全文获取类型
收费全文 | 16879篇 |
免费 | 375篇 |
国内免费 | 195篇 |
专业分类
17449篇 |
出版年
2012年 | 1490篇 |
2011年 | 1756篇 |
2010年 | 412篇 |
2009年 | 194篇 |
2008年 | 1368篇 |
2007年 | 1411篇 |
2006年 | 1234篇 |
2005年 | 1083篇 |
2004年 | 948篇 |
2003年 | 958篇 |
2002年 | 838篇 |
2001年 | 548篇 |
2000年 | 756篇 |
1999年 | 336篇 |
1998年 | 108篇 |
1997年 | 78篇 |
1996年 | 92篇 |
1995年 | 59篇 |
1994年 | 87篇 |
1993年 | 125篇 |
1992年 | 117篇 |
1991年 | 121篇 |
1990年 | 104篇 |
1989年 | 103篇 |
1988年 | 119篇 |
1987年 | 136篇 |
1986年 | 92篇 |
1985年 | 129篇 |
1984年 | 130篇 |
1983年 | 147篇 |
1982年 | 111篇 |
1981年 | 104篇 |
1980年 | 85篇 |
1979年 | 93篇 |
1978年 | 85篇 |
1966年 | 48篇 |
1965年 | 134篇 |
1964年 | 106篇 |
1963年 | 127篇 |
1962年 | 54篇 |
1959年 | 41篇 |
1958年 | 189篇 |
1957年 | 155篇 |
1956年 | 131篇 |
1955年 | 93篇 |
1954年 | 82篇 |
1953年 | 81篇 |
1952年 | 61篇 |
1951年 | 66篇 |
1950年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
872.
Genetic Cancer Risk Assessment and Counseling: Recommendations of the National Society of Genetic Counselors 总被引:4,自引:0,他引:4
Trepanier A Ahrens M McKinnon W Peters J Stopfer J Grumet SC Manley S Culver JO Acton R Larsen-Haidle J Correia LA Bennett R Pettersen B Ferlita TD Costalas JW Hunt K Donlon S Skrzynia C Farrell C Callif-Daley F Vockley CW;National Society of Genetic Counselors 《Journal of genetic counseling》2004,13(2):83-114
These cancer genetic counseling recommendations describe the medical, psychosocial, and ethical ramifications of identifying at-risk individuals through cancer risk assessment with or without genetic testing. They were developed by members of the Practice Issues Subcommittee of the National Society of Genetic Counselors Cancer Genetic Counseling Special Interest Group. The information contained in this document is derived from extensive review of the current literature on cancer genetic risk assessment and counseling as well as the personal expertise of genetic counselors specializing in cancer genetics. The recommendations are intended to provide information about the process of genetic counseling and risk assessment for hereditary cancer disorders rather than specific information about individual syndromes. Key components include the intake (medical and family histories), psychosocial assessment (assessment of risk perception), cancer risk assessment (determination and communication of risk), molecular testing for hereditary cancer syndromes (regulations, informed consent, and counseling process), and follow-up considerations. These recommendations should not be construed as dictating an exclusive course of management, nor does use of such recommendations guarantee a particular outcome. These recommendations do not displace a health care provider's professional judgment based on the clinical circumstances of a client. 相似文献
873.
In the present experiments, we examined whether shifts of attention selectively interfere with the maintenance of both verbal
and spatial information in working memory and whether the interference produced by eye movements is due to the attention shifts
that accompany them. In Experiment 1, subjects performed either a spatial or a verbal working memory task, along with a secondary
task requiring fixation or a secondary task requiring shifts of attention. The results indicated that attention shifts interfered
with spatial, butnot with verbal, working memory, suggesting that the interference is specific to processes within the visuospatial sketchpad.
In Experiment 2, subjects performed a primary spatial working memory task, along with a secondary task requiring fixation,
an eye movement, or an attention shift executed in the absence of an eye movement. The results indicated that both eye movements
and attention shifts interfered with spatial working memory. Eye movements interfered to a much greater extent than shifts
of attention, however, suggesting that eye movements may contribute a unique source of interference, over and above the interference
produced by the attention shifts that accompany them. 相似文献
874.
How rapidly can attention move from one object to the next? Previous studies in which the dwell time paradigm was used have estimated attentional switch times of 200–500 msec, results incompatible with the search rate estimates of 25–50 msec shown in numerous visual search studies. It has been argued that dwell times are so long in the dwell time paradigm because the attentional shifts measured are unlike those used in visual search. In the present experiment, a variation of a visual search task was used, in which serial endogenous (volitional) deployments of attention were measured directly by means of a probe reaction time task. The experiment revealed a dwell time of about 250 msec, consistent with the faster estimates from other dwell time studies. This result suggests that endogenous shifts of attention may be relatively slow and that the faster attentional shifts estimated from visual search tasks may be due to the involvement of bottom-up processes. 相似文献
875.
Postextinction infusion of a mitogen-activated protein kinase inhibitor into the medial prefrontal cortex impairs memory of the extinction of conditioned fear 下载免费PDF全文
We investigated whether postextinction training infusion of PD098059, a selective inhibitor of mitogen-activated protein kinase (MAPK) activation, into the medial prefrontal cortex, would impair retention of extinction learning in rats. We found that immediate, but not late (2 or 4 h), postextinction infusion of PD098059 provoked a full return of conditioned freezing. These results suggest that activation of prefrontal MAPK in early stages of postextinction training participates in processes that protect against spontaneous recovery of aversive responses. 相似文献
876.
