全文获取类型
收费全文 | 78475篇 |
免费 | 3071篇 |
国内免费 | 33篇 |
出版年
2020年 | 897篇 |
2019年 | 1030篇 |
2018年 | 1435篇 |
2017年 | 1502篇 |
2016年 | 1559篇 |
2015年 | 1158篇 |
2014年 | 1348篇 |
2013年 | 6516篇 |
2012年 | 2543篇 |
2011年 | 2527篇 |
2010年 | 1540篇 |
2009年 | 1585篇 |
2008年 | 2222篇 |
2007年 | 2147篇 |
2006年 | 1927篇 |
2005年 | 1680篇 |
2004年 | 1681篇 |
2003年 | 1632篇 |
2002年 | 1580篇 |
2001年 | 2422篇 |
2000年 | 2297篇 |
1999年 | 1710篇 |
1998年 | 837篇 |
1997年 | 738篇 |
1996年 | 788篇 |
1995年 | 724篇 |
1992年 | 1486篇 |
1991年 | 1381篇 |
1990年 | 1363篇 |
1989年 | 1316篇 |
1988年 | 1255篇 |
1987年 | 1200篇 |
1986年 | 1220篇 |
1985年 | 1303篇 |
1984年 | 1082篇 |
1983年 | 961篇 |
1981年 | 743篇 |
1979年 | 1141篇 |
1978年 | 838篇 |
1977年 | 727篇 |
1975年 | 959篇 |
1974年 | 1068篇 |
1973年 | 1117篇 |
1972年 | 959篇 |
1971年 | 910篇 |
1970年 | 806篇 |
1969年 | 833篇 |
1968年 | 1039篇 |
1967年 | 947篇 |
1966年 | 897篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Most studies of suicide in younger patients have demonstrated significant alterations in the serotonin system. Although a high percentage of completed suicides occur in late-life, to date very few studies of the biology of suicide have focused on this age group. This chapter describes age-related changes in the central nervous system pertinent to the biology of suicide, then reviews post-mortem biological studies of the brains of suicides and suicide attempters. As suicide attempts in the elderly are characterized by the use of violent means, biologic studies of impulsive violence are discussed. Finally we describe data on the effect of degenerative diseases on the serotonin system and the possible link to increased suicidal behavior in affected patients. This review underscores the need for further study of the biology of suicide in the geriatric age group. 相似文献
42.
John M. Pearce Helen Kaye Louis Collins 《The Quarterly Journal of Experimental Psychology Section B: Comparative and Physiological Psychology》1985,37(4):379-396
Three experiments, each using a single group of pigeons, are reported. In Experiment 1 subjects were initially trained with two stimuli, one of which was always followed by food, the other being reinforced according to a 50% partial reinforcement schedule. Subsequently a serial procedure was adopted in which an additional stimulus, C, was consistently followed by the partially reinforced CS. A second additional stimulus, A, was followed on half of its occurrences by the continuously reinforced CS, its remaining presentations being followed by nothing. The rate of autoshaped keypecking was substantially greater during A than during C. In the remaining experiments subjects received first-order conditioning with a single stimulus that was either partially (Experiment 2) or continuously (Experiment 3) reinforced. The stimuli A and C were then again introduced for serial autoshaping. Stimulus A was occasionally paired with the CS and occasionally followed by nothing, whereas stimulus C was always followed by the CS. As in Experiment 1, the rate of responding during A was greater than during C. It is proposed that one influence on the rate of autoshaped keypecking during a CS is the accuracy with which the immediate consequences of that CS are predicted. 相似文献
43.
Convergent and divergent stereo mechanisms were compared in their ability to recover structure from motion. Contrary to a recent result reported by Richards and Lieberman, no difference in their performance was found; both mechanisms appeared equally capable of supporting the perception of good structure from motion. Possible reasons for the disparate results are discussed. 相似文献
44.
45.
John Y. H. Bai Sarah Cowie Anne C. Macaskill Douglas Elliffe Christopher A. Podlesnik 《Journal of the experimental analysis of behavior》2020,113(2):363-389
It is widely assumed that reinforcers are biologically relevant stimuli, or stimuli that have been associated with biologically relevant stimuli. However, brief, arbitrary stimuli have also been reported to have reinforcement-like effects, despite being unrelated to biologically relevant stimuli like food. The present study explored the potential reinforcement-like effects of brief stimuli across 5 experiments. In Experiments 1 through 4, pigeon subjects responded for food reinforcement and brief stimulus presentations in a 2-component multiple schedule. Neither baseline response rates nor resistance to change during disruption tests were systematically greater in a component with versus without brief stimulus presentations. Increasing the rate and duration of brief stimulus presentations in Experiment 4 did not reveal reinforcement-like effects when compared directly with food. In Experiment 5, pigeons chose between independent terminal links in a concurrent-chains procedure. Across conditions, varying the location, duration, and rate of brief stimulus presentations in the terminal links had no systematic effects on preference. In contrast, varying rates of food reinforcers resulted in large and reliable shifts in preference. Therefore, the present study found no systematic evidence that brief stimuli unrelated to food reliably increase response rates, resistance to change, or preference. These data demonstrate the value of systematic replication, and a behavioral momentum approach to assessing potential reinforcement-like effects. 相似文献
46.
47.
48.
49.
50.