全文获取类型
收费全文 | 138687篇 |
免费 | 10784篇 |
国内免费 | 5490篇 |
专业分类
电工技术 | 7570篇 |
技术理论 | 11篇 |
综合类 | 8508篇 |
化学工业 | 22989篇 |
金属工艺 | 7280篇 |
机械仪表 | 8457篇 |
建筑科学 | 10798篇 |
矿业工程 | 3992篇 |
能源动力 | 3943篇 |
轻工业 | 8723篇 |
水利工程 | 2279篇 |
石油天然气 | 7657篇 |
武器工业 | 943篇 |
无线电 | 17072篇 |
一般工业技术 | 17425篇 |
冶金工业 | 7052篇 |
原子能技术 | 1590篇 |
自动化技术 | 18672篇 |
出版年
2024年 | 582篇 |
2023年 | 2332篇 |
2022年 | 3969篇 |
2021年 | 5531篇 |
2020年 | 4247篇 |
2019年 | 3555篇 |
2018年 | 3991篇 |
2017年 | 4441篇 |
2016年 | 3929篇 |
2015年 | 5281篇 |
2014年 | 6521篇 |
2013年 | 8121篇 |
2012年 | 8517篇 |
2011年 | 9090篇 |
2010年 | 7886篇 |
2009年 | 7729篇 |
2008年 | 7672篇 |
2007年 | 7134篇 |
2006年 | 7329篇 |
2005年 | 6500篇 |
2004年 | 4468篇 |
2003年 | 3770篇 |
2002年 | 3390篇 |
2001年 | 3182篇 |
2000年 | 3287篇 |
1999年 | 3827篇 |
1998年 | 3269篇 |
1997年 | 2831篇 |
1996年 | 2552篇 |
1995年 | 2134篇 |
1994年 | 1714篇 |
1993年 | 1324篇 |
1992年 | 1051篇 |
1991年 | 809篇 |
1990年 | 657篇 |
1989年 | 545篇 |
1988年 | 421篇 |
1987年 | 323篇 |
1986年 | 232篇 |
1985年 | 183篇 |
1984年 | 116篇 |
1983年 | 87篇 |
1982年 | 94篇 |
1981年 | 67篇 |
1980年 | 53篇 |
1979年 | 33篇 |
1978年 | 26篇 |
1977年 | 26篇 |
1976年 | 42篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
Meng Wai Woo 《Drying Technology》2008,26(1):15-26
Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem. 相似文献
66.
67.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
68.
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
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.