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   18549篇
  免费   385篇
  18934篇
  2015年   160篇
  2014年   184篇
  2013年   754篇
  2012年   280篇
  2011年   321篇
  2010年   288篇
  2009年   428篇
  2008年   352篇
  2007年   350篇
  2006年   311篇
  2005年   272篇
  2004年   233篇
  2003年   216篇
  2002年   267篇
  1999年   144篇
  1998年   134篇
  1997年   132篇
  1996年   184篇
  1995年   187篇
  1994年   141篇
  1993年   252篇
  1992年   240篇
  1991年   234篇
  1990年   252篇
  1989年   427篇
  1988年   376篇
  1987年   471篇
  1986年   408篇
  1985年   409篇
  1984年   349篇
  1983年   274篇
  1982年   330篇
  1981年   347篇
  1980年   330篇
  1979年   332篇
  1978年   374篇
  1977年   416篇
  1976年   435篇
  1975年   465篇
  1974年   310篇
  1973年   176篇
  1972年   176篇
  1971年   170篇
  1970年   175篇
  1969年   146篇
  1968年   146篇
  1967年   134篇
  1964年   170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 0 毫秒
21.
22.
Treatment of painful hand neuromas by their transfer into bone   总被引:2,自引:0,他引:2  
Painful neuromas in the hand are not only very disabling for the patient, but difficult to treat. We present the results of 20 painful neuromas treated by burying the neuroma in the bone. Eighteen of the 20 neuromas operated on had acceptable results, according to the criteria of Herndon et al. We present our technique and compare our results with other treatments in the literature.  相似文献   
23.
24.
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   
25.
Ribonuclease III: new sense from nuisance.   总被引:6,自引:0,他引:6  
RNases play an important role in the processing of precursor RNAs, creating the mature, functional RNAs. The ribonuclease III family currently is one of the most interesting families of endoribonucleases. Surprisingly, RNase III is involved in the maturation of almost every class of prokaryotic and eukaryotic RNA. We present an overview of the various substrates and their processing. RNase III contains one of the most prominent protein domains used in RNA-protein recognition, the double-stranded RNA binding domain (dsRBD). Progress in the understanding of this domain is summarized. Furthermore, RNase III only recently emerged as a key player in the new exciting biological field of RNA silencing, or RNA interference. The eukaryotic RNase III homologues which are likely involved in this process are compared with the other members of the RNase III family.  相似文献   
26.
27.
28.
29.
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   
30.
A retrospective study of disease and mortality in zebra finches   总被引:1,自引:0,他引:1  
Few published reports exist describing morbidity and mortality in domestic zebra finch colonies maintained in a laboratory animal setting. A retrospective study of clinical disease and mortality in quarantined adult zebra finches was performed. Animals were observed during the 2 week quarantine period and for at least 1 month afterwards (42 days). Signs of disease, including feather and beak abnormalities, oculonasal discharge, increased respiratory rate or stridor, abdominal enlargement, pasty vent, diarrhea, lameness and pectoral muscle loss, were evaluated in our colony during this time. History, physical examination, laboratory testing and postmortem evaluation were used to determine causes of clinical disease. Common clinical findings in sick finches included sudden death, ruffled feathers, increased respiratory rate or gape mouthed breathing, pasty vent or frank diarrhea, and beak discoloration. Organisms frequently isolated were Staphylococcus spp., E. coli, Enterobacter spp., and Coccidia spp. Of the finches that died while in the colony (29.5%), 23.0% died in the first week after arrival. Pathogens frequently isolated from tissues cultured at necropsy included: E. coli, Staphylococcus aureus, Enterobacter spp., and Candida albicans. When observed, pathological lesions consisted of air sacculitis, fibrinopurulent polyserositis and ventriculitis.  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