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   16798篇
  免费   1603篇
  国内免费   700篇
  19101篇
  2023年   139篇
  2022年   351篇
  2021年   605篇
  2020年   366篇
  2019年   505篇
  2018年   499篇
  2017年   376篇
  2016年   562篇
  2015年   831篇
  2014年   1012篇
  2013年   1057篇
  2012年   1296篇
  2011年   1155篇
  2010年   717篇
  2009年   636篇
  2008年   727篇
  2007年   725篇
  2006年   676篇
  2005年   568篇
  2004年   551篇
  2003年   530篇
  2002年   514篇
  2001年   370篇
  2000年   357篇
  1999年   333篇
  1998年   186篇
  1997年   176篇
  1996年   195篇
  1995年   134篇
  1994年   145篇
  1993年   125篇
  1992年   179篇
  1991年   181篇
  1990年   171篇
  1989年   142篇
  1988年   140篇
  1987年   130篇
  1986年   112篇
  1985年   117篇
  1984年   75篇
  1983年   79篇
  1982年   78篇
  1981年   79篇
  1980年   56篇
  1979年   80篇
  1978年   78篇
  1977年   54篇
  1976年   48篇
  1975年   53篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
The rabbit oviductal epithelium synthesizes and secretes a family of antigenically related, sulfated oviductal glycoproteins (SOG). Anti-SOG monoclonal antibodies (Mabs) were produced and two (Mab 1 and Mab 2) were selected for further characterization. Periodate oxidation of Western blots of oviductal fluid did not affect the binding of Mab 1 or Mab 2, thus suggesting that these antibodies recognized protein rather than carbohydrate epitopes on SOG. The specificity of Mab 1 was determined by Western blot analysis of tissues obtained from estrous rabbits and from the male rabbit reproductive tract. SOG was identified in tissue extracts of both the oviductal ampulla and isthmus. Cervix was the only non-oviductal tissue with which Mab 1 cross-reacted. Mab 1 was used to isolated SOG from whole oviductal fluid by immuno-affinity chromatography. Affinity-purified SOG and Mab 1 were used to develop a quantitative, SOG-specific, competitive enzyme-linked immunosorbent assay. This assay was used to quantify SOG in rabbit oviductal fluid collected during estrus and pseudopregnancy. SOG secretion during pseudopregnancy was resolved into two transient episodes of increased secretion. Maximum SOG secretion (X = 1039 +/- 199 micrograms/day) occurred within 48 h of the induction of pseudopregnancy. A second period of enhanced SOG secretion (X = 308 +/- 46 micrograms/day) occurred during the fifth and sixth days of pseudopregnancy. Baseline SOG secretion occurred during estrus at approximately 60% of maximum postovulatory secretion.  相似文献   
15.
16.
17.
18.
19.
Human ejaculated spermatozoa are heterogeneous and can be separated into two distinct populations according to their respective buoyant densities. In order to investigate the functional differences between these two types of spermatozoa, we have searched for the presence of galactosyltransferase. A Western blot of sperm proteins following their electrophoresis was probed with an anti-galactosyltransferase serum revealing that this enzyme is present in human spermatozoa. Furthermore, galactosyltransferase is detectable only in those proteins isolated from the head of high density spermatozoa. These results suggest that ejaculated spermatozoa consist of two populations that are functionally different.  相似文献   
20.
Summary The exact time course of phosphate consumption in a tetracycline production byStreptomyces aureofaciens has been determined. The data have been compared with model simulations according to a model proposed by Votruba et al. (1984). This led to a revision of his equation for the rate of phosphate consumption and to the proposal that phosphate is consumed proportionally to the growth rate. In contradiction to the model simulations it was found that the length of the time lag of the production is independent of the initial phosphate concentration. While the model explains the time lag through inhibition of the production by phosphate, the measured data show that there must be another or an additional reason for the lag. Simultaneously with the start of the production the organism changes from an organic substrate to ammonia as nitrogen source.All experiments have been carried out in a bubble column of 651 working volume as fed batch fermentation. An autoanalyzer and a HPLC was coupled to the reactor for automatic measurement of phosphate, ammonia, sucrose and products in short intervals. Composition of the outlet gas, pH, pO2, temperature and weight of the substrate flasks were monitored on-line.  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