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   569148篇
  免费   6362篇
  国内免费   1026篇
电工技术   10548篇
综合类   478篇
化学工业   90560篇
金属工艺   23370篇
机械仪表   18547篇
建筑科学   12593篇
矿业工程   4315篇
能源动力   14550篇
轻工业   46018篇
水利工程   6954篇
石油天然气   15006篇
武器工业   40篇
无线电   60655篇
一般工业技术   116606篇
冶金工业   95782篇
原子能技术   14688篇
自动化技术   45826篇
  2021年   5527篇
  2019年   5314篇
  2018年   9257篇
  2017年   9532篇
  2016年   9882篇
  2015年   6079篇
  2014年   10338篇
  2013年   26281篇
  2012年   15889篇
  2011年   21260篇
  2010年   17104篇
  2009年   18946篇
  2008年   19180篇
  2007年   18848篇
  2006年   16371篇
  2005年   14857篇
  2004年   14113篇
  2003年   13763篇
  2002年   13308篇
  2001年   12904篇
  2000年   12379篇
  1999年   12056篇
  1998年   27719篇
  1997年   20079篇
  1996年   15666篇
  1995年   12034篇
  1994年   10894篇
  1993年   10655篇
  1992年   8367篇
  1991年   8120篇
  1990年   7998篇
  1989年   7789篇
  1988年   7494篇
  1987年   6761篇
  1986年   6546篇
  1985年   7402篇
  1984年   6710篇
  1983年   6446篇
  1982年   5780篇
  1981年   5905篇
  1980年   5640篇
  1979年   5740篇
  1978年   5669篇
  1977年   6186篇
  1976年   7692篇
  1975年   5114篇
  1974年   4908篇
  1973年   4983篇
  1972年   4281篇
  1971年   4042篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 95–112, March–April, 1994.  相似文献   
63.
64.
The process of combustion of homogeneous and heterogeneous nongasifying and slightly gasifying systems over the range of a number of parameters characterizing the reactive composition and the conditions for the arrangement of the combustion process is studied by using thermocouple and optical methods. The regions of the implementation of different combustion regimes, namely, steady, pulsating, multiple-point, and spin, are determined experimentally.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 407–411, October, 1993.  相似文献   
65.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
66.
An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model  相似文献   
67.
68.
69.
A systematic and straightforward procedure is developed for the synthesis and analysis of transformer-isolated power converters. The procedure can be used to determine the ranges of duty-ratio over which the transformer-isolated power converters of a given class can be operated without transformer saturation. The procedure can also be used to study the dependence of the power converter switch stresses on duty-ratios. This information is useful in the selection of the transformer-isolated power converter most suitable for a given application and in the design of this power converter with minimum switch stresses, high power density, and low cost  相似文献   
70.
Carboxyl-terminated butadiene-acrylonitrile-rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber-modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.  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