全文获取类型
收费全文 | 185926篇 |
免费 | 8022篇 |
国内免费 | 157篇 |
专业分类
194105篇 |
出版年
2020年 | 2794篇 |
2019年 | 3448篇 |
2018年 | 3601篇 |
2017年 | 4069篇 |
2016年 | 4688篇 |
2015年 | 3943篇 |
2014年 | 4812篇 |
2013年 | 23502篇 |
2012年 | 4820篇 |
2011年 | 4062篇 |
2010年 | 4041篇 |
2009年 | 4840篇 |
2008年 | 4245篇 |
2007年 | 3739篇 |
2006年 | 4242篇 |
2005年 | 4225篇 |
2004年 | 3726篇 |
2003年 | 3380篇 |
2002年 | 3174篇 |
2001年 | 3914篇 |
2000年 | 3742篇 |
1999年 | 3479篇 |
1998年 | 2890篇 |
1997年 | 2697篇 |
1996年 | 2602篇 |
1995年 | 2436篇 |
1994年 | 2403篇 |
1993年 | 2361篇 |
1992年 | 2935篇 |
1991年 | 2782篇 |
1990年 | 2638篇 |
1989年 | 2535篇 |
1988年 | 2480篇 |
1987年 | 2502篇 |
1986年 | 2486篇 |
1985年 | 2734篇 |
1984年 | 2731篇 |
1983年 | 2440篇 |
1982年 | 2428篇 |
1981年 | 2410篇 |
1980年 | 2221篇 |
1979年 | 2432篇 |
1978年 | 2303篇 |
1977年 | 2259篇 |
1976年 | 2032篇 |
1975年 | 2225篇 |
1974年 | 2313篇 |
1973年 | 2246篇 |
1972年 | 1801篇 |
1971年 | 1705篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
891.
The authors warn against a trivialization of the AIDS problem and against the call for state control. Since sexuality is ultimately uncontrollable, they plead instead for the greater clarification of the conflicts which those who are infected with HIV and those who are not infected experience in dealing with each other. The continuing mystification of these conflicts would result in mutual jeopardy through acting-out. 相似文献
892.
893.
The developmental change in subjective probability during adolescence, an important period for establishing the probability concept, was investigated. 75 Japanese adolescents, from 12 to 23 yr. of age, were asked to make probability judgments for a lottery under 15 conditions. Analysis showed that with increase in age their subjective probability came closer to the objective probability. Discussion of these results took into consideration recent studies on the development of the concept of probability. 相似文献
894.
A quasi-nonmetric method for multidimensional scaling VIA an extended euclidean model 总被引:1,自引:0,他引:1
An Extended Two-Way Euclidean Multidimensional Scaling (MDS) model which assumes both common and specific dimensions is described and contrasted with the standard (Two-Way) MDS model. In this Extended Two-Way Euclidean model then stimuli (or other objects) are assumed to be characterized by coordinates onR common dimensions. In addition each stimulus is assumed to have a dimension (or dimensions) specific to it alone. The overall distance between objecti and objectj then is defined as the square root of the ordinary squared Euclidean distance plus terms denoting the specificity of each object. The specificity,s
j
, can be thought of as the sum of squares of coordinates on those dimensions specific to objecti, all of which have nonzero coordinatesonly for objecti. (In practice, we may think of there being just one such specific dimension for each object, as this situation is mathematically indistinguishable from the case in which there are more than one.)We further assume that
ij
=F(d
ij
) +e
ij
where
ij
is the proximity value (e.g., similarity or dissimilarity) of objectsi andj,d
ij
is the extended Euclidean distance defined above, whilee
ij
is an error term assumed i.i.d.N(0, 2).F is assumed either a linear function (in the metric case) or a monotone spline of specified form (in the quasi-nonmetric case). A numerical procedure alternating a modified Newton-Raphson algorithm with an algorithm for fitting an optimal monotone spline (or linear function) is used to secure maximum likelihood estimates of the paramstatistics) can be used to test hypotheses about the number of common dimensions, and/or the existence of specific (in addition toR common) dimensions.This approach is illustrated with applications to both artificial data and real data on judged similarity of nations. 相似文献
895.
To assess temporal variations in the perception of "phasic" heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This "double-tracking" procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for "tonic" heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. +/- 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures. 相似文献
896.
H N Levinson 《Perceptual and motor skills》1989,68(2):471-484
As prior studies indicated abnormal cerebellar-vestibular-based sensorimotor mechanisms and neurological and ENG diagnostic parameters in anxiety disorders and because ocular fixation and sequential scanning are cerebellar-vestibular-modulated, it appeared reasonable to measure these and related ocular functions in matched samples of anxiety-disordered and control subjects. In this study, the optokinetically-determined fixation, sequential scanning, and perceptual span capacities obtained by means of a newly revised blurring-speed method were significantly lower or impaired in 70 anxiety-disordered patients vs 70 controls. Such data supported further the hypothesis that there may be cerebellar-vestibular predispositions to anxiety disorders and the optokinetically-based tracking method may prove useful in separating a diverse array of CV-determined or related anxiety symptoms from those of other origins. However, independent validation as well as additional studies of anxiety disorders using larger samples vs random or "normal" controls are required before conclusions are justified. 相似文献
897.
S Koga 《Perceptual and motor skills》1989,69(1):19-26
To examine the acquisition of voluntary control of a novel muscular activity from the initial stage to the self-control stage, the m. auricularis posterior, which had generally degenerated and had nearly lost its function of drawing an auricle backward in the human body, was selected as a target muscle to be studied. One female undergraduate student who could not move her auricles intentionally was required to activate her left m. auricularis posterior and underwent rest, pretest, training, and posttest sessions once a day for five days. At the subject's request, the electromyograph (EMG) from her left m. auricularis posterior on an oscillograph was provided for her as the feedback signal on each training trial. The picture of her left ear on television was handled in the same way. The EMG measures indicated that the subject could learn to activate her left m. auricularis posterior differentially. The number of training trials on which the subject requested the feedback signals suggested that EMG feedback signal was more useful to her than the video and that the usefulness of the feedback signals varied as the training sessions advanced. It was also concluded from analysis of the self-report data that the acquisition process of self-control of a novel muscular activity could be divided into at least four stages. 相似文献
898.
Robert L. Beck 《Journal of Family Therapy》1989,11(3):231-241
This paper describes the use of concurrent individual and conjoint sessions in couples psychotherapy. The introduction of these individual interviews is seen as supporting the individual changes which must be made to effect change in the structure of the relationship. The benefits of this interventive scheme in dynamically oriented couples' treatment will be illustrated through the presentation of case examples. 相似文献
899.
I. Bennun 《Journal of Family Therapy》1989,11(3):243-255
Thirty-five families completed ratings describing their perceptions of their therapists. These ratings were then correlated with measures of outcome to assess whether there was a relationship between experiences of the therapist and treatment outcome. Further, the study addresses whether some family members' perceptions are more influential in affecting the course of treatment. The results showed that family members' perception of the therapist does have an impact on treatment outcome, but not all members affect the outcome equally. Further results and their implications are discussed. 相似文献
900.