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   345764篇
  免费   5259篇
  国内免费   1944篇
电工技术   7687篇
技术理论   3篇
综合类   1724篇
化学工业   48880篇
金属工艺   17121篇
机械仪表   14494篇
建筑科学   9092篇
矿业工程   2537篇
能源动力   8583篇
轻工业   23791篇
水利工程   3679篇
石油天然气   6056篇
武器工业   173篇
无线电   43196篇
一般工业技术   71006篇
冶金工业   55184篇
原子能技术   6314篇
自动化技术   33447篇
  2022年   1940篇
  2021年   3129篇
  2020年   2286篇
  2019年   2557篇
  2018年   12034篇
  2017年   12690篇
  2016年   8645篇
  2015年   3622篇
  2014年   5209篇
  2013年   12970篇
  2012年   10236篇
  2011年   18140篇
  2010年   15930篇
  2009年   15720篇
  2008年   15890篇
  2007年   17755篇
  2006年   8606篇
  2005年   11068篇
  2004年   8923篇
  2003年   8749篇
  2002年   7330篇
  2001年   7146篇
  2000年   6627篇
  1999年   6994篇
  1998年   16949篇
  1997年   11811篇
  1996年   9172篇
  1995年   6923篇
  1994年   6219篇
  1993年   6089篇
  1992年   4311篇
  1991年   4157篇
  1990年   3920篇
  1989年   3714篇
  1988年   3637篇
  1987年   3059篇
  1986年   2975篇
  1985年   3228篇
  1984年   2940篇
  1983年   2834篇
  1982年   2650篇
  1981年   2552篇
  1980年   2468篇
  1979年   2316篇
  1978年   2111篇
  1977年   2609篇
  1976年   3566篇
  1975年   1769篇
  1974年   1731篇
  1973年   1668篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
121.
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   
122.
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   
123.
124.
125.
126.
Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A1, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A1- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A1-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates.  相似文献   
127.
128.
129.
Fusion behavior of poly(vinyl chloride) (PVC) compounds plays an important role in the development of physical properties of processed material. The fusion characteristics in PVC processing are governed by material variables that affect the fusion with some interactions. In this research, the aim was to characterize the effects of formulation ingredients on fusion characteristics of PVC. Four material parameters, including the contents of nanoclay (NC), azodicarbonamide, calcium stearate, and processing aid, are proposed as affecting variables. The fusion time (FT) as well as fusion factor (FF) are considered fusion indicators and are experimentally determined in some different levels of affecting parameters. The multivariable regression analysis (MRA) and the Artificial Neural Network (ANN) modeling are considered as two analytical methods. The regression analysis result for the FT denotes, in part, significant linear and quadratic effects of NC and also its significant interactions with azodicarbonamide and calcium stearate, whereas that of FF indicates only a linear effect of NC. ANN modeling is performed with a three‐layer (input, hidden, and output) neural network. The results of the comparison of the MRA and ANN predictions with experimental values are reported as the correlation coefficient (R2), mean‐square error, and mean absolute percentage error for both FF and FT parameters. The obtained values clearly denote that the ANN results are more precise and especially more general than those of MRA. However, in the case of FT, improvement of the ANN modeling is much greater than that of FF. J. VINYL ADDIT. TECHNOL., 21:147–155, 2015. © 2014 Society of Plastics Engineers  相似文献   
130.
Neural Computing and Applications - With an increase in online longitudinal users’ interactions, capturing users’ precise preferences and giving accurate recommendations have become an...  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