首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1691篇
  免费   146篇
  国内免费   18篇
电工技术   46篇
综合类   8篇
化学工业   440篇
金属工艺   74篇
机械仪表   65篇
建筑科学   86篇
矿业工程   4篇
能源动力   128篇
轻工业   131篇
水利工程   27篇
石油天然气   26篇
无线电   181篇
一般工业技术   254篇
冶金工业   73篇
原子能技术   16篇
自动化技术   296篇
  2024年   8篇
  2023年   37篇
  2022年   56篇
  2021年   101篇
  2020年   84篇
  2019年   106篇
  2018年   153篇
  2017年   138篇
  2016年   158篇
  2015年   88篇
  2014年   114篇
  2013年   189篇
  2012年   126篇
  2011年   90篇
  2010年   86篇
  2009年   59篇
  2008年   45篇
  2007年   34篇
  2006年   19篇
  2005年   9篇
  2004年   11篇
  2003年   13篇
  2002年   14篇
  2001年   11篇
  2000年   8篇
  1999年   5篇
  1998年   13篇
  1997年   3篇
  1996年   5篇
  1995年   12篇
  1994年   5篇
  1993年   4篇
  1992年   6篇
  1991年   5篇
  1990年   4篇
  1989年   6篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1985年   3篇
  1984年   1篇
  1983年   3篇
  1982年   5篇
  1979年   3篇
  1975年   1篇
  1973年   2篇
  1970年   2篇
  1969年   1篇
排序方式: 共有1855条查询结果,搜索用时 15 毫秒
51.
52.
Commercial casting Al-Si (A356)-based composites reinforced with different volume fractions of alumina (Al2O3) nanoparticulates (average particle size 50 nm) were synthesized in this study. Particle distribution, hardness, and tensile properties in the as-cast condition were experimentally investigated. The A356 alloy composite showed an increase in hardness, elastic modulus, and tensile strength compared with monolithic alloys. Finally, a combination of an artificial neural network and the finite element method (FEM) was implemented to predict the microstructure and mechanical properties including grain size, length of silicon rods, amount of porosity, hardness, tensile yield stress, ultimate tensile stress, and elongation percentage.  相似文献   
53.
Aluminum is the best metal for producing metal matrix composites which are known as one of the most useful and high-tech composites in our world. Combining aluminum and nano Al2O3 particles will yield a material with high mechanical properties. Characterization of tribological properties revealed that the presence of nano particles significantly increased wear resistance of the composite. In case of unreinforced Al alloy, the depth of penetration is governed by the hardness of the specimen surface and applied load. But, in case of Al matrix composite, the depth of penetration of the harder asperities of hardened steel disk is primarily governed by the protruded hard ceramic reinforcement. The hard Al2O3 particles act as a protrusion over the matrix, carries a major portion of the applied load and protect the abrasives from penetration into the specimen surface.  相似文献   
54.
The aim of this study was to analyse input–output energy and economical assessment of almond production in three age groups of orchards (group I 6–10, group II 11–15 and group III 16–20 years old) in Chahrmahal-Va-Bakhtiari province, Iran. Data for almond production were collected by administering questionnaire in face-to-face interviews from the orchards selected based on random sampling method during a 3-year period. The results showed that 57,027.13, 60,341.14 and 61,640.43 MJ ha?1 energy was consumed by group I, group II and group III, respectively. The most energy input was consumed by electricity, followed by chemical fertilizer. Energy indices were calculated, and the results revealed that energy efficiency was 0.62, 1.12 and 0.81 in the triple groups of orchards, respectively. Economical assessment showed that total production cost of almond in group I, II and III was $4547.54, $5799.26 and $5687.05 ha?1, respectively. In all orchard groups, the shares of variable and fixed production costs found to be same nearly. Net return for almond production was $14,516.22, $30,735.19 and $21,395.57ha?1, respectively. According to the research results, it was concluded that although almond production in the study region was not an efficient process in terms of energy consumption, it was a profitable agricultural operation.  相似文献   
55.
56.
57.
CuInS2/CuS nanocomposite were synthesized by a copper complex, [bis(ethylenediamine)copper(ΙΙ)] sulfate. Eight sulfur sources were used for this experiment. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis spectroscopy, and room temperature photoluminescence spectroscopy. Thin film of nanocomposite powder was fabricated and its feature (Voc, Jsc and FF) was calculated by current–voltage (I–V) curve.  相似文献   
58.
An efficient approach was introduced for improving the condition of major controlled rolling process parameters of roughing, finishing and coiling temperatures and optimizing these parameters to obtain minimum grain size and maximum dome height simultaneously. Taguchi method combined with grey relational analysis was applied to achieve optimum grain size and dome height during controlled rolling process. For this purpose, four levels for the above temperatures were chosen and sixteen experiments were conducted based on orthogonal array of Taguchi method. Based on Taguchi approach, signal-to-noise (S/N) ratios were calculated and used in order to obtain the optimum levels for every input parameter. Analysis of variance revealed that finishing and coiling temperatures have the maximum effect on the grain size and dome height of microalloyed steels. The confirmation tests with the optimal levels of parameters indicated that the grain size and dome height of controlled rolled microalloyed steels can be improved effectively through this approach.  相似文献   
59.
Pyrolysis, so-called devolatilization, is one of the first steps of all thermochemical processes occurring in an inert atmosphere. The authors discuss the main kinetic features of heavy oil pyrolysis, on the basis of the data derived m from a TGA analysis and by using a kinetic model. The samples were heated over a range of temperature from 400 K to 430°C at various heating rates between 10 and 80°C/min. Experimental results showed that the effect of time is considerable in the case of tar conversion, compared to char and gases.  相似文献   
60.
Clean Technologies and Environmental Policy - This paper presents a methodological approach for intelligent control of fuel cell vehicles based on traffic condition recognition. For this purpose,...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号