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   1383篇
  免费   80篇
  国内免费   1篇
  2024年   3篇
  2023年   16篇
  2022年   25篇
  2021年   26篇
  2020年   44篇
  2019年   43篇
  2018年   100篇
  2017年   97篇
  2016年   68篇
  2015年   39篇
  2014年   40篇
  2013年   176篇
  2012年   91篇
  2011年   86篇
  2010年   62篇
  2009年   44篇
  2008年   79篇
  2007年   65篇
  2006年   55篇
  2005年   48篇
  2004年   43篇
  2003年   33篇
  2002年   29篇
  2001年   12篇
  2000年   11篇
  1999年   20篇
  1998年   7篇
  1997年   12篇
  1996年   6篇
  1995年   3篇
  1994年   11篇
  1993年   5篇
  1992年   7篇
  1991年   3篇
  1990年   2篇
  1989年   6篇
  1988年   3篇
  1987年   4篇
  1986年   2篇
  1985年   5篇
  1982年   2篇
  1981年   6篇
  1980年   2篇
  1976年   2篇
  1974年   4篇
  1972年   2篇
  1968年   2篇
  1965年   2篇
  1962年   2篇
  1960年   1篇
排序方式: 共有1464条查询结果,搜索用时 31 毫秒
931.
Learning disabilities (LD) are one of the most frequent problems for elementary school-aged children. In this paper, event-related EEG oscillations to semantically related and unrelated pairs of words were studied in a group of 18 children with LD not otherwise specified (LD-NOS) and in 16 children with normal academic achievement. We propose that EEG oscillations may be different in LD NOS children versus normal control children that may explain some of the deficits observed in the LD-NOS group. The EEGs were recorded using the 10/20 system. EEG segments were edited by visual inspection 1000ms before and after the stimulus, and only correct responses were considered in the analysis. Time-frequency (1-50Hz) topographic maps were obtained for the increases and decreases of power after the event with respect to the pre-stimulus average values. Significant differences between groups were observed in the behavioral responses. LD-NOS children show less number of correct responses and more omissions and false alarms than the control group. The event-induced EEG responses showed significant differences between groups. The control group showed greater power increases in the frequencies 1-6Hz than the LD-NOS group from 300 to 700ms. These differences were mainly observed in frontal regions, both to related and non-related words. This was interpreted as a deficit in attention, both to internal and external events, deficits in activation of working memory and deficits in encoding and memory retrieval in the LD-NOS children. Differences between groups were also observed in the suppression of alpha and beta rhythms in the occipital regions to related words in frequencies between 8 and 17Hz from 450 to 750ms. LD-NOS children showed shorter durations of the decreases in power than the control group. These results suggest also deficits in attention and memory retrieval. It may be concluded that LD-NOS children showed physiological differences from normal children that may explain their cognitive deficiencies.  相似文献   
932.
This study examined the role of sympathetic nerves in the control of cerebral hemodynamics during air-jet stress. In adult male Sprague-Dawley rats, blood flow velocity (pulsed Doppler) was measured in both internal carotid arteries 1 week after excision of one superior cervical ganglion. Blood pressure (BP) and carotid blood flows (CBFs) were simultaneously recorded during exposure to air-jet stress. In 5 out of 13 rats, stress was applied after β(2)-adrenoceptor blockade with ICI 118551 (0.4 mg/kg, then 0.2 mg/kg/h, i.v). Stress evoked an immediate rise in BP, CBFs, and vascular conductances. Vasodilatation was much larger on the denervated side than on the intact side (mean ± SEM: 78 ± 7 versus 19 ± 4%; P < 0.02) and lasted about 10 s. Thereafter, blood flows returned to or near normal and showed parallel variations while BP remained elevated. There was, therefore, a net vasoconstriction on both sides. In ICI 118551-treated rats, the initial vasodilatation was not significantly reduced on the denervated side (64 ± 4%), but the subsequent vasoconstriction was enhanced (P < 0.05) on both sides. In conclusion, air-jet stress evokes an immediate, short-lasting vasodilatation through a mechanism unrelated to β(2)-adrenoceptor stimulation. Sympathetic nerves powerfully limit this phenomenon, and thus contribute to protect the cerebral circulation from stress-induced BP surges.  相似文献   
933.
We discuss three different areas in which policies on gender and the family have been debated and formulated in Brazil, revealing both the forces of change and the many contradictions that are at work within this society today. After a brief look at the historical vicissitudes of families and family life in Brazil, as representations and as forms of social organization, we come to our more immediate context: the re-democratization processes that engulfed Brazilian society as of the 1980s and the social actors generated therein. Issues relating to gender and sexuality become increasingly visible on the broad political agenda that, notwithstanding national specificities, also converges with social, political and cultural trends emerging all over the world in the latter decades of the twentieth century. The three specific issues we discuss here—the Maria da Penha Law on domestic violence, efforts regarding the legalization of abortion and recent debates that have emerged around a bill introduced to give legal status to same-sex relationships—provide testimony of a society characterized by tensions between mechanisms sustaining restrictive definitions of family, linked to male dominance, heterosexism and hierarchical gender roles, and those that push toward more egalitarian, diverse and democratic family relations.  相似文献   
934.
