全文获取类型
收费全文 | 43418篇 |
免费 | 4859篇 |
国内免费 | 2599篇 |
专业分类
电工技术 | 3769篇 |
综合类 | 2965篇 |
化学工业 | 11488篇 |
金属工艺 | 3813篇 |
机械仪表 | 1969篇 |
建筑科学 | 3961篇 |
矿业工程 | 652篇 |
能源动力 | 4009篇 |
轻工业 | 2087篇 |
水利工程 | 516篇 |
石油天然气 | 1670篇 |
武器工业 | 732篇 |
无线电 | 3491篇 |
一般工业技术 | 6511篇 |
冶金工业 | 1692篇 |
原子能技术 | 728篇 |
自动化技术 | 823篇 |
出版年
2024年 | 259篇 |
2023年 | 864篇 |
2022年 | 1281篇 |
2021年 | 1642篇 |
2020年 | 1799篇 |
2019年 | 1598篇 |
2018年 | 1477篇 |
2017年 | 1792篇 |
2016年 | 1768篇 |
2015年 | 1803篇 |
2014年 | 2543篇 |
2013年 | 2942篇 |
2012年 | 2959篇 |
2011年 | 3041篇 |
2010年 | 2266篇 |
2009年 | 2392篇 |
2008年 | 2055篇 |
2007年 | 2649篇 |
2006年 | 2566篇 |
2005年 | 1981篇 |
2004年 | 1730篇 |
2003年 | 1383篇 |
2002年 | 1281篇 |
2001年 | 1109篇 |
2000年 | 968篇 |
1999年 | 759篇 |
1998年 | 657篇 |
1997年 | 601篇 |
1996年 | 481篇 |
1995年 | 372篇 |
1994年 | 287篇 |
1993年 | 248篇 |
1992年 | 241篇 |
1991年 | 218篇 |
1990年 | 181篇 |
1989年 | 151篇 |
1988年 | 113篇 |
1987年 | 65篇 |
1986年 | 63篇 |
1985年 | 65篇 |
1984年 | 60篇 |
1983年 | 44篇 |
1982年 | 45篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1959年 | 7篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius‐type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius‐type models. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
23.
本文对激光结晶a-Si∶H SOI结构砷注入和快速退火行为作了研究.a-Si∶H激光结晶有Lp-LCR,OD,FCR-2,FCR-1四个结晶区.用剖面电镜观察了结晶区的结构.扩展电阻测量表明Lp-LCR区中有两种扩散机制,即杂质在晶粒体内扩散和沿缺陷扩散.OD区中有三种扩散形式,除有上述两种以外,还有沿缺陷的扩散.首次比较了沿晶界和缺陷的扩散速度. 相似文献
24.
U. Amato G. Amodeo V. Brandi V. Cuomo D. Ruggi C. Serio V. Silvestrini G. C. Tosato 《国际能源研究杂志》1985,9(1):33-51
In Italy solar thermal energy and energy from biogas are two possible means of reducing dependence on energy imports. Using a multiperiod LP model (MARKAL) the authors assessed the likely potential of both technologies under various circumstances. The study covered the period 1980–2005, in five segments of five years. It focused only on the subsystem of the energy end-uses which can be substituted for by solar thermal and biogas technologies. The overall non-renewable sources which can be saved in 20 years by these technologies total 450 PJ (1 PJ = 101 5 J) if the fuel prices rise at 0 per cent average annual, 1450 PJ if the fuel prices rise at 4.2 per cent average annual, 1860 PJ if the fuel prices rise at 7.2 per cent average annual and 3780 PJ if the fuel prices rise at 15 per cent average annual. However the most competitive technologies appear to be solar water heaters used mainly in the private and commercial sectors and biogas systems used mainly in the agricultural sector. The study was carried out by APRE under ENEA (formerly CNEN) contract and was intended to serve as an analytical basis for establishing an overall development and demonstration strategy for end-use renewable technologies in Italy. 相似文献
25.
I. N. Ishchuk 《Measurement Techniques》2007,50(10):1081-1086
A three-dimensional solution of the direct problem of heat conduction when a linear pulsed heat source acts in the plane of
contact of two semibounded bodies is presented. The solution is obtained by the method of finite differences. An example of
the modeling is considered.
__________
Translated from Izmeritel’naya Tekhnika, No. 10, pp. 42–45, October, 2007. 相似文献
26.
基于高抗热震性能的陶瓷刀具材料的微观结构设计 总被引:1,自引:0,他引:1
本文以现有的抗热震断裂和抗热震损伤的评价理论为基础,通过对材料中微裂纹的长度进行预测,从而实现了对陶瓷刀具材料的抗热震性能的微观结构设计。根据此理论对现有材料的抗热震性能的进行预测,预测结果与实际的测量结果相符,验证了该理论的正确性。 相似文献
27.
28.
A. J. Slifka T. Hall E. S. Boltz 《Journal of research of the National Institute of Standards and Technology》2003,108(2):151-156
A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips. 相似文献
29.
采用先加入絮凝剂脱灰,再经减压蒸馏切割420~500℃馏分的方法,将辽河催化裂化澄清油预处理,考察了澄清油、加入絮凝剂脱灰后的澄清油以及脱灰后再减压蒸馏所得的中间馏分这3种原料在热转化过程中中间相的转化历程,并采用偏光显微镜观察热转化产物。结果表明,澄清油预处理效果明显,所得中间馏分具有较低的H/C原子比(nH/nC)和适宜的组成分布,是生产针状焦的理想原料。热转化产物的光学组织结构属于各向异性发达的广域-流线型结构。 相似文献
30.
This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from 13C MAS‐NMR and 29Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献