全文获取类型
收费全文 | 23285篇 |
免费 | 2983篇 |
国内免费 | 653篇 |
专业分类
化学 | 2334篇 |
晶体学 | 45篇 |
力学 | 1734篇 |
综合类 | 203篇 |
数学 | 5134篇 |
物理学 | 3583篇 |
无线电 | 13888篇 |
出版年
2024年 | 60篇 |
2023年 | 275篇 |
2022年 | 436篇 |
2021年 | 585篇 |
2020年 | 624篇 |
2019年 | 439篇 |
2018年 | 452篇 |
2017年 | 817篇 |
2016年 | 1014篇 |
2015年 | 1084篇 |
2014年 | 1780篇 |
2013年 | 1657篇 |
2012年 | 1701篇 |
2011年 | 1664篇 |
2010年 | 1268篇 |
2009年 | 1322篇 |
2008年 | 1459篇 |
2007年 | 1411篇 |
2006年 | 1266篇 |
2005年 | 1084篇 |
2004年 | 931篇 |
2003年 | 1019篇 |
2002年 | 706篇 |
2001年 | 558篇 |
2000年 | 508篇 |
1999年 | 434篇 |
1998年 | 358篇 |
1997年 | 276篇 |
1996年 | 257篇 |
1995年 | 236篇 |
1994年 | 187篇 |
1993年 | 138篇 |
1992年 | 103篇 |
1991年 | 104篇 |
1990年 | 74篇 |
1989年 | 58篇 |
1988年 | 62篇 |
1987年 | 48篇 |
1986年 | 41篇 |
1985年 | 66篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 47篇 |
1979年 | 44篇 |
1978年 | 26篇 |
1977年 | 35篇 |
1976年 | 39篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
Quality of service (QoS) support for multimedia services in the IEEE 802.11 wireless LAN is an important issue for such WLANs
to become a viable wireless access to the Internet. In this paper, we endeavor to propose a practical scheme to achieve this
goal without changing the channel access mechanism. To this end, a novel call admission and rate control (CARC) scheme is
proposed. The key idea of this scheme is to regulate the arriving traffic of the WLAN such that the network can work at an
optimal point. We first show that the channel busyness ratio is a good indicator of the network status in the sense that it
is easy to obtain and can accurately and timely represent channel utilization. Then we propose two algorithms based on the
channel busyness ratio. The call admission control algorithm is used to regulate the admission of real-time or streaming traffic
and the rate control algorithm to control the transmission rate of best effort traffic. As a result, the real-time or streaming
traffic is supported with statistical QoS guarantees and the best effort traffic can fully utilize the residual channel capacity
left by the real-time and streaming traffic. In addition, the rate control algorithm itself provides a solution that could
be used above the media access mechanism to approach the maximal theoretical channel utilization. A comprehensive simulation
study in ns-2 has verified the performance of our proposed CARC scheme, showing that the original 802.11 DCF protocol can
statically support strict QoS requirements, such as those required by voice over IP or streaming video, and at the same time,
achieve a high channel utilization.
Hongqiang Zhai received the B.E. and M.E. degrees in electrical engineering from Tsinghua University, Beijing, China, in July 1999 and January
2002 respectively. He worked as a research intern in Bell Labs Research China from June 2001 to December 2001, and in Microsoft
Research Asia from January 2002 to July 2002. Currently he is pursuing the PhD degree in the Department of Electrical and
Computer Engineering, University of Florida. He is a student member of IEEE.
Xiang Chen received the B.E. and M.E. degrees in electrical engineering from Shanghai Jiao Tong University, Shanghai, China, in 1997
and 2000, respectively, and the Ph.D. degree in electrical and computer engineering from the University of Florida, Gainesville,
in 2005. He is currently a Senior Research Engineer at Motorola Labs, Arlington Heights, IL. His research interests include
resource management, medium access control, and quality of service (QoS) in wireless networks. He is a Member of Tau Beta
Pi and a student member of IEEE.
Yuguang Fang received a Ph.D degree in Systems and Control Engineering from Case Western Reserve University in January 1994, and a Ph.D
degree in Electrical Engineering from Boston University in May 1997.
From June 1997 to July 1998, he was a Visiting Assistant Professor in Department of Electrical Engineering at the University
of Texas at Dallas. From July 1998 to May 2000, he was an Assistant Professor in the Department of Electrical and Computer
Engineering at New Jersey Institute of Technology. In May 2000, he joined the Department of Electrical and Computer Engineering
at University of Florida where he got the early promotion with tenure in August 2003 and has been an Associate Professor since
then. He has published over one hundred (100) papers in refereed professional journals and conferences. He received the National
Science Foundation Faculty Early Career Award in 2001 and the Office of Naval Research Young Investigator Award in 2002.
He is currently serving as an Editor for many journals including IEEE Transactions on Communications, IEEE Transactions on
Wireless Communications, IEEE Transactions on Mobile Computing, and ACM Wireless Networks. He is also actively participating
in conference organization such as the Program Vice-Chair for IEEE INFOCOM’2005, Program Co-Chair for the Global Internet
and Next Generation Networks Symposium in IEEE Globecom’2004 and the Program Vice Chair for 2000 IEEE Wireless Communications
and Networking Conference (WCNC’2000). 相似文献
36.
37.
38.
Scheduling Algorithms for Packet-Oriented MAC Protocols in Wireless Multimedia Systems 总被引:1,自引:1,他引:0
Romano Fantacci Giovanni Giambene Francesco Petiti 《Wireless Personal Communications》2003,24(3):363-388
Future generation wireless multimediacommunications will require efficient Medium AccessControl (MAC) protocols able to guarantee suitable Qualityof Service (QoS) levels for different traffic classes whileachieving a high utilization of radio resources. This paperproposes a new scheduling technique to be adopted at the MAClevel in wireless access systems, named Dynamic Scheduling-Time DivisionDuplexing (DS-TDD), that efficiently managesvideo, voice, Web and background traffics. A theoretical approachis proposed in this paper to evaluate the DS-TDD performance withvoice and Web traffics. Simulation results have permitted tohighlight the following promising characteristics of the DS-TDDscheme: (i) a high capacity of real-time traffics isattained with a QoS insensitive to Web and background trafficloads; (ii) a high throughput can be guaranteed whilepreserving the QoS levels of the different traffic classes;(iii) heavier downlink traffic loads do not modify the QoSof uplink traffics. Finally, extensive comparisons with differentscheduling schemes proposed in the literature have permitted tohighlight the better performanceof DS-TDD. 相似文献
39.
系统仿真技术是一种以对实际系统建立正确的数学模型为基础,以计算机为工具的对实际系统进行模拟的技术。计算机技术的高速发展,使系统仿真技术在各个领域中都得到了广泛的应用。以化工及工业锅炉自动控制系统中水箱系统的液位控制问题为例,阐述了系统仿真技术在自动控制领域中的应用。 相似文献
40.
针对CDMA系统中抗干扰技术,提出一种结合多用户检测、波束成形和功率控制的算法,对接收信号在时域和空间上进行联合处理,能大大抑制干扰,提高系统容量。 相似文献