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1.
The limitations of commonly used separable extensions of one-dimensional transforms, such as the Fourier and wavelet transforms, in capturing the geometry of image edges are well known. In this paper, we pursue a "true" two-dimensional transform that can capture the intrinsic geometrical structure that is key in visual information. The main challenge in exploring geometry in images comes from the discrete nature of the data. Thus, unlike other approaches, such as curvelets, that first develop a transform in the continuous domain and then discretize for sampled data, our approach starts with a discrete-domain construction and then studies its convergence to an expansion in the continuous domain. Specifically, we construct a discrete-domain multiresolution and multidirection expansion using nonseparable filter banks, in much the same way that wavelets were derived from filter banks. This construction results in a flexible multiresolution, local, and directional image expansion using contour segments, and, thus, it is named the contourlet transform. The discrete contourlet transform has a fast iterated filter bank algorithm that requires an order N operations for N-pixel images. Furthermore, we establish a precise link between the developed filter bank and the associated continuous-domain contourlet expansion via a directional multiresolution analysis framework. We show that with parabolic scaling and sufficient directional vanishing moments, contourlets achieve the optimal approximation rate for piecewise smooth functions with discontinuities along twice continuously differentiable curves. Finally, we show some numerical experiments demonstrating the potential of contourlets in several image processing applications. Index Terms-Contourlets, contours, filter banks, geometric image processing, multidirection, multiresolution, sparse representation, wavelets.  相似文献
2.
压缩感知理论及其研究进展   总被引:113,自引:10,他引:103       下载免费PDF全文
 信号采样是联系模拟信源和数字信息的桥梁.人们对信息的巨量需求造成了信号采样、传输和存储的巨大压力.如何缓解这种压力又能有效提取承载在信号中的有用信息是信号与信息处理中急需解决的问题之一.近年国际上出现的压缩感知理论(Compressed Sensing,CS)为缓解这些压力提供了解决方法.本文综述了CS理论框架及关键技术问题,并着重介绍了信号稀疏变换、观测矩阵设计和重构算法三个方面的最新进展,评述了其中的公开问题,对研究中现存的难点问题进行了探讨,最后介绍了CS理论的应用领域.  相似文献
3.
Multicluster, mobile, multimedia radio network   总被引:90,自引:0,他引:90  
A multi-cluster, multi-hop packet radio network architecture for wireless adaptive mobile information systems is presented. The proposed network supports multimedia traffic and relies on both time division and code division access schemes. This radio network is not supported by a wired infrastructure as conventional cellular systems are. Thus, it can be instantly deployed in areas with no infrastructure at all. By using a distributed clustering algorithm, nodes are organized into clusters. The clusterheads act as local coordinators to resolve channel scheduling, perform power measurement/control, maintain time division frame synchronization, and enhance the spatial reuse of time slots and codes. Moreover, to guarantee bandwidth for real time traffic, the architecture supports virtual circuits and allocates bandwidth to circuits at call setup time. The network is scalable to large numbers of nodes, and can handle mobility. Simulation experiments evaluate the performance of the proposed scheme in static and mobile environments.This work was supported by the U.S. Department of Justice/Federal Bureau of Investigation, ARPA/CSTO under Contract J-FBI-93-112 Computer Aided Design of High Performance Wireless Networked Systems.  相似文献
4.
5.
DV Based Positioning in Ad Hoc Networks   总被引:81,自引:0,他引:81  
Many ad hoc network protocols and applications assume the knowledge of geographic location of nodes. The absolute position of each networked node is an assumed fact by most sensor networks which can then present the sensed information on a geographical map. Finding position without the aid of GPS in each node of an ad hoc network is important in cases where GPS is either not accessible, or not practical to use due to power, form factor or line of sight conditions. Position would also enable routing in sufficiently isotropic large networks, without the use of large routing tables. We are proposing APS – a localized, distributed, hop by hop positioning algorithm, that works as an extension of both distance vector routing and GPS positioning in order to provide approximate position for all nodes in a network where only a limited fraction of nodes have self positioning capability.  相似文献
6.
SPINS: Security Protocols for Sensor Networks   总被引:77,自引:0,他引:77  
Wireless sensor networks will be widely deployed in the near future. While much research has focused on making these networks feasible and useful, security has received little attention. We present a suite of security protocols optimized for sensor networks: SPINS. SPINS has two secure building blocks: SNEP and TESLA. SNEP includes: data confidentiality, two-party data authentication, and evidence of data freshness. TESLA provides authenticated broadcast for severely resource-constrained environments. We implemented the above protocols, and show that they are practical even on minimal hardware: the performance of the protocol suite easily matches the data rate of our network. Additionally, we demonstrate that the suite can be used for building higher level protocols.  相似文献
7.
