首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   73255篇
  免费   3035篇
  国内免费   31篇
  76321篇
  2020年   824篇
  2019年   987篇
  2018年   1421篇
  2017年   1468篇
  2016年   1535篇
  2015年   1110篇
  2014年   1308篇
  2013年   6270篇
  2012年   2407篇
  2011年   2426篇
  2010年   1463篇
  2009年   1478篇
  2008年   2077篇
  2007年   2088篇
  2006年   1871篇
  2005年   1591篇
  2004年   1629篇
  2003年   1553篇
  2002年   1508篇
  2001年   2445篇
  2000年   2289篇
  1999年   1715篇
  1998年   792篇
  1997年   694篇
  1996年   784篇
  1995年   701篇
  1994年   682篇
  1993年   670篇
  1992年   1429篇
  1991年   1336篇
  1990年   1332篇
  1989年   1263篇
  1988年   1247篇
  1987年   1148篇
  1986年   1171篇
  1985年   1198篇
  1984年   989篇
  1983年   850篇
  1979年   1041篇
  1978年   776篇
  1975年   841篇
  1974年   990篇
  1973年   1012篇
  1972年   849篇
  1971年   795篇
  1970年   731篇
  1969年   690篇
  1968年   900篇
  1967年   794篇
  1966年   737篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
This paper reports the results of a study designed to separate the voicing redundancy from nasality in American English and to determine their individual saliencies. Sixty-seven subjects judged the similarity of nonnasal pairs versus nasal pairs of CV and VC nonsense syllables on a 5-point magnitude-estimation task. The 80 stimuli were constructed to control and to demand subjects' cognitive strategies for coping with redundancy rather than experimental manipulation of the data. They were developed from the consonantal repertoire of / b d g m n p t k / paired with the vowels / i a u /, totaling 72 pairs of dyads. Eight additional stimuli of similar structure, testing multifeature and identity contrasts, were included to monitor the validity of the experimental procedure. Results indicated that (a) speech redundancy can be circumvented cognitively, (b) nasality was more salient (different) than voicing, and (c) a recency effect was found. These findings are discussed in reference to existing data.  相似文献   
942.
In [2] a semantics for implication is offered that makes use of stories — sets of sentences assembled under various constraints. Sentences are evaluated at an actual world and in each member of a set of stories. A sentence B is true in a story s just when B s. A implies B iff for all stories and the actual world, whenever A is true, B is true. In this article the first-order language of [2] is extended by the addition of the operator the story ... says that ..., as in The story Flashman among the Redskins says that Flashman met Sitting Bull. The resulting language is shown to be sound and complete.  相似文献   
943.
944.
The relationship between risk factors and the severity and type of childhood disorder, as measured by parent-completed Child Behavior Checklists, was examined for 768 children, ages 4–16, seen at a child mental health center. Regression analyses revealed no significant relationships between any combination of risk factors and the total number of behavior problems, internalizing, or externalizing scores for the entire group, males and females separately, or for the age and sex groupings of 6- to 11- and 12-to 16-yearolds. Chi-square tests revealed no relationship of profile type with any risk factor or with total number of risk factors. Implications for broad-based child assessment and risk factor research within a clinical population are discussed.We wish to thank Orin Bolstad, Linda Magnuson, and Julian Taplin for their assistance in this project.  相似文献   
945.
Twenty-nine children 9 to 12 years old who were identified as moderately to severely depressed using the Children's Depression Inventory were randomly assigned to either a self-control, behavioral problem-solving, or waiting list condition. The self-control treatment focused on teaching children self-management skills. The behavioral problem-solving therapy consisted of education, self-monitoring of pleasant events, and group problem solving directed toward improving social behavior. Subjects were assessed pre-and posttreatment and at 8-week follow-up with multiple assessment procedures and from multiple perspectives. At posttreatment, subjects in both active treatments reported significant improvement on self-report and interview measures of depression while subjects in the waiting list condition reported minimal change. Results were maintained at follow-up. The general success of the experimental treatments was discussed and recommendations for further treatment components were provided.Second authorship on this article is shared by Drs. Reynolds and Kaslow. The authors would like to thank Mr. Ed Guzwieski, Principal, and the teachers of Oregon Middle School for their cooperation with this study. The authors also would like to thank Mary Wysopal for conducting the posttreatment and follow-up interviews, and Carol Fairbanks for rating the audiotapes.  相似文献   
946.
