全文获取类型
收费全文 | 3085篇 |
免费 | 304篇 |
国内免费 | 809篇 |
出版年
2024年 | 10篇 |
2023年 | 33篇 |
2022年 | 57篇 |
2021年 | 101篇 |
2020年 | 121篇 |
2019年 | 91篇 |
2018年 | 122篇 |
2017年 | 145篇 |
2016年 | 104篇 |
2015年 | 103篇 |
2014年 | 90篇 |
2013年 | 275篇 |
2012年 | 201篇 |
2011年 | 259篇 |
2010年 | 226篇 |
2009年 | 233篇 |
2008年 | 242篇 |
2007年 | 344篇 |
2006年 | 319篇 |
2005年 | 276篇 |
2004年 | 175篇 |
2003年 | 127篇 |
2002年 | 83篇 |
2001年 | 62篇 |
2000年 | 48篇 |
1999年 | 65篇 |
1998年 | 39篇 |
1997年 | 36篇 |
1996年 | 28篇 |
1995年 | 31篇 |
1994年 | 19篇 |
1993年 | 22篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
排序方式: 共有4198条查询结果,搜索用时 15 毫秒
251.
One-dimensional silicon nanowires have been grown by thermal evaporation and their growth orientations determined by transmission electron microscopy studies. The nanowires, which are often highly curved in morphology and heavily twinned in microstructure, are crystallographically separated into several sections, each with a characteristic crystallographic orientation along the wire axis. Straight nanowires, or straight sections in a curved nanowire, are found to have non-unique crystallographic orientations when {111} twinning occurs. 相似文献
252.
The average velocities of screw dislocations in Ni 3 Al single crystals have been directly measured as a function of resolved shear stress (RSS) and orientation in the temperature domain of the flow stress anomaly using the etch-pit technique. The velocity was found to be extremely sensitive to the RSS in all cases. In contrast with ordinary metals, the screw dislocation velocities in Ni 3 Al show anomalous behaviour; under a constant RSS, the velocities decrease dramatically with increasing temperature. Furthermore, the velocities and the tension-compression asymmetry of the velocities depend on the orientation of applied stress. 相似文献
253.
The aggregation behavior of Au atoms and atomic islands on silicone oil surfaces has been systematically investigated by analyzing the evolution of surface coverage. The apparent Au surface coverage increases linearly with the nominal film thickness at low thicknesses and the rate of increase is almost independent of deposition flux. However, as the deposition flux increases, the surface coverage goes up linearly. Further analysis reveals that the deposition flux strongly affects the system free-energy of the island-oil system and therefore the aggregation behavior of the Au atoms and islands. 相似文献
254.
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
255.
功能核磁共振成像技术在探讨欺骗机制和开发测谎技术中的应用是目前的研究热点,前者使用多种范式来考察假装失忆、故意错误及人际交互中的欺骗行为的认知和神经机制,而后者主要沿用传统的GKT和CQT范式检测欺骗行为。已有研究突显了前额叶和顶叶这些参与执行控制过程的脑区在欺骗中的核心作用,但基于这些脑区信号进行测谎时,得到的准确率不容乐观。未来研究应探索除执行控制过程外的欺骗的其它认知成分,尝试从"记忆痕迹"和"欺骗结果"等方面寻找测谎的新线索。并应揭示"欺骗特质"的神经基础,以启发"忠诚度"的测量方法。 相似文献
256.
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
257.
Huaiyu Zhang Delishia M. Pittman Nicole L. Fischer Tomina J. Schwenke Erika R. Carr 《Journal of aggression, maltreatment & trauma》2013,22(5):501-519
Childhood maltreatment places individuals, including African American women who are undereducated and economically disadvantaged, at risk for developing posttraumatic stress disorder (PTSD) symptoms. Participants were 192 African American women with a history in the prior year of both a suicide attempt and intimate partner violence (IPV) exposure. They were recruited from a public hospital that provides medical and mental health treatment to mostly low-income patients. A simple mediator model was used to examine if (a) existential well-being (sense of purpose) or religious well-being (relationship with God) mediated the link between childhood maltreatment and adult PTSD symptoms. Sequential multiple mediator models determined if physical and nonphysical IPV enhanced our understanding of the mediational association among the aforementioned variables. Findings suggest that existential well-being mediated the association between childhood maltreatment and adult PTSD symptoms in a simple mediator model, and existential well-being and recent nonphysical IPV served as sequential multiple mediators of this link. However, religious well-being and physical IPV were not significant mediators. Findings underscore the importance of enhancing existential well-being in the treatment of suicidal African American women with a history of childhood maltreatment and IPV. 相似文献
258.
259.
260.
采用家庭功能与同伴行为模式问卷和学习自我调节问卷,对913名青少年进行了测试。考察青少年同伴行为模式的发展特点,以及同伴行为模式在家庭功能与青少年学习自我调节关系中的中介作用。结果表明:青少年同伴行为模式对学习支持度随年级升高而下降;随年级升高,青少年在学习自我调节各维度上及总分的平均分越来越低;青少年的同伴行为模式可以正向预测学习自我调节,并在家庭功能与学习自我调节之间起部分中介的作用。家庭功能除直接影响学习自我调节外,还通过青少年的同伴行为模式间接影响他们的学习自我调节。 相似文献