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   254641篇
  免费   3229篇
  国内免费   872篇
电工技术   4826篇
综合类   195篇
化学工业   36734篇
金属工艺   9537篇
机械仪表   7574篇
建筑科学   6238篇
矿业工程   942篇
能源动力   7264篇
轻工业   21296篇
水利工程   2256篇
石油天然气   3231篇
武器工业   15篇
无线电   34435篇
一般工业技术   50253篇
冶金工业   48706篇
原子能技术   5091篇
自动化技术   20149篇
  2021年   2188篇
  2020年   1571篇
  2019年   1930篇
  2018年   3292篇
  2017年   3329篇
  2016年   3457篇
  2015年   2267篇
  2014年   4029篇
  2013年   11557篇
  2012年   6361篇
  2011年   8684篇
  2010年   6978篇
  2009年   7964篇
  2008年   8491篇
  2007年   8382篇
  2006年   7496篇
  2005年   6554篇
  2004年   6328篇
  2003年   6596篇
  2002年   6089篇
  2001年   6542篇
  2000年   6012篇
  1999年   6426篇
  1998年   16513篇
  1997年   11438篇
  1996年   8818篇
  1995年   6630篇
  1994年   5936篇
  1993年   5878篇
  1992年   4158篇
  1991年   4053篇
  1990年   3890篇
  1989年   3676篇
  1988年   3581篇
  1987年   3038篇
  1986年   2965篇
  1985年   3234篇
  1984年   2961篇
  1983年   2851篇
  1982年   2669篇
  1981年   2576篇
  1980年   2483篇
  1979年   2337篇
  1978年   2132篇
  1977年   2631篇
  1976年   3592篇
  1975年   1793篇
  1974年   1758篇
  1973年   1686篇
  1972年   1486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