The functional development of cardiac and adrenal medullary responses to reflex activation of the sympathetic nervous system was studied in preweanling spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats. Pups of the two strains received injections of insulin or saline at 2, 4, 8, 12, or 16 days of age and were sacrificed 3 h later. Insulin administration produces a significant decrease in circulating levels of glucose which in turn results in a centrally mediated increase in sympathetic outflow. The induction of ornithine decarboxylase (ODC) in heart and the depletion of epinephrine from the adrenal medulla served as tissue markers of functional sympathetic neurotransmission. WKY and SHR pups had comparable levels of ODC activity in heart under basal conditions. In contrast, levels of catecholamines in the adrenals were greater in SHR pups at 2 and 4 days of age. Following insulin administration, SHR pups exhibited a greater induction of cardiac ODC activity at 2, 4, and 8 days of age compared to age-matched WKY controls. However, there were no differences between SHR and WKY pups in the magnitude of the adrenal medullary response to insulin-induced hypoglycemia. These alterations in sympathetic-target tissue development during the first postnatal week of life may contribute in part to the higher arterial pressures maintained by SHRs throughout the lifespan.  相似文献   
947.
A long-term temporal component of working memory of rats trained on the radial maze has been shown to be susceptible to disruption by the protein synthesis inhibitor, anisomycin. It is not clear whether protein synthesis played a role in working memory because accurate performance on the radial maze required the storage of a large amount of information, or because the information was to be held in store for relatively long periods of time. This experiment tested these hypotheses by assessing the effect of anisomycin on choice accuracy in a comparatively simple spatial delayed alternation task. Results indicate that under the present training conditions, protein involvement in working memory is related more to the length of the retention interval than to the amount of information retained.  相似文献   
948.
This psychophysiological evaluation of an aerobic exercise program examined specifically whether aerobic training modified Pattern A for those individuals at behavioral risk for developing coronary heart disease, i.e., young Type A individuals. At pretest and posttest of this secondary prevention study, Type A and Type B subjects were assessed in three conditions: aerobic exercise program, nonaerobic activity (Aikido, a martial art) control, and notreatment control. After 10 weeks, Type A but not Type B subjects exhibited lower Pattern A behavior in the aerobic program than in control conditions. Average workout pulse rates and differentially reliable increases in aerobic capacity indicated that aerobic training was indeed aerobic, whereas aikido activity was not. Even though selected nonaerobic factors, such as locus of control and group participation, did not mediate the Pattern A decrease for Type A's when comparing aikido and aerobic conditions, changes in aerobic capacity may have been the mediator. Generalizability of the results and implications for theoretical development and clinical intervention are discussed.  相似文献   
949.
Reaction-time and accuracy data obtained from studies of sentence verification have not been rich enough to answer certain important theoretical questions about structures and processes in human semantic memory. However, a new technique called speed-accuracy decomposition (Meyer, Irwin, Osman, & Kounios, 1986) may help solve this problem. The technique allows intermediate products of sentence verification to be analyzed more precisely. Three experiments with speed-accuracy decomposition indicate that verification processes produce useful partial information before they are completed. Such information appears to accumulate continuously at a rate whose magnitude depends on the degree of relatedness between semantic categories. This outcome is consistent with continuous computational (e.g., semantic-feature comparison) models of semantic memory. An analysis of reaction-time minima suggests that a discrete all-or-none search process may also contribute at least occasionally to sentence verification. Further details regarding the nature of these processes and the memory structures on which they operate can be inferred from additional results obtained through speed-accuracy decomposition.  相似文献   
950.
Mechanisms underlying satiation of feeding behavior of the mollusc Aplysia   总被引:1,自引:0,他引:1  
Animals filled almost to satiation by nonnutritive bulk do not satiate when they ingest a small amount of seaweed. This suggests that satiation is not triggered by chemostimulation of an anteriorly located "hot spot." Inflation of a balloon placed in the gut of the animal results in satiation as reflected in a number of different parameters of feeding behavior. The suppressive effect of a relatively brief inflation is rapidly and fully reversible, although repeated inflation and deflation appeared to produce slowly reversible or irreversible effects. The parameters of the changes in feeding during gut inflation are comparable to those of normal animals that are slowly fed individual pieces of food. The inflation volume needed to satiate the animal is a function of the rate of inflation--more rapid inflations requiring larger volumes. Cutting of the esophageal nerves results in a significant increase in the volume needed to satiate the animals, but nevertheless they eventually cease feeding and generally do not show a burst gut. The evidence indicates that the satiation that eventually occurs in nerve-sectioned animals, at least in part, is due to depression of feeding following very prolonged sensory stimulation. The data suggest that for a rapidly consumed meal, satiation results primarily due to distension-related gut signals conveyed by the esophageal nerves, whereas for very slowly consumed meals, the former factor interacts with a process associated with sensory stimulation, such as receptor adaptation. The current results indicate that balloon distension can serve as a reasonable stimulus in experiments in simplified preparations in which the nervous system can be studied.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号