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   328263篇
  免费   5678篇
  国内免费   961篇
电工技术   5563篇
综合类   414篇
化学工业   53743篇
金属工艺   12876篇
机械仪表   9433篇
建筑科学   8130篇
矿业工程   1979篇
能源动力   7832篇
轻工业   32478篇
水利工程   3499篇
石油天然气   7314篇
武器工业   28篇
无线电   33464篇
一般工业技术   63486篇
冶金工业   59779篇
原子能技术   7783篇
自动化技术   27101篇
  2021年   3235篇
  2019年   2776篇
  2018年   4900篇
  2017年   4726篇
  2016年   5168篇
  2015年   3606篇
  2014年   5665篇
  2013年   14623篇
  2012年   8956篇
  2011年   11656篇
  2010年   9459篇
  2009年   10551篇
  2008年   10812篇
  2007年   10517篇
  2006年   9175篇
  2005年   8417篇
  2004年   7759篇
  2003年   7384篇
  2002年   7389篇
  2001年   7070篇
  2000年   6711篇
  1999年   6883篇
  1998年   17478篇
  1997年   12736篇
  1996年   9767篇
  1995年   7251篇
  1994年   6527篇
  1993年   6377篇
  1992年   4692篇
  1991年   4656篇
  1990年   4449篇
  1989年   4502篇
  1988年   4422篇
  1987年   3770篇
  1986年   3761篇
  1985年   4395篇
  1984年   4155篇
  1983年   3785篇
  1982年   3560篇
  1981年   3737篇
  1980年   3596篇
  1979年   3485篇
  1978年   3546篇
  1977年   4173篇
  1976年   5548篇
  1975年   3241篇
  1974年   3078篇
  1973年   3127篇
  1972年   2687篇
  1971年   2512篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
141.
Alkyd resins are generally used in the production of printing inks. All industries look for alternative raw materials in the production of ink with the growing inclination toward using natural products. Resins forming the vehicle of the ink to be obtained from natural resources will provide benefits for the environment, nature, and living creatures. The aim of the study was to promote the use of natural resin in the ink system. Natural Pinus pinaster resin was added into vegetable and mineral oil-based solvents in pure form with alkyd resin in different amounts and ink varnishes of different combinations were prepared. Then, printing inks were produced from these varnishes in pure and hybrid form. Following the assessment of the rheological properties of the inks prepared, printing tests were conducted to assess the printing quality parameters. Ideal mixing ratios of the natural resins in the ink were determined for printability. The environmental importance and advantages of the use of natural resins were discussed. Recommendations were given in line with the results to encourage widespread use of natural resins in near future.  相似文献   
142.
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size.  相似文献   
143.
144.
This study presents a back-analysis of geotechnical parameters on prefabricated vertical drain improved ground at a site in the Mekong Delta. Various time?settlement behaviors that reflected different clay thicknesses and loading patterns were observed. The total surface settlement behavior at several monitoring locations was simulated using an updated exponential method that considered staged construction. The analyzed results were validated by substituting the values into a theoretical solution for radial consolidation. The estimated theoretical behaviors were comparable with the monitored behaviors. The geotechnical parameters were back-analyzed by applying the previously analyzed results to various theoretical and empirical formulas. However, the use of extensometer data that were installed at large intervals produced different values of the geotechnical properties. Furthermore, finite element analysis supported the back-analyzed total settlement behaviors and nearly disregarded the application of the geotechnical properties that were obtained using either surface or subsurface settlement data. However, settlements and excess pore pressures in the sublayers were not successfully predicted even when the geotechnical properties were adjusted. Thus, subsurface instruments that can be installed closely in thick clay deposits are required to reliably reevaluate the variations in geotechnical properties along a certain depth.  相似文献   
145.
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers  相似文献   
146.
Technical Physics Letters - The C–V characteristics of Au/Al2O3/In0.52Al0.48As and Au/SiO2/In0.52Al0.48As metal–insulator–semiconductor structures have been studied. It has been...  相似文献   
147.
148.
149.
150.
Water Resources Management - A number of models have been developed to simulate seawater intrusion in coastal aquifers, which differ in the accuracy level and computational demands, based on the...  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