2005   总被引:73,自引:0,他引:73  
In recent years, wireless Internet service providers (WISPs) have established Wi-Fi hotspots in increasing numbers at public venues, providing local coverage to traveling users and empowering them with the ability to access email, Web, and other Internet applications on the move. In this paper, we observe that while the mobile computing landscape has changed both in terms of number and type of hotspot venues, there are several technological and deployment challenges remaining before hotspots can become an ubiquitous infrastructure. These challenges include authentication, security, coverage, management, location services, billing, and interoperability. We discuss existing research, the work of standards bodies, and the experience of commercial hotspot providers in these areas, and then describe compelling open research questions that remain. Anand Balachandran has been a member of the research staff at Intel Research, Seattle since October 2003. His research interests include wireless networking systems, wireless Internet, infrastructure and ad-hoc networks, and mobile and ubiquitous computing. He received his Bachelor of Technology degree from the Indian Institute of Technology, Madras in 1995, his Master’s degree from Columbia University, in 1997, and his Ph.D. degree in Computer Science and Engineering from the University of California at San Diego in 2003. Geoffrey M. Voelker is an assistant professor at the University of California at San Diego. His research interests include operating systems, distributed systems, networking, and mobile computing. He received a BS degree in Electrical Engineering and Computer Science from the University of California at Berkeley in 1992, and the M.S. and Ph.D. degrees in Computer Science and Engineering from the University of Washington in 1995 and 2000, respectively. In 2000, he received the first Computing Research Association (CRA) Digital Government Fellowship, and in 2002 he received the Hellman Young Faculty Fellowship at UCSD. Victor Bahl is a Senior Researcher and the Manager of the Networking Group in Microsoft Research. His research interests span a variety of problems in wireless networking. In addition to making many product contributions, he has authored over 65 scientific papers, 44 issued and pending patent applications and several book chapters. He is the co-founder and Chairman of the ACM Special Interest Group in Mobility (SIGMOBILE); the founder and past Editor-in-Chief of ACM Mobile Computing and Communications Review, and the founder and Steering Committee Chair of ACM/USENIX Mobile Systems Conference (MobiSys); He has served on the editorial board of IEEE Journal on Selected Areas in Communications, and is currently serving on the editorial boards of Elsevier’s Adhoc Networking Journal, Kulwer’s Telecommunications Systems Journal, and ACM’s Wireless Networking Journal. He has served as a guest editor for several IEEE and ACM journals and on networking review panels organized by the National Science Foundation (NSF), the National Research Council (NRC) and European Union’s COST. He has served as the General Chairman, Program Chair and Steering Committee member of several IEEE and ACM conferences and on the Technical Program Committee of over 45 international conferences and workshops. He is the recipient of Digital’s Doctoral Engineering Award (1994) and ACM SIGMOBILE’s Distinguished Service Award (2001). He is a Fellow of the ACM, a Senior Member of the IEEE and a past president of the electrical engineering honor society Eta kappa Nu-Zeta Pi. Dr. Bahl received his Ph. D in Computer Systems Engineering from the University of Massachusetts Amherst.This revised version was published online in August 2005 with a corrected cover date.  相似文献
8.
9.
The nonsubsampled contourlet transform: theory, design, and applications.   总被引:68,自引:0,他引:68  
In this paper, we develop the nonsubsampled contourlet transform (NSCT) and study its applications. The construction proposed in this paper is based on a nonsubsampled pyramid structure and nonsubsampled directional filter banks. The result is a flexible multiscale, multidirection, and shift-invariant image decomposition that can be efficiently implemented via the à trous algorithm. At the core of the proposed scheme is the nonseparable two-channel nonsubsampled filter bank (NSFB). We exploit the less stringent design condition of the NSFB to design filters that lead to a NSCT with better frequency selectivity and regularity when compared to the contourlet transform. We propose a design framework based on the mapping approach, that allows for a fast implementation based on a lifting or ladder structure, and only uses one-dimensional filtering in some cases. In addition, our design ensures that the corresponding frame elements are regular, symmetric, and the frame is close to a tight one. We assess the performance of the NSCT in image denoising and enhancement applications. In both applications the NSCT compares favorably to other existing methods in the literature.  相似文献
10.
Image quality assessment: from error visibility to structural similarity   总被引:63,自引:0,他引:63  
Objective methods for assessing perceptual image quality traditionally attempted to quantify the visibility of errors (differences) between a distorted image and a reference image using a variety of known properties of the human visual system. Under the assumption that human visual perception is highly adapted for extracting structural information from a scene, we introduce an alternative complementary framework for quality assessment based on the degradation of structural information. As a specific example of this concept, we develop a Structural Similarity Index and demonstrate its promise through a set of intuitive examples, as well as comparison to both subjective ratings and state-of-the-art objective methods on a database of images compressed with JPEG and JPEG2000.  相似文献
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