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21.
Lei Wang Yanpeng Qi Xianping Zhang Dongliang Wang Zhaoshun Gao Chunlei Wang Chao Yao Yanwei Ma 《Physica C: Superconductivity and its Applications》2011,471(23-24):1689-1691
A critical issue in depressing critical current density in polycrystalline iron pnictides is intrinsic weak-link behavior. Using well established, industrial scalable, deformation processes, we have achieved c-axis aligned grains in powder-in-tube Sr0.6K0.4Fe2As2 tapes. This is followed by a short high-temperature annealing to enhance the connectivity. The resultant Sr1?xKxFe2As2 superconducting tapes have transport critical current densities exceeding 5000 A/cm2 at 4.2 K in self field. This advance open up possibilities for fabricating iron-based superconducting tapes capable of carrying high currents. 相似文献
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通过制备MgB2/MgO超导复合材料,获得了典型的MgB2弱连接颗粒超导体,并测量了该样品在不同温度下的Ⅰ-Ⅴ特性曲线.在Ⅰ-Ⅴ曲线中,我们发现:当电流超过临界电流时,电压随着电流先是缓慢的增长,在电流升到一定值时,电压有一个很陡的突变.我们对这一变化进行了研究,认为这是由于MgO杂质使MgB2的晶界效应增强所引起的.该样品的临界电流和温度的关系满足:jc(T)∝(1-T/Tc)1/3,利用三维Josephson结网络系统的渗流模型进行计算发现,当颗粒超导系统处于非均匀状态时,临界电流和温度满足关系式jc(T)∝(1-T/Tc)4/3,这一结果和我们的实验符合的非常好. 相似文献
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Silver amalgamated electrodes are a good substrate to determine lead (Pb) and cadmium (Cd) in seawater because they have properties similar to mercury but without the free mercury (Hg). Here a silver amalgamated microwire (SAM) electrode is optimised for the determination of Pb and Cd in coastal waters and uncontaminated ocean waters. The SAM was vibrated during the deposition step to increase the sensitivity, and electroanalytical parameters were optimised. The Hg coating required plating from a relatively concentrated (millimolar) solution, much greater (500×) than used for instance to coat glassy carbon electrodes. However, the coating on the ex situ amalgamated electrode was found to be stable and could be used for up to a week to determine trace levels of Pb in seawater of natural pH. The limit of detection square-wave ASV (50 Hz) using the pre-plated SAM electrode was 8 pM Pb using a 1-min plating time at pH 4.5. The limit of detection in pH 2 seawater was 4 pM using a 5-min plating time, and it was 12 pM using a 10-min plating time at natural pH in the presence of air, using a square-wave frequency of 700 Hz. The vibrating SAM electrode was tested on the determination of Pb in reference seawater samples from the open Atlantic (at the 20 pM level), Pacific, and used for a study of Pb in samples collected over 24 h in Liverpool Bay (Irish Sea). 相似文献
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充分发展圆管湍流的实验研究 总被引:4,自引:0,他引:4
采用粒子数字图像测速(digital particle image velocimetry,DPIV)和定量流动显示技术(quantitative flow visualization,QFA)对充分发展的圆管湍流进行了研究。测量结果和直接数值模拟(direct numerical simulation,DNS)结果进行了比较,结果表明作者开发的DPIV技术取得了满意的精度。在此基础上对圆管湍流的动力学机理进行了研究,分析了上抛和下扫在湍流生成中的贡献以及流动显示结构内的脉动速度分布,测量结果显示在圆管湍流的近壁区存在横向强脉冲现象和流动显示所能观察到的结构为上抛占主导地位的结构。 相似文献
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Dongliang Wang Xianping Zhang Zhaoshun Gao Lei Wang Yanwei Ma Satoshi Awaji Gen Nishijima Kazuo Watanabe E. Mossang 《Physica C: Superconductivity and its Applications》2009,469(1):23-26
Correlation of phase formation, critical transition temperature Tc, microstructure, and critical current density Jc with sintering temperature has been studied for acetone doped MgB2/Fe tapes. Sintering was performed at 600–850 °C for 1 h in a flowing Ar atmosphere. High boron substitution by carbon was obtained with increasing the sintering temperature; however, the acetone doped samples synthesized at 800 °C contain large size MgB2 grains and more MgO impurities. Incomplete reaction for the acetone doped samples heated at 600 °C result in bad intergrain connectivity. At 4.2 K, the best Jc value was achieved in the acetone doped sample sintered at 700 °C, which reached 24,000 A/cm2 at 10 T and 10,000 A/cm2 at 12 T, respectively. Our results indicate that the small grain size and less impurity were also important for the improvement of Jc–B properties besides the substitutions of B by C. 相似文献
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The paper briefly reviews the progress in turbulence research in the 20th century and a number of issues are addressed based
on achievements. The modern theroy of Navier-Stokes equation provides the theoretical basis for the development of turbulence
research. The significance and bottle neck of DNS and the physical experiment in exploring turbulent flows are analyzed. The
active manipulation of turbulence is directly guided by the knowledge of large-scale coherent structures. The existing problems
in the large-eddy simulation are also pointed out. Scalar turbulence, which behaves quite different from fluid turbulence
in many aspects, has drawn much attention in recent years. Besides the analysis of the difficulties in turbulence research,
a number of examples are also presented to show how to use modern theory, computer and high technology to explore the nature
of turbulence.
The project supported by the National Natural Science Foundation of China (NSFC) (19572041 and 19732005) 相似文献