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   34460篇
  免费   3336篇
  国内免费   2035篇
电工技术   6266篇
综合类   2803篇
化学工业   1569篇
金属工艺   441篇
机械仪表   1878篇
建筑科学   1444篇
矿业工程   836篇
能源动力   1258篇
轻工业   385篇
水利工程   1044篇
石油天然气   3073篇
武器工业   263篇
无线电   6937篇
一般工业技术   1524篇
冶金工业   561篇
原子能技术   125篇
自动化技术   9424篇
  2024年   113篇
  2023年   374篇
  2022年   650篇
  2021年   769篇
  2020年   988篇
  2019年   703篇
  2018年   645篇
  2017年   979篇
  2016年   1299篇
  2015年   1586篇
  2014年   2797篇
  2013年   2232篇
  2012年   3499篇
  2011年   3356篇
  2010年   2395篇
  2009年   2344篇
  2008年   2323篇
  2007年   2530篇
  2006年   2153篇
  2005年   1627篇
  2004年   1363篇
  2003年   1130篇
  2002年   864篇
  2001年   746篇
  2000年   571篇
  1999年   444篇
  1998年   308篇
  1997年   280篇
  1996年   230篇
  1995年   172篇
  1994年   109篇
  1993年   56篇
  1992年   52篇
  1991年   30篇
  1990年   23篇
  1989年   30篇
  1988年   15篇
  1987年   7篇
  1986年   5篇
  1985年   7篇
  1984年   10篇
  1983年   3篇
  1982年   4篇
  1980年   1篇
  1979年   3篇
  1977年   1篇
  1975年   1篇
  1965年   1篇
  1960年   1篇
  1957年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
以无线通讯方式实现多台PLC之间以及PLC与微机之间的数据交换,在遥控监控站上完成对移动设备的控制与监视。  相似文献   
62.
张昕 《石油机械》1998,26(4):14-15,22
为提高抽油机减速器齿轮铸件的机械性能,提出以Sn代替Mo作为合金元素,并通过试验确定了合理的Si、Cu、Sn的加入量。指出Si加入量应控制在1.9%-2.1%范围内,同时加入0.36%~0.9%的Cu和0.025%~0.07%的Sn,可保证球铁的强度和延伸率都满足QT700-2的要求。鉴于试件与实际铸件的表面硬度有一定的差值,为提高铸件表面硬度,进行了余热正火试验,并给出了铸件在铸型内的时间-冷却温度曲线。最后根据球铁化学成分的选择结果,进行了齿轮生产试验。  相似文献   
63.
条形药包药量计算公式探讨   总被引:5,自引:2,他引:3  
杨年华 《爆破》1994,11(4):65-67
本文通过现有诸药量计算公式的总结和统计分析,认为经验函数划(n)以二次式较合适。并根据流体动力学理论和临界能量密度破碎准则,推导出f(n)的二次项公式,得q=KW2(1十n2)/2;该式较符合实际,故推荐供参考。  相似文献   
64.
以生产润滑油基础油的老三套工艺为基础,开发了改善油品氧化安定性的组合工艺。该工艺的主要特点是包括一步络合脱氮过程。实验证明,该组合工艺既可以有效地提高基础油的氧化安定性,又能降低溶剂精制深度,提高基础油收率。  相似文献   
65.
采用足够小的直线段拟合机组全特性曲线平直部分,采用二次多项式拟合机组全特性曲线弯曲部分,推导了有关方程,并对模拟的方程进行了处理,编制了较通用的计算机程序,利用该计算机程序对我国蒲石河抽水蓄能电站进行了计算分析,计算结果表明:该计算机程序计算速度较快、计算准确度较高,提出的水泵水轮机的数值模拟方法具有实用价值.  相似文献   
66.
介绍了福建炼油化工有限公司重油催化裂化装置自开工投产以来存在的问题,以及针对这些问题进行改造和改造后所取得的成效,如针对原料重质化、重金属含量高,如何提高产品收率;催化剂跑损,第一、二段再生器烟气混合后发生尾燃的现象以及汽提效率、烧焦效果等问题得到了根本的解决。  相似文献   
67.
王建茹  贾宝敦  马剑哲  王敏 《微计算机信息》2007,23(26):293-294,142
本文介绍了一种地面无线三维定位系统,说明了其结构、功能、硬件、软件及其实现。采用信息广播机制的无线三维定位方法,实现独立网络支持下的具有分层结构的建筑区域中的移动人员的无线三维定位,可应用于大型、中型、小型等各类系统中。  相似文献   
68.
