全文获取类型
收费全文 | 591983篇 |
免费 | 68894篇 |
国内免费 | 48209篇 |
专业分类
电工技术 | 53307篇 |
技术理论 | 3篇 |
综合类 | 64435篇 |
化学工业 | 73172篇 |
金属工艺 | 41283篇 |
机械仪表 | 43086篇 |
建筑科学 | 46567篇 |
矿业工程 | 25515篇 |
能源动力 | 15758篇 |
轻工业 | 60624篇 |
水利工程 | 20115篇 |
石油天然气 | 21575篇 |
武器工业 | 9681篇 |
无线电 | 63173篇 |
一般工业技术 | 48881篇 |
冶金工业 | 22685篇 |
原子能技术 | 9558篇 |
自动化技术 | 89668篇 |
出版年
2024年 | 3055篇 |
2023年 | 8758篇 |
2022年 | 22066篇 |
2021年 | 28672篇 |
2020年 | 20555篇 |
2019年 | 14457篇 |
2018年 | 15453篇 |
2017年 | 17700篇 |
2016年 | 15990篇 |
2015年 | 25969篇 |
2014年 | 33193篇 |
2013年 | 38793篇 |
2012年 | 49596篇 |
2011年 | 52155篇 |
2010年 | 49833篇 |
2009年 | 47429篇 |
2008年 | 49019篇 |
2007年 | 47880篇 |
2006年 | 41182篇 |
2005年 | 33546篇 |
2004年 | 24144篇 |
2003年 | 16213篇 |
2002年 | 15169篇 |
2001年 | 13714篇 |
2000年 | 10777篇 |
1999年 | 4503篇 |
1998年 | 1681篇 |
1997年 | 1343篇 |
1996年 | 1070篇 |
1995年 | 914篇 |
1994年 | 657篇 |
1993年 | 618篇 |
1992年 | 486篇 |
1991年 | 333篇 |
1990年 | 306篇 |
1989年 | 336篇 |
1988年 | 201篇 |
1987年 | 144篇 |
1986年 | 143篇 |
1985年 | 68篇 |
1984年 | 86篇 |
1983年 | 83篇 |
1982年 | 62篇 |
1981年 | 101篇 |
1980年 | 176篇 |
1979年 | 117篇 |
1977年 | 11篇 |
1965年 | 16篇 |
1959年 | 115篇 |
1951年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
213.
Frequency Insertion Strategy for Channel Assignment Problem 总被引:1,自引:0,他引:1
This paper presents a new heuristic method for quickly finding a good feasible solution to the channel assignment problem
(CAP). Like many other greedy-type heuristics for CAP, the proposed method also assigns a frequency to a call, one at a time.
Hence, the method requires computational time that increases only linear to the number of calls. However, what distinguishes
the method from others is that it starts with a narrow enough frequency band so as to provoke violations of constraints that
we need to comply with in order to avoid radio interference. Each violation is then resolved by inserting frequencies at the
most appropriate positions so that the band of frequencies expands minimally. An extensive computational experiment using
a set of randomly generated problems as well as the Philadelphia benchmark instances shows that the proposed method perform
statistically better than existing methods of its kind and even yields optimum solutions to most of Philadelphia benchmark
instances among which two cases are reported for the first time ever, in this paper.
Won-Young Shin was born in Busan, Korea in 1978. He received B.S. in industrial engineering from Pohang University of Science and Technology
(POSTECH) in 2001 and M.S in operation research and applied statistics from POSTECH in 2003. Since 2003 he has been a researcher
of Agency for Defense Development (ADD) in Korea. He is interested in optimization of communication system and applied statistics.
Soo Y. Chang is an associate professor in the Department of Industrial Engineering at Pohang University of Science and Technology (POSTECH),
Pohang, Korea. He teaches linear programming, discrete optimization, network flows and operations research courses. His research
interests include mathematical programming and scheduling. He has published in several journals including Discrete Applied
Mathematics, Computers and Mathematics with Application, IIE Transactions, International Journal of Production Research, and
so on. He is a member of Korean IIE, and ORMSS.
Jaewook Lee is an assistant professor in the Department of Industrial Engineering at Pohang University of Science and Technology (POSTECH),
Pohang, Korea. He received the B.S. degree in mathematics with honors from Seoul National University, and the Ph.D. degree
from Cornell University in applied mathematics in 1993 and 1999, respectively. He is currently an assistant professor in the
department of industrial engineering at the Pohang University of Science and Technology (POSTECH). His research interests
include nonlinear systems, neural networks, nonlinear optimization, and their applications to data mining and financial engineering.
