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   26369篇
  免费   255篇
  国内免费   430篇
安全科学   660篇
废物处理   1274篇
环保管理   3161篇
综合类   3776篇
基础理论   6841篇
环境理论   4篇
污染及防治   7027篇
评价与监测   2072篇
社会与环境   2074篇
灾害及防治   165篇
  2023年   136篇
  2022年   321篇
  2021年   294篇
  2020年   195篇
  2019年   258篇
  2018年   441篇
  2017年   439篇
  2016年   682篇
  2015年   487篇
  2014年   747篇
  2013年   2273篇
  2012年   868篇
  2011年   1143篇
  2010年   1022篇
  2009年   1046篇
  2008年   1180篇
  2007年   1264篇
  2006年   1096篇
  2005年   927篇
  2004年   929篇
  2003年   913篇
  2002年   856篇
  2001年   1135篇
  2000年   784篇
  1999年   479篇
  1998年   337篇
  1997年   307篇
  1996年   371篇
  1995年   375篇
  1994年   322篇
  1993年   301篇
  1992年   307篇
  1991年   283篇
  1990年   273篇
  1989年   270篇
  1988年   247篇
  1987年   215篇
  1986年   167篇
  1985年   192篇
  1984年   227篇
  1983年   204篇
  1982年   241篇
  1981年   189篇
  1980年   157篇
  1979年   190篇
  1978年   146篇
  1977年   137篇
  1976年   130篇
  1973年   120篇
  1972年   120篇
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
391.
Maternal serum CA 125 levels were determined at 9–11 menstrual weeks for 26 cases of trisomy 13 (n = 4), trisomy 18 (n = 7), trisomy 21 (n = 15), and appropriate controls. There were no statistically significant differences between groups.  相似文献   
392.
One hundred and fifty-one women of advanced maternal age who underwent genetic termination of pregnancy (TOP) were studied for their reproductive behaviour and the type of procedure for prenatal diagnosis in a subsequent pregnancy. A total of 59 women (39 per cent) had a further pregnancy. In all continuing pregnancies prenatal diagnosis was performed, of which 75 per cent consisted of chorionic villus sampling (CVS). Reproductive behaviour following a genetic termination was negatively correlated with maternal age and parity. Both reproductive behaviour and the choice to undergo a diagnostic procedure in the next pregnancy were independent of the type of diagnostic procedure in the previous affected pregnancy.  相似文献   
393.
394.
395.
Ninety-two families with spinal muscular atrophy (SMA) applied for genetic counselling and further prenatal diagnosis. To minimize expenses, only one tightly linked informative marker was determined in the course of preliminary examination, and non-radioactive allele detection was preferably used. Four prenatal diagnoses of SMA type I, four of SMA type II, and one of SMA type III were made. This trial programme shows the considerable requirements, importance, and potential effectiveness of prenatal prediction of SMA in Russia.  相似文献   
396.
397.
398.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography.  相似文献   
399.
The polymerase chain reaction (PCR) was used on material from a blighted ovum to confirm indirectly the carrier status of a woman with a family history of Becker muscular dystrophy. Conventional testing including creatine kinase levels, muscle biopsy, and EMG had been inconclusive, and on the basis of one elevated creatine kinase level, the woman had been designated a possible carrier. Ultrasound examination at 10 weeks of pregnancy indicated a blighted ovum, from which DNA was subsequently extracted and subjected to PCR testing for determination of sex and genotypic status with respect to the known familial deletion of the dystrophin gene. The blighted ovum was found to have a Y chromosome and also to be deleted for at least exon 6 of the dystrophin gene, indirectly indicating that the mother most likely carried the family mutation for Becker muscular dystrophy.  相似文献   
400.
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