催化重整装置的几点设计改进   总被引:2,自引:0,他引:2  
以一套500kt/a规模的催化重整装置的设计为例进行分析和讨论,提出对今后催化重整装置设计的几点改进建议,包括原料的加氢预处理流程,提纯重整产氢,优化预分馏塔及稳定塔的塔盘层数,选择合适的预加氢进料换热器及甲苯塔、二甲苯塔的加压操作等。  相似文献   
69.
A Practical Cross-Layer Mechanism For Fairness in 802.11 Networks   总被引:2,自引:0,他引:2  
Many companies, organizations and communities are providing wireless hotspots that provide networking access using 802.11b wireless networks. Since wireless networks are more sensitive to variations in bandwidth and environmental interference than wired networks, most networks support a number of transmission rates that have different error and bandwidth properties. Access points can communicate with multiple clients running at different rates, but this leads to unfair bandwidth allocation. If an access point communicates with a mix of clients using both 1 Mb/s and 11 Mb/s transmission rates, the faster clients are effectively throttled to 1 Mb/s as well. This happens because the 802.11 MAC protocol approximate “station fairness”, with each station given an equal chance to access the media. We provide a solution to provide “rate proportional fairness”, where the 11 Mb/s stations receive more bandwidth than the 1 Mb/s stations. Unlike previous solutions to this problem, our mechanism is easy to implement, works with common operating systems and requires no change to the MAC protocol or the stations. Joseph Dunn received an M.S. in computer science from the University of Colorado at Boulder in 2003, and B. S. in coputer science and mathematics from the University of Arizona in 2001. His research interests are in the general area of computer systems, primarily focusing on security and scalability in distributed systems. He is currently working on his Ph.D. in computer science from the University of Colorado at Boulder. Michael Neufeld received a Ph.D. in Computer Science from the University of Colorado at Boulder in December of 2004, having previously received an M.S. in Computer Science from the University of Colorado at Boulder in 2000 and an A.B. in Computer Science from Princeton University in 1993. His research interests are in the general area of computer system, specifically concentrating on wireless networking, software defind/cognitive radio, and streerable antennas. He is currently a postdoc in the Computer Science department at the University of Calorado at Boulder pursuing research related to software defined radio and new MAC protocols for steerable phase array antennas. Anmol Sheth is a Ph.D. student in Computer Science at the University of Colorado at Boulder. He received his B.S. in Computer Science from the University of Pune, India in 2001. He has been co-leading the development of the MANTIS operating system. He has co-authored three papers include MAC layer protocol design, energy-efficient wireless communication, and adapting communications to mobility. Dirk Grunwald received his Ph.D. from the University of Illinois in 1989 and joined the University of Colorado the same year. His work addresses research and teaching in the broad area of “computer systems”, which includes computer architecture, operating systems, networks, and storage systems. His interests also include issues in pervasive computing, novel computing models, and enjoying the mountains. He is currently an Associate Professor in the Department of Computer Science and in Electrical and Computer Engineering and is also the Director of the Colorado Center for Information Storage. John Bennett is a Professor of Computer Science with a joint appointment in Electrical and Computer Engineering at the University of Colorado at Boulder. He also serves as Associate Dean for Education in the College of Engineering and Applied Science. He joined the CU-Boulder faculty in 2000, after serving on the faculty of Rice University for 11 years. While at Rice, Bennett pioneered a course in engineering design for both engineering and non-engineering students that has been emulated at several universities and high schools. In addition to other teaching awards, Bennett received the Keck Foundation National Award for Engineering Teaching Excellence for his work on this course. Bennett received his Ph.D. in 1988 from the University of Washington. Prior to completing his doctoral studies, he was a U.S. Naval Officer for several years and founded and served as President of Pacific Mountain Research, Inc., where he supervised the design and development of a number of commercial computing systems. Bennett's primary research interests are broadly focused in the area of distributed systems, and more narrowly in distributed information management and distributed robotic macrosensors.  相似文献   
70.
周秋珍 《节能》2005,(3):10-11,20
介绍了标准型直燃机的分类、原理及长庆至呼和浩特输气管道工程冷冻供热站的设计实例 ,重点论述了标准型直燃机在严寒地区使用的利弊  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