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   69449篇
  免费   2766篇
  国内免费   23篇
  72238篇
  2020年   687篇
  2019年   870篇
  2018年   1220篇
  2017年   1207篇
  2016年   1311篇
  2015年   964篇
  2014年   1136篇
  2013年   5232篇
  2012年   2133篇
  2011年   2284篇
  2010年   1418篇
  2009年   1399篇
  2008年   2031篇
  2007年   2045篇
  2006年   1857篇
  2005年   1680篇
  2004年   1571篇
  2003年   1461篇
  2002年   1574篇
  2001年   2218篇
  2000年   2141篇
  1999年   1652篇
  1998年   801篇
  1997年   738篇
  1996年   722篇
  1993年   662篇
  1992年   1390篇
  1991年   1288篇
  1990年   1254篇
  1989年   1139篇
  1988年   1115篇
  1987年   1070篇
  1986年   1164篇
  1985年   1181篇
  1984年   992篇
  1983年   916篇
  1982年   648篇
  1981年   662篇
  1979年   1054篇
  1978年   774篇
  1975年   852篇
  1974年   938篇
  1973年   1016篇
  1972年   843篇
  1971年   804篇
  1970年   728篇
  1969年   756篇
  1968年   977篇
  1967年   860篇
  1966年   763篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Questionnaires concerning attitudes toward use of microcomputers at home, in school, and at video arcades were administered to 879 high school students. Direct observations of adolescent proxemics and sex differences, and of various parameters of video games in 18 video arcades were made. A thorough and representative content analysis of sex bias of microcomputer software advertising brochures was carried out. Results supported previous findings of overrepresentation of masculine culture in the adolescent world of microcomputers, particularly regarding video games. Various types of computer-related activity were not related to socioeconomic class of the parents or to academic grades except for use of home microcomputers, which was mildly positively related to socioeconomic class (r = .124, p less than .001). Nearly half the activity in the arcades was strictly solitary. None of the arcade video games allowed for cooperative play. Most allowed only for sequential competition (86%) or simultaneous competition (7%); as many as 7% did not provide a display of the scores for a second player.  相似文献   
972.
The Christian has a unique resource for responding to the problem of how competent adults can exercise responsibly the right to control the last stages of their living/dying. Recent natural death legislation offers only a partial solution, because it does not specify what counts as life-sustaining procedures which may be discontinued if the individual fills out a directive to the physician. One of the most troublesome questions continues to be whether the withholding or withdrawal of artificial feeding, or indeed natural feeding, is ever justifiable. An adaptation of principles included in the Christian idea of fasting seems to provide adequate criteria for determining when forgoing nourishment by the terminally ill adult is morally justifiable.  相似文献   
973.
Squirrel monkeys were trained to respond under a multiple fixed-interval, fixed-interval schedule in which the first response after 5 min terminated a visual stimulus in the presence of which electric shocks could occur. During one component of the schedule, correlated with one color of stimulus lights, every 30th response also produced electric shock; responding was suppressed during this component to approximately 10 to 12% of that occurring in the alternate component in which responding was not punished. In contrast to previous research, morphine (0.03 to 1.0 mg/kg) increased punished responding. Unpunished responding, however, was either not affected or decreased at doses of morphine that increased punished responding. Increases in rate of punished responding also occurred when the single-schedule punishment condition was studied alone in these animals. Subsequent experimentation, which systematically analyzed the development of the rate-enhancing effects of morphine on punished responding, involved the study of drug effects in additional monkeys trained initially under a single-schedule punishment condition. The effects of morphine on punished responding were studied before, after, and then during exposure to the multiple schedule that included a component in which responding was not punished. Increases in response rate with morphine did not occur until it was administered during exposure to the multiple schedule that included a component in which responding was not punished. As with the other monkeys, once the rate increases in punished responding occurred under the multiple schedule, these effects of morphine persisted, even when the multiple schedule was removed.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
974.
