全文获取类型
收费全文 | 657篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 1篇 |
综合类 | 1篇 |
数学 | 23篇 |
物理学 | 21篇 |
无线电 | 650篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 18篇 |
2020年 | 26篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 25篇 |
2016年 | 25篇 |
2015年 | 23篇 |
2014年 | 57篇 |
2013年 | 41篇 |
2012年 | 65篇 |
2011年 | 63篇 |
2010年 | 42篇 |
2009年 | 42篇 |
2008年 | 41篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 33篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
排序方式: 共有696条查询结果,搜索用时 31 毫秒
51.
针对数字电视地面广播传输标准(DTMB)的频谱感知问题,提出了一种新的基于DTMB信号帧中伪随机(PN)序列累积自相关的频谱感知算法。所提算法的创新性在于通过联合多个不同相关间隔的累积自相关结果作为频谱感知的检验统计量,充分利用了有限频谱感知时间内的信号信息。仿真结果表明,当把感知时间设为50 ms时,为了确保频谱感知检测的虚警概率和漏验概率都低于0.01,针对DTMB信号的3种帧头模式,所提算法所需的信噪比分别为-20.5 dB、-21 dB和-22 dB,优于已有的频谱感知算法。此外,仿真结果还表明载波频偏和多径衰落对所提算法的性能几乎没有影响。 相似文献
52.
随着IT技术的发展,电台传统的业务面临着来自以互联网为基础的新媒体业务的挑战,电台的传统业务已经不能完全满足电台未来发展的需要。广播节目本身的时效性和不受时间空间限制的伴随性越来越受广大听众的喜爱,经济效益也稳步提升,因此各地电台纷纷加大投入,力争奉献给听众优质的节目。发展离不开优质的节目以及安全的播出。因此一套好的制播软件系统,在电台工作中可谓是重中之重。主要从优质制播软件在节目制作播出中的表现及作用方面加以阐述。 相似文献
53.
IP广播平台可以满足几千个节目同时在网上跑,几万个终端同时播出,采用IP广播平台建设“村村响”广播工程,构建农村公共服务体系,对农村政务、经济和灾害预警等信息的发布,丰富农村的精神文化生活有着重要意义.主要就IP广播平台在“村村响”广播工程建设中的应用做一些介绍,供同行参考. 相似文献
54.
55.
Efficient multi‐hop wireless broadcast protocol in vehicular networks using automated threshold function design 下载免费PDF全文
Michael Slavik Imad Mahgoub Mohammed Alwakeel 《International Journal of Communication Systems》2015,28(12):1829-1846
Vehicular networking applications often use multi‐hop wireless broadcasting as a primary data dissemination mechanism. Therefore, protocols that efficiently and thoroughly propagate application data while adapting to a wide range of network density, vehicle distribution pattern, channel quality, and other conditions are critical for vehicular communications. Here, we design the Statistical Vehicular Broadcast (SVB) protocol to efficiently distribute data via multi‐hop broadcast in vehicular networks. First, we present an automated optimization technique for the design of threshold functions in statistical broadcasting methods. Next, we compare and analyze known statistical techniques, including different fundamental methods, assessment delay algorithms, and failsafe mechanisms. All combinations of these techniques are given threshold functions optimized using the proposed automated procedure then are evaluated in a wide range of simulations. High‐level statistical design principles and recommendations are established based on analysis of these results. Finally, we apply those principles to design SVB. It is evaluated in JiST/SWANS and is shown to achieve a high target reachability level while consuming less bandwidth than similar protocols across urban and highway vehicular networking scenarios.Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
56.
Profit‐based exclusive‐or coding algorithm for data retransmission in DVB‐H with a recovery network 下载免费PDF全文
You‐Chiun Wang 《International Journal of Communication Systems》2015,28(9):1580-1597
The digital video broadcasting‐handheld (DVB‐H) standard is developed by European Telecommunications Standards Institute to broadcast digital videos to handheld devices, but data loss is a critical issue due to the broadcast behavior. On the other hand, DVB‐Internet protocol datacasting (DVB‐IPDC) integrates DVB‐H with an Internet protocol‐based wireless network to provide bidirectional communication. We adopt this wireless network to deal with data retransmission and call it a recovery network. The paper argues that network coding can improve retransmission efficiency of the recovery network because DVB‐H packet loss often exhibits high correlation. In addition, DVB‐H packets may be heterogeneous in the sense that they have different importance. According to these two arguments, the paper considers that DVB‐H packets are associated with different profit depending on their importance and proposes an α‐maximum profit network coding problem. It asks the base station in the recovery network to use no more than α coded packets for handheld devices to retrieve the lost DVB‐H packets such that the overall profit is the maximum. An efficient exclusive‐or coding scheme, namely the profit‐based exclusive‐or network coding (PEN) algorithm, is proposed to solve this problem. Extensive simulation results also verify the effectiveness of the PEN algorithm. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
57.
This paper addresses the issues on spectrum sharing in a cognitive radio network consisting of a primary user and a group of cognitive users. Each cognitive user may occupy a non‐overlapped sub‐band of the primary spectrum, but it needs to perform spectrum sensing independently before accessing the sub‐band. To reduce the complexity of spectrum sensing and thus energy consumption, this paper proposes a scheduled spectrum sensing scheme. First, we consider a single spectrum sensing scenario where only one cognitive user is elected to perform spectrum sensing, and then it broadcasts its sensing results to the other cognitive users. The scheduled spectrum sensing scheme works in both network‐centric and user‐centric ways. Next, the scheduled spectrum sensing scheme is further generalized to work in a multiple spectrum sensing scenario. The results show the effectiveness of the proposed schemes compared with the traditional schemes where all cognitive users may perform spectrum sensing at the same time. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
58.
IPTV broadcast channels and video content distribution are increasingly saturating network paths. New solutions based on inter‐domain multicast protocols could contribute to the enhancement of multimedia content distribution over the Internet. The aim of this paper is to propose new capabilities for an existing inter‐domain multicast protocol, the Protocol Independent Multicast‐Sparse Mode. We describe the modified protocol and analyze its behavior using newly developed tools based on an open‐source software simulator. The resulting protocol does not require topology information, which is advantageous for easier deployment. In addition, the adopted solution avoids inherent problems with inter‐domain multicast routing, such as multiple paths and path asymmetries. 相似文献
59.
Dongyan Wei Wenbo Wang Mugen Peng Dong Liang Yang Liu 《International Journal of Communication Systems》2011,24(7):911-924
In wireless broadcast system, where feedback is limited and channel state information is only available at the receiver side, layered broadcasting approach has been proposed to fully utilize the channel resources by providing different levels of service quality to users with different channel conditions. However, no upper bound has been given yet to show how the layered broadcast scheme will outperform the conventional broadcast (CB) scheme. In this paper, system average achievable rate (SAAR) is defined as the mean achievable rate of all users within the coverage. Based on continuum superposition coding (SC) with infinite layers, the upper bound of the SAAR of layered broadcasting is given by the derivation of the optimal power distribution function among the superposed layers. The results show that, by promoting the experience of stronger users (users with better channel conditions) without seriously degrading the performance of weaker users (users with worse channel conditions), layered broadcasting approach greatly increases the average system performance. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
60.