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   39073篇
  免费   1469篇
  国内免费   13篇
  2019年   417篇
  2018年   569篇
  2017年   548篇
  2016年   593篇
  2015年   413篇
  2014年   573篇
  2013年   2919篇
  2012年   978篇
  2011年   1075篇
  2010年   695篇
  2009年   682篇
  2008年   995篇
  2007年   959篇
  2006年   919篇
  2005年   771篇
  2004年   800篇
  2003年   767篇
  2002年   774篇
  2001年   1029篇
  2000年   1106篇
  1999年   807篇
  1998年   442篇
  1997年   419篇
  1996年   424篇
  1995年   407篇
  1992年   736篇
  1991年   693篇
  1990年   706篇
  1989年   659篇
  1988年   666篇
  1987年   610篇
  1986年   666篇
  1985年   651篇
  1984年   553篇
  1983年   522篇
  1981年   404篇
  1979年   625篇
  1978年   512篇
  1977年   416篇
  1976年   428篇
  1975年   532篇
  1974年   636篇
  1973年   689篇
  1972年   539篇
  1971年   550篇
  1970年   475篇
  1969年   533篇
  1968年   648篇
  1967年   601篇
  1966年   591篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
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   
822.
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   
823.
824.
825.
The present study based on the indirect Clausen-test using NTA and PHA as antigens contributed to therapy control and possibly prognosis assessment rather than to immunological differential diagnosis.  相似文献   
826.
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   
827.
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   
828.
829.
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   
830.
M. W. Bunder 《Studia Logica》1984,43(1-2):75-78
In positive logic the negation of a propositionA is defined byA X whereX is some fixed proposition. A number of standard properties of negation, includingreductio ad absurdum, can then be proved, but not the law of noncontradiction so that this forms a paraconsistent logic. Various stronger paraconsistent logics are then generated by putting in particular propositions forX. These propositions range from true through contingent to false.  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