全文获取类型
收费全文 | 59637篇 |
免费 | 1608篇 |
国内免费 | 27篇 |
出版年
2020年 | 425篇 |
2019年 | 543篇 |
2018年 | 3980篇 |
2017年 | 3329篇 |
2016年 | 2922篇 |
2015年 | 745篇 |
2014年 | 762篇 |
2013年 | 3495篇 |
2012年 | 1816篇 |
2011年 | 3500篇 |
2010年 | 3164篇 |
2009年 | 2260篇 |
2008年 | 2729篇 |
2007年 | 3204篇 |
2006年 | 1125篇 |
2005年 | 1165篇 |
2004年 | 1083篇 |
2003年 | 1003篇 |
2002年 | 984篇 |
2001年 | 1219篇 |
2000年 | 1255篇 |
1999年 | 933篇 |
1998年 | 499篇 |
1997年 | 462篇 |
1996年 | 440篇 |
1995年 | 446篇 |
1994年 | 416篇 |
1992年 | 762篇 |
1991年 | 708篇 |
1990年 | 669篇 |
1989年 | 653篇 |
1988年 | 641篇 |
1987年 | 596篇 |
1986年 | 597篇 |
1985年 | 653篇 |
1984年 | 567篇 |
1983年 | 536篇 |
1982年 | 461篇 |
1979年 | 587篇 |
1978年 | 479篇 |
1977年 | 441篇 |
1976年 | 456篇 |
1975年 | 493篇 |
1974年 | 569篇 |
1973年 | 589篇 |
1972年 | 495篇 |
1971年 | 407篇 |
1968年 | 479篇 |
1967年 | 412篇 |
1966年 | 405篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
981.
Four pigeons were exposed to a two-key DRL procedure. At the start of a trial, key A was illuminated. A response to the lighted key turned it off and simultaneously illuminated key B. Reinforcement was available for responses on key B which followed the initial key A response by more than 2 sec. In the course of exposure to these conditions, all birds acquired superstitious response chains on key A. The distribution of the number of responses on key A preceding a key B response and the distribution of intervals elapsing from the initial key A response to the key B response were of the same form. The suggestion is made that the superstitious responding on key A served to mediate the required delay interval. However, when intervals between successive key A responses were recorded for one subject, they were found to be regularly spaced in time. Thus, the problem remains of how this behavior is itself timed. 相似文献
982.
Roger T. Kelleher William C. Riddle Leonard Cook 《Journal of the experimental analysis of behavior》1963,6(4):507-517
Squirrel monkeys were trained on a multiple schedule in which 10-min periods on a continuous shock avoidance schedule, indicated by a yellow light, alternated with 10-min periods on a 1.5-min variable interval schedule of food reinforcement (VI 1.5). A white light indicated that VI 1.5 was in effect, except for the middle 2 min of the period on VI 1.5, in which a blue light appeared and terminated with the delivery of a 0.5-sec unavoidable shock. Stable response rates developed in the avoidance and VI 1.5 components. However, the highest response rates occurred in the blue, preshock stimulus. A series of experiments showed that responding in the blue stimulus persisted even when responding had been extinguished on both the VI schedule of food reinforcement and the shock avoidance schedule. Responding in the blue stimulus ceased when the blue stimulus terminated without shock or when it terminated with a response-contingent shock. Each time responding ceased, it was restored by terminating the blue stimulus with an unavoidable shock. When the blue stimulus was on throughout each session and unavoidable shocks were delivered at regular 10-min intervals, responding was well maintained. These results show that in monkeys that have been trained on a continuous avoidance schedule, unavoidable shocks can maintain responding even under conditions where responses have no programmed consequences. 相似文献
983.
984.
985.
986.
987.
988.
Shimp CP 《Journal of the experimental analysis of behavior》1967,10(1):57-65
When a pigeon's choices between two keys are probabilistically reinforced, as in discrete trial probability learning procedures and in concurrent variable-interval schedules, the bird tends to maximize, or to choose the alternative with the higher probability of reinforcement. In concurrent variable-interval schedules, steady-state matching, which is an approximate equality between the relative frequency of a response and the relative frequency of reinforcement of that response, has previously been obtained only as a consequence of maximizing. In the present experiment, maximizing was impossible. A choice of one of two keys was reinforced only if it formed, together with the three preceding choices, the sequence of four successive choices that had occurred least often. This sequence was determined by a Bernoulli-trials process with parameter p. Each of three pigeons matched when p was ½ or ¼. Therefore, steady-state matching by individual birds is not always a consequence of maximizing. Choice probability varied between successive reinforcements, and sequential statistics revealed dependencies which were adequately described by a Bernoulli-trials process with p depending on the time since the preceding reinforcement. 相似文献
989.
C P Shimp 《Journal of the experimental analysis of behavior》1967,10(5):425-434
Five contingencies were superimposed successively on a variable-interval schedule of reinforcement. In each of the resulting conditions, a different short, interresponse time was reinforced and an interresponse-time distribution was obtained from each of three pigeons. The lower bound of the reinforced interresponse times ranged from 0.3 to 2.4 sec. The resulting distributions were combined, according to a rationale based upon concurrent operants, induction, and a property of variable-interval schedules, to describe the interresponse-time distributions from a variable-interval schedule. 相似文献
990.