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81.
采用湿化学还原法在自组装的单层阵列二氧化硅纳米粒子表面沉积银膜制备了SiO2核/Ag帽复合纳米结构。通过透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)和紫外-可见分光光度计(UV/Vis)研究和表征了该复合纳米结构的表面形貌、结构及光学性质。所制备的复合纳米粒子表面粗糙,其表面呈现无数纳米级谷粒状结构,SiO2内核粒径为350nm的银纳米帽的表面等离子共振吸收的2个共振峰分别位于382和689nm处。以亚甲基蓝作为探测分子研究了SiO2粒径为350和450nm的SiO2/Ag帽状复合纳米粒子的表面增强拉曼散射(SERS)活性,增强因子分别为3.6×109和3.9×109。结果表明,湿化学还原法制备的SiO2核/Ag帽复合纳米结构是很好的拉曼活性基底。 相似文献
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Li-Jun Xie Deng-Yu Zhang Xin-Wen Wang Shi-Qing Tang Xiao-Gui Zhan Feng Gao 《International Journal of Theoretical Physics》2011,50(10):3096-3104
The entanglement dynamics of three-qubit states coupled to a general XY spin-chain with a three-site interaction environment is investigated. By using negativity as entanglement measure, we find
that the entanglement evolution depends on not only the system-environment couplings but also the strength of three-site interaction.
In the strong-coupling region, the three-site interaction can remarkably enhance the decay of the entanglement of three-qubit
states. However, in the weak-coupling region, the process of disentanglement depends on the strength of the three-site interaction. 相似文献
85.
采用自组装-化学镀法制备了以SiO2为核,Au为壳层的核壳结构纳米粒子(Au/SiO2),以生物染色剂结晶紫为探针分子,研究了Au/SiO2的表面增强拉曼散射(SERS)效应,并考察了Cl-对SERS增强效应的影响。实验表明,Cl-对SERS有明显的增强效果,这主要是由于Cl-的加入使得Au/SiO2发生团聚,产生大量"热点",从而使SERS增强效果进一步加强。以Au/SiO2(5×1010 mL-1)为活性基底,KCl(0.01 mol/L)为额外增强剂,在水溶液中实现了对结晶紫(CV)的痕量检出,最低检测浓度可达到5×10-10mol/L。 相似文献
86.
不可定向的流形曲面不仅在拓扑学中占据重要的地位,在可视化和极小曲面等问题中也有很多的应用.从拓扑学的观点来看,二流形曲面的每个局部与圆盘同胚,该性质与曲面的全局可定向性无关.但在离散化的网格表示上,可定向的二流形曲面常用半边结构来表达,而不可定向的二流形曲面大多表达成若干多边形的集合,这给以可定向网格曲面为主要研究对象的数字几何处理带来很多不便.本文提出了把不可定向的二流形网格曲面上的测地距离问题转化到可定向曲面上进行处理的一般算法框架.该框架有望在不可定向的二流形网格曲面与传统数字几何处理方法之间搭起一座桥梁.为了展示该算法框架的普适性,本文将其应用于不可定向曲面上的三个重要场合,包括测地距离的求解、离散指数映射和最远点采样. 相似文献
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In this paper we report rheo-optical and rheological observations made through a transparent slit die attached to a capillary
rheometer. We find that the flow birefringence signal oscillates periodically near the die exit when sharkskin-like extrudate
distortion is present. In contrast, steady behavior is observed in the die inland region. Specifically, the flow birefringence
varies at the die exit with a period identical to that measured directly from the sharkskin extrudate. We also show that the
exit flow instability leading to sharkskin can be observed directly through cross-polarizers in terms of the temporal change
of the retardation order. We demonstrate that the same kind of interfacial flow instability can occur at a boundary discontinuity
within the die land where the upper portion of a clean die wall meets the lower portion of a polysiloxane-coated die wall.
Finally, stress relaxation upon the cessation of the slit die flow of two polybutadiene melts is studied through time-dependent
flow birefringence measurements. The stress relaxation is then correlated with sharkskin time scales to describe the role
of relaxation in sharkskin ridge formation.
Received: 8 February 1999 Accepted: 28 July 1999 相似文献
89.
We demonstrate that the multipartite Bell-inequality violations can be fully destroyed in a finite time in three- qubit systems under decoherence induced by stochastic dephasing. It is significant that the study of tripartite systems can show fundamental characteristics which do not exist in bipartite systems. 相似文献
90.
Using a particle tracking velocimetric technique, we show direct evidence of nonlinear velocity profiles during simple-shear flow of an entangled polymer solution, offering new insight into the origins of such characteristics as stress overshoot. Upon a startup shear by imposing a constant velocity on one of the two surfaces that confine the sample, the velocity field evolves from the initial linearity across the gap to a final state with a shear rate gradient. The unexpected deviation from the widely assumed linear variation of the velocity along the gap direction is most plausibly due to the entangled polymer's ability to disentangle in the presence of high shear that can orient the polymer chains leading to anisotropy in their mutual constraint. 相似文献