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   756836篇
  免费   84828篇
  国内免费   509篇
  2016年   8256篇
  2015年   11385篇
  2014年   13393篇
  2013年   18894篇
  2012年   21129篇
  2011年   21674篇
  2010年   14757篇
  2009年   13779篇
  2008年   19605篇
  2007年   20594篇
  2006年   19489篇
  2005年   18580篇
  2004年   18616篇
  2003年   17581篇
  2002年   17461篇
  2001年   32237篇
  2000年   32675篇
  1999年   26101篇
  1998年   9167篇
  1997年   9562篇
  1996年   8885篇
  1995年   8473篇
  1994年   8258篇
  1993年   8312篇
  1992年   21598篇
  1991年   21183篇
  1990年   20695篇
  1989年   20079篇
  1988年   19066篇
  1987年   18173篇
  1986年   17149篇
  1985年   17201篇
  1984年   14281篇
  1983年   12320篇
  1982年   9651篇
  1981年   8819篇
  1980年   8297篇
  1979年   13843篇
  1978年   11113篇
  1977年   10231篇
  1976年   9711篇
  1975年   10710篇
  1974年   12007篇
  1973年   11755篇
  1972年   10951篇
  1971年   9873篇
  1970年   8728篇
  1969年   8567篇
  1968年   8032篇
  1967年   6846篇
排序方式: 共有10000条查询结果,搜索用时 254 毫秒
971.
972.
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity.  相似文献   
973.
Protoplasts of Schizosaccharomyces pombe, grown on a rich nutrient medium, were treated with a peptide factor isolated from cultures of the protozoan Tetrahymena pyriformis. The peptide factor is known to inhibit RNA synthesis in Tetrahymena. It has now been shown that the peptide factor also inhibits RNA synthesis in yeast protoplasts without affecting protein synthesis.  相似文献   
974.
Big, beautiful organisms are useful for biological education, increasing evolution literacy, and biodiversity conservation. But if educators gloss over the ubiquity of streamlined and miniaturized organisms, they unwittingly leave students and the public vulnerable to the idea that the primary evolutionary plot of every metazoan lineage is “progressive” and "favors" complexity. We show that simple, small, and intriguingly repulsive invertebrate animals provide a counterpoint to misconceptions about evolution. Our examples can be immediately deployed in biology courses and outreach. This context emphasizes that chordates are not the pinnacle of evolution. Rather, in the evolution of animals, miniaturization, trait loss, and lack of perfection are at least as frequent as their opposites. Teaching about invertebrate animals in a “tree thinking” context uproots evolution misconceptions (for students and the public alike), provides a mental scaffold for understanding all animals, and helps to cultivate future ambassadors and experts on these little‐known, weird, and fascinating taxa.  相似文献   
975.
A rapid, sensitive method has been developed to detect antibody-antigen complexes on “Western blots.” The methods of H. Towbin, T. Staehlin, and J. Gordon were used to separate and blot the antigens onto nitrocellulose. The remaining sites of attachment were blocked and the nitrocellulose was washed with polyoxyethylenesorbitan monolaurate (Tween 20). The blot was then reacted with the antiserum or hybridoma supernate to be tested. After the antigen-antibody reaction was completed, the blot was washed and treated with anti-antibody which has been conjugated to alkaline phosphatase. The alkaline phosphatase was detected by the reduction of the tetrazolium salt to diformazan by the hydrogen ions released in the formation of indigo by the reaction of the phosphatase on the indoxyl phosphate. The advantages of this method over previously described techniques are (1) use of Tween 20 allows the blot to be stained with Coomassie blue, (2) the substrates of the alkaline phosphatase reaction are stable for long periods of time, (3) the reaction products form an intense blue color which does not fade, (4) the resolution is extremely good with little to no band broadening, (5) the reaction is sensitive to picogram quantities of antigen, and (6) the reaction is quantitative.  相似文献   
976.
977.
The isolation of spirochaetes from the rat caecum   总被引:1,自引:1,他引:0  
Spirochaetes indigenous to the conventional rat caecum were cultivated on agar medium using selective isolation techniques. The 27 axenic isolates represented four morphological types of spirochaetes differing in cell size, cell coiling pattern and number of protoplasmic flagella.  相似文献   
978.
S J Henriksen  G Chouvet  F E Bloom 《Life sciences》1982,31(16-17):1785-1788
Recent immunohistochemical and radioimmunochemical observations have demonstrated a differential distribution of immunoreactive dynorphin (DYN) in rat brain. The presence of DYN immunoreactivity in a major intrinsic fiber pathway within the rat hippocampus (the mossy fiber system) has led us to evaluate the possible role of DYN and other closely related peptides in this structure. Single cell activity and hippocampal field potentials have been recorded from the CA1-CA3 cellular fields in halothane or urethane anesthetized rats. DYN, DYN1-13, DYN1-8, and alpha-neo-endorphin had an excitatory effect on most CA1-CA3 neurons encountered as has been previously observed for opiates and other opioid peptides. This response could be blocked by naloxone or by co-administration of Mg++ ion suggesting an indirect (synaptic) mechanism of excitation similar to that hypothetized for enkephalin. A significant number of CA3 neurons, however, exhibited a non-naloxone sensitive inhibitory response to DYN, related opioid peptides, and the kappa agonist WIN 35-197 (ethylketocyclazocine). Field potential analysis of CA1-CA3 neuronal responses to mossy fiber activation also indicated an excitatory, Mg++ reversible, action of iontophoretically applied DYN. These observations support our cytochemical and assay studies indicating diverse opioid systems within the rat hippocampus. In addition, these functional studies are congruent with other evidence suggesting multiple opioid mechanisms in this structure.  相似文献   
979.
Editorial     
  相似文献   
980.
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