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   51698篇
  免费   1442篇
  国内免费   25篇
  2020年   384篇
  2019年   472篇
  2018年   3973篇
  2017年   3287篇
  2016年   2861篇
  2015年   668篇
  2014年   653篇
  2013年   2625篇
  2012年   1624篇
  2011年   3345篇
  2010年   3059篇
  2009年   2148篇
  2008年   2542篇
  2007年   2996篇
  2006年   802篇
  2005年   894篇
  2004年   854篇
  2003年   720篇
  2002年   694篇
  2001年   1088篇
  2000年   1111篇
  1999年   792篇
  1998年   348篇
  1997年   316篇
  1995年   311篇
  1992年   628篇
  1991年   589篇
  1990年   572篇
  1989年   547篇
  1988年   540篇
  1987年   480篇
  1986年   482篇
  1985年   528篇
  1984年   434篇
  1983年   399篇
  1982年   312篇
  1979年   475篇
  1978年   331篇
  1977年   302篇
  1976年   327篇
  1975年   362篇
  1974年   436篇
  1973年   464篇
  1972年   400篇
  1971年   341篇
  1970年   317篇
  1969年   335篇
  1968年   418篇
  1967年   370篇
  1966年   358篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Sleep patterns of aged, infirm, demented, chronically institutionalized residents of a skilled-care nursing facility were studied. The purpose of this naturalistic study was to describe sleep and wakefulness (S/W) within the limits afforded by brief behavioral observations and to examine homeostasis and diurnal rhythmicity of S/W as a function of psychoactive drug intake. Observers noted S/W every 15 min, 24 hr a day for 10 days in 24 Ss. Results indicated substantial individual variation in daytime hours. Daily and weekly variation within Ss was minimal. Sleep was least likely near sunset. Ss on psychoactive drugs showed dampened diurnal variation in S/W rhythms. In Ss not on such drugs, there was a suggestion of homeostasis of S/W between sleep during the morning and evening hours. Results are discussed methodologically (viability of approach), theoretically (age-related change in sleep), and practically (potential treatments).  相似文献   
922.
Critical Flicker Fusion Thresholds (CFFTs) were measured in 644 elderly people identified from community-based general practice records, and the relationship of CFFT with age was investigated. The CFFT was measured using the method of limits with mean scores for three ascending (flicker/fusion) and three descending (fusion/flicker) presentations being recorded. The difference between the ascending and descending means was found to be significantly correlated with age (r=−0.131,P<0.001) and may reflect a reduced sensitivity of the Central Nervous System to suprathreshold flicker with increasing age. The results suggest that CFFT measurement has an important role to play in gerontological research as an objective measure of cognitive aspects of the ageing process.  相似文献   
923.
A subsample of 814 sexually experienced adolescent females from the 1979 U.S. National Survey of Young Women was analyzed to assess the correlates of age at 1st sexual intercourse. Multiple regression procedures were used to examine sets of variables sequentially. In the hierarchical regression model, the control variables (respondent's age, race, religion, and age at menarche), along with 3 independent variables (household income, ideal age at 1st marriage, and ideal age for 1st birth), predicted age at 1st intercourse. The control variables accounted for a major portion of the variance in the model. Of the controls, chronological age and age at menarche were highly significant across all models tested.  相似文献   
924.
Should counseling psychology remain a distinct specialty or should it merge with clinical psychology? Recently, a growing amount of attention has been directed toward the increasing similarities between the counseling and clinical specialties, and musings about integrating them into a generic training model have emerged. This position paper considers some problems with the current divisions existing between counseling and clinical psychology. Three basic points are examined: (a) the effects of language systems on the counseling and clinical specialties; (b) the normal-abnormal dimension of behavior as a weak justification for distinct specialties; and (c) the fostering of distorted views of human behavior through counseling and clinical training programs.  相似文献   
925.
926.
927.
928.
929.
Although cerebral anoxia is not thought to be responsible for triggering near-death experiences (NDEs), the issue is not so clear in the case of hypercapnia. Detection of normal blood gases in Michael Sabom's (1982) case study seems to be the major reply to suggestions that hypercapnia may have a causal role in NDEs. We argue, however, that routine arterial measures of blood gases are not a reliable indicator of cerebral levels.  相似文献   
930.
In this article the perspective shifts to the “upstream” end of the agricultural knowledge and information system (AKIS). Because knowledge policy and strategic decision-making are not the prerogative of the public sector, organizations such as cooperative unions and multinational companies are included. After considering the influence of the changing environment on the nature of the AKIS, the role of knowledge management and policy in the emerging knowledge and information market is examined. Special attention is given to public and private R&D. The article then looks where information technology (IT) fits in and what considerations determine strategic investment in IT projects and sustained services. Some of the European experiences with this strategic investment are evaluated.  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