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   46135篇
  免费   1534篇
  国内免费   21篇
  2019年   446篇
  2018年   773篇
  2017年   807篇
  2016年   908篇
  2015年   611篇
  2014年   657篇
  2013年   3307篇
  2012年   1381篇
  2011年   1481篇
  2010年   777篇
  2009年   737篇
  2008年   1042篇
  2007年   1074篇
  2006年   961篇
  2005年   2105篇
  2004年   1435篇
  2003年   1190篇
  2002年   983篇
  2001年   1398篇
  2000年   1349篇
  1999年   1036篇
  1998年   451篇
  1997年   400篇
  1996年   405篇
  1992年   853篇
  1991年   832篇
  1990年   856篇
  1989年   798篇
  1988年   781篇
  1987年   754篇
  1986年   770篇
  1985年   788篇
  1984年   623篇
  1983年   555篇
  1982年   424篇
  1981年   403篇
  1979年   719篇
  1978年   511篇
  1977年   455篇
  1976年   417篇
  1975年   612篇
  1974年   715篇
  1973年   712篇
  1972年   601篇
  1971年   559篇
  1970年   521篇
  1969年   559篇
  1968年   680篇
  1967年   621篇
  1966年   595篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
911.
DETERMINANTS OF R AND D COMPENSATION STRATEGIES IN THE HIGH TECH INDUSTRY   总被引:1,自引:0,他引:1  
This study indicates that sales volume, stage in the product life cycle, profitability and turnover are all important predictors of the method and magnitude of financial rewards provided by high tech firms to R and D employees. The most favorable situational factors for R and D incentive compensation are a low sales volume high tech company, operating in the growth stage of the product life cycle, with high turnover rates, and capable of linking profitability to incentive rewards such as bonuses.  相似文献   
912.
The peak amplitude of EMG activity was measured from the orbicularis oris superior (OOS), orbicularis oris inferior (OOI) and masseter muscles for 3 normal 4-yr.-old children and compared to past data gathered on a group of articulatory disordered children, normal children, and adults. The 4-yr.-olds evidenced greater average peak EMG activity than the other groups, suggesting that speech-sound production becomes more efficient with maturation. Also, levels of variability obtained for the younger children were considerably smaller than for the normal speakers across the three muscles, showing that motor equivalence changes with age whereby the flexibility in the control of articulators increases. The coefficient of variation for the OOI muscle for the disordered children, however, was similar to that for the 4-yr.-olds, while the corresponding data for the other two muscles paralleled those for normal ones. These findings were interpreted as reflecting a delay in the development of speech-motor equivalence that affects certain muscles while sparing others.  相似文献   
913.
This experiment concerned the contribution of polydipsia on the temporal discrimination of rats during a fixed-interval 60-sec. schedule. In this study, the timing accuracy of 12 rats which had access to water during training was compared to that of 12 rats which had no water during training. The rats were trained for 25 sessions on an FI 60-sec. schedule. In early sessions before polydipsia was fully developed, no differences existed between the timing accuracy of the water group and no-water group. As the amount of water drunk by the water group increased as the number of sessions increased, a parallel increase was noted in the timing accuracy of the water group. In the final sessions, a significant difference was found between the timing accuracy of rats in the water group and that of those in the no-water group. It was concluded that polydipsia facilitated the development of the temporal discrimination which is characteristic of a fixed-interval 60-sec. schedule.  相似文献   
914.
This study was designed to determine possible differences in the cognitive, perceptual, and personal-social development of prematurely and maturely born 3-yr.-olds which might foreshadow later learning problems. The subjects were 40 prematurely born graduates of a neonatal intensive care unit (birth weight less than 2,500 gm, less than 37 wk. gestation) matched on the pair-level with full-term controls on sex, race, post-conceptual age, and socioeconomic background. All subjects were singletons and parity was matched at the group level. No differences were found between the groups on tests of higher mental processes including the General Cognitive, Verbal, Quantitative, and Memory Scales of the McCarthy Scales of Children's Abilities, and researcher-devised measures of problem-solving competence. No differences in parental reports of personal-social development were noted. Prematures did not perform as well as controls on perceptual performance tasks, and this difference was interpreted as reflecting relatively impaired visual-motor coordination.  相似文献   
915.
Cross-modal effects on visual and auditory object perception   总被引:1,自引:0,他引:1  
  相似文献   
916.
917.
918.
919.
The investigation of enzyme activity in cerebrospinal fluid has been without relevant results for laboratories analysing spinal fluid. For neurochemical purposes, it is interesting that the Substance P is convered by Depeptidyl-aminopeptidase IV (DP IV), liberating dipeptides. The hydrolysis of nitroanilids of the form Xaa-Pro-NHNp in cerebrospinal fluid was analysed using them as peptidases substrates. Finally a method for measuring the activity was proposed.  相似文献   
920.
The somatic and psychosocial development of 80 subjects with manifest affective-phasic psychoses is studied retrospectively and compared with that of an identically sized control group consisting of neuropsychiatrically healthy subjects. Statistically significant differences were found particularly in the answers to questions dealing with social situation and social adaptability. Achievement at school and vocational qualifications were lower among the parents of the patients than among those of the healthy subjects. Characteristic features of the patients' childhood and adolescence were transient depression, often for no apparent cause, and maladaption, and vocational wishes were fulfilled less often than among the controls. The patients experienced greater difficulty in settling in to a new group due to their contact difficulties.  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