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   333381篇
  免费   24093篇
  国内免费   12545篇
电工技术   17965篇
技术理论   56篇
综合类   19707篇
化学工业   56600篇
金属工艺   18578篇
机械仪表   21204篇
建筑科学   25744篇
矿业工程   10968篇
能源动力   9780篇
轻工业   18687篇
水利工程   5263篇
石油天然气   23003篇
武器工业   2612篇
无线电   36664篇
一般工业技术   39814篇
冶金工业   18385篇
原子能技术   3219篇
自动化技术   41770篇
  2024年   1293篇
  2023年   5218篇
  2022年   8896篇
  2021年   12551篇
  2020年   9835篇
  2019年   8016篇
  2018年   9213篇
  2017年   10401篇
  2016年   9292篇
  2015年   12240篇
  2014年   15891篇
  2013年   19201篇
  2012年   20197篇
  2011年   22467篇
  2010年   19226篇
  2009年   18356篇
  2008年   17992篇
  2007年   17412篇
  2006年   18296篇
  2005年   16144篇
  2004年   10354篇
  2003年   9142篇
  2002年   8155篇
  2001年   7481篇
  2000年   8007篇
  1999年   9660篇
  1998年   8158篇
  1997年   6775篇
  1996年   6364篇
  1995年   5344篇
  1994年   4380篇
  1993年   3093篇
  1992年   2493篇
  1991年   1964篇
  1990年   1506篇
  1989年   1232篇
  1988年   1019篇
  1987年   681篇
  1986年   535篇
  1985年   343篇
  1984年   243篇
  1983年   204篇
  1982年   196篇
  1981年   129篇
  1980年   130篇
  1979年   67篇
  1978年   33篇
  1977年   38篇
  1976年   55篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
In this article we report the system structure and test results of an experimental optical burst switching network with three edge router's and one core node. Wavelength-selective switches developed for this system and their characteristics are depicted. The implementation and performance of our new scheme for the just-in-time protocol are described. We also report experimental results of FTP and VOD services on this system. Some parameters, including traffic rate, average burst data length, and assembly time, are studied.  相似文献   
162.
略论中国传统合院住宅形式的固化与沿用   总被引:1,自引:1,他引:0  
王鲁民  段建强 《华中建筑》2005,23(5):128-129
合院式住宅是中国人沿用了二千多年的典型形制,除了其能满足采光、通风的要求和建造相对简化外,中国传统社会早期的中霤祭祀和以五行为基本元素的统括万物的宇宙模式对于中国式合院住宅的固化与沿用,也起了不可忽视的作用。  相似文献   
163.
This letter presents some further results on the local stability in equilibrium for Internet congestion control algorithm proposed by Low et al., (IEEE/ACM Transactions on Networking, 1999). The propagation delay d(t) is assumed to be time-varying and have maximum and minimum delay bounds (i.e., d/sub m//spl les/d(t)/spl les/d/sub M/), which is more general than the assumption (0相似文献   
164.
Generalized difference control of parallel streams temperatures   总被引:1,自引:0,他引:1  
A furnace with multiple parallel passes and multiple burners is commonly seen in petroleum refineries. In order to maintain the furnace running in a safe, stable, and high-efficiency state it is necessary to control the outlet temperatures of the multiple passes to be the same. Due to the fact that the process of the oil heating in such furnace is nonlinear, multivariable, time varying, has serious coupling among passes, has frequent dynamic changes and a large time delay, traditional control methods have trouble in controlling these temperatures, and some advanced control methods, including predictive control, adaptive control, and robust control, are usually too complex for convenient use. In this paper, a control technique, called differences control technique (DsCT), is proposed to distribute the stream flowrates such that the stream temperatures are as identical as possible. The principle of the proposed technique is explained and demonstrated, and the results of its application to a real-life petroleum refinery furnace are also reported. The DsCT technique has the following advantages: it does not need complicated design procedures, the controller structure is simple, it is easy to apply, and it can be canonically applied to furnaces with different number of passes.  相似文献   
165.
166.
介绍并分析了春光油田现代油藏经营管理模式的构建与运作及实施效果.  相似文献   
167.
168.
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry  相似文献   
169.
印染废水处理工艺研究及实例   总被引:1,自引:0,他引:1  
本文简要介绍了印染废水水质特征,提出了处理工艺,并利用两个工程实例说明了该工艺的可行性.  相似文献   
170.
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