全文获取类型
收费全文 | 119889篇 |
免费 | 8822篇 |
国内免费 | 4559篇 |
专业分类
电工技术 | 6301篇 |
技术理论 | 11篇 |
综合类 | 7239篇 |
化学工业 | 20196篇 |
金属工艺 | 6262篇 |
机械仪表 | 7205篇 |
建筑科学 | 9305篇 |
矿业工程 | 3286篇 |
能源动力 | 3325篇 |
轻工业 | 7297篇 |
水利工程 | 1891篇 |
石油天然气 | 6572篇 |
武器工业 | 757篇 |
无线电 | 14861篇 |
一般工业技术 | 15090篇 |
冶金工业 | 6259篇 |
原子能技术 | 1304篇 |
自动化技术 | 16109篇 |
出版年
2024年 | 472篇 |
2023年 | 1882篇 |
2022年 | 3084篇 |
2021年 | 4310篇 |
2020年 | 3320篇 |
2019年 | 2780篇 |
2018年 | 3216篇 |
2017年 | 3606篇 |
2016年 | 3163篇 |
2015年 | 4160篇 |
2014年 | 5269篇 |
2013年 | 6722篇 |
2012年 | 7093篇 |
2011年 | 7733篇 |
2010年 | 6753篇 |
2009年 | 6641篇 |
2008年 | 6666篇 |
2007年 | 6146篇 |
2006年 | 6479篇 |
2005年 | 5776篇 |
2004年 | 3969篇 |
2003年 | 3543篇 |
2002年 | 3190篇 |
2001年 | 3051篇 |
2000年 | 3053篇 |
1999年 | 3587篇 |
1998年 | 3046篇 |
1997年 | 2668篇 |
1996年 | 2387篇 |
1995年 | 2003篇 |
1994年 | 1624篇 |
1993年 | 1268篇 |
1992年 | 1007篇 |
1991年 | 769篇 |
1990年 | 625篇 |
1989年 | 517篇 |
1988年 | 404篇 |
1987年 | 301篇 |
1986年 | 212篇 |
1985年 | 182篇 |
1984年 | 112篇 |
1983年 | 81篇 |
1982年 | 87篇 |
1981年 | 61篇 |
1980年 | 48篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
Stress analysis of spontaneous Sn whisker growth 总被引:5,自引:0,他引:5
K. N. Tu Chih Chen Albert T. Wu 《Journal of Materials Science: Materials in Electronics》2007,18(1-3):269-281
Spontaneous Sn whisker growth is a surface relief phenomenon of creep, driven by a compressive stress gradient. No externally
applied stress is required for the growth, and the compressive stress is generated within, from the chemical reaction between
Sn and Cu to form the intermetallic compound Cu6Sn5 at room temperature. To obtain the compressive stress gradient, a break of the protective oxide on the Sn surface is required
because the free surface of the break is stress-free. Thus, spontaneous Sn whisker growth is unique that stress relaxation
accompanies stress generation. One of the whisker challenging issues in understanding and in finding effective methods to
prevent spontaneous Sn whisker growth is to develop accelerated tests of whisker growth. Use of electromigration on short
Sn stripes can facilitate this. The stress distribution around the vicinity and the root of a whisker can be obtained by using
the micro-beam X-ray diffraction utilizing synchrotron radiation. A discussion of how to prevent spontaneous Sn whisker growth
by blocking both stress generation and stress relaxation is given. 相似文献
64.
Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles. 相似文献
65.
66.
Charalambous C.D. Bultitude R.J.C. Li X. Zhan J. 《Wireless Communications, IEEE Transactions on》2008,7(2):434-439
This paper is concerned with modeling and identification of wireless channels using noisy measurements. The models employed are governed by stochastic differential equations (SDEs) in state space form, while the identification method is based on the expectation-maximization (EM) algorithm and Kalman filtering. The algorithm is tested against real channel measurements. The results presented include state space models for the channels, estimates of inphase and quadrature components, and estimates of the corresponding Doppler power spectral densities (DPSDs), from sample noisy measurements. Based on the available measurements, it is concluded that state space models of order two are sufficient for wireless flat fading channel characterization. 相似文献
67.
镁钴铝类水滑石催化合成安息香甲醚 总被引:1,自引:0,他引:1
采用共沉淀法制备了镁钴铝类水滑石化合物(MgCoAl-HTLcs),并用 X 射线衍射、扫描电子显微镜、NH_3程序升温脱附等方法对 MgCoAl-HTLcs 进行了表征,并以 MgCoAl-HTLcs 为催化剂催化苯甲醛与甲醇反应合成安息香甲醚,研究了n(Mg):n(Co):n(Al)、催化剂用量、原料配比、反应温度、反应时间对合成反应的影响。表征结果显示,MgCoAl-HTLcs 的晶相完整,表面主要为弱酸、弱碱性。催化合成安息香甲醚的适宜条件为:MgCoAl-HTLcs 催化剂用量0.10 g(约为原料总质量的0.23%),n(Mg):n(Co):n(Al)=0.4:1.6:1.0,V(苯甲醛):V(甲醇)=3:50,反应温度50℃,反应时间150 min。在此条件下,苯甲醛的平衡转化率达77.49%,安息香甲醚选择性接近100%。为洁净合成安息香甲醚开辟了一条新的途径。 相似文献
68.
镍氢电池负极用低成本储氢合金的研究 总被引:1,自引:0,他引:1
研究了ABS型储氢合金在低Co含量条件下,随B组元替代元素Co,Al,Si等含量的变化对合金电化学性能的影响规律,同时研究了A组元中不同La/Ce比对合金电化学性能的影响情况。结果表明,随合金中Co含量的降低,合金的活化性能和放电容量得以改善,但合金的循环寿命下降也比较明显;在试验范围内,随Al元素的加入,合金的循环寿命得以改善,但材料的放电容量和活化性能均有所下降;随合金La/Ce比的降低,合金的放电容量略有下降,但其循环寿命和放电电压平台有较大提高。 相似文献
69.
Mixtures of Cr and Mo elemental powders, with the nominal compositions Cr25Mo75, Cr50Mo50, and Cr75Mo25, are processed by high-energy ball milling at ambient temperature. Milling is observed to force the mixing of the immiscible
bcc elements Cr and Mo into solid solutions. The lattice parameter of these solid solutions, measured by X-ray diffraction
(XRD), displays the expected positive deviation from Vegard’s law. These deviations are compared to the ones predicted by
Eshelby’s inclusion model for dilute alloys. The conventional Williamson-Hall approach is shown to fail to determine the grain
size in as-milled samples, probably due to the high density of dislocations. Annealing at 700 °C for 10 hours under argon
leads to a large reduction in structural defect density, without inducing any significant decomposition. The mixing measured
in Cr-Mo is discussed in the broader context of the mechanical mixing forced by ball milling in moderately immiscible systems. 相似文献
70.