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   566985篇
  免费   6228篇
  国内免费   1004篇
电工技术   10509篇
综合类   466篇
化学工业   90095篇
金属工艺   23335篇
机械仪表   18501篇
建筑科学   12535篇
矿业工程   4314篇
能源动力   14432篇
轻工业   45811篇
水利工程   6944篇
石油天然气   14962篇
武器工业   39篇
无线电   60300篇
一般工业技术   116256篇
冶金工业   95586篇
原子能技术   14683篇
自动化技术   45449篇
  2021年   5488篇
  2019年   5278篇
  2018年   9208篇
  2017年   9415篇
  2016年   9835篇
  2015年   6032篇
  2014年   10248篇
  2013年   26114篇
  2012年   15780篇
  2011年   21103篇
  2010年   16978篇
  2009年   18829篇
  2008年   19085篇
  2007年   18767篇
  2006年   16293篇
  2005年   14752篇
  2004年   14011篇
  2003年   13697篇
  2002年   13252篇
  2001年   12860篇
  2000年   12332篇
  1999年   12013篇
  1998年   27660篇
  1997年   20055篇
  1996年   15634篇
  1995年   12011篇
  1994年   10863篇
  1993年   10612篇
  1992年   8334篇
  1991年   8103篇
  1990年   7991篇
  1989年   7766篇
  1988年   7479篇
  1987年   6750篇
  1986年   6533篇
  1985年   7390篇
  1984年   6700篇
  1983年   6438篇
  1982年   5776篇
  1981年   5896篇
  1980年   5630篇
  1979年   5733篇
  1978年   5663篇
  1977年   6180篇
  1976年   7685篇
  1975年   5108篇
  1974年   4903篇
  1973年   4980篇
  1972年   4280篇
  1971年   4038篇
排序方式: 共有10000条查询结果,搜索用时 31 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