全文获取类型
收费全文 | 51548篇 |
免费 | 6568篇 |
国内免费 | 2675篇 |
专业分类
电工技术 | 2219篇 |
技术理论 | 10篇 |
综合类 | 3158篇 |
化学工业 | 16612篇 |
金属工艺 | 3548篇 |
机械仪表 | 1619篇 |
建筑科学 | 3366篇 |
矿业工程 | 1773篇 |
能源动力 | 3952篇 |
轻工业 | 2521篇 |
水利工程 | 538篇 |
石油天然气 | 2480篇 |
武器工业 | 226篇 |
无线电 | 3346篇 |
一般工业技术 | 9874篇 |
冶金工业 | 3820篇 |
原子能技术 | 784篇 |
自动化技术 | 945篇 |
出版年
2024年 | 183篇 |
2023年 | 1150篇 |
2022年 | 1680篇 |
2021年 | 1968篇 |
2020年 | 2071篇 |
2019年 | 1934篇 |
2018年 | 1805篇 |
2017年 | 1966篇 |
2016年 | 2125篇 |
2015年 | 1996篇 |
2014年 | 3135篇 |
2013年 | 3213篇 |
2012年 | 3961篇 |
2011年 | 4292篇 |
2010年 | 3179篇 |
2009年 | 3220篇 |
2008年 | 2497篇 |
2007年 | 3024篇 |
2006年 | 2913篇 |
2005年 | 2434篇 |
2004年 | 2096篇 |
2003年 | 1819篇 |
2002年 | 1503篇 |
2001年 | 1163篇 |
2000年 | 1056篇 |
1999年 | 805篇 |
1998年 | 665篇 |
1997年 | 502篇 |
1996年 | 438篇 |
1995年 | 358篇 |
1994年 | 339篇 |
1993年 | 247篇 |
1992年 | 200篇 |
1991年 | 154篇 |
1990年 | 147篇 |
1989年 | 91篇 |
1988年 | 60篇 |
1987年 | 60篇 |
1986年 | 37篇 |
1985年 | 68篇 |
1984年 | 53篇 |
1983年 | 47篇 |
1982年 | 55篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1959年 | 7篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
101.
102.
103.
104.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
105.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
106.
One of the new physical methods that provides much information about the processes going on in a friction contact zone in real time is acoustic emission (AE). Basic experimental results of AE in friction are presented and analysed. Using AE signals we can get an indication about the state of the friction processes, about the quality of solid and liquid layers on the contacting surfaces in real time, sometimes about intensity of wear, changing of wear and friction regimes and so on. The influence of sliding velocity, load, roughness and some physical and mechanical properties of the body on the parameters of AE are also given. Some attention to the practical implementation of these techniques for control of capability for work of friction pairs in real conditions are given. Modern methods and devices enable condition monitoring of sliding and rolling bearings. 相似文献
107.
Renjith Devasia CP Reghunadhan Nair P Sivadasan KN Ninan 《Polymer International》2005,54(8):1110-1118
Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry 相似文献
108.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献
109.
110.