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   4229篇
  免费   192篇
  国内免费   1篇
  2022年   15篇
  2021年   27篇
  2020年   13篇
  2019年   18篇
  2018年   32篇
  2017年   34篇
  2016年   57篇
  2015年   90篇
  2014年   109篇
  2013年   473篇
  2012年   211篇
  2011年   226篇
  2010年   153篇
  2009年   148篇
  2008年   218篇
  2007年   258篇
  2006年   231篇
  2005年   262篇
  2004年   295篇
  2003年   234篇
  2002年   244篇
  2001年   33篇
  2000年   32篇
  1999年   40篇
  1998年   50篇
  1997年   52篇
  1996年   34篇
  1995年   43篇
  1994年   44篇
  1993年   53篇
  1992年   47篇
  1991年   33篇
  1990年   28篇
  1989年   36篇
  1988年   38篇
  1987年   36篇
  1986年   37篇
  1985年   38篇
  1984年   41篇
  1983年   35篇
  1982年   41篇
  1981年   48篇
  1980年   40篇
  1979年   22篇
  1978年   25篇
  1977年   22篇
  1976年   28篇
  1975年   15篇
  1974年   19篇
  1973年   17篇
排序方式: 共有4422条查询结果,搜索用时 15 毫秒
991.
Many 1,2-benzisoxazole-3-acetamides were synthesized and their herbicidal activities in the paddy field were studied. Of the compounds tested, N-α,α-dimethylbenzyl-2-bromo-(1,2-benzisoxazol-3-yl)acetamide 10a was the most effective. Details of the synthesis and the results of herbicidal evaluations are given.  相似文献   
992.
A protease from the lotus seed (Nelumbo nucifera Gaertn) was purified by acid-treatment, ammonium sulfate-fractionation, ethylalcohol-fractionation, TEAE-cellulose-treatment and Sephadex G-100 gel-filtration.

The enzyme was purified about 870-fold and was homogeneous in electrophoretic and ultracentrifugal analyses.

Purified lotus seed protease is an acid protease with a pH optimum at 3.8 toward urea-denatured casein. It is active for casein and hemoglobin. But other proteins such as edestin, zein, lotus seed globulin and soybean casein are slightly hydrolyzed and egg albumin is hardly hydrolyzed. This enzyme is most stable at pH 4.0 below 40°C. The enzyme is not a thiol protease, and its activity was completely inhibited by potassium permanganate, remarkably inhibited by sodium dodecylsulfate and accelerated by hydrogen peroxide.  相似文献   
993.
994.
Scapuloperoneal spinal muscular atrophy (SPSMA) is a neuromuscular disorder characterized by weakness in the distribution of shoulder girdle and peroneal muscles. We have previously described a large New England kindred with autosomal dominant SPSMA and have subsequently linked this family trait to 12q24.1-q24.31. In this family, disease expression becomes more severe and progressive in successive generations, suggesting genetic anticipation. Accordingly, we have investigated the thirteen known CAG/CTG repeat loci on chromosome 12 that could be tested by using the polymerase chain reaction as candidate genetic mutations in SPSMA. None of these loci is expanded. Received: 12 June 1996 / Revised: 24 January 1997  相似文献   
995.
Abstract The structure of the region necessary for replication of the plasmid pLA103 from Lactobacillus acidophilus TK8912 has been characterized. Sequence analysis revealed that the replication region contained an open reading frame (OrfA) encoding a 282-amino acid peptide preceded by a 22-bp tandem repeat sequence region. The predicted OrfA protein showed homology to the replication protein of a plasmid from Pediococcus halophilus . The plasmid containing the repeat sequence region preceding OrfA was able to replicate in the Lactobacillus host when provided with OrfA in trans , suggesting that the repeat sequence region contains the origin sequence essential for the pLA103 replication.  相似文献   
996.
997.
998.
Abstract A 5.7-kb Eco RI DNA fragment has been isolated from Bacillus sp. strain N-4 chromosome DNA. This fragment contained both the pNK1-encoded cellulase ( celB ) gene and the pNK2-encoded cellulase ( celA ) gene which were highly homologous [13]. These results demonstrate the tandem location of these genes on the chromosomal DNA. The homologous sequence, which may play an important role for the gene duplication, were observed 5' upstream of the celA gene, between the celA and celB genes, and 3' downstream from the celB gene.  相似文献   
999.
1000.
Effects of aging on the biological discrimination between calcium (Ca) and strontium (Sr) by the kidneys and bone were studied in male and female rats of 5 to 50 wk of age by examining Sr/Ca ratios in the plasma, urine, and bone. The Ca-Sr discrimination at the reabsorption process in the kidneys was not affected by aging in male or female rats. On the other hand, discrimination between the two elements was shown to be age-related at the absorption process in the digestive tract, and became more strict with age. The reverse situation was observed in the discrimination of Ca and Sr in the femur; younger rats discriminated the two elements more strictly than older animals.  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