全文获取类型
收费全文 | 44892篇 |
免费 | 873篇 |
国内免费 | 5篇 |
专业分类
45770篇 |
出版年
2019年 | 511篇 |
2018年 | 692篇 |
2017年 | 669篇 |
2016年 | 788篇 |
2015年 | 571篇 |
2014年 | 708篇 |
2013年 | 4231篇 |
2012年 | 1180篇 |
2011年 | 1191篇 |
2010年 | 802篇 |
2009年 | 758篇 |
2008年 | 1137篇 |
2007年 | 1023篇 |
2006年 | 979篇 |
2005年 | 841篇 |
2004年 | 842篇 |
2003年 | 846篇 |
2002年 | 856篇 |
2001年 | 1271篇 |
2000年 | 1230篇 |
1999年 | 981篇 |
1998年 | 506篇 |
1996年 | 584篇 |
1995年 | 588篇 |
1994年 | 557篇 |
1993年 | 529篇 |
1992年 | 993篇 |
1991年 | 894篇 |
1990年 | 881篇 |
1989年 | 776篇 |
1988年 | 766篇 |
1987年 | 743篇 |
1986年 | 750篇 |
1985年 | 756篇 |
1984年 | 694篇 |
1983年 | 611篇 |
1982年 | 492篇 |
1981年 | 542篇 |
1980年 | 479篇 |
1979年 | 680篇 |
1978年 | 552篇 |
1976年 | 484篇 |
1975年 | 623篇 |
1974年 | 619篇 |
1973年 | 652篇 |
1972年 | 615篇 |
1971年 | 535篇 |
1970年 | 477篇 |
1968年 | 577篇 |
1967年 | 490篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
Irwin D. J. Bross 《Theoretical medicine and bioethics》1981,2(2):145-153
Alarmed by Three Mile Island, Love Canal, and other disastrous deployments of new technologies, the public is demanding more voice in the decision-making on technology. To make this possible, it is proposed that metatechnology be evolved that will provide a practical technology for the safe, effective, and economical use of technology. A case history of a specific metatechnology is presented. Here the metatechnology enabled a realistic balancing of the benefits of mass screening of women by mammography against the hazards from the X-rays. By showing that the screening of women under 50 was counterproductive, this metatechnology helped to ban such screening in a program involving a quarter of a million women. The strategic mistake in setting up this and other technological programs was that the decisions were made by the technologists. They benefited the technologists but were not beneficial to the women. One of the potentials of metatechnology is that in its fully computerized versions it could be used directly by the public for decision-making on the deployment of technologies. 相似文献
882.
883.
Michael J. Flower Ph.D. 《The Journal of medical humanities》1981,3(2):112-127
The public debate on recombinant DNA research has ended even though significant issues of public interest remain undecided or untouched. The reason for the termination of other than muted public discussion is not simply the removal of an initial fear of catastrophic biohazards. With the cessation of public debate over such hazards came also the dissolution of most public forums. The ends to which recombinant DNA research and development ought to be directed are not matters of public debate. With the transfer of basic research knowledge to the private sector, that sector's proprietary interests and ownership prerogatives effectively deny any continued public participation in charting the future of genesplicing technology and its application. 相似文献
884.
R. L. Ray S. Lease S. J. Olson D. E. Anderson 《Integrative psychological & behavioral science》1981,16(4):204-211
The purpose of this study was to illustrate the use of time-series analysis with long-term cardiovascular responding. Analyses of two successive 1000-minute mean blood pressure and heart-rate series in five chronically instrumented dogs showed that the autocorrelation function of the original series appeared highly nonstationary and that differencing the data produced a simple autocorrelation pattern which could be successfully modeled with stepwise autoregression. Evidence for reliable individual differences as well as change over sessions is presented and discussed. 相似文献
885.
Twenty subjects viewed displays of square and trapezoidal luminous dot figures rotating about a vertical axis in both polar and parallel projections. The frequency of reported oscillation of the rotating figures was as high for the squares as for the trapezoids, provided that the squares contained static slant information in the form of internal texture gradients. Previously reported oscillation effects using shapes other than trapezoids have generally been unreliable, with a subject as likely to see rotation as oscillation for a given cycle, and then only in parallel projection. As a consequence, linear perspective information in trapezoidal shape has been taken to be the indispensable element for obtaining a strong oscillation effect. The authors argue that in the construction of the rotating object, a required condition for reliably producing the effect is a violation ofsome optical constraint regarding slant information, not necessarily one involving linear perspective. 相似文献
886.
James R. Pomerantz David M. Goldberg Patrick S. Golder Sheldon Tetewsky 《Attention, perception & psychophysics》1981,29(6):605-611
Subjective contours were compared with objective contours in their ability to facilitate performance in speeded tasks that required judging the position of a dot or the slope of a line segment relative to the contour. Subjective contours were found to reduce both reaction times and error rates for dot localization but not for the more difficult slope discrimination task. These results add to the growing body of evidence suggesting that subjective contours have functional properties similar to those of objective contours. 相似文献
887.
D. O. Bowker 《Attention, perception & psychophysics》1981,29(6):568-577
Using an adjustment procedure, human observers matched the apparent spatial frequencies of sinusoidal gratings presented in different orientations (0, 45, 90, and 135 deg). Matches were made between all possible pairwise orientation combinations. Significant match deviations indicated that the apparent frequency of a grating depends on its orientation. The most consistent deviations were found between horizontal and vertical gratings, with horizontal gratings appearing to be of a lower spatial frequency than vertical gratings. These effects were relatively independent of stimulus contrast and persisted when the optics of the eye were bypassed with laser interferometry. A neurophysiological explanation of these effects is proposed. 相似文献
888.
I Rock D Smith 《Journal of experimental psychology. Human perception and performance》1981,7(1):19-29
It has been assumed that certain stimulus transformations lead directly to depth effects, that is, that such transformations are the necessary and sufficient conditions for kinetically generated depth perception. An alternative is to view such perception as the preferred solution to the problem posed by the transforming stimulus as to what even in the world is producing that transformation. In several experiments it is shown that when other solutions are supportable by the stimulus, those same transformations will no longer lead to depth perception. These other solutions become preferred on the basis of rejection of certain coincidental features of the stimulus that otherwise would have to be accepted were the kinetic depth solution to be maintained. The findings are interpreted as challenging any theory that perception is simply the direct result of stimulation or of extraction of stimulus information and as supporting the Helmkoltzian rule of perception as a construction of the most reasonable representation. 相似文献
889.
890.
Alexander Pollatsek Shmuel Bolozky Arnold D. Well Keith Rayner 《Brain and language》1981,14(1):174-180
Native Israeli readers read Hebrew and English text as their eye movements were monitored. A window of text moved in synchrony with their eye movements and the window was either symmetrical about the fixation point or offset to the left or right. When subjects were reading Hebrew, the perceptual span was asymmetric to the left and when they were reading English it was asymmetric to the right. The results point out the importance of attentional factors in reading. 相似文献