全文获取类型
收费全文 | 27810篇 |
免费 | 3602篇 |
国内免费 | 976篇 |
专业分类
化学 | 2467篇 |
晶体学 | 53篇 |
力学 | 2014篇 |
综合类 | 265篇 |
数学 | 6619篇 |
物理学 | 5046篇 |
无线电 | 15924篇 |
出版年
2024年 | 50篇 |
2023年 | 306篇 |
2022年 | 467篇 |
2021年 | 629篇 |
2020年 | 682篇 |
2019年 | 489篇 |
2018年 | 539篇 |
2017年 | 905篇 |
2016年 | 1136篇 |
2015年 | 1182篇 |
2014年 | 1992篇 |
2013年 | 1968篇 |
2012年 | 1963篇 |
2011年 | 1930篇 |
2010年 | 1529篇 |
2009年 | 1644篇 |
2008年 | 1828篇 |
2007年 | 1745篇 |
2006年 | 1581篇 |
2005年 | 1332篇 |
2004年 | 1203篇 |
2003年 | 1249篇 |
2002年 | 913篇 |
2001年 | 756篇 |
2000年 | 665篇 |
1999年 | 570篇 |
1998年 | 506篇 |
1997年 | 383篇 |
1996年 | 366篇 |
1995年 | 325篇 |
1994年 | 223篇 |
1993年 | 186篇 |
1992年 | 146篇 |
1991年 | 146篇 |
1990年 | 94篇 |
1989年 | 88篇 |
1988年 | 79篇 |
1987年 | 60篇 |
1986年 | 49篇 |
1985年 | 75篇 |
1984年 | 46篇 |
1983年 | 34篇 |
1982年 | 41篇 |
1981年 | 33篇 |
1980年 | 51篇 |
1979年 | 51篇 |
1978年 | 29篇 |
1977年 | 39篇 |
1976年 | 37篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
42.
43.
44.
45.
46.
提出了一种基于光纤环的光缓存器的结构,对结合半导体光放大器作光开关的此结构的物理模型进行了详细描述,并根据此模型分析了其增益、噪声、信噪比等方面的特性. 相似文献
47.
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
48.
49.
欧洲主要电信运营商所处国度的经济和人口布局情况不同,竞争环境也有差别,在专线资费方面的做法也有许多不同之处。考虑到地区之间竞争的差异。目前多数国家都取消了地区交叉补贴的做法,但还有一部分国家仍然坚持统一费率。在资费方面的基本促销手段为接合同年限和用户的支出额打折。从2000年到2003年资费演变的基本情况是;接入费扣2Mbit/s以下较低速率的专线租费保持平稳略有下降,较高速率专线的租费则有较大的下调幅虚。 相似文献
50.