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   265570篇
  免费   5376篇
  国内免费   2089篇
电工技术   5981篇
技术理论   5篇
综合类   1432篇
化学工业   42630篇
金属工艺   11508篇
机械仪表   8160篇
建筑科学   6990篇
矿业工程   1842篇
能源动力   5736篇
轻工业   26117篇
水利工程   3055篇
石油天然气   6559篇
武器工业   291篇
无线电   28335篇
一般工业技术   49791篇
冶金工业   47376篇
原子能技术   5674篇
自动化技术   21553篇
  2021年   2878篇
  2020年   1920篇
  2019年   2291篇
  2018年   3607篇
  2017年   3564篇
  2016年   3893篇
  2015年   3086篇
  2014年   4930篇
  2013年   11748篇
  2012年   8088篇
  2011年   10594篇
  2010年   8507篇
  2009年   8979篇
  2008年   9792篇
  2007年   9897篇
  2006年   8697篇
  2005年   7605篇
  2004年   6809篇
  2003年   6331篇
  2002年   6326篇
  2001年   6405篇
  2000年   5978篇
  1999年   5937篇
  1998年   12889篇
  1997年   9571篇
  1996年   7308篇
  1995年   5544篇
  1994年   5097篇
  1993年   4964篇
  1992年   3950篇
  1991年   3755篇
  1990年   3823篇
  1989年   3770篇
  1988年   3530篇
  1987年   3019篇
  1986年   3052篇
  1985年   3406篇
  1984年   3320篇
  1983年   3073篇
  1982年   2698篇
  1981年   2902篇
  1980年   2642篇
  1979年   2839篇
  1978年   2736篇
  1977年   2841篇
  1976年   3693篇
  1975年   2457篇
  1974年   2290篇
  1973年   2320篇
  1972年   1981篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally.  相似文献   
32.
Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...  相似文献   
33.
At the hydroelectric unit No. 11 of the Nizhnekamsk hydroelectric power plant, the filling wedges of a rotor were investigated by ultrasound in the free st  相似文献   
34.
Russian Journal of Non-Ferrous Metals - Rolling bearing rings comprise a large reserve for expanding powder metallurgy production. This reserve is being incompletely implemented. The hot forging of...  相似文献   
35.
Metallurgical and Materials Transactions B - The process of obtaining titanium tetrachloride (TiCl4) from the quartz-leucoxene concentrate (QLC) from the Yaregskoe oil-titanium field was studied....  相似文献   
36.
37.
38.
The crystallization of capped ultrathin polymer films is closely dependent on film thickness and interfacial interaction. Using dynamic Monte Carlo simulations, the crystallization behaviors of polymer films confined between two substrates were investigated. The crystallization rate of confined polymers is reduced with high interfacial interactions. Above a critical strength of interfacial interaction, polymer crystallization in the thin film is inhibited within the simulation time scales. An increase in film thickness leads to a rise in critical interfacial interaction. In thicker films, the chains have more space to change conformation to form crystal stems. In addition, there are fewer absorbed segments in confined chains for the thicker films, and thus the chains have stronger ability to adjust their conformation. Therefore an increase in film thickness can cause a reduction in the entropic barrier required for the formation of crystals and thus an increase in the critical interfacial interaction. © 2018 Society of Chemical Industry  相似文献   
39.
Fefelov  S. A.  Kazakova  L. P.  Bogoslovskiy  N. A.  Bylev  A. B.  Yakubov  A. O. 《Semiconductors》2020,54(4):450-453
Semiconductors - The current–voltage characteristics measured on Ge2Sb2Te5 thin films in the current mode are studied. The effect of multilevel recording is established when applying...  相似文献   
40.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.  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