全文获取类型
收费全文 | 30621篇 |
免费 | 3665篇 |
国内免费 | 2604篇 |
专业分类
电工技术 | 2147篇 |
技术理论 | 3篇 |
综合类 | 2724篇 |
化学工业 | 2142篇 |
金属工艺 | 495篇 |
机械仪表 | 2593篇 |
建筑科学 | 544篇 |
矿业工程 | 268篇 |
能源动力 | 297篇 |
轻工业 | 366篇 |
水利工程 | 292篇 |
石油天然气 | 216篇 |
武器工业 | 341篇 |
无线电 | 15635篇 |
一般工业技术 | 3656篇 |
冶金工业 | 335篇 |
原子能技术 | 263篇 |
自动化技术 | 4573篇 |
出版年
2024年 | 109篇 |
2023年 | 446篇 |
2022年 | 652篇 |
2021年 | 851篇 |
2020年 | 971篇 |
2019年 | 763篇 |
2018年 | 786篇 |
2017年 | 1098篇 |
2016年 | 1077篇 |
2015年 | 1371篇 |
2014年 | 1871篇 |
2013年 | 1967篇 |
2012年 | 2310篇 |
2011年 | 2188篇 |
2010年 | 1644篇 |
2009年 | 1659篇 |
2008年 | 1771篇 |
2007年 | 2061篇 |
2006年 | 1932篇 |
2005年 | 1759篇 |
2004年 | 1420篇 |
2003年 | 1446篇 |
2002年 | 1084篇 |
2001年 | 1115篇 |
2000年 | 915篇 |
1999年 | 652篇 |
1998年 | 498篇 |
1997年 | 438篇 |
1996年 | 397篇 |
1995年 | 300篇 |
1994年 | 272篇 |
1993年 | 235篇 |
1992年 | 188篇 |
1991年 | 167篇 |
1990年 | 140篇 |
1989年 | 108篇 |
1988年 | 49篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
21.
22.
Uplink scheduling in wireless systems is gaining importance due to arising uplink intensive data services (ftp, image uploads
etc.), which could be hampered by the currently in-built asymmetry in favor of the downlink. In this work, we propose and
study algorithms for efficient uplink packet-data scheduling in a CDMA cell. The algorithms attempt to maximize system throughput
under transmit power limitations on the mobiles assuming instantaneous knowledge of user queues and channels. However no channel
statistics or traffic characterization is necessary. Apart from increasing throughput, the algorithms also improve fairness
of service among users, hence reducing chances of buffer overflows for poorly located users.
The major observation arising from our analysis is that it is advantageous on the uplink to schedule “strong” users one-at-a-time,
and “weak” users in larger groups. This contrasts with the downlink where one-at-a-time transmission for all users has shown
to be the preferred mode in much previous work. Based on the optimal schedules, we propose less complex and more practical
approximate methods, both of which offer significant performance improvement compared to one-at-a-time transmission, and the
widely acclaimed Proportional Fair (PF) algorithm, in simulations. When queue content cannot be fed back, we propose a simple modification of PF, Uplink PF (UPF), that offers similar improvement.
Hereafter, we refer to users with low recieved power at the base even when transmitting at peak transmit power as “weak” users,
and the strongly recieved users at the base as “strong” users.
Krishnan Kumaran is currently a member of the Complex Systems Modeling section in the Corporate Strategic Research of ExxonMobil Corp., Clinton,
NJ. Formerly, he was a Member of Technical Staff in the Mathematics of Networks and Systems Research Department at Bell Labs
in Murray Hill, NJ, where his research interests were in modeling, analysis and simulation of design, resource management
and scheduling issues in telecommunication networks.
Lijun Qian is an assistant professor in the Department of Electrical Engineering at Prairie View A&M University. He received his B.S.
from Tsinghua University in Beijing, M.S. from Technion-Israel Institute of Technology, and Ph.D. from WINLAB, Rutgers University,
all in electrical engineering. Before joining PVAMU, he was a researcher at Networks and Systems Research Department of Bell
Labs in Murray Hill, NJ. His major research interests are in wireless communications and networking technologies, especially
in radio resource management, protocol design, TCP/RLP optimization and MPLS traffic engineering. 相似文献
23.
以亚欧海底光缆S2段为例,介绍亚欧海底光缆远供电源(PFE)的供电方式,以及其在正常运行时和故障维修时的维护管理方法。探讨在实际维护中如何贯彻落实及灵活运用系统联合维护文档,总结适合中国国情的远供电源维护经验,确保亚欧海底光缆远供电源安全稳定运行。 相似文献
24.
25.
26.
天波超视距雷达是低空防御系统中一种有效的预警手段。通过采用光纤传输技术,利用其信息传输容量大,速度快,频带宽,抗干扰能力强,线路损耗低。易于施工等特点,实现全相参雷达的信息传输和系统控制,具有优良的保密性,稳定性、抗干扰性和抗摧毁能力。 相似文献
27.
28.
Communicating with sensors has long been limited either to wired connections or to proprietary wireless communication protocols. Using a ubiquitous and inexpensive wireless communication technology to create Sensor Area Networks (SANs) will accelerate the extensive deployment of sensor technology. Bluetooth, an emerging, worldwide standard for inexpensive, local wireless communication is a viable choice for SANs because of its inherent support for some of the important requirements – low power, small form factor, low cost and sufficient communication range. In this paper we outline an approach, centered on the Bluetooth technology, to support a sensor network composed of fixed wireless sensors for health monitoring of highways, bridges and other civil infrastructures. We present a topology formation scheme that not only takes into account the traffic generated by different sensors but also the associated link strengths, buffer capacities and energy availability. The algorithm makes no particular assumptions as to the placement of nodes, and not all nodes need to be in radio proximity of each other. The output is a tree shaped scatternet rooted at the sensor hub (data logger) that is balanced in terms of traffic carried on each of the links. We also analyze the scheduling, routing and healing aspects of the resulting sensor-net topology. 相似文献
29.
30.