全文获取类型
收费全文 | 166篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 1篇 |
现状及发展 | 39篇 |
研究方法 | 20篇 |
综合类 | 112篇 |
自然研究 | 1篇 |
出版年
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 10篇 |
2009年 | 5篇 |
2008年 | 15篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 320 毫秒
171.
Mapping photonic entanglement into and out of a quantum memory 总被引:2,自引:0,他引:2
Developments in quantum information science rely critically on entanglement-a fundamental aspect of quantum mechanics that causes parts of a composite system to show correlations stronger than can be explained classically. In particular, scalable quantum networks require the capability to create, store and distribute entanglement among distant matter nodes by means of photonic channels. Atomic ensembles can play the role of such nodes. So far, in the photon-counting regime, heralded entanglement between atomic ensembles has been successfully demonstrated through probabilistic protocols. But an inherent drawback of this approach is the compromise between the amount of entanglement and its preparation probability, leading to intrinsically low count rates for high entanglement. Here we report a protocol where entanglement between two atomic ensembles is created by coherent mapping of an entangled state of light. By splitting a single photon and performing subsequent state transfer, we separate the generation of entanglement and its storage. After a programmable delay, the stored entanglement is mapped back into photonic modes with overall efficiency of 17%. Together with improvements in single-photon sources, our protocol will allow 'on-demand' entanglement of atomic ensembles, a powerful resource for quantum information science. 相似文献
172.
Calcium signalling in astrocytes couples changes in neural activity to alterations in cerebral blood flow by eliciting vasoconstriction or vasodilation of arterioles. However, the mechanism for how these opposite astrocyte influences provide appropriate changes in vessel tone within an environment that has dynamic metabolic requirements remains unclear. Here we show that the ability of astrocytes to induce vasodilations over vasoconstrictions relies on the metabolic state of the rat brain tissue. When oxygen availability is lowered and astrocyte calcium concentration is elevated, astrocyte glycolysis and lactate release are maximized. External lactate attenuates transporter-mediated uptake from the extracellular space of prostaglandin E(2), leading to accumulation and subsequent vasodilation. In conditions of low oxygen concentration extracellular adenosine also increases, which blocks astrocyte-mediated constriction, facilitating dilation. These data reveal the role of metabolic substrates in regulating brain blood flow and provide a mechanism for differential astrocyte control over cerebrovascular diameter during different states of brain activation. 相似文献
173.
Numerical simulations were used to optimize the casting design and conditions for large cast iron castings for marine engines, Simulations of the mold filling and solidification sequences were used to analyze the problems of previous casting conditions with marked improvements for large cylinder liner parts, The amount and positions of chills were optimized to improve the mechanical properties and to minimize the shrinkage and micro porosity in the castings. Ultra sonic testing, penetration testing, and mechanical property testing show no defects in the castings with the productivity significantly increased. 相似文献