Chi-Hyuck Jun was born in Seoul, Korea in 1954. He received B.S. in mineral and petroleum engineering from Seoul National University in
1977, M.S. in industrial engineering from Korea Advanced Institute of Science and Technology in 1979 and Ph.D. in operations
research from University of California, Berkeley, in 1986. Since 1987 he has been with the department of industrial engineering,
Pohang University of Science and Technology (POSTECH) and he is now a professor and the department head. He is interested
in performance analysis of communication and production systems. He has published in several journals including IIE Transactions,
IEEE Transactions, Queueing Systems and Chemometrics and Intelligent Laboratory Systems. He is a member of IEEE, INFORMS and
ASQ. 相似文献
214.
215.
考察了双河油田双河联、江河联注入水堵塞地层的因素;膨胀性黏土,悬浮固体颗粒。细菌及悬浮污油。含膨胀性黏土的双河南、双河北及不含膨胀性黏土的双江岩心粉,在注入水中相对于地层水中的体积膨胀度分别为14.5%、11.1%及0.02%;注入100PV不含悬浮颗粒的等体积比地层水、注入水混合水使双河、双江岩心渗透率分别下降7%和4%、9%和7%。注入水中悬浮颗粒引起岩心渗透率下降,粒径越大、颗粒浓度越大、注入量越大,则渗透率越低。在粒径2.1μm或颗粒浓度3mg/L前后下降幅度变化较大。注入水中硫酸盐还原菌引起岩心渗透率下降,含菌量越大则渗透率开始下降时的注水量越小,注入含菌50个/L的水100PV使岩心渗透率下降7%。岩心对注水合油量敏感,注入含油量20mg/L的水50PV使岩心渗透率下降20%。在岩心注水实验中渗透率下降最严重的是双河南岩心,其次是双河北岩心.江河岩心较轻,注入精细过滤水的双河北岩心渗透率下降大大减少.说明悬浮固体是造成注水堵塞的主要因素。为了解除双河油田注水井的堵塞,研制了含黏土稳定剂、缓蚀剂、铁离子稳定剂、互溶剂的土酸液,与南阳油田使用的低伤害酸液一起,用于1口注水井的解堵,效果良好。图7表4参5。 相似文献
216.
217.
鄂尔多斯盆地三叠系延长组层序地层与生储盖组合特征 总被引:14,自引:2,他引:12
鄂尔多斯盆地三叠系延长组地层层序划分方案较多。在V ail经典层序地层学理论指导下,综合利用露头、岩芯、钻井、地震和古生物等资料,通过古水深分析和层序界面的识别与划分,认为将鄂尔多斯盆地三叠系延长组划分为7个三级层序更为合理,指出层序4水进体系域(生)+层序5低位体系域(储)+层序5水进体系域(盖)和层序4水进体系域(生)+层序4低位体系域(储)+层序4水进体系域(盖)是相对较佳的2套生储盖组合,并指出了鄂尔多斯盆地延长组最主要的2套生储盖勘探目的层。 相似文献
218.
异构分层无线网络中基于逗留时间的动态流量均衡算法研究 总被引:1,自引:1,他引:0
为使异构分层无线网络能服务更多的移动用户,提出了一种基于逗留时间的动态流量均衡算法.该算法首先根据用户移动模型计算其在小区内的逗留时间,然后基于小区呼叫到达率和重叠覆盖小区的流量状态来确定一个周期内呼叫转移的数量,最后依据逗留时间门限值将重负载小区中满足条件的呼叫转移到轻负载的重叠覆盖小区中.为降低切换呼叫掉线率,还对异构网间的呼叫切换策略做了改进.仿真实验结果表明,本算法在新呼叫阻塞率和切换呼叫掉线率等性能指标上比传统方法有显著的提高. 相似文献
219.
220.
实现嵌入式汇编技术就是直接把汇编语言的代码写到高级语言的代码中并一起进行编译,不需要独立的汇编系统和另外的连接步骤。嵌入式汇编技术在不同的高级语言中语法各不相同。文章主要给出了在Delphi环境中嵌入汇编的具体用法。采用嵌入式汇编技术对Intel8255和8254接口芯片的具体操作,以及介绍了数据采集软件的设计流程和程序的具体实现方法。 相似文献