全文获取类型
收费全文 | 261篇 |
免费 | 26篇 |
国内免费 | 17篇 |
专业分类
化学 | 35篇 |
晶体学 | 3篇 |
物理学 | 46篇 |
无线电 | 220篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 8篇 |
2013年 | 18篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 15篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1990年 | 5篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 246 毫秒
21.
22.
Dong‐Cai Zhao Geng‐Jie Xiao Ni Ren Zhan‐Ji Ma Sheng‐Hu Wu 《Surface and interface analysis : SIA》2011,43(11):1392-1396
The composites, such as CFRP and GFRP, have been widely applied in spaceflight, for their low specific gravity, low cost, and additional structural stability. However, the high resistivity of the composites severely inhibits their further applications. Therefore, Cr/Al films with low resistivity and high adhesion were deposited on composites by cathodic arc technique. The films were characterized by pull test, Dektak 8 Stylus Profilometer, SEM, XPS, XRD and Z‐82 standard four probes. Results show that the aluminum film of fcc structure is compact and uniform, with resistivity as low as bulk Al. The adhesion between Cr buffer layer and composite substrate was greatly enhanced because of the formation of the chemical bonds, such as Cr? C, Cr? O and Cr? N, at the Cr/composite interface. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
23.
We have studied the band structure and the band gap closure in phase I of solid iodine under high pressure, using the methods based on the quasiparticle theory, i.e. GW approximation. Our calculations show that the band gap in the Cmca structure, which is the structure of the phase I of solid iodine, closes around 20 GPa. This pressure is near the upper boundary of phase I. We discuss the possible metallic transition in the molecular phase of solid iodine and the possible changes of the crystal structure. 相似文献
24.
Abstract In the melts of Te, Se, S, I2 and Mg3Bi2 the nonmetal-metal transitions were found under pressure. The transitions are accompanied by a decrease of the volume. The transitions seem to terminate at high temperature by “critical regions”. For S and Se the kinetics of the transitions and the pressure influence on the solidification of the melts were investigated. The existence of the transitions of this kind gives an explanation of anomalies of melting curves of some substances. 相似文献
25.
26.
Eutectic solder balls (63Sn-37Pb) joined to Cu pads with an Au/Ni metallization have been widely used in wafer-level chip-size
package (WLCSP) technology for providing electrical and mechanical interconnections between components. However, some reliability
issues must be addressed regarding the intermetallic compounds (IMCs). The formation of a brittle IMC layer between the solder/Cu
pad interface impacts considerably upon the solder-ball shear strength. In addition, it will degrade the long-term operating
reliability of the WLCSP. This study investigates, by means of experiments, the growth of the IMC layer under isothermal aging
for the eutectic Sn-Pb solder reflowed on a Cu pad with an Au/Ni metallization. Forming the Cu pad with an Au/Ni metallization
was achieved by a simple semiconductor-manufacturing process. The effects of the intermetallic layer on solder-ball shear
strength were examined for various parameters, including the thickness of the Au layer, solder-ball size, and the diameter
of the Cu pad. Experimental results indicate that two IMC layers, Au0.5Ni0.5Sn4 and Ni3Sn4, form at the solder/Cu pad interface after aging. The Au0.5Ni0.5Sn4 intermetallic layer dominates the total thickness of the IMC layer and grows with aging time while the solder-ball shear
strength decreases after aging. The degradation of the solder-ball shear strength was found to be caused mainly by the formation
of the Au0.5Ni0.5Sn4 layer. The experimental results established that a thinner Au layer on Cu pad can effectively control the degradation of
solder-ball shear strength, and this is especially true for smaller ball sizes. 相似文献
27.
This work summarizes the interfacial reaction between lead-free solder Sn-3.5Ag and electrolessly plated Ni-P metallization
in terms of morphology and growth kinetics of the intermetallic compounds (IMC). Comparison with pure Ni metallization is
made in order to clarify the role of P in the solder reaction. During reflow, the IMCs formed with the Ni-P under-bump metallization
(UBM) exist in chunky crystal blocks and small crystal agglomerates, while the ones with the sputtered Ni UBM exhibit uniformly
scallop grains with faceted surfaces. The IMC thickness increases with reflow time following approximately a t1/3 power law for both systems. The IMC growth rate is higher with the Ni-P UBM than the Ni UBM. The thickness of the Ni3Sn4 layer increases linearly with the square root of thermal aging time, indicating that the growth of the IMCs is a diffusion-controlled
process. The activation energy for Ni3Sn4 growth in solid-state reaction is found to be 110 kJ/mol and 91 kJ/mol for the Ni-P and sputtered Ni UBMs, respectively.
Kirkendall voids are detected inside the Ni3P layer in the Sn-3.5Ag/Ni-P system. No such voids are found in the Sn-3.5Ag/Ni system. 相似文献
28.
用于半导体激光器热沉的金刚石膜/Ti/Ni/Au金属化体系的研究 总被引:2,自引:2,他引:0
提出了一种用于半导体激光器热沉的金刚石膜/ Ti/ Ni/ Au金属化体系.采用金属化前期预处理、电子束蒸镀技术和后续低温真空热处理,金属层和金刚石膜之间获得了良好的结合强度.AES分析表明Ti/ Ni/ Au金刚石膜金属化体系中,Ni层起到了良好的阻挡效果;XRD显示预处理过的金刚石膜,镀膜后经过6 73K,2 h低温真空热处理,Ti/金刚石膜界面形成Ti O和Ti C;RBS分析进一步证实该金属化体系在6 73K,1h真空加热条件下具有良好的热稳定性.采用完全相同的半导体激光器结构,金刚石膜热沉的热阻仅为氮化铝热沉的4 0 % . 相似文献
29.
BeO瓷的金属化和封接 总被引:4,自引:1,他引:3
综述了氧化铍瓷的金属化及其封接技术,指出氧化铍瓷和Al2O3瓷在金属化工艺上的差异,论文最后汇集了国内外常用烧结金属粉末法15种配方和工艺参数,以资同行专家参考. 相似文献
30.
Ni-7wt.%V is commonly used as the barrier layer material in the under-bump metallurgy in the microelectronic industry. Although
interfacial reactions between various solders with the nickel substrate have been investigated intensively, the effects of
vanadium addition upon the solder/(Ni,V) interfacial reactions have not been studied. Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial
reactions at 250°C were investigated in this study using the reaction couple technique. The vanadium contents of the (Ni,V)
substrates examined in this study are 3 wt.%, 5 wt.%, 7 wt.%, and 12 wt.% and the reaction time is 12 h. The results indicate
that when the vanadium contents in the (Ni,V) substrate are 5 wt.% and higher, the Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial
reactions are different from those in the solder/Ni couples. Besides the Ni3Sn4 phase as commonly formed in the reaction with Ni substrate, a new ternary T phase has been found, and the reaction path is
L/Ni3Sn4/T/(Ni,V). A 250°C Sn-Ni-V isothermal section is proposed based on the three constituent binary systems and limited experimental
results obtained in this study. The reaction path is illustrated with the proposed Sn-Ni-V isothermal section. No stable ternary
Sn-Ni-V phase is found from the phase equilibria study, and the new T phase is likely a metastable phase. 相似文献