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   25670篇
  免费   232篇
  国内免费   244篇
安全科学   666篇
废物处理   892篇
环保管理   3323篇
综合类   5995篇
基础理论   6103篇
环境理论   9篇
污染及防治   6400篇
评价与监测   1569篇
社会与环境   1058篇
灾害及防治   131篇
  2022年   178篇
  2018年   308篇
  2017年   313篇
  2016年   458篇
  2015年   369篇
  2014年   577篇
  2013年   1882篇
  2012年   710篇
  2011年   954篇
  2010年   741篇
  2009年   851篇
  2008年   950篇
  2007年   1005篇
  2006年   904篇
  2005年   768篇
  2004年   749篇
  2003年   779篇
  2002年   693篇
  2001年   962篇
  2000年   640篇
  1999年   445篇
  1998年   280篇
  1997年   298篇
  1996年   329篇
  1995年   344篇
  1994年   356篇
  1993年   290篇
  1992年   326篇
  1991年   335篇
  1990年   349篇
  1989年   319篇
  1988年   299篇
  1987年   248篇
  1986年   251篇
  1985年   270篇
  1984年   247篇
  1983年   260篇
  1982年   263篇
  1981年   266篇
  1980年   222篇
  1979年   223篇
  1978年   227篇
  1977年   195篇
  1976年   213篇
  1975年   178篇
  1974年   227篇
  1973年   195篇
  1972年   198篇
  1971年   173篇
  1967年   201篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
952.
Twenty-nine cases of spontaneous abortion following first-trimester chorionic villus sampling (CVS) were reviewed out of a series of 722 patients. Of the 29 cases, there were only four abnormal CVS results. Pathological examination was performed in 79 per cent of cases, and this did not identify any characteristic pathological feature associated with spontaneous abortion after CVS. There was no obvious difference in the pathological features following the transabdominal (TA) or the transcervical (TC) methods. The majority of miscarriages occurred within 4 weeks of the procedure, but 38 per cent of cases aborted between 7 and 14 weeks after CVS. The TC method was used in 22 patients; the TA in 6; and both methods in 1 patient. The TA method was associated with a significantly lower fetal loss rate than the TC method (TA 2 per cent, TC 9 per cent, p < 0.001).  相似文献   
953.
Risks appropriate for mid-trimester prenatal screening for autosomal trisomies have been estimated from a combination of maternal age and maternal serum (MS) alpha-fetoprotein (AFP) levels at 16–20 weeks gestation. Published data on the frequency of Down's syndrome births relative to maternal age were modified to include the additional age-related frequency of trisomy 18 and trisomy 13 cases to provide an overall risk for an autosomal trisomy at midtrimester. MSAFP results from a retrospective study of 142 affected (114 trisomy 21, 19 trisomy 18, and 9 trisomy 13)and 113 000 unaffected pregnancies were converted to multiples of the appropriate gestational median (MOM). The AFP levels in the autosomal trisomy pregnancies were found to be significantly reduced at 0.72 MOM of the unaffected pregnancies. Risks (likelihood ratios) were derived from the overlapping log Gaussian distributions for affected and unaffected pregnancies and combined with maternal age risks to give the overall odds of an affected pregnancy. A mid-trimester cut-off risk of 1:280 gave an estimated 37 per cent detection rate for autosomal trisomies in the west of Scotland population for a follow-up (false-positive) rate of 6.6 per cent. These figures compare with a 30 per cent detection and 6.7 per cent false-positive rate if age 35 years and over is used as the sole criterion for selection of at-risk pregnancies.  相似文献   
954.
955.
956.
Bacterial cell wall components such as lipopolysaccharide, a variety of membrane proteins, murein, and lipoprotein can act as immunoadjuvants for bacterial vaccines, thus enhancing protection from bacterial infections. Synthetically prepared N-terminal parts of the lipoprotein from Enterobacteria carrying three fatty acid residues or lipopeptide analogs containing one to four aminoacids bound to S-glycerylcysteine act as potent immunoadjuvants in vivo in combination with or covalently linked to antiges. Here we demonstrate that the supplementation ofSalmonella vaccines with these synthetic lipopeptides significantly enhances their vaccine efficiency in mice. Variations in the native lipopeptide structure regarding chain length and amino acid sequence of the peptide moiety, as well as modifications of the lipoamino acid, lead to reduction or even complete loss of the adjuvant activity. The immunoadjuvant properties of the lipopeptides as described here are mediated by an enhancement of the humoral immune response.  相似文献   
957.
958.
959.
960.
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