首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2469篇
  免费   219篇
  国内免费   164篇
电工技术   217篇
综合类   162篇
化学工业   8篇
金属工艺   4篇
机械仪表   85篇
建筑科学   10篇
矿业工程   11篇
能源动力   8篇
轻工业   4篇
水利工程   3篇
石油天然气   2篇
武器工业   11篇
无线电   1224篇
一般工业技术   29篇
原子能技术   2篇
自动化技术   1072篇
  2023年   9篇
  2022年   6篇
  2021年   14篇
  2020年   31篇
  2019年   13篇
  2018年   28篇
  2017年   37篇
  2016年   55篇
  2015年   56篇
  2014年   118篇
  2013年   125篇
  2012年   177篇
  2011年   244篇
  2010年   235篇
  2009年   309篇
  2008年   278篇
  2007年   309篇
  2006年   268篇
  2005年   179篇
  2004年   121篇
  2003年   119篇
  2002年   58篇
  2001年   23篇
  2000年   14篇
  1999年   5篇
  1998年   7篇
  1997年   4篇
  1996年   3篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1987年   1篇
排序方式: 共有2852条查询结果,搜索用时 16 毫秒
1.
针对IEEE1588时钟同步过程中存在时钟频率漂移问题,提出了一种基于滑模控制的新型时钟同步算法。首先根据主从时钟偏差与漂移的递推关系,建立系统状态空间模型;然后运用滑模控制缩小时钟偏差与时钟漂移;最后结合滑动平均滤波对实验过程中的频率抖动和随机误差进行优化。结果表明,基于滑模控制的时钟同步算法可有效抑制时钟漂移引起的时钟偏差线性增长,将时钟偏差控制在1μs以下,从而实现亚微秒级网络对时。相比传统IEEE1588协议同步方法,所提方法提供了更高的同步精度。  相似文献   
2.
ABSTRACT

Wireless Interoperability for Multiple Access (WiMAX) is one of the emerging fields of high-speed wireless communication that has enormous capabilities due to its range and the connection speed. Like wireless local area networks (LANs), WiMAX networks implement multiple quality of service (QoS) frameworks at the Media Access Control (MAC) level for assured data, voice, and video services. The question of ensuring QoS is basically how to distribute available resources to users in order to satisfy QoS parameters such as latency, jitter and throughput requirements. IEEE 802.16 standard does not have any particular guidelines on scheduling of incoming and outgoing data. This has caught the attention of researchers working on WiMAX. This article discusses the various issues in WiMAX along with a classification of various scheduling approaches based upon the type of scheduler for the sake of better understanding the scheduling problem and analyzing various available theories.  相似文献   
3.
《Microelectronics Journal》2015,46(6):415-421
A 5 GHz LC VCO (voltage-controlled oscillator) with automatic amplitude control (AAC) and automatic frequency-band selection (AFBS) for 2.4 GHz ZigBee transceivers is presented. Instead of continuous feedback loop, an alternative amplitude calibration scheme is proposed in this paper to alleviate the deficiencies inherent in the conventional approach. It helps to keep the VCO at optimum amplitude to avoid saturation of the cross-coupled transistors and therefore stabilizes the phase noise performance over process, voltage and temperature variations. For the ZigBee application with 16 frequency channels, a coarse tuning loop is added in this work to implement the frequency-band selection using the AFBS mechanism. The VCO core and the digital AAC, AFBS modules have been fully integrated in a 2.4 GHz ZigBee transceiver which was fabricated in a 0.18 μm RF-CMOS technology. The current consumption is 4.7 mA at 4.85 GHz with 1.8 V power supply and a chip area of about 0.285 mm2 is occupied. The VCO is capable of operating from 4.67 GHz to 5.18 GHz and the measured phase-noise level is –120 dBc/Hz at 1 MHz offset from a 4.85 GHz carrier. The tuning sensitivity KVCO of the VCO is about 78 MHz/V with 0.9 V control voltage.  相似文献   
4.
5.
In recent years, medical service has been evolving from systems designed around centralized hospitals to Ubiquitous Healthcare (U‐Healthcare). U‐Healthcare system can facilitate real‐time monitoring of patient states, and can provide medical checkups and management whenever and wherever the medical staff deems necessary. U‐Healthcare services can provide chronic condition monitoring in the early stages of diseases and help execute decisive medical action in emergencies. However, thus far, the application of U‐Healthcare systems has been limited to diseases such as obesity, diabetes, etc. Acute myocardial infarction (AMI) is among the most critical chronic diseases and requires early detection and treatment. In this paper, we propose an AMI diagnostic software technique and protocol that can support real‐time communication between the patient and medical personnel. Our monitoring and diagnostic system has been developed using a protocol based on ISO/IEEE 11073. When data is transferred from the patient's smartphone to a server in hospital, the medical personnel consult the patient's biosensor data to determine the status of the relevant disease and provide appropriate medical service. The relevant information is sent back to the patient's smartphone through a wireless network, and patients can view their data in graphical format through their smartphone. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
6.
为了准确评估实际网络中IEEE 802.11b分布式协调功能(Distributed Coordination Function,DCF)的系统性能,提出了一种三维Markov链路模型,该模型综合考虑了DCF协议退避计数器冻结状态和有限重传次数,并结合M/M/1/K排队模型给出了在负载有限的情况下DCF系统性能的理论模型。仿真结果表明,该模型能准确地预测IEEE 802.11b DCF协议的系统性能。  相似文献   
7.
The IEEE 802.16 standard for wireless broadband networks includes the mesh mode in its specifications, where network nodes interact to deliver packets from a client to a remote destination through intermediate nodes. This paper presents a study of the capacity of IEEE 802.16 wireless networks in mesh mode by using M/G/1/L queuing model that represents each network node by incorporating the features of the standard in order to calculate the average delay and throughput in the node. An iterative method integrates the calculation results at each node, obtaining the end‐to‐end delay from any node of the mesh to the Base Station. Because of multiple hops, a node far from the Base Station may have its flows damaged. To minimize this problem, we propose a criterion for a fair distribution of resources. We show the numerical results of the model which indicate a good fit when compared with simulation results. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
8.
刘康宁  赵增华  王宇 《电子学报》2018,46(12):2942-2949
通过在实验床上的大量真实测量,分析了长距离无线链路中导致吞吐率低下的原因,总结了数据帧出错模式和丢包特点.在此基础上,提出了MAC(Media Access Control)层自适应编码算法AdaCode.该算法将帧间编码和帧内编码有机结合起来,帧间编码使用喷泉码LT(Luby Transform)码,帧内编码使用RS(Reed Solomon)码,根据链路中数据帧误比特率和丢包率的实时变化,动态选择最佳编码率,使接收端能够解码出所有数据帧,从而避免重传,极大提升了链路吞吐率.在MATLAB平台上实现了AdaCode,并使用实验床测得的真实数据进行仿真.仿真结果表明在固定物理层发送速率和可变发送速率两种情况下,AdaCode都能有效提升链路吞吐率.  相似文献   
9.
简单介绍了IEEE1588协议的时间同步机制,提出了一种在物理层内部标记时间戳的方案,并采用FPGA设计实现了支持时间戳标记电路的10G Base-R PHY,仿真和测试结果表明这种PHY具有最多一个时钟周期的延迟抖动,极大地降低了网络延时抖动对时间同步精度的影响,满足高精度时间同步的要求.  相似文献   
10.
IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号