  2001年   1655篇
  2000年   1145篇
  1999年   731篇
  1998年   588篇
  1997年   577篇
  1996年   583篇
  1995年   651篇
  1994年   623篇
  1993年   535篇
  1992年   561篇
  1991年   530篇
  1990年   545篇
  1989年   573篇
  1988年   480篇
  1987年   423篇
  1986年   385篇
  1985年   421篇
  1984年   426篇
  1983年   457篇
  1982年   452篇
  1981年   401篇
  1980年   342篇
  1979年   375篇
  1978年   321篇
  1977年   271篇
  1976年   258篇
  1975年   267篇
  1974年   256篇
  1973年   245篇
  1972年   292篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
861.
This paper reports eight cases of non-mosaic, rare, and typically lethal trisomies diagnosed in chorionic villi and not confirmed by amniocentesis. Four cases were 47,XX, + 16; two cases were 47,XX, +2; one was 47,XX, + 12; and one was 47,XY, +7. There have been no known complications in any of these gestations. These eight cases were found in a series of approximately 12 000 samples processed in our laboratory (0.07 per cent). We conclude that (1) rare non-mosaic trisomy not reflecting the fetal condition is an occasional source of diagnostic ambiguity in chorionic villus sampling; and (2) when encountered, a follow-up amniocentesis should be recommended to the patient to confirm or rule out the abnormality. We propose the term ‘confined placental abnormality’ to describe non-mosaic trisomies and other related abnormalities found only in chorionic tissue.  相似文献   
862.
In 19 pregnancies at risk for 21-hydroxylase deficiency (21OHD) in 18 families with at lea one affected child, prenatal diagnosis was performed by RFLP analysis using the enzymi Taq I and EcoRI and the DNA probes specific for the 21 OH genes, the closely linke complement C4 genes and the highly polymorphic HLA class II genes DRB, DQB, and DPI For fetal DNA analysis either chorionic villi or cultivated amniotic cells were used. In all 1 cases, a clear prenatal diagnosis was possible either with the 21OH probe alone or in mo cases, by combining the results of the different closely linked loci.  相似文献   
863.
A pregnant woman with indeterminate Duchenne muscular dystrophy (DMD) carrier status, but with DMD diagnosed in her deceased brother (unavailable for study), presented for prenatal diagnosis, intending to continue the pregnancy only if proven unaffected with DMD with near absolute certainty. Creatine kinase (CK) assays to clarify carrier status were inconclusive. Male sex in the fetus was identified, but DNA restriction fragment length polymorphism (RFLP) analysis was not yet available to this centre to investigate the possible transmission of the DMD gene, and the pregnancy was terminated. Tissue histology and dystrophin protein analysis demonstrated the absence of DMD. In a situation with proven maternal carrier status, future fetal inheritance of the opposite maternal X chromosome would indicate the presence of DMD. However, maternal carrier status remained in doubt through a second pregnancy, even with RFLP studies, and was finally established when dystrophin analysis confirmed the presence of DMD in the second fetus. Histologic findings are presented, contrasting features in the two fetuses. The value of dystrophin analysis for establishing the diagnosis of fetal DMD, in this case proving maternal carrier status in a difficult situation, and for demonstrating DMD gene:RFLP haplotype relationships is illustrated.  相似文献   
864.
The discussion on the possible increase of solar UV on earth due to the destruction of the stratospheric ozone has led to a renewed interest in the action of ultraviolet radiation on biological systems. The paper deals with changes at the cellular level stressing particularly molecular alterations in deoxyribonucleic acid, the carrier of genetic information. The most important repair processes by which lesions are removed or bypassed are described. It is also discussed whether the effectivity of a complex spectrum can be predicted on the basis of measurements with monochromatic radiation. Furthermore, possible consequences on human health are outlined which may be derived from cellular studies.  相似文献   
865.
Gross scoliosis of the fetal thoracic spine was diagnosed at 18 weeks gestation. The pregnancy was terminated and the fetus found to have webbing of the neck and an imperforate anus in addition to vertebral defects.  相似文献   
866.
867.
868.
869.
870.
各种环境因素的协同作用已经导致保护运动在解释保护运动的基本信念时尤其缺乏信心。“反对派”行动主义者以为他们的论据是得到证实的,而“制度派”战术主义者倾向于采取他们并不赞同的功利主义的或经济的观点。根据现有的证据,在几百年以后,这个星球上主要的自然区域将基本消失,人类的生活质量将会受到极大的威胁。一种更可靠的观点认为:自然界是人类体验自由(这也是一种精神环境)的能力中不可或缺的一部分。这一观点将改变我们对待自然环境的方式,也关乎今后生物多样性长期生存的前景。  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