According to the perceptual symbols theory (Barsalou, 1999), sensorimotor simulations underlie the representation of concepts.
Simulations are componential in the sense that they vary with the context in which the concept is presented. In the present
study, we investigated whether representations are affected by recent experiences with a concept. Concept names (e.g., APPLE)
were presented twice in a property verification task with a different property on each occasion. The two properties were either
from the same perceptual modality (e.g.,green, shiny) or from different modalities (e.g.,tart, shiny). All stimuli were words. There was a lag of several intervening trials between the first and second presentation. Verification
times and error rates for the second presentation of the concept were higher if the properties were from different modalities
than if they were from the same modality. 相似文献
877.
The efficacy of antiepileptic drugs (AEDs) and psychotropic medications in children with autism is limited to the treatment of seizures or to specific behaviors such as irritability, impulsivity, hyperactivity, repetitive behaviors, or aggression. The reliability and value of the available data--to determine the efficacy of these medications in autism--are limited by lack of controlled clinical trials, the small number of subjects, the heterogeneity of the population studied, and the brief duration of most drug trials. Indeed, few controlled clinical trials using AEDs in autism, with or without seizures, have been conducted. Because some AEDs also have a positive effect on mood, the benefits that children with autism sometimes obtain from these medications may not be due to the treatment of the abnormal electrical activity or the seizures per se but to an effect on common neuronal systems responsible for both behavior and epilepsy. The relationship between epilepsy and autism, and specifically the effects that abnormal electrical activity may have on the developing brain, may provide some valuable insights into the type of studies that are needed to help us understand the pathophysiology of autism. 相似文献
878.
The lexically based Five-Factor Personality Inventory (FFPI) was correlated with the factors and facets of the Revised NEO Personality Inventory (NEO-PI-R) in Belgian (N = 265), American (N = 116), and Hungarian (N = 320) samples. Results were similar across the three cultures. Analysis of orthogonalized FFPI factors showed that three of them--emotional stability, extraversion, and agreeableness--showed a direct correspondence to their NEO-PI-R counterparts. Autonomy, however, was not clearly related to openness, and facet analysis suggested that it might be interpreted as a dominance factor Better matches to NEO-PI-R conscientiousness and openness could be obtained by using vectors rotated 30 degrees from the FFPI positions. Raw scale scores showed similar results. Researchers should not assume that all measures of the Five-Factor Model are qualitatively similar 相似文献
879.
Short and long-term motor skill learning in an accelerated rotarod training paradigm 总被引:1,自引:0,他引:1
Rodent models of motor skill learning include skilled forelimb reaching and acrobatic locomotor paradigms. This study characterizes motor skill learning in the accelerated rotarod task. Thirty Long-Evans rats (300-400 g) were trained on an accelerated rotarod (1cm/s(2)) over eight consecutive sessions (=days, 20 trials each). Improvement in rotarod velocities mastered before falling off the rod was observed within and between sessions (plateau after five sessions). Intrasession improvement was incompletely retained at the beginning of the next day's session. Over several training sessions, intrasession improvement diminished, suggesting a ceiling effect. After 1 week of pause, the rotarod skill was retained. Locomotor exercise in a running wheel for 30 min before the first rotarod session did not affect intrasession improvement. Running-wheel exposure for 6 days did not diminish the rate of rotarod skill learning (steepness of the learning curve) but improved overall performance (upward shift of curve). Video analysis of gait on the rotarod showed that rats developed a motor strategy by modifying their gait patterns during training. The data demonstrate that rotarod improvement is not the result of enhanced general locomotor ability or fitness, which are trained in the running wheel, but requires a change in the motor strategy to master the task. Accelerated rotarod training can be regarded a valid paradigm for motor skill learning over short (intrasession, minutes) and long time frames (intersession, days). 相似文献
880.
Lawler CP Croen LA Grether JK Van de Water J 《Mental retardation and developmental disabilities research reviews》2004,10(4):292-302
The potential role of environmental factors in autism spectrum disorders (ASD) is an area of emerging interest within the public and scientific communities. The high degree of heritability of ASD suggests that environmental influences are likely to operate through their interaction with genetic susceptibility during vulnerable periods of development. Evaluation of the plausibility of specific neurotoxicants as etiological agents in ASD should be guided by toxicological principles, including dose-effect dependency and pharmacokinetic parameters. Clinical and epidemiological investigations require the use of sufficiently powered study designs with appropriate control groups and unbiased case ascertainment and exposure assessment. Although much of the existing data that have been used to implicate environmental agents in ASD are limited by methodological shortcomings, a number of efforts are underway that will allow more rigorous evaluation of the role of environmental exposures in the etiology and/or phenotypic expression of the disorder. Surveillance systems are now in place that will provide reliable prevalence estimates going forward in time. Anticipated discoveries in genetics, brain pathology, and the molecular/cellular basis of functional impairment in ASD are likely to provide new opportunities to explore environmental aspects of this disorder. 相似文献