全文获取类型
收费全文 | 1846篇 |
免费 | 342篇 |
国内免费 | 658篇 |
出版年
2024年 | 4篇 |
2023年 | 61篇 |
2022年 | 88篇 |
2021年 | 72篇 |
2020年 | 145篇 |
2019年 | 135篇 |
2018年 | 124篇 |
2017年 | 143篇 |
2016年 | 170篇 |
2015年 | 90篇 |
2014年 | 147篇 |
2013年 | 422篇 |
2012年 | 129篇 |
2011年 | 156篇 |
2010年 | 89篇 |
2009年 | 122篇 |
2008年 | 112篇 |
2007年 | 110篇 |
2006年 | 96篇 |
2005年 | 81篇 |
2004年 | 59篇 |
2003年 | 56篇 |
2002年 | 41篇 |
2001年 | 27篇 |
2000年 | 20篇 |
1999年 | 21篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 4篇 |
排序方式: 共有2846条查询结果,搜索用时 250 毫秒
241.
A numerical model is proposed to simulate fracture induced by the coalescence of numerous microcracks, in which the condition for coalescence between two randomly nucleated microcracks is determined in terms of a load-sharing principle. The results of the simulation show that, as the number density of nucleated microcracks increases, stochastic coalescence first occurs followed by a small fluctuation, and finally a newly nucleated microcrack triggers a cascade coalescence of microcracks resulting in catastrophic failure. The fracture profiles exhibit self-affine fractal characteristics with a universal roughness exponent, but the critical damage threshold is sensitive to details of the model. The spatiotemporal distribution of nucleated microcracks in the vicinity of critical failure follows a power-law behaviour, which implies that the microcrack system may evolve to a critical state. 相似文献
242.
We report on the effect of cooling rate on the size-dependent atomic ordering of CoPt nanoparticles using aberration corrected high-resolution transmission electron microscopy. It was found that cooling rate plays a crucial role in promoting atomic ordering during the cooling process after annealing. Nanoparticles of ≈3?nm in diameter show the A1-disordered phase after annealing at 873?K for 1?h followed by rapid cooling (110?K/min), while the L10-ordered phase is obtained when the cooling rate is slow (1.5?K/min). The disordered phase is also obtained by rapid cooling after annealing at 973?K for 1?h. These results unambiguously indicate that the order–disorder transformation temperature is reduced to a temperature at least lower than 873?K for CoPt nanoparticles smaller than 3?nm in diameter. The slow cooling process promotes the atomic ordering, which resulted in an enhancement of magnetic coercivity as high as 2200?Oe. This study demonstrates that hard magnetic properties of the CoPt nanoparticles can be improved by controlling the cooling rate after heat treatments. 相似文献
243.
In this letter, the dislocation patterns on the common primary slip plane in a fatigued \[1-34]-\[182-7] copper bicrystal with a Sigma=19b grain boundary (GB) have been investigated using the electron channelling contrast technique in a scanning electron microscope. The results show that the two-phase dislocation structure, such as veins and persistent slip band (PSB) walls, embedded within veins, can be clearly seen on the common primary slip plane. In particular, the interactions of PSBs with the GB are clearly revealed. It is found that there are three kinds of interaction mode between the GB and the dislocations during cyclic deformation, and those are discussed. It is suggested that the dislocations carried by PSBs cannot transfer through the GB continuously even though the bicrystal has a common primary slip plane and its surface slip bands are continuous across the GB. 相似文献
244.
The specific heat and magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite have been studied. The anomalies caused by the ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions are revealed in the specific heat curve. Direct and inverse MCE are observed at the Curie and Néel points correspondingly. A value of the inverse MCE in the heating run is smaller than in the cooling regime. We attribute this effect to the competition between FM and AFM interactions. A significant advantage of PrBaMn2O6 as a magnetocaloric material is an MCE spanning a broad range of temperature with a maximum at room temperature. 相似文献
245.
Koen Put Johan Wagemans Arne Jaspers Werner F. Helsen 《Psychology of sport and exercise》2013,14(4):577-585
ObjectiveThe present study examined to what extent off-field offside decision-making training transfers to real-life offside situations.Design/methodsEighteen Belgian assistant referees were included in the experiment. Ten assistant referees (i.e., training group) were exposed to a pre- and posttest and, in between, four off-field offside training sessions via a web-based training protocol. The remaining eight assistant referees participated in the control group and only completed the pre- and posttest. During both test sessions, which were conducted separately for each group, both an on- and off-field offside decision-making test was completed.ResultsFirst, an increase in response accuracy and a decrease in flag errors were observed for the training group from pre- to posttest in both the on- and off-field offside test. Second, only the training group improved in the recall and recognition accuracy of the position of the receiving attacker at the moment of the pass.ConclusionsThis study demonstrates that perceptual-cognitive skill training results in a positive and direct transfer to on-field offside decisions. Therefore, the structure and the content of the current training intervention mimics the perceptual difficulties of real-match situations and can help the assistant referees to mediate and enhance their offside decision-making skills, both on- and off-field. 相似文献
246.
