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   2762篇
  免费   125篇
  国内免费   1篇
  2888篇
  2023年   18篇
  2022年   15篇
  2021年   29篇
  2020年   43篇
  2019年   53篇
  2018年   74篇
  2017年   81篇
  2016年   114篇
  2015年   60篇
  2014年   88篇
  2013年   322篇
  2012年   139篇
  2011年   147篇
  2010年   93篇
  2009年   82篇
  2008年   134篇
  2007年   120篇
  2006年   109篇
  2005年   89篇
  2004年   103篇
  2003年   95篇
  2002年   64篇
  2001年   64篇
  2000年   54篇
  1999年   40篇
  1998年   34篇
  1997年   37篇
  1996年   33篇
  1995年   39篇
  1994年   27篇
  1993年   31篇
  1992年   32篇
  1991年   27篇
  1990年   36篇
  1989年   21篇
  1988年   32篇
  1987年   16篇
  1986年   13篇
  1985年   22篇
  1984年   23篇
  1983年   14篇
  1982年   23篇
  1979年   20篇
  1978年   12篇
  1977年   16篇
  1974年   17篇
  1972年   13篇
  1971年   10篇
  1970年   11篇
  1968年   11篇
排序方式: 共有2888条查询结果,搜索用时 0 毫秒
281.
Studies on adults have revealed a disadvantageous effect of negative emotional stimuli on executive functions (EF), and it is suggested that this effect is amplified in children. The present study’s aim was to assess how emotional facial expressions affected working memory in 9- to 12-year-olds, using a working memory task with emotional facial expressions as stimuli. Additionally, we explored how degree of internalizing and externalizing symptoms in typically developing children was related to performance on the same task. Before employing the working memory task with emotional facial expressions as stimuli, an independent sample of 9- to 12-year-olds was asked to recognize the facial expressions intended to serve as stimuli for the working memory task and to rate the facial expressions on the degree to which the emotion was expressed and for arousal to obtain a baseline for how children during this age recognize and react to facial expressions. The first study revealed that children rated the facial expressions with similar intensity and arousal across age. When employing the working memory task with facial expressions, results revealed that negatively valenced expressions impaired working memory more than neutral and positively valenced expressions. The ability to successfully complete the working memory task increased between 9 to 12 years of age. Children’s total problems were associated with poorer performance on the working memory task with facial expressions. Results on the effect of emotion on working memory are discussed in light of recent models and empirical findings on how emotional information might interact and interfere with cognitive processes such as working memory.  相似文献   
282.
Structural modulations hosted by complex oxides are–beyond relative orientation changes of ‘rigid units’–accompanied by characteristic distortions of coordination polyhedra. Electronic structure calculations in the local density approximation, performed at model clusters derived from positionally modulated structures, proved that the molecular–orbital structure also sensitively reflects such distortions. The latter crystal-field splitting of unoccupied states is accessible by high-resolution electron energy-loss near-edge structure (ELNES) spectroscopy. However, since ELNES spectra average over many different individual target-ion environments, the resulting ELNES possesses significantly broadened spectral features. In this contribution, such broadening is shown to dramatically influence the spectral shape of the Ti-L 2,3 ELNES acquired at the strongly modulated fresnoite framework compound Sr2TiSi2O8.  相似文献   
283.
High-resolution annular dark field imaging has been used to study small precipitates in the Al matrix of 6XXX-series aluminium alloys. Cu-containing columns in precipitates were imaged by atomic number contrast along a 〈100〉 matrix direction. At an under-aged condition, large, lath-shaped particles of the Cu-containing Q′-phase were observed at grain boundaries. At over-aged conditions, Q′ was the main matrix phase. In both cases the laths showed an Al {150} habit plane. A precursor phase was found, with different arrangement of Cu-rich columns from that of the Q′-phase and sharing Al {100} habit planes. Precipitates containing elements of both the Q′-phase and the precursor were found to be common. Annular dark field imaging can differentiate directly between phases. The method complements and aids interpretation of conventional high-resolution TEM images and nano beam diffraction observations. The results obtained contribute to an improved understanding of the crystallography of the precursor and details of the structural transformation taking place during the precipitation process.  相似文献   
284.
