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   44408篇
  免费   1686篇
  国内免费   20篇
  2019年   456篇
  2018年   672篇
  2017年   716篇
  2016年   753篇
  2015年   553篇
  2014年   658篇
  2013年   3369篇
  2012年   1155篇
  2011年   1226篇
  2010年   786篇
  2009年   723篇
  2008年   1064篇
  2007年   1054篇
  2006年   951篇
  2005年   863篇
  2004年   841篇
  2003年   829篇
  2002年   877篇
  2001年   1303篇
  2000年   1257篇
  1999年   993篇
  1998年   452篇
  1997年   454篇
  1996年   471篇
  1992年   879篇
  1991年   844篇
  1990年   826篇
  1989年   771篇
  1988年   797篇
  1987年   730篇
  1986年   786篇
  1985年   766篇
  1984年   641篇
  1983年   580篇
  1982年   435篇
  1981年   456篇
  1979年   719篇
  1978年   562篇
  1977年   475篇
  1976年   472篇
  1975年   582篇
  1974年   752篇
  1973年   791篇
  1972年   603篇
  1971年   620篇
  1970年   592篇
  1969年   596篇
  1968年   751篇
  1967年   671篇
  1966年   674篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
This paper presents the results of an in-depth study of parameters characterizing sequenced saccadic eye movements for a group of dyslexic children and a comparative normal control group with ages in the range greater than 8.0 yr. and less than 13.0 yr. No parameters were statistically different for the two groups, which supports the findings of Brown, et al. and contradicts the findings of Pavlidis. Our results indicate that sequenced saccadic eye movements are not diagnostically useful for early detection of dyslexia.  相似文献   
952.
Previous research aimed at quantifying and reducing the decrements encountered in performing manual tasks in cold weather has not described the relationships between task characteristics and cold-induced impairments. The amount of decrement and, often times, the optimal means for reducing the decrement, appear to be task-specific. The research reported here is one in a series of studies formulated to explore those relationships. The strategy is to use tasks from the battery developed by Fleishman (1967) to measure the factorially 'pure' abilities needed to perform all manual tasks. 24 U.S. Marines performed this battery of nine tasks across a range of cold temperatures. To determine if the decrement due to wearing gloves might be less than the decrement due to cold hands as the air temperature decreased, performance on the battery of tasks was measured with and without gloves. Only three of the tasks (abilities) were affected by cold temperatures, and the amount of decrement increased as the air temperature decreased. Three tasks deteriorated due to wearing of gloves, two of those affected by cold and one other. Temperature affected performance independently of the glove effect. Half of the subjects did not complete bare-handed testing at -18 degrees C (approximately 20 min.), indicating this is the lower end of the temperature range in which bare-handed performance for more than a few minutes is practical.  相似文献   
953.
954.
955.
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   
956.
By 48 patients with Wilson's disease the brainstem acoustic evoked potentials were stated. There were 35 pathological findings (73%), 13 were normal (27%). The waves, determined by the middle and upper brainstem (Pons and Mesencephalon) showed most of all pathological changes. Those patients with forms of Wilson's disease called Pseudoskelerose and Pseudoparkinson showed the most pathological findings. But one could watch these findings by about 30% of patients in preclinical stage. This method can possibly be used for early detection of disorders of brainstem functions and in the same way it can be used for control of treatment by patients in preclinical stage.  相似文献   
957.
958.
959.
960.
This paper proposes test statistics based on the likelihood ratio principle for testing equality of proportions in correlated data with additional incomplete samples. Powers of these tests are compared through Monte Carlo simulation with those of tests proposed recently by Ekbohm (based on an unbiased estimator) and Campbell (based on a Pearson-Chi-squared type statistic). Even though tests based on the maximum likelihood principle are theoretically expected to be superior to others, at least asymptotically, results from our simulations show that the gain in power could only be slight.  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