全文获取类型
收费全文 | 54256篇 |
免费 | 2251篇 |
国内免费 | 30篇 |
出版年
2020年 | 656篇 |
2019年 | 832篇 |
2018年 | 1174篇 |
2017年 | 1168篇 |
2016年 | 1230篇 |
2015年 | 820篇 |
2014年 | 1012篇 |
2013年 | 4824篇 |
2012年 | 1815篇 |
2011年 | 1948篇 |
2010年 | 1145篇 |
2009年 | 1151篇 |
2008年 | 1744篇 |
2007年 | 1713篇 |
2006年 | 1507篇 |
2005年 | 1374篇 |
2004年 | 1332篇 |
2003年 | 1189篇 |
2002年 | 1245篇 |
2001年 | 1769篇 |
2000年 | 1670篇 |
1999年 | 1278篇 |
1998年 | 681篇 |
1997年 | 584篇 |
1996年 | 523篇 |
1995年 | 521篇 |
1994年 | 500篇 |
1993年 | 528篇 |
1992年 | 1018篇 |
1991年 | 955篇 |
1990年 | 942篇 |
1989年 | 852篇 |
1988年 | 815篇 |
1987年 | 801篇 |
1986年 | 804篇 |
1985年 | 856篇 |
1984年 | 668篇 |
1983年 | 578篇 |
1982年 | 471篇 |
1979年 | 656篇 |
1978年 | 488篇 |
1976年 | 452篇 |
1975年 | 590篇 |
1974年 | 621篇 |
1973年 | 596篇 |
1972年 | 539篇 |
1971年 | 474篇 |
1968年 | 540篇 |
1967年 | 540篇 |
1966年 | 475篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
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
22.
23.
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
24.
A. C ndido A. Maldonado J. L. Megias A. Catena 《The Quarterly Journal of Experimental Psychology Section B: Comparative and Physiological Psychology》1992,45(1):15-32
In three experiments, successive negative contrast was examined in one-way avoidance learning. Reward magnitude in first (pre-shift) and second (post-shift) phases was manipulated by time spent in the safe compartment. Experiment 1 demonstrated that when time in the danger compartment was held constant, a group shifted from a large reward--30 sec spent in the safe compartment--to a small reward--1 sec--showed poor performance and longer response latency than a group conditioned with the small reward in both phases. Experiment 2 replicated this effect with a less intense shock and also demonstrated that a group shifted from large to small reward performed more poorly than a group exposed to large reward--30 sec--in both phases. Finally, Experiment 3 showed that changes in intertrial interval, defined as total time spent in the safe compartment and the danger compartment before the onset of the warning signal, were not responsible for this contrast effect. These results suggest that time spent in a safe place can act as appetitive incentive during one-way avoidance learning. 相似文献
25.
Jose A. Diez 《Synthese》2002,130(1):13-47
26.
A. N. WILLIAMS 《Modern Theology》2004,20(4):505-526
The essay examines intellectual virtue in the Summa theologiae, taking it as an interpretative key to the epistemology of the Summa theologiae as a whole. Because Aquinas blurs the line between the acquired and the theological virtues, and between virtues and the gifts of the Spirit, it becomes impossible to maintain the distinction between the realms of nature and grace, or between natural reason and revealed truth: grace permeates the most ordinary activities of human reasoning. This reading of the Summa theologiae raises questions about many contemporary debates, particularly those concerning natural law. 相似文献
27.
28.
29.
30.
M. D. A. Freeman 《Journal of applied philosophy》1999,16(1):1-17
Gay marriages (as such) are not as yet allowed anywhere but the demand for them is increasing. Most countries take a liberal attitude towards marriage: few obstacles are put in its way. But objections to gay marriages continue to be raised. These objections are refuted and the case for gay marriage is assessed through the prism of various forms of liberalism. The normative argument for allowing gay marriage is shown to be both strong and consistent with many of the values upheld by the opponents of such unions. 相似文献