全文获取类型
收费全文 | 814篇 |
免费 | 16篇 |
国内免费 | 35篇 |
专业分类
化学 | 110篇 |
力学 | 108篇 |
综合类 | 5篇 |
数学 | 39篇 |
物理学 | 85篇 |
无线电 | 518篇 |
出版年
2024年 | 1篇 |
2023年 | 25篇 |
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 21篇 |
2016年 | 13篇 |
2015年 | 35篇 |
2014年 | 46篇 |
2013年 | 45篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 31篇 |
2009年 | 41篇 |
2008年 | 55篇 |
2007年 | 44篇 |
2006年 | 42篇 |
2005年 | 42篇 |
2004年 | 34篇 |
2003年 | 33篇 |
2002年 | 26篇 |
2001年 | 32篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 18篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有865条查询结果,搜索用时 195 毫秒
121.
文章通过一些实例介绍了IT类电子产品3C工厂检查的现场指定接地电阻试验的测试要求、测试原理、测试部位和测试注意事项。 相似文献
122.
鲜飞 《电子工业专用设备》2009,38(1):8-14
表面组装技术自20世纪80年代以来以在电子工业中得到了广泛应用和发展,从SMT生产线、SMT设备、元器件和工艺材料等几个方面浅谈SMT技术的发展趋势。 相似文献
123.
124.
Konstantina Lambrinou Wout Maurissen Paresh Limaye Bart Vandevelde Bert Verlinden Ingrid De Wolf 《Journal of Electronic Materials》2009,38(9):1881-1895
This work addresses a new mode of brittle failure that occurs in the bulk of tin-based lead-free solder joints, unlike the
typical brittle failures that occur in the interfacial intermetallics. Brittle failures in the joint bulk result from the
low-temperature ductile-to-brittle transition in the fracture behavior of β-tin. The bulk embrittlement of these joints is
discussed by referring to the results of impact tests performed on both solder joints and bulk solder specimens. The mechanism
of bulk embrittlement is largely explained based on the results of a fractography study performed on the bulk joint failures
using scanning electron microscopy. 相似文献
125.
无铅波峰焊设备的特点 总被引:1,自引:0,他引:1
相对于传统的Sn-Pb焊料,无铅焊料需要较高的焊接温度,而且润湿性差,另外免清洗助焊剂和水溶性助焊剂的固体含量低,活性温度高和活性区间窄。无铅焊料和助焊剂的特性决定了无铅波峰焊设备在结构和材料选用上有很大不同。通过对无铅波峰焊设备的各个部分的特点进行分析,为传统的旧波峰焊设备的改造提供参考。 相似文献
126.
Joule Heating Enhanced Phase Coarsening in Sn37Pb and Sn3.5Ag0.5Cu Solder Joints during Current Stressing 总被引:1,自引:0,他引:1
This paper investigated the effect of Joule heating on the phase coarsening in Sn37Pb and Sn3.5Ag0.5Cu ball grid array (BGA)
solder joints stressed at −5°C and 125°C with a 6.0 × 102 A/cm2 electric current. The phase growth under current stressing was also compared with those under aging at 125°C. It was found
that the current stressing produced a substantial Joule heating in the solder joints and conductive traces. Hence, the solder
joints underwent a considerable temperature rise by 30–35°C when stressed at −5°C and 125°C in this study. Coarsening of Pb-rich
and Ag-rich phases was confirmed to be accelerated by the current stressing as a result of enhanced diffusion at elevated
temperature and atomic stimulation due to numerous collisions between electrons and atoms. Different controlling kinetics
were suggested for the cases stressed or aged at different temperatures. 相似文献
127.
Recent Observations on Tin Pest Formation in Solder Alloys 总被引:1,自引:0,他引:1
W.J. Plumbridge 《Journal of Electronic Materials》2008,37(2):218-223
The most recent observations of the response of bulk samples of several lead-free solder alloys, exposed to temperatures below
the allotropic transition for tin for extended periods, are reported. Tin pest has been observed in Sn-0.5Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu,
and Sn-3.0Ag-0.5Cu alloys at both −18°C and −40°C. The process is slow and inconsistent, usually requiring several years,
but may eventually result in complete disintegration of the sample. No tin pest was detected in Sn-Zn-3Bi or in the traditional
Sn-37Pb solder alloy after exposure for up to 4 and 10 years, respectively. It is suggested that nucleation is affected by
local composition and that extremely small amounts of either intentional solute or impurity are influential. Growth of tin
pest is accompanied by a large volume change, and it is likely that stress relaxation ahead of the expanding grey tin front
is a controlling factor. A stronger matrix would be more resistant in this case, and at the temperatures of exposure Sn-37Pb
is stronger than either Sn-3.5Ag or Sn-0.5Cu. The absence of tin pest, to date, on actual joints is attributed to their restricted
free surface area and the greater strength associated with very small samples. 相似文献
128.
129.
Maren Gast Marc Kntges Rolf Brendel 《Progress in Photovoltaics: Research and Applications》2008,16(2):151-157
We demonstrate lead‐free laser soldering of standard industrial solar cells. The laser‐soldered contacts stay stable for more than 240 accelerated ageing cycles by humidity–freeze test and withstand peel forces in excess of 10 N/cm. Laser soldering is demonstrated while the cells are lying on the ethylene vinyl acetate (EVA) foil. This permits to connect the solar cells to the lead‐free tinned copper ribbons directly on the lamination materials. We also demonstrate soldering on the bottom side by lasering through the glass and the non‐polymerized EVA. With the aid of a pick and place robot it thus becomes possible to avoid all string handling. On‐laminate laser soldering (OLLS) technique, which permits a high level of automation and process control, induces little thermal and mechanical stress, reduces the handling and should thus be of particular advantage for assembling modules with very thin cells at a high yield. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
130.