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   455454篇
  免费   52384篇
  国内免费   751篇
  2018年   4335篇
  2017年   4159篇
  2016年   5978篇
  2015年   8724篇
  2014年   10078篇
  2013年   13519篇
  2012年   16113篇
  2011年   16505篇
  2010年   10884篇
  2009年   9910篇
  2008年   14519篇
  2007年   14913篇
  2006年   13995篇
  2005年   13388篇
  2004年   13414篇
  2003年   12505篇
  2002年   12086篇
  2001年   19055篇
  2000年   18963篇
  1999年   15191篇
  1998年   5746篇
  1997年   5727篇
  1996年   5443篇
  1995年   5218篇
  1994年   4911篇
  1993年   4916篇
  1992年   12541篇
  1991年   12502篇
  1990年   12255篇
  1989年   11723篇
  1988年   10896篇
  1987年   10256篇
  1986年   9783篇
  1985年   9560篇
  1984年   7937篇
  1983年   6884篇
  1982年   5196篇
  1981年   4678篇
  1980年   4371篇
  1979年   7401篇
  1978年   6000篇
  1977年   5328篇
  1976年   4998篇
  1975年   5815篇
  1974年   6360篇
  1973年   6165篇
  1972年   5490篇
  1971年   5089篇
  1970年   4290篇
  1969年   4221篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
141.
142.
143.
144.
145.
The relations between the saccus lacrimalis and different portions of the musculus orbicularis oculi were studied in orbital regions of human fetuses sectioned into numbered series. No insertions of the pars lacrimalis or Horner's muscle on the saccus were found. These muscular fibres pass along the dorsal wall of the saccus and are separated from it by the reflex tendon of the ligamentum palpebrale mediale. The only muscular fibres that insert on the saccus are those that approach the anterior face of the saccus and the fornix. The fibres that insert on the anterior face proceed from the deep bundles of the pars preseptalis of the lower eyelids, and those that insert on the fornix derive from the deep bundles of the pars preseptalis of the upper eyelid.  相似文献   
146.
Two new species of Haptoglossa , one zoosporic, H. northumbrica , and one aplanosporic, H. polymorphs, , were isolated from samples of manure and horse dung in north-east England. The zoosporic H. northumbrica is morphologically similar to H. dickii but differs in having slightly smaller infection gun cells with a unique internal arrangement of cones in the apical missile chamber. The thallus of the aplanosporic H. polymorpha is similar to H. heteromorpha but produces three different types of aplanospore. The smaller cysts either develop into broad, arcuate gun cells or form curved adhesive cells that have a rounded base. These curved adhesive cells have very different internal ultrastructural organization. The large cysts develop into infection cells that are morphologically similar to the curved adhesive cells, but their internal structure has not yet been observed.  相似文献   
147.
We studied 654 healthy ten- to twelve-year-old children living in the Russian Far North (Taimyr peninsula) and in Siberia (town of Krasnoyarsk). The state of the body oxygenation and the systems responsible for oxygen delivery were studied according to the length of time living in the Russian Far North and season of the year. An examination of newcomer children revealed the following changes during the first year of living in the Russian Far North: an increased respiration rate and changes in its circadian rhythm; an increase in the heart rate, cardiac output, and cardiac index; an increase in the mean corpuscular volume in the red blood system; the activation of lipid peroxidation, and the changes in electrolyte balance of cells. The control mechanisms of oxygen transport system gradually stabilized during the ages of two to five years. In children living more than five years in the Russian Far North, the increased oxygen demand was met by the activation of cardiovascular and red blood systems aimed at more effective and adequate oxygen delivery to tissues.  相似文献   
148.
A novel biocatalytic reaction of transamidation of non-activated amides with amines is reported. Among 45 different lipolytic and proteolytic enzymes tested, only the lipase from Candida antarcticawas able to catalyze this reaction. The reaction proceeded with up to ca. 80% conversion in anhydrous methyl tert-butyl ether and worked with both N-substituted and unsubstituted amides. The biocatalytic transamidation is an equilibrium process and, therefore, higher conversions to the desired amide were achieved by using increased concentrations of the amine nucleophile.  相似文献   
149.
150.
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