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   473613篇
  免费   7433篇
  国内免费   2613篇
电工技术   9032篇
技术理论   5篇
综合类   1345篇
化学工业   73060篇
金属工艺   17754篇
机械仪表   13796篇
建筑科学   12418篇
矿业工程   2162篇
能源动力   11838篇
轻工业   48579篇
水利工程   4636篇
石油天然气   7680篇
武器工业   248篇
无线电   55649篇
一般工业技术   87296篇
冶金工业   88472篇
原子能技术   8282篇
自动化技术   41407篇
  2021年   3918篇
  2020年   2812篇
  2019年   3468篇
  2018年   5465篇
  2017年   5445篇
  2016年   6026篇
  2015年   4614篇
  2014年   7517篇
  2013年   21523篇
  2012年   13112篇
  2011年   18104篇
  2010年   14239篇
  2009年   15663篇
  2008年   16801篇
  2007年   16922篇
  2006年   15258篇
  2005年   13542篇
  2004年   12574篇
  2003年   12150篇
  2002年   11721篇
  2001年   12088篇
  2000年   11135篇
  1999年   11594篇
  1998年   26933篇
  1997年   19313篇
  1996年   14717篇
  1995年   11141篇
  1994年   10037篇
  1993年   9774篇
  1992年   7279篇
  1991年   6913篇
  1990年   6858篇
  1989年   6587篇
  1988年   6328篇
  1987年   5261篇
  1986年   5185篇
  1985年   6118篇
  1984年   5732篇
  1983年   5284篇
  1982年   4728篇
  1981年   4980篇
  1980年   4561篇
  1979年   4637篇
  1978年   4387篇
  1977年   4783篇
  1976年   6170篇
  1975年   3828篇
  1974年   3602篇
  1973年   3677篇
  1972年   3021篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Uses a Markov process to model a real-time expert system architecture characterized by message passing and event-driven scheduling. The model is applied to the performance evaluation of rule grouping for real-time expert systems running on this architecture. An optimizing algorithm based on Kernighan-Lin heuristic graph partitioning for the real-time architecture is developed and a demonstration system based on the model and algorithm has been developed and tested on a portion of the advanced GPS receiver (AGR) and manned manoeuvring unit (MMU) knowledge bases  相似文献   
62.
63.
64.
65.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  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.
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   
69.
70.
This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.  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