Theories of observing differ in predicting whether or not a signal for absence of reinforcement (S−) is capable of reinforcing observing responses. Experiments in which S− was first removed from and then restored to the procedure have yielded mixed results. The present experiments suggest that failure to control for the direct effect of presenting S− may have been responsible. Pigeons and operant procedures were used. Experiment 1 showed that presentations of S−, even when not contingent on observing, can raise the rate of an observing response that was reinforced only by presentations of a signal (S+) that accompanied a schedule of food delivery. Experiment 2 showed that this effect resulted from bursts of responding that followed offsets of S−. Experiment 3 showed that, when the presence of S− was held constant, lower rates occurred when S− was dependent on, rather than independent of, observing. These results support theories that characterize S− as incapable of reinforcing observing responses.  相似文献   
975.
A concurrent-chain procedure was used to examine choice between segmented and less segmented response-independent schedules of reinforcement. A pair of independent, concurrent variable-interval 60-s schedules were presented in the initial link, along with a 1.5-s changeover delay. A chained fixed-interval fixed-time and its corresponding tandem schedule constituted the terminal links. The length of the fixed-interval schedule in the terminal link was varied between 5 s and 30 s while that of the fixed-time schedule was kept at 5 s over conditions. The first components of both terminal-link schedules were accompanied by the same stimulus. Except in the baseline condition, the onset of the second component of the terminal-link chained schedule was accompanied by either a localized (key color) or a nonlocalized (dark houselight) stimulus change. Stimulus conditions were constant during the terminal-link tandem schedule. With three exceptions, pigeons demonstrated a slight preference for the tandem over the chained schedule in the terminal link. Furthermore, this preference varied inversely with the length of the first component. In general, these results are consistent with previous studies that reported an adverse effect on choice by segmenting an interval schedule into two or more components, but they are inconsistent with studies that reported preference for signaled over unsignaled delay of reinforcement.  相似文献   
976.
Relationship between Knapp's metaphor scale of attitudes toward time and subjective estimation of fixed time intervals, measured by a modification of Lovett Doust's method, was described. Results were discussed within the framework of studies relating the measurements of cognitive styles and altered consciousness states to the dilated or accelerated perceptions of time.  相似文献   
977.
In previous studies subjects who have learned a positioning response with kinesthetic feedback tended to make greater errors when visual feedback was provided during later trials. These subjects have always performed with both kinesthetic and visual feedback available. This study determined whether subjects with only visual feedback would produce errors similar to those who received kinesthetic plus visual feedback. Blindfolded subjects learned to move a handle to a criterion location with knowledge of results following each trial. Subjects then were assigned to one of three experimental groups, with only kinesthetic feedback, with kinesthetic plus visual feedback, or with only visual feedback. Subjects had 9 trials without knowledge of results in these feedback conditions. When visual feedback was available, subjects tended to make longer response errors. This finding replicates previous studies. Also, the similarity of performances from the conditions with visual feedback indicated the dominance of visual information in the condition with kinesthetic plus visual feedback.  相似文献   
978.
Speech-mediated retention in dyslexics   总被引:2,自引:0,他引:2  
Dyslexics (6 to 9 yr. old) and a control group of 12 normal readers (second-graders) were tested on a memory task with rhyming and non-rhyming items. The most important finding is that both groups were penalized by rhyme, indicating speech coding. It was observed that the dyslexics were not less penalized by rhyme than were controls. The present results are compared with those of other recent studies.  相似文献   
979.
86 stutterers' disfluency patterns were examined in relation to their laterality preferences. Results suggest that young stutterers are a heterogeneous group and that specific disfluency variables were not related to ear preferences on a dichotic consonant-vowel listening task.  相似文献   
980.
53 female and 45 male undergraduates were administered the Spatial Antecedents Questionnaire (Activities, Academic Courses, Self-assessments, and Environmental Mapping subscales), the Spatial Dimensionality Test (Embedded Figures, Card Rotations, Paper Folding, Surface Development, Horizontal/Vertical Rotations, and Cube Perspectives subtests), and Revised-Individual Differences Questionnaire of Paivio. Scores from the Academic Courses and Self-assessment scales accounted for the most variability in spatial performance. Visual processing style correlated with performance on spatial tests for men, but not for women. Different patterns of activities and experiences correlated with spatial test performance for men and women.  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