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   252797篇
  免费   3178篇
  国内免费   858篇
电工技术   4806篇
综合类   193篇
化学工业   35963篇
金属工艺   9506篇
机械仪表   7551篇
建筑科学   6098篇
矿业工程   878篇
能源动力   7253篇
轻工业   21161篇
水利工程   2205篇
石油天然气   3232篇
武器工业   15篇
无线电   34302篇
一般工业技术   50027篇
冶金工业   48675篇
原子能技术   5078篇
自动化技术   19890篇
  2021年   2154篇
  2020年   1560篇
  2019年   1918篇
  2018年   3278篇
  2017年   3314篇
  2016年   3406篇
  2015年   2227篇
  2014年   3969篇
  2013年   11493篇
  2012年   6257篇
  2011年   8594篇
  2010年   6920篇
  2009年   7907篇
  2008年   8423篇
  2007年   8311篇
  2006年   7383篇
  2005年   6505篇
  2004年   6305篇
  2003年   6567篇
  2002年   6047篇
  2001年   6537篇
  2000年   5995篇
  1999年   6412篇
  1998年   16558篇
  1997年   11450篇
  1996年   8817篇
  1995年   6617篇
  1994年   5910篇
  1993年   5852篇
  1992年   4132篇
  1991年   4027篇
  1990年   3859篇
  1989年   3651篇
  1988年   3564篇
  1987年   3019篇
  1986年   2945篇
  1985年   3209篇
  1984年   2929篇
  1983年   2828篇
  1982年   2640篇
  1981年   2545篇
  1980年   2465篇
  1979年   2308篇
  1978年   2109篇
  1977年   2607篇
  1976年   3573篇
  1975年   1765篇
  1974年   1731篇
  1973年   1667篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
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   
93.
94.
The use of proteins as therapeutics has a long history and is becoming ever more common in modern medicine. While the number of protein-based drugs is growing every year, significant problems still remain with their use. Among these problems are rapid degradation and excretion from patients, thus requiring frequent dosing, which in turn increases the chances for an immunological response as well as increasing the cost of therapy. One of the main strategies to alleviate these problems is to link a polyethylene glycol (PEG) group to the protein of interest. This process, called PEGylation, has grown dramatically in recent years resulting in several approved drugs. Installing a single PEG chain at a defined site in a protein is challenging. Recently, there is has been considerable research into various methods for the site-specific PEGylation of proteins. This review seeks to summarize that work and provide background and context for how site-specific PEGylation is performed. After introducing the topic of site-specific PEGylation, recent developments using chemical methods are described. That is followed by a more extensive discussion of bioorthogonal reactions and enzymatic labeling.  相似文献   
95.
96.
97.
This paper presents results of experimental investigations on spherical and cylindrical flame propagation in pre-mixed H2/air-mixtures in unconfined and semi-confined geometries. The experiments were performed in a facility consisting of two transparent solid walls with 1 m2 area and four weak side walls made from thin plastic film. The gap size between the solid walls was varied stepwise from thin layer geometry (6 mm) to cube geometry (1 m). A wide range of H2/air-mixtures with volumetric hydrogen concentrations from 10% to 45% H2 was ignited between the transparent solid walls. The propagating flame front and its structure was observed with a large scale high speed shadow system. Results of spherical and cylindrical flame propagation up to a radius of 0.5 m were analyzed. The presented spherical burning velocity model is used to discuss the self-acceleration phenomena in unconfined and unobstructed pre-mixed H2/air flames.  相似文献   
98.
99.
100.
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