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   29632篇
  免费   437篇
  国内免费   4篇
  30073篇
  2023年   75篇
  2022年   68篇
  2021年   135篇
  2020年   211篇
  2019年   169篇
  2018年   3662篇
  2017年   2993篇
  2016年   2520篇
  2015年   425篇
  2014年   352篇
  2013年   1052篇
  2012年   1063篇
  2011年   2792篇
  2010年   2768篇
  2009年   1717篇
  2008年   2046篇
  2007年   2518篇
  2006年   359篇
  2005年   547篇
  2004年   486篇
  2003年   392篇
  2002年   358篇
  2001年   209篇
  2000年   186篇
  1999年   174篇
  1998年   139篇
  1997年   138篇
  1996年   108篇
  1995年   93篇
  1994年   88篇
  1993年   95篇
  1992年   108篇
  1991年   97篇
  1990年   105篇
  1989年   79篇
  1988年   65篇
  1987年   85篇
  1986年   84篇
  1985年   91篇
  1984年   89篇
  1983年   87篇
  1982年   67篇
  1981年   87篇
  1980年   77篇
  1979年   89篇
  1978年   78篇
  1977年   79篇
  1976年   79篇
  1975年   74篇
  1974年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
At the work site, smoking accounts for increased health care expenses and worker absenteeism due to smoking-related illness and reduced productivity and lost wages. Developing comprehensive and accessible smoking cessation programs at the work site is an important objective for health care professionals. In this study, employees of 43 corporations participated in a televised smoking cessation program accompanied by self-help manuals. The media component involved presenting a smoking cessation program on a network television affiliate station during the 4:30 p.m. and 10:00 p.m. news for 20 days. Employees at half the corporations also had access to semiweekly self-help group meetings. Adding self-help support groups to a program involving self-help manuals and the media reports was found to significantly increase abstinence and its maintenance over time. The implications of using the media, self-help groups, and work site locations in large-scale community-based interventions are discussed.  相似文献   
72.
Regional cerebral blood flow (rCBF) may be measured with inhalation techniques that use end-expired values of radioactivity to estimate the isotope concentration in arterial blood. These end-expired data are used as an input function in a mathematical equation to derive rCBF. End-expired air is assumed normally to be in equilibrium with the arterial blood at the alveolar surface of the lung during regular (passive) breathing; this assumption may not be valid during continuous phonation. We therefore have analyzed breathing (inhalation/exhalation) patterns and end-expired radioactivity (133Xe) during (1) speaking, (2) singing, and (3) humming of the national anthem, and also during (4) passive breathing. Statistically significant differences in breathing patterns were measured between a group of nonmusicians and two groups of musicians (singers) during the phonation tasks: The nonmusicians breathed more often (and more rapidly) and exhibited less variability in their breathing patterns than did the musicians. Notwithstanding these differences, the shapes of smoothed functions derived from the end-expired values were not influenced appreciably during phonation (except possibly during talking). The latter finding suggests that estimates of rCBF derived with these data should not be confounded seriously because of the continuous phonation.  相似文献   
73.
74.
Several theories have been presented that predict differences between women and men in attitudes toward the environment due to differences in sex roles. Research on which these theories can be tested has tended to examine general environmental concern, and the results have generally been weak and inconclusive. Using an approach suggested in the literature, this study examines sex differences in concern and knowledge, using multi-item scales for each, about one environmental issue — acid rain. The results contradict the theories being tested, however: if there is a sex difference, men are found to be more concerned and knowledgeable about the environmental problem.  相似文献   
75.
76.
A classifier based on the linear regression model was developed to automatically detect sharp transients in EEG, matching the definition of spikes and sharp waves accepted by IFSECN. Practical applications proved the accuracy of the method which succeeded in detecting 84% of sharp transients previously found by an experienced electronencephalographer. Computerized search for sharp transients in EEG records will be particularly useful in long term EEG records obtained from epileptic patients.  相似文献   
77.
The results of an evaluation of the perfusion scintigraphy findings of 350 hospitalised neurological patients and 55 more strictly selected neurosurgical patients with cerebrovascular complaints, revealed an accuraty of 83%, a sensitivity of 89%, and a specificity of 83%. The selection of the patients had no influence on the results as a whole. Compared with contrast-medium angiography, incorrect diagnosis must be expected in 17% of the cases. This includes erroneous negative findings in 10% of the cases. Grounds for misinterpretations are suggested, and the biological and methodological limitations of the method are set forth.  相似文献   
78.
The use of computer based diagnostic decision and artificial intelligence are discussed in relation to the problems of validity and reliability of psychiatric diagnoses. The authors suggest a definition of a computer aided classificator as an existent decision system for an automatically analysis of findings.  相似文献   
79.
An investigation into the diagnostic value of psychometric methods for the diagnosis of depressive states involved five psychometric questionnaires, one concentration test procedure, and one problem-solving approach to register cognitive processes. The data obtained for 80 depressive patients of varied aetiology were compared with those of sample of 80 neurotics without depressive aberration. Even univariate comparisons revealed statistically significant differences between the two samples. Multivariate methods (factor analysis, discriminative analysis) yielded more differentiated information. The "Scale for depression depth measurements" was found to be of particular diagnostic relevance; it was standardized for the time being.  相似文献   
80.
Some experiments on the breakdown effect in apparent motion   总被引:2,自引:0,他引:2  
  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