全文获取类型
收费全文 | 28890篇 |
免费 | 1298篇 |
国内免费 | 17篇 |
专业分类
30205篇 |
出版年
2021年 | 285篇 |
2020年 | 461篇 |
2019年 | 450篇 |
2018年 | 802篇 |
2017年 | 718篇 |
2016年 | 738篇 |
2015年 | 457篇 |
2014年 | 614篇 |
2013年 | 2495篇 |
2012年 | 1163篇 |
2011年 | 1224篇 |
2010年 | 700篇 |
2009年 | 640篇 |
2008年 | 1032篇 |
2007年 | 933篇 |
2006年 | 889篇 |
2005年 | 741篇 |
2004年 | 641篇 |
2003年 | 610篇 |
2002年 | 562篇 |
2001年 | 861篇 |
2000年 | 892篇 |
1999年 | 648篇 |
1998年 | 275篇 |
1997年 | 241篇 |
1996年 | 228篇 |
1992年 | 521篇 |
1991年 | 450篇 |
1990年 | 522篇 |
1989年 | 440篇 |
1988年 | 411篇 |
1987年 | 384篇 |
1986年 | 394篇 |
1985年 | 455篇 |
1984年 | 355篇 |
1983年 | 300篇 |
1982年 | 228篇 |
1979年 | 336篇 |
1978年 | 268篇 |
1976年 | 213篇 |
1975年 | 306篇 |
1974年 | 355篇 |
1973年 | 358篇 |
1972年 | 280篇 |
1971年 | 253篇 |
1970年 | 216篇 |
1969年 | 235篇 |
1968年 | 300篇 |
1967年 | 258篇 |
1966年 | 284篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
241.
242.
243.
White KG Pipe ME McLean AP Redman S 《Journal of the experimental analysis of behavior》1985,44(2):207-215
Distributions of reinforcers between two components of multiple variable-interval schedules were varied over a number of conditions. Sensitivity to reinforcement, measured by the exponent of the power function relating ratios of responses in the two components to ratios of reinforcers obtained in the components, did not differ between conditions with 15-s or 60-s component durations. The failure to demonstrate the “short-component effect,” where sensitivity is high for short components, was consistent with reanalysis of previous data. With 60-s components, sensitivity to reinforcement decreased systematically with time since component alternation, and was higher in the first 15-s subinterval of the 60-s component than for the component whose total duration was 15 s. Varying component duration and sampling behavior at different times since component transition may not be equivalent ways of examining the effects of average temporal distance between components. 相似文献
244.
Two experiments examined pigeons' response rates during short trials signaled by stimuli closely spaced along a wavelength continuum. In Experiment 1 separate halves of the continuum were correlated with different reinforcement schedules. In Experiment 2, the middle stimulus was accompanied by a lower probability of reinforcement than were the remaining wavelengths. Both procedures resulted in dimensional contrast “shoulders,” seen as relatively enhanced or depressed response rates in the presence of stimuli between the extreme of the continuum and the border separating the positive and negative stimuli. Sequential analyses addressed possible contributions of the following interactions: (a) local contrast, seen when rate during a given schedule depends on the schedule in the just-preceding trial; (b) modification of local contrast by the similarity of the signaling stimuli (P. Blough, 1983); and (c) schedule-independent rate contrast, seen when rate in a given trial depends on the rate controlled by the stimulus that accompanied the just-preceding trial (Malone & Rowe, 1981). Dimensional contrast functions were similar when isolated according to the schedule, to the similarity of the signaling stimulus, and to the response rate of the just-preceding trial. The interactions noted above do not appear to make important contributions to this effect. 相似文献
245.
Pigeons' not pecking or pecking constituted choice between a delayed, large reinforcer and an immediate, small reinforcer (self-control) and at other times between a delayed reinforcer and no reinforcer (omission). Both a tone and a keylight were tested as choice signals, and the delayed reinforcer was either response independent or response dependent. Pigeons pecked during the choice signals on over 95% of the trials in the self-control procedure, and pecked during the choice signals on over 75% of the trials in the omission procedure. Consistent pecking was observed with either the tone or the keylight as a choice signal, with the exception that a tone paired with a response-independent delayed reinforcer did not maintain pecking in the omission procedure. Pigeons pecked during more choice signals when delayed reinforcers were response dependent than when the delayed reinforcers were response independent. These results indicate that Pavlovian conditioning influences self-control experiments, especially in single-key procedures. 相似文献
246.
247.
R Witkowski E Ullrich P Pietsch K Weber K Heller T Losanowa I Nitz 《Psychiatrie, Neurologie, und medizinische Psychologie》1985,37(5):255-261
We present four cases of Prader-Willi syndrome. Two of them have an abnormality of a chromosome 15, the other both show different chromosomal abnormalities. Translocations or deletions were found recently in the bands 15q11/12 in about 60% of the cases of Prader-Willi syndrome. The consequences for diagnosis, symptomatology and genetic counselling of the syndrome are discussed. 相似文献
248.
This paper reports an experiment testing two hypotheses. The first is that the value or utility associated with a payment to one's self and a payment to a co-worker can be represented as an additive function of a utility for own payment (nonsocial utility) and a utility for the difference between own and other's payment (social utility). The second hypothesis is that changes in the amount of work accomplished by one's self and/or the other should influence the social, but not the the nonsocial utilities. Support for both hypotheses is reported. 相似文献
249.
Preweanling (21 days old) and adult (60-80 days old) rats were exposed to ethanol odor either paired with the early stages of apomorphine-induced toxicosis, paired with the recovery from toxicosis, or unpaired with the induction of distress. Twenty four hours later, ethanol preferences were measured in a spatial olfactory test (ethanol vs lemon odor) or a drinking test (5.6% v/v ethanol vs 0.25% w/v citric acid solutions). During the olfactory test both young and adult rats expressed substantial ethanol odor aversions when previously exposed to this odor paired with toxicosis. However, changes in ethanol intake became apparent only in preweanling subjects. Preweanlings which received the ethanol odor paired with illness drank significantly less of the ethanol solution relative to controls, while subjects experiencing the odor paired with recovery from distress significantly increased their consumption of the ethanol solution. These prior aversive and appetitive olfactory experiences had no effect upon ethanol intake in adult rats. These results implicate both an ontogenetic and a sensorial factor in the regulation of ethanol intake. 相似文献
250.
The suppression of corticosterone synthesis with metyrapone (25 mg/kg) reduced the hyperactivity and altered the exploratory activity of hippocampally lesioned animals (HPC) in the open field to the level of cortical and sham controls (Experiment 1). In a second experiment, corticosterone (600 micrograms/kg) pretreatment 2 h, but not 1 h, before metyrapone partially restored the hyperactivity of HPC animals that had been decreased by the corticosteroid-suppressant drug. Alterations in exploratory behavior induced by metyrapone were also prevented by corticosterone pretreatment. The results suggest that the suppression of corticosterone in hippocampally lesioned animals produces a normalization of behavior that can be prevented by pretreatment with corticosterone. 相似文献