全文获取类型
收费全文 | 68923篇 |
免费 | 5912篇 |
国内免费 | 5657篇 |
专业分类
电工技术 | 2020篇 |
综合类 | 3456篇 |
化学工业 | 10571篇 |
金属工艺 | 28360篇 |
机械仪表 | 3367篇 |
建筑科学 | 1525篇 |
矿业工程 | 1395篇 |
能源动力 | 1251篇 |
轻工业 | 1355篇 |
水利工程 | 78篇 |
石油天然气 | 1063篇 |
武器工业 | 896篇 |
无线电 | 2786篇 |
一般工业技术 | 11842篇 |
冶金工业 | 7452篇 |
原子能技术 | 651篇 |
自动化技术 | 2424篇 |
出版年
2024年 | 335篇 |
2023年 | 1138篇 |
2022年 | 2092篇 |
2021年 | 2330篇 |
2020年 | 2350篇 |
2019年 | 1824篇 |
2018年 | 1817篇 |
2017年 | 2304篇 |
2016年 | 2210篇 |
2015年 | 2315篇 |
2014年 | 3342篇 |
2013年 | 3629篇 |
2012年 | 4140篇 |
2011年 | 5190篇 |
2010年 | 3816篇 |
2009年 | 4187篇 |
2008年 | 3495篇 |
2007年 | 4744篇 |
2006年 | 4789篇 |
2005年 | 3778篇 |
2004年 | 3262篇 |
2003年 | 2853篇 |
2002年 | 2338篇 |
2001年 | 2071篇 |
2000年 | 1712篇 |
1999年 | 1430篇 |
1998年 | 1070篇 |
1997年 | 987篇 |
1996年 | 943篇 |
1995年 | 676篇 |
1994年 | 609篇 |
1993年 | 475篇 |
1992年 | 437篇 |
1991年 | 339篇 |
1990年 | 297篇 |
1989年 | 262篇 |
1988年 | 146篇 |
1987年 | 82篇 |
1986年 | 75篇 |
1985年 | 67篇 |
1984年 | 67篇 |
1983年 | 49篇 |
1982年 | 62篇 |
1981年 | 55篇 |
1980年 | 42篇 |
1978年 | 44篇 |
1977年 | 39篇 |
1976年 | 48篇 |
1975年 | 54篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
John Bensted 《Cement and Concrete Composites》2003,25(8):873-877
Two main formation routes for thaumasite exist below 15 °C. One is the direct route from C–S–H reacting with appropriate carbonate, sulfate, Ca2+ ions and excess water. The other route is the woodfordite route from ettringite reacting with C–S–H, carbonate, Ca2+ ions and excess water, in which thaumasite arises through the intermediate formation of the solid solution woodfordite. The woodfordite route for thaumasite formation appears to be relatively quicker (although still slow) than the direct route, presumably because with the former the ettringite already has the octahedral [M(OH)6] units that can facilitate the critical change from [Al(OH)6]3− to [Si(OH)6]2− groupings. Both routes are mutually dependent on each other. The presence of magnesium salts can modify the path to thaumasite formation. High pressure might be able to stabilise [Si(OH)6]2− groupings and allow thaumasite to become formed above 15 °C. This possibility is discussed. 相似文献
2.
应用静态吸附、动态吸附、程序升温脱附和程序升温还原等实验方法,考察了噻吩在Ni基非晶态合金上的吸附和脱附行为。常温下,噻吩分子首先吸附在清洁的Ni表面,并立刻被活化,发生氢解反应,C-S键断裂,释放出烃类部分,S留在Ni原子上。噻吩可以在Ni基非晶态合金表面发生强度不同的化学吸附。弱化学吸附的噻吩可以脱附;强化学吸附的噻吩不会脱附,而在高温下发生氢解反应。 相似文献
3.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
4.
5.
This article presents a method that can be applied to molten AA-6101 alloy to improve electrical properties of the aluminium part of the optical ground wire (OPGW) used in overhead transmission lines to protect phase conductors from lightning strike and to transmit signals and data. AA-6101 alloy in casting of the log as 6 m length and 178 mm diameter for extrusion has been inoculated by AlB2 to decrease detrimental effects of Cr, Ti, V, and Zr on the conductivity of the material. After inoculation, improved billets were extruded as 9.5 mm diameter feedstock. Required wires drawn from the feedstock according to the construction types of OPGW to be tested were exposed to aging at 175°C, 6 h (T-8). Upon completion of the back-twist and performing-type stranding process, resistance, and short-circuit current capacity and breaking load of the OPGW 88/44 constructions with other metal combinations have been examined and tested to show improvement. Results are summarized in tables and graphically. 相似文献
6.
Al-10Mg型固溶合金自然时效稳定性研究 总被引:3,自引:0,他引:3
测定了ZL30 5合金自然时效 33年的力学性能变化 ,观察了晶界的析出相 ,研究了组织和性能的关系 ,从而确定了ZL30 5合金具有长期自然时效稳定性。 相似文献
7.
Effect of Stoichiometry on Properties of Rare-Earth-Based Hydrogen Storage Alloy for Nickel-Metal Hydride Secondary Battery 总被引:2,自引:0,他引:2
Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys. 相似文献
8.
机械合金化Fe-Ni粉末的相结构 总被引:1,自引:0,他引:1
使用XRD和Moessbauer等方法,研究了在Ar气氛下机械合金化Fe—Ni粉末相结构的变化.结果表明,在机械合金化Fe64-Ni36粉末过程中,fcc相的数量随着球磨时间的增加先增加然后减少,与加乙醇球磨Fe64-Ni36的情形相同.当Ni的含量(原子分数)大于50%时,有fcc相、顺磁相和FeNi3形成,当Ni的含量低于50%时,bcc相的数量随着Ni含量减少而增加.Moessbauer谱的结果表明,因球磨时间或Fe、Ni比例的不同,Fe—Ni球磨粉末固溶体具有不同结构的原子配比。 相似文献
9.
10.
Examination of the wreckage of a light aircraft revealed that approximately 20 cm was missing from one tip of the aluminum
alloy propeller. Fractographic and metallographic examination of the remaining portion of the propeller revealed extensive
grain-boundary separation in the vicinity of the fracture, and grain edges and corners rounded by corrosion on the fracture
surface. Energy dispersive X-ray analysis (EDXA) revealed fluorine on, and in the vicinity of, the fracture surface. In the
ensuing litigation, it was asserted that the crash occurred because the propeller fractured in flight as the result of intergranular
attack caused by the use of a fluorine-bearing cleaner. 相似文献