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   17710篇
  免费   237篇
  国内免费   4篇
  17951篇
  2023年   157篇
  2016年   133篇
  2015年   147篇
  2014年   156篇
  2013年   778篇
  2012年   275篇
  2011年   304篇
  2010年   250篇
  2009年   368篇
  2008年   271篇
  2007年   300篇
  2006年   227篇
  2005年   259篇
  2004年   180篇
  2003年   176篇
  2002年   187篇
  2000年   135篇
  1996年   148篇
  1995年   145篇
  1994年   116篇
  1993年   232篇
  1992年   204篇
  1991年   205篇
  1990年   225篇
  1989年   392篇
  1988年   345篇
  1987年   453篇
  1986年   392篇
  1985年   392篇
  1984年   323篇
  1983年   259篇
  1982年   311篇
  1981年   328篇
  1980年   316篇
  1979年   312篇
  1978年   363篇
  1977年   406篇
  1976年   426篇
  1975年   457篇
  1974年   307篇
  1973年   175篇
  1972年   176篇
  1971年   169篇
  1970年   170篇
  1969年   140篇
  1968年   138篇
  1967年   132篇
  1964年   166篇
  1958年   131篇
  1957年   163篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Three experiments were performed to study the influence of challenging incentives on feedback-assisted heart rate reduction for coronary-prone (Type A) and non-coronary-prone (Type B) males. In the first experiment, when subjects were given a competitive instructional set, Type As were significantly more successful relative to Type Bs in reducing their heart rate; with a noncompetitive set, Type Bs were significantly more successful than were Type As. In the second experiment, when told that heart rate reduction was a scarce ability, Type As reduced heart rate significantly better than did Type Bs; when told that heart rate reduction was a common ability, Type Bs achieved significantly greater heart rate reduction than did Type As. In the third experiment, when heart rate reduction was described as being instrumental to time-urgency (i.e., getting more done in less time), Type As reduced heart rate significantly bettern than did Type Bs; when heart rate reduction was described as being instrumental to relaxation, Type Bs were significantly better able to reduce heart rate. In all three studies, the incentives had no effect on heart rate when feedback was not provided. The results are discussed as support for the notion that Type A behavioral pattern characteristics can be exploited to reduce Type A symptoms. Implications for how coronary-prone individuals may be challenged to modify symptoms within the clinical setting are discussed.  相似文献   
23.
24.
25.
26.
An approach to episodic associative memory is presented, which has several desirable properties as a human memory model. The design is based on topological feature map representation of data. An ordinary feature map is a classifier, mapping an input vector onto a topologically meaningful location on the map. A trace feature map, in addition, creates a memory trace on that location. The traces can be stored episodically in a single presentation, and retrieved with a partial cue. Nearby traces overlap, which results in plausible memory interference behavior. Performance degrades gracefully as the memory is overloaded. More recent traces are easier to recall as are traces that are unique in the memory.This research was supported in part by an ITA Foundation grant and by fellowships from the Academy of Finland, the Emil Aaltonen Foundation and the Foundation for the Advancement of Technology (Finland) when the author was at UCLA  相似文献   
27.
A high percentage of plantlets, in which PVX, PVM, and PVS were no longer detectable by precipitin tests was obtained from 100% virus-infected stocks of the potato varieties Rosa and Priobskij rannija by combining meristem (tip) culture with antiphytoviral chemotherapy. When 2,4 - dioxohexahydro 1,3,5-triazinc (DHT) was added to the nutrient media, no virus was detectable serologically in 72% of the corresponding explants of the variety Rosa and in 66% of that of the variety Priobskij rannija, respectively. Contrary to this, all untreated control explants proved virusinfected. Treatment with 2-thiouracil resulted in 46.6%, with cyanoguanidine in 28.6% of plantlets, in which no virus was detectable serologically.  相似文献   
28.
Monoclonal antibodies were produced to electrophoretically pure hydrogenase fromThiocapsa roseopersicina. Protein immunoelectroblotting was used to identify the hydrogenase-specific antibodies. Among the 18 monoclonal antibodies selected by enzyme immunoassay, three were found to react with highly immunogenic trace contaminating proteins. One cell line produced antibody that inhibitied hydrogenase activity. This was the first specific inhibitor of the hydrogenase function. The results suggest that monoclonal antibodies could provide valuable new informations about the enzyme structure as well.  相似文献   
29.
30.
Summary Consecutive sections of certain neurons in the central ganglia of the pond snail Lymnaea stagnalis appear to be immunoreactive to anti-dopamine and anti-serotonin. The Cerebral Giant Neurons stain in addition with antivasotocin. The observations indicate the presence of two biogenic amines within the same neuron and in addition their co-existence with a biologically active peptide.  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