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   58190篇
  免费   7010篇
  国内免费   3928篇
电工技术   4805篇
技术理论   3篇
综合类   5157篇
化学工业   8708篇
金属工艺   3381篇
机械仪表   3771篇
建筑科学   4779篇
矿业工程   1871篇
能源动力   1749篇
轻工业   6064篇
水利工程   1416篇
石油天然气   2566篇
武器工业   713篇
无线电   6949篇
一般工业技术   5633篇
冶金工业   2035篇
原子能技术   552篇
自动化技术   8976篇
  2024年   458篇
  2023年   1451篇
  2022年   2862篇
  2021年   3636篇
  2020年   2533篇
  2019年   1964篇
  2018年   2073篇
  2017年   2205篇
  2016年   1929篇
  2015年   2909篇
  2014年   3439篇
  2013年   3692篇
  2012年   4548篇
  2011年   4665篇
  2010年   4011篇
  2009年   3880篇
  2008年   3675篇
  2007年   3354篇
  2006年   2941篇
  2005年   2399篇
  2004年   1801篇
  2003年   1654篇
  2002年   1821篇
  2001年   1499篇
  2000年   978篇
  1999年   688篇
  1998年   391篇
  1997年   335篇
  1996年   272篇
  1995年   241篇
  1994年   193篇
  1993年   152篇
  1992年   117篇
  1991年   81篇
  1990年   57篇
  1989年   39篇
  1988年   37篇
  1987年   28篇
  1986年   25篇
  1985年   11篇
  1984年   7篇
  1983年   5篇
  1982年   18篇
  1981年   10篇
  1980年   22篇
  1979年   9篇
  1978年   1篇
  1959年   2篇
  1951年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
本文提出了强扩散准则,强雪崩效应以及扩散效应的逼近优势等相关概念,给出了差分均匀性与强k阶扩散准则之间的相互关系,利用给出的设计准则改进了Rijndael密码的S盒。  相似文献   
32.
择形催化合成2,6-DMN的研究进展   总被引:2,自引:1,他引:1  
殷伟山  郭新闻  王祥生 《石油化工》2003,32(11):1007-1011
介绍了2,6-二甲基萘(2,6-DMN)的制备方法,详细论述了萘、甲基萘在分子筛催化剂上择形催化合成2,6-DMN的研究进展,提出了择形催化合成2,6-DMN的研究方向。  相似文献   
33.
憎水性栀子蓝色素制备的研究   总被引:1,自引:0,他引:1  
以浓盐酸为催化剂,采用乙酸酐酯化处理水溶性栀子蓝色素,制备了憎水性栀子蓝色素.探讨了栀子蓝色素与乙酸酐料液比、反应时间和反应温度等因素对憎水性栀子蓝色素色价的影响.结果表明:采用料液比1:20,在常温下反应4 h,为制备憎水性栀子蓝色素的最优条件.同时,通过红外光谱、可见吸收光谱及溶解性对栀子蓝色素的酯化改性进行了初步的探讨.  相似文献   
34.
基于OpenGL和MFC的石油井管道的绘制   总被引:1,自引:0,他引:1  
介绍了O penGL的知识和石油井的基本概念,利用O penGL实现石油井管道的绘制,包括石油井数据的变换和管道起始点的跟踪和角度的旋转。纹理光照效果增强图形生动性,交互操作改变图形视角。并且利用DAO数据库和L istv iew控件实现数据保存和修改。该程序能够完成石油井的管道绘制和数据保存。  相似文献   
35.
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control).  相似文献   
36.
37.
Evolving artificial neural network ensembles   总被引:3,自引:0,他引:3  
Using a coordinated group of simple solvers to tackle a complex problem is not an entirely new idea. Its root could be traced back hundreds of years ago when ancient Chinese suggested a team approach to problem solving. For a long time, engineers have used the divide-and-conquer strategy to decompose a complex problem into simpler sub-problems and then solve them by a group of solvers. However, knowing the best way to divide a complex problem into simpler ones relies heavily on the available domain knowledge. It is often a manual process by an experienced engineer. There have been few automatic divide-and-conquer methods reported in the literature. Fortunately, evolutionary computation provides some of the interesting avenues to automatic divide-and-conquer methods. An in-depth study of such methods reveals that there is a deep underlying connection between evolutionary computation and ANN ensembles. Ideas in one area can be usefully transferred into another in producing effective algorithms. For example, using speciation to create and maintain diversity had inspired the development of negative correlation learning for ANN ensembles, and an in-depth study of diversity in ensembles. This paper will review some of the recent work in evolutionary approaches to designing ANN ensembles.  相似文献   
38.
In this paper, the design of controllers that incorporate structural and multiobjective performance requirements is considered. The control structures under study cover nested, chained, hierarchical, delayed interaction and communications, and symmetric systems. Such structures are strongly related to several modern-day and future applications including integrated flight propulsion systems, platoons of vehicles, micro-electro-mechanical systems, networked control, control of networks, production lines and chemical processes. It is shown that the system classes presented have the common feature that all stabilizing controllers can be characterized by convex constraints on the Youla-Kucera parameter. Using this feature, a solution to a general optimal performance problem that incorporates time domain and frequency domain constraints is obtained. A synthesis procedure is provided which at every step yields a feasible controller together with a measure of its performance with respect to the optimal. Convergence to the optimal performance is established. An example of a multinode network congestion control problem is provided that illustrates the effectiveness of the developed methodology.  相似文献   
39.
Colour is the most widely used attribute in image retrieval and object recognition. A technique known as histogram intersection has been widely studied and is considered to be effective for color‐image indexing. The key issue of this algorithm is the selection of an appropriate color space and optimal quantization of the selected color space. The goal of this article is to measure the model performance in predicting human judgment in similarity measurement for various images, to explore the capability of the model with a wide set of color spaces, and to find the optimal quantization of the selected color spaces. Six color spaces and twelve quantization levels are involved in evaluating the performance of histogram intersection. The categorical judgment and rank order experiments were conducted to measure image similarity. The CIELAB color space was found to perform at least as good as or better than the other color spaces tested, and the ability to predict image similarity increased with the number of bins used in the histograms, for up to 512 bins (8 per channel). With more than 512 bins, further improvement was negligible for the image datasets used in this study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 265–274, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20122  相似文献   
40.
用保形样条方法求解非定常对流扩散方程   总被引:1,自引:0,他引:1  
在欧拉-拉格朗日分裂方法的基础上,本文发展了一种固定网格上的欧拉-拉格朗日分裂方法.保形样条方法(SPSM)被用来解决倒特征线插值问题.通过求解几个有精确解的例子,说明SPSM方法的解是单调无振荡的,并且数值耗散也是比较小的.  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