全文获取类型
收费全文 | 50719篇 |
免费 | 1956篇 |
国内免费 | 28篇 |
专业分类
52703篇 |
出版年
2019年 | 638篇 |
2018年 | 887篇 |
2017年 | 953篇 |
2016年 | 951篇 |
2015年 | 714篇 |
2014年 | 795篇 |
2013年 | 3992篇 |
2012年 | 1404篇 |
2011年 | 1538篇 |
2010年 | 974篇 |
2009年 | 955篇 |
2008年 | 1321篇 |
2007年 | 1307篇 |
2006年 | 1183篇 |
2005年 | 1041篇 |
2004年 | 960篇 |
2003年 | 1001篇 |
2002年 | 973篇 |
2001年 | 1800篇 |
2000年 | 1744篇 |
1999年 | 1272篇 |
1998年 | 560篇 |
1997年 | 475篇 |
1996年 | 488篇 |
1992年 | 1077篇 |
1991年 | 1044篇 |
1990年 | 996篇 |
1989年 | 939篇 |
1988年 | 928篇 |
1987年 | 892篇 |
1986年 | 870篇 |
1985年 | 939篇 |
1984年 | 742篇 |
1983年 | 614篇 |
1982年 | 472篇 |
1981年 | 478篇 |
1979年 | 769篇 |
1978年 | 563篇 |
1977年 | 508篇 |
1976年 | 486篇 |
1975年 | 651篇 |
1974年 | 737篇 |
1973年 | 793篇 |
1972年 | 637篇 |
1971年 | 577篇 |
1970年 | 553篇 |
1969年 | 548篇 |
1968年 | 691篇 |
1967年 | 616篇 |
1966年 | 636篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
811.
In two experiments, we investigated the factors that influence the perceived similarity of speech sounds at two developmental levels. Kindergartners and second graders were asked to classify nonsense words, which were related by syllable and phoneme correspondences. The results support the existence of a developmental trend toward increased attention to individual phonemic segments. Moreover, one significant factor in determining the perceived similarity of speech sounds appears to be the position of the component correspondences; attention to the beginning of utterances may have developmental priority. An unexpected finding was that the linguistic status of the unit involved in a correspondence (whether it was a syllable or a phoneme) did not seem particularly important. Apparently, the factors which contribute to the perceived similarity of speech sounds in the classification task are not identical to those which underlie performance in explicit segmentation and manipulation tasks, since in the latter sort of task, syllables are more accessible than phonemes for young children. The present task may tap a level of processing that is closer to the one entailed in word recognition and lexical access. 相似文献
812.
Intermediate prepositional logics we consider here describe the setI() of regular informational types introduced by Yu. T. Medvedev [7]. He showed thatI() is a Heyting algebra. This algebra gives rise to the logic of infinite problems from [13] denoted here asLM
1. Some other definitions of negation inI() lead to logicsLM
n
(n ). We study inclusions between these and other systems, proveLM
n
to be non-finitely axiomatizable (n ) and recursively axiomatizable (n < ). We also show that formulas in one variable do not separateLM
from Heyting's logicH, andLM
n
(n < ) from Scott's logic (H+S). 相似文献
813.
814.
Twenty-two right hemisphere brain-damaged and 22 non-brain-damaged patients were given a multiple-choice recognition task which contained true statements, statements which were inferentially true but not actually heard before, and false statements. It was hypothesized that if right hemisphere brain damage disturbs the ability to comprehend inferences, these subjects, unlike their normal counterparts, would not falsely recognize true inferences as heard before. This hypothesis was not confirmed. However, the right hemisphere group was poorer than controls at rejecting false statements. This behavior was speculated to be a retrieval difficulty, which was exacerbated if the information contained spatial or semantically similar material. 相似文献
815.
The behavior of individual subjects is compared with a hierarchical control system model of behavioral organization. Subjects varied the position of two control handles simultaneously to keep the distance constant between two pairs of lines. Three variations on this basic experiment that illustrate some fundamental properties of coordinated action are shown: first, how independent actions, compensating for unpredictable and undetectable disturbances, can produce a single behavioral result; second, how the ability to produce a particular result is maintained when the connection between action and result is changed; and third, how two independent outputs can appear to be related as coordinative structures when one output disturbs a result being controlled by the other. The correlation between the behavior of subjects and model in all experiments is typically on the order of .99. A detailed examination of the operation of the model shows that actions are structured by perception, not by central commands or equations of constraint. 相似文献
816.
It has been suggested that the systematic decline of partial report as the delay of the partial-report cue increases is due to a time-related loss of location information. Moreover, the backward masking effect is said to be precipitated by the disruption of location information before and after identification. Results from three experiments do not support these claims when new indices of location information and of item information are used. Instead, it was found that the systematic decline in partial report was due to a time-related loss of item information, and location information was affected neither by the delay of the partial-report cue nor by the delay of backward masking. Subjects adopted the "select-then-identify" mode of processing. 相似文献
817.
A homogeneous sample of normal adults living in a religious order in a study of age effects on reference as a cohesive device in discourse production and comprehension. Narrative and procedural discourse were examined across various levels of complexity and stimulus/response requirements. Results indicate that significant ambiguity of reference emerges in the younger elderly group (age 64-76) in comparison to the middle-aged group (age 27 to 55), and increases markedly in the older elderly group (age 77-92). Related impairments of comprehension and cognition were also observed. These findings are interpreted to be general features of linguistic variation with advancing age. Communicative consequences of ambiguous reference are discussed. 相似文献
818.
W H Warren D S Young D N Lee 《Journal of experimental psychology. Human perception and performance》1986,12(3):259-266
Running over uneven ground requires visually regulating step length to secure proper footing. To examine how this is achieved, we studied subjects running on a treadmill on a series of irregularly spaced targets. The movements of their lower limbs and coccyx relative to the targets were monitored opto-electronically by a Selspot system. The results indicated that step length was adjusted to strike the targets primarily by varying the vertical component of impulse applied to the ground during the stance phase. In contrast, horizontal impulse was not varied significantly, and changing the reach forward of the foot on landing contributed little to variation in step length. Changing the vertical impulse simply altered the step time proportionately. Thus the data are consistent with a time-based model in which vertical impulse is modulated by the optic variable delta tau (Lee, 1976) specifying the time gap that has to be bridged by the runner between two targets. 相似文献
819.
A home centred family therapy approach is described based on the McMaster model. This approach was applied in a controlled trial of three forms of intervention for mother and toddler problems. In this paper the experience of applying the approach is reported. 相似文献
820.
The experiments examined the contributions of forebrain noradrenaline and environmental enrichment to recovery of place navigation ability in rats after hemidecortication in infancy or adulthood. Noradrenaline depletion did not affect recovery from neonatal hemidecortication, although the early hemidecortications did allow sparing of function relative to adult operates. Noradrenaline depletion also failed to attenuate the positive effects of enriched housing on otherwise normal rats. Noradrenaline depletion did retard recovery of adult hemidecorticate rats housed in standard laboratory cages, but it did not retard recovery of adult hemidecorticate rats housed in enriched environments. The results suggest that noradrenaline is importantly involved in enhancing recovery from brain damage when other sources of compensation (e.g., neonatal injury, enriched environment) are absent. 相似文献