视觉环境中不变的空间布局信息能够引导观察者将注意快速指向特定的位置并促进对该位置上目标物体的识别,这种现象称为空间情境提示效应.在系统回顾以往研究的基础上,对空间情境提示效应的经典研究和实验范式,空间情境学习的性质、内容与过程,以及空间情境提示效应的产生机制和神经基础进行分析梳理.文章在最后总结了以往研究中存在的5个争议性的问题,并指出未来研究可以操纵研究材料和任务难度等关键变量来解决这些问题. 相似文献
247.
信念偏差效应是指人们已有的知识信念对逻辑推理的影响现象.对此,双加工理论认为这是由于信念偏向系统和逻辑分析系统之间的冲突所导致的.近年来,该理论得到来自认知神经科学证据的有力支持:一方面,基于功能磁共振成像(fMRI)、近红外光谱(NIRS)以及重复性经颅磁刺激(rTMS)等技术的研究从不同角度证实右侧前额皮层与信念偏差抑制有关;另一方面,基于脑电(ERP)的研究表明,晚期正成分和晚期负成分可能参与了不同推理类型下信念偏差效应的认知加工.未来的研究可以从工作记忆、不同加工阶段、推理前提本身可信度、实验分析、实验材料生态学效度以及思维训练等方面对信念偏差效应作进一步探索. 相似文献
248.
Benjamin Balas 《Visual cognition》2013,21(9-10):1138-1164
The other-race effect emerges during infancy following the perceptual narrowing of face recognition. Other-race faces that were previously discriminable in early infancy cannot be distinguished by older infants. I discuss a Bayesian model of this process that posits that the other-race effect may be a consequence of learning to distinguish between intrapersonal variation (changes to face appearance that preserve identity) and extrapersonal variation (changes that do not preserve identity) in a visual environment in which a subset of race categories dominate. I demonstrate that race categories, which I have previously argued are a critical precursor to the emergence of the other-race effect in infancy, are a natural by-product of this model. Perceptual narrowing for race may thus be a natural consequence of visual experience and the estimation of face variability based on a growing number of exemplars. I describe the basic architecture of the model, its applicability to a range of visual learning scenarios, and identify critical choices one faces in applying the model to a specific perceptual task. Despite the success of the model in accounting for these behavioural results, I conclude by identifying important shortcomings of the model and describe important challenges for future efforts to characterize the development of the other-race effect computationally. 相似文献
249.
Peter A. White 《Visual cognition》2013,21(3):340-366
Simple animations in which one object contacts another give rise to visual impressions that the former object causes the outcome for the latter, and that the former object is exerting force on the latter. How does the impression of force relate to the impression of causality? The main aim of this research was to investigate this issue using stimuli in which there is a gap between the objects at closest approach. Delay between the first object stopping and the second object starting to move had a strong effect on reported force impressions, which is consistent with findings of research on the causal impression. However, the reported force impression was little affected by either the size of the gap or the presence and features of an object in the gap, whereas the causal impression was strongly affected by both. The findings support the conclusion that the force impression and the causal impression are distinct components of the visual interpretation of the stimulus. 相似文献
250.
Perceivers remember own-race faces more accurately than other-race faces (i.e., Own-Race Bias). In the current experiments, we manipulated participants' attentional resources and social group membership to explore their influence on own and other-race face recognition memory. In Experiment 1, Chinese participants viewed own-race and Caucasian faces, and between-subjects we manipulated whether participants attention was divided during face encoding. We found that divided attention eliminated the Own-Race Bias in memory due to a reduction of memory accuracy for own-race faces, implicating that attention allocation plays a role in creating the bias. In Experiment 2, Chinese participants completed an ostensible personality test. Some participants were informed that their personality traits were most commonly found in Caucasian (i.e., other-race) individuals, resulting in these participants sharing a group membership with other-race targets. In contrast, other participants were not told anything about the personality test, resulting in the default own-race group membership. The participants encoded the faces for a subsequent recognition memory test either with or without performing a concurrent arithmetic distracting task. Results showed that other-race group membership and reducing attention during encoding independently eliminated the typical Own-Race Bias in face memory. The implications of these findings on perceptual-expertise and social-categorization models are discussed. 相似文献