The main objective of this study was to build a model, which includes personal and social factors, that helps to highlight factors that promote health-related quality of Life (HRQoL) in children and in adolescents. A sample of 3195 children and adolescents was acquired from 5th and 7th graders from all five Portuguese regions. In this study three independent latent variables were specified--Physical, Psychological and Social and two dependent latent variables were measured: Health behavior and Quality of Life. The integrative model was composed by different components: (1) health-related quality of life, integrated by 8 dimensions from KIDSCREEN-52; (2) health behavior, (3) variables related to physical health; (4) variables related to social health; (5) variables related to psychological health. As results were found strong correlation between psychological dimensions and self-esteem and other factors and a structural equation model was developed. The model presented a RMSEA index of .08. Similarly, adjustment levels for the CFI, NFI and IFI vary above or around .90, which suggests a good adjustment for the hypothesized model. The model presented significant qui-square. This study showed that in all the samples studied, the psychological variables were those that contributed at a superior level to HRQoL.  相似文献   
935.
The aim of this research was to determine to what extent a psychopath screening device (the APSD) is useful in forensic assessments to predict general and violent offending. For this purpose, a cross-sectional study was done and 238 young people serving a sentence were assessed. The gold standard instrument used to measure psychopathy was the Psychopathy Checklist: Youth Version (PCL:YV; Forth, Kosson & Hare, 2003). The results indicate that the association found between the screening device scores and several indicators of risk is low if compared with those obtained with the PCL:YV, suggesting that it is less useful as a tool in order to predict offending or violent offences. However, an Area Under the Curve of .784 and a validity index of 62.5 support its use as a screening device or as a preliminary approach to assess psychopathy in this population. The usefulness of this instrument to make assessments with young people in the forensic setting is discussed.  相似文献   
936.
There is a phenomenon contributing to the current pattern of alcohol consumption among youngsters in Spain known as "botellon". From research financed by the National Plan on Drugs (2004-2007), data of 6009 youngsters (14-25 years old) were collected from three Spanish cities. Only individuals who engage in intensive consumption of alcohol (n = 2807) have been included. The purpose of this work has been to identify the different types of consumers at risk through a cluster analysis and to establish a profile for each particular group. Four groups were differentiated by age, gender, alcohol consumption and years of consumption. It was observed that adolescent students and university students of the same sex consume similar quantities of alcohol, and justify their consumption alluding to personal factors, whereas university students refer to issues related to control of leisure. The consumption by males is the highest, and they are the most likely to seek drunkenness. They associate to a lesser degree their consumption with the possibility of developing an addictive process. In general, all youngsters consider that their consumption will have no negative consequences. These results indicate the need to come up with different alternatives, addressing the particularities of each group.  相似文献   
937.
Numerical cognition is based on two components - number processing and calculation. Its development is influenced by biological, cognitive, educational, and cultural factors. The objectives of the present study were to: i) assess number processing and calculation in Brazilian children aged 7-12 years from public schools using the Zareki-R (Battery of neuropsychological tests for number processing and calculation in children, Revised; von Aster & Dellatolas, 2006) in order to obtain normative data for Portuguese speakers; ii) identify how environment, age, and gender influences the development of these mathematical skills; iii) investigate the construct validity of the Zareki-R by the contrast with the Arithmetic subtest of WISC-III. The sample included 172 children, both genders, divided in two groups: urban (N = 119) and rural (N = 53) assessed by the Zareki-R. Rural children presented lower scores in one aspect of number processing; children aged 7-8 years demonstrated an inferior global score than older; boys presented a superior performance in both number processing and calculation. Construct validity of Zareki-R was demonstrated by high to moderate correlations with Arithmetic subtest of WISC-III. The Zareki-R therefore is a suitable instrument to assess the development of mathematical skills, which is influenced by factors such as environment, age, and gender.  相似文献   
938.
939.
Knowledge of the factors that contribute to pedestrian crashes is fundamental to the design of engineering, enforcement and education measures to decrease the number and severity of these crashes. To identify the factors that contribute to pedestrian crashes on rural highways crossing urban areas in the Federal District, Brazil, an investigatory procedure was developed. The procedure was implemented by the Federal District Road Department (DER–DF) for a period of 6 months. This study presents the investigatory method and the results. Data analysis indicated the importance of conducting detailed studies of the factors that contribute to pedestrian crashes. The main contributory factors identified are presented and discussed.  相似文献   
940.
ObjectivesThe emergent nature and dynamics of Task-Related Thoughts (TRT) during accumulated physical effort was used to test a model of attention focus based on the application of nonlinear dynamic systems theory (NDST).DesignA one-group two-trials quasi experimental design was employed.MethodsEleven physically active participants ran twice on a treadmill at an intensity of 80% of their HRmax until voluntary exhaustion. During the first run their intrinsic dynamics of attention focus was established. Accordingly, during the second run they were asked to intentionally maintain Task-Unrelated Thoughts (TUT), and reporting back about spontaneous switches from TUT to TRT, and vice versa.ResultsResults revealed that the intentionally imposed TUT was stable at the beginning of the test, switched spontaneously to TRT with accumulated effort, competing with TUT and showing metastability, until a final TRT state prevails.ConclusionsThe observed phenomena points to a nonlinear dynamic self-regulation of attention focus during accumulated effort.  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