全文获取类型
收费全文 | 21761篇 |
免费 | 851篇 |
国内免费 | 11篇 |
专业分类
22623篇 |
出版年
2019年 | 254篇 |
2018年 | 368篇 |
2017年 | 390篇 |
2016年 | 411篇 |
2015年 | 317篇 |
2014年 | 348篇 |
2013年 | 1735篇 |
2012年 | 621篇 |
2011年 | 640篇 |
2010年 | 385篇 |
2009年 | 362篇 |
2008年 | 490篇 |
2007年 | 544篇 |
2006年 | 463篇 |
2005年 | 440篇 |
2004年 | 414篇 |
2003年 | 406篇 |
2002年 | 435篇 |
2001年 | 742篇 |
2000年 | 710篇 |
1999年 | 537篇 |
1998年 | 215篇 |
1996年 | 219篇 |
1995年 | 198篇 |
1992年 | 448篇 |
1991年 | 440篇 |
1990年 | 425篇 |
1989年 | 400篇 |
1988年 | 418篇 |
1987年 | 375篇 |
1986年 | 387篇 |
1985年 | 386篇 |
1984年 | 306篇 |
1983年 | 274篇 |
1982年 | 204篇 |
1981年 | 205篇 |
1979年 | 349篇 |
1978年 | 253篇 |
1977年 | 213篇 |
1976年 | 198篇 |
1975年 | 279篇 |
1974年 | 354篇 |
1973年 | 366篇 |
1972年 | 288篇 |
1971年 | 282篇 |
1970年 | 281篇 |
1969年 | 251篇 |
1968年 | 349篇 |
1967年 | 307篇 |
1966年 | 284篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Behavioral contrast as a function of the temporal location of reinforcement 总被引:2,自引:2,他引:0 下载免费PDF全文
Williams BA 《Journal of the experimental analysis of behavior》1976,26(1):57-64
Pigeons were trained on a multiple variable-interval variable-interval schedule of reinforcement. One component was then changed to a variation of a fixed-interval schedule in which the same rate of reinforcement was obtained as previously but the location of the reinforcer was fixed within the component. The effects of different temporal locations were compared. An increase in response rate for the unchanged variable-interval component (behavioral contrast) occurred when the reinforcer was located in the middle or at the end of the FI component, but response suppression occurred when it was located at the beginning of the component. The pattern of results cannot be explained by any previous theories of contrast. The overall response rates, and the pattern of local rates within the components, were consistent with the hypothesis that the major determinant of the contrast effect was the transition to a lower reinforcement rate following the unchanged component. 相似文献
912.
913.
914.
We have established a procedure for behavioral assessment of periodicity pitch perception in the cat. This procedure requires the training of cats to make a differential response to two different pure tones, and then testing for the transfer of learning when complex stimuli known to produce periodicity pitch sensations in humans are substituted for the pure tones. Complex stimuli consisted of three to five harmonically related frequencies of the same amplitude and phase. Eight cats were the subjects of these experiments. Two of them were controls. It is demonstrated here that cats do perceive periodicity pitch. We also used this procedure to measure the upper frequency limit of periodicity pitch perception for two cats. The frequencies tested were 100, 200, 300, 400, 600, 800, 900, and 1,200 Hz. The data indicate that the upper frequency limit of periodicity pitch perception in the cat is on the order of 600 to 800 Hz. There is a trend of decreasing prominence of the perception of periodicity pitch as the component frequencies are increased. These results are parallel to the human psychophysical data. 相似文献
915.
C. L. G. Whitmore R. B. Lawson C. E. Kozora 《Attention, perception & psychophysics》1976,19(2):211-213
Stereoscopic depth and subjective contour clarity were manipulated by varying the type of monocular configuration as well as magnitude and direction of disparity. The clarity of the subjective contours was influenced significantly by both magnitude and direction of disparity and by the type of monocular configuration. Subjective contours were always less clear when the objective monocular contour was discontinuous regardless of disparity. Stereoscopic depth estimates varied directly with magnitude and direction of disparity; however, depth magnitude reports were truncated when the disparity was carried by discontinuously defined patterns. 相似文献
916.
Virginia B. Collings Lauren Lindberg Donald H. McBurney 《Attention, perception & psychophysics》1976,19(1):69-71
Two nearby loci on the human tongue were stimulated with solutions representing the four basic taste qualities. The recognition threshold for each test stimulus was measured when a strong concentration of one of the four qualities or water was placed nearby. Decreased sensitivity for the test stimulus resulted when both stimuli were the same quality, with the exception of an enhancement of bitter sensitivity by QHCl. The only effect across qualities was a suppression of citric acid by NaC1. In contrast, classical studies reported across-quality enhancement. Stimulation of two loci on the same half of the tongue and the use of modern psychophysical techniques may explain the differences between these and earlier results. 相似文献
917.
Several devices have been developed enabling the blind to adapt to digital and visual displays. Most require extensive training and are relatively expensive. The audio-tactile display described in this paper requires very little training and promises to be inexpensive. Prototypes of the display have been developed for a digital stopwatch, a digital clock, and several electronic calculators. Because the device makes use of electrical impulses to communicate with the blind, it also has numerous potential capabilities as a research tool. The device is based on a panel containing columns of braille digits that are made active through a logic circuit interfacing the braille display with a calculator or other device. The subject scans the braille columns and discovers the digits active in each column when a tone is produced simultaneously with the finger contacting the braille digit. 相似文献
918.
919.
920.
In two experiments, a speeded sorting task was administered to children. In each sorting, the child was instructed to sort a deck of cards according to values on one dimension while the values of a second irrelevant dimension were held constant, were correlated, or were varied orthogonally. Experiment 1 evaluated developmental changes in perceived structure as compared with such changes in the control of attention. Different groups of kindergarten, 2d-, and 5th-grade children performed the task with spatially integrated vs spatially separated dimensions. The results indicate that with spatially integrated dimensions there is a trend from holistic to featural perception and an increase in attentional control with increasing age. Spatially separate dimensions are perceived dimensionally at all ages, but show a trend in attentional development. In Experiment 2, the spatially integrated dimensions of Experiment 1 were made separable by portraying different targets within a configuration in different colors. The theoretical implications of the results are discussed. 相似文献