The devitrification process of Zr46.75Ti8.25Cu7.5Ni10Be27.5 metallic glass during annealing in the supercooled liquid region has been studied by conventional, high-resolution and analytical transmission electron microscopy (TEM). Two kinds of particle appear during devitrification: quasicrystals and crystalline precipitates. Nanoanalysis with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy reveal that quasicrystals are Be free, while the crystallites have the ZrBe2 hexagonal structure. These experiments confirm the key role of Be during devitrification. They also indicate that quasicrystals can form in the system Zr–Ti–Cu–Ni (without Be), as further evidenced by direct synthesis and an in situ neutron diffraction investigation, according to the chemical composition deduced from the TEM analysis.  相似文献   
285.
Human sensitivity for social cues is exquisite, as illustrated by the ease with which simplified point-light movements invoke social and emotional responses. Compared to faces, these biological motion stimuli only recently started to be used to explore questions regarding social cognition and anxiety. We presented human point-light walkers that could be perceived as facing towards or facing away from the observer, and tested whether participants with high social anxiety would perceive these bistable stimuli differently, because this type of stimuli has particular relevance for them. The results showed that observers with high social anxiety tended to see walkers as facing away more frequently than those with low social anxiety. This may mean that high socially anxious observers are biased towards the more positive perceptual alternative because they are motivated to protect themselves against threatening social experiences, but we also explore alternative explanations. The findings are in line with the evidence for a positivity bias in perception, also called wishful seeing, but in contrast with the attentional negativity bias often found in social anxiety. We discuss reasons for this divergence and possible limitations of the current study.  相似文献   
286.
Deployment may lead the soldiers to dichotomise their profession and their family life, resulting in unwanted effects on family or career. Effects on reintegration and functioning within family are considered. Reunions may be characterized by perceived negative reception and consequences could spill over to children as parents attempt to equivocate their differences. Risks exist for fragmentation of the family system or divorce. Social support may serve to buffer families with members on deployment.  相似文献   
287.
ABSTRACT

This article responds to calls for conceptual clarification in the media effects domain by providing a definition for attitudinal cultivation effects. Our definition contains 5 core characteristics: the (a) linear effects of (b) repeated media exposure on (c) the evaluation as given by memory associations (d) strengthened by and (e) valenced in line with those media messages. We reason that, when accepting this definition, the cultivation hypothesis predicts effects of repeated media use on evaluations to primarily occur at the level of gut evaluations given by automatically activated memory associations. Corroborating this logic for the effects of alcohol use portrayals in television fiction, we find the relationship between fiction exposure and self-reported alcohol use evaluations to be (a) moderated by speed of expressing those evaluations and (b) mediated by responses to self-reports tapping into gut feelings. The implications of these findings for future media effects studies are discussed.  相似文献   
288.
Often data are collected that consist of different blocks that all contain information about the same entities (e.g., items, persons, or situations). In order to unveil both information that is common to all data blocks and information that is distinctive for one or a few of them, an integrated analysis of the whole of all data blocks may be most useful. Interesting classes of methods for such an approach are simultaneous-component and multigroup factor analysis methods. These methods yield dimensions underlying the data at hand. Unfortunately, however, in the results from such analyses, common and distinctive types of information are mixed up. This article proposes a novel method to disentangle the two kinds of information, by making use of the rotational freedom of component and factor models. We illustrate this method with data from a cross-cultural study of emotions.  相似文献   
289.
Although dependence in effect sizes is ubiquitous, commonly used meta-analytic methods assume independent effect sizes. We describe and illustrate three-level extensions of a mixed effects meta-analytic model that accounts for various sources of dependence within and across studies, because multilevel extensions of meta-analytic models still are not well known. We also present a three-level model for the common case where, within studies, multiple effect sizes are calculated using the same sample. Whereas this approach is relatively simple and does not require imputing values for the unknown sampling covariances, it has hardly been used, and its performance has not been empirically investigated. Therefore, we set up a simulation study, showing that also in this situation, a three-level approach yields valid results: Estimates of the treatment effects and the corresponding standard errors are unbiased.  相似文献   
290.
ABSTRACT

This study investigated the effects of using digital augmentation to enhance an exhibit device to influence conceptual understanding about a science topic in a science museum setting. In particular, the study considered how students in Grades 6–8 engaged with the device that was available in both augmented and nonaugmented (control) conditions. Results show increased cognitive (critical thinking) skills when the digital augmentation was present that we hypothesize led to increased conceptual gains. We illustrate how this research contributes to three important areas of need identified in informal science literature: the need for evidence of conceptual and cognitive gains; the need for understanding how digital platforms improve the learning experience; and the need to demonstrate how designed interactive devices may impact higher order skills such as critical thinking and theorizing.  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