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   2008篇
  免费   11篇
  国内免费   17篇
系统科学   9篇
丛书文集   16篇
教育与普及   2篇
理论与方法论   7篇
现状及发展   910篇
研究方法   64篇
综合类   1024篇
自然研究   4篇
  2012年   31篇
  2011年   29篇
  2010年   12篇
  2009年   10篇
  2008年   36篇
  2007年   40篇
  2006年   42篇
  2005年   70篇
  2004年   82篇
  2003年   38篇
  2002年   27篇
  2001年   59篇
  2000年   55篇
  1999年   57篇
  1996年   10篇
  1994年   259篇
  1992年   37篇
  1991年   21篇
  1990年   35篇
  1989年   33篇
  1988年   37篇
  1987年   31篇
  1986年   29篇
  1985年   44篇
  1984年   29篇
  1983年   19篇
  1982年   22篇
  1981年   19篇
  1980年   30篇
  1979年   64篇
  1978年   29篇
  1977年   39篇
  1976年   29篇
  1975年   30篇
  1974年   39篇
  1973年   49篇
  1972年   44篇
  1971年   42篇
  1970年   44篇
  1969年   40篇
  1968年   43篇
  1967年   47篇
  1966年   31篇
  1965年   21篇
  1964年   18篇
  1959年   14篇
  1958年   16篇
  1957年   18篇
  1956年   12篇
  1955年   13篇
排序方式: 共有2036条查询结果,搜索用时 15 毫秒
221.
Cloning and sequencing of the complementary DNA for platelet-derived endothelial cell growth factor indicates that it is a novel factor distinct from previously characterized proteins. The factor, a protein with a relative molecular mass of about 45,000, stimulates endothelial cell growth and chemotaxis in vitro and angiogenesis in vivo.  相似文献   
222.
223.
H Kamiya  K Muramoto  T Hoshino  U Raj 《Experientia》1985,41(9):1201-1202
The sponge Dysidea herbacea (Keller) was found to possess hemagglutinins. The major component, DHA-I, is a protein with a mol. wt of 26,000, which dissociates into subunits of equal size (14,000). It contains large amounts of glutamic acid and aspartic acid residues, but no half-cystine, methionine or histidine residues. DHA-I reacted with rabbit and human AB0 erythrocytes. D-galactose and lactose were effective inhibitors of DHA-I. The sponge also contained a minor component(s) which reacted preferentially with rabbit erythrocytes but not with human AB0 erythrocytes.  相似文献   
224.
225.
The atrial and ventricular myosin light chains of human, monkey and sheep hearts were compared by dodecylsulfate polyacrylamide gel electrophoresis. The atrial light chain 2 and ventricular light chain 2 are similar among these mammals. However, the atrial light chain 1 of monkey has different electrophoretic mobility from those of human and sheep. The monkey ventricular light chain 1 has same mobility as that of sheep but different from that of human.  相似文献   
226.
Light-dependent antibody labelling of photoreceptors   总被引:1,自引:0,他引:1  
G W Balkema  U C Dr?ger 《Nature》1985,316(6029):630-633
Monoclonal antibodies are tools widely used to analyse the structure of the nervous system. Whereas some labelling patterns are highly reproducible, others appear to vary from one preparation to the next, as we noticed in particular for some antibodies with respect to photoreceptor labelling. To establish whether some of this variability can be linked to functional criteria, we tested for light-dependence. We found two antibodies that label photoreceptor outer segments, only when the retina has been illuminated, and a third antibody that has a selective affinity for dark-adapted outer segments. The two antibodies against light-activated sites are primarily directed against the highly phosphorylated neurofilament subunit at relative molecular mass 200,000 (200K). One of them, RT97, recognizes on immunoblots, in addition to neurofilaments, a light-activated epitope on a protein that resembles the photopigment rhodopsin, presumably a phosphorylation-dependent site. Antibodies like those described here may allow the study of physiological processes such as light and dark adaptation using morphological techniques.  相似文献   
227.
228.
提出了一种适应于二值图像的快速细化算法,该算法利用边缘跟踪、根据边缘跟踪特点所设计的判断规则及单向链表结构存储边缘信息等技术,大大地加快了细化速度,而且占内存少,当仅需对目标模式进行细化处理时,该算法更为有效。  相似文献   
229.
Nb2O5掺杂及TiO2压敏陶瓷埋烧工艺的研究   总被引:3,自引:0,他引:3  
通过微结构分析、I-V特性及复阻抗频谱的测量,比较了埋烧和传统的裸烧工艺对于Nb^5 掺杂的TiO2压敏陶瓷材料的压敏电压和非线性系数的影响,结果表明掩埋法烧结可以降低该类陶瓷材料的压敏电压和非线性系数;考察了Nb2O5掺杂的作用,表明Nb^5 固溶于TiO2中取代Ti^4 使晶粒半导化.Nb2O5掺杂量对TiO2压敏陶瓷的I-V特性和微观结构都会有影响作用,适量Nb^5 的掺杂有助于晶粒的生长.  相似文献   
230.
Transgenic cultigens may become feral as we know of some non-transgenic cultigens. The article explains two basic ways how cultigens become feral: through hybridization with a closely related wild plant and through revert to the wild-type. A long list of examples of cultigens becoming feral in Central Europe is presented. The process of becoming feral is compared to the naturalization of non-native species (Exotic Species Model). Ecological long-term effects of both cultigens becoming feral and non-native species being naturalized are discussed with special regard to the predictability of such events. The ecological aspects discussed in the article are as significant for transgenic cultigens as for non-transgenic cultigens.  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