全文获取类型
收费全文 | 13811篇 |
免费 | 1921篇 |
国内免费 | 417篇 |
专业分类
化学 | 2029篇 |
晶体学 | 20篇 |
力学 | 370篇 |
综合类 | 141篇 |
数学 | 2180篇 |
物理学 | 2634篇 |
无线电 | 8775篇 |
出版年
2024年 | 71篇 |
2023年 | 295篇 |
2022年 | 467篇 |
2021年 | 618篇 |
2020年 | 531篇 |
2019年 | 329篇 |
2018年 | 337篇 |
2017年 | 419篇 |
2016年 | 504篇 |
2015年 | 502篇 |
2014年 | 789篇 |
2013年 | 935篇 |
2012年 | 860篇 |
2011年 | 768篇 |
2010年 | 747篇 |
2009年 | 837篇 |
2008年 | 879篇 |
2007年 | 963篇 |
2006年 | 741篇 |
2005年 | 679篇 |
2004年 | 544篇 |
2003年 | 528篇 |
2002年 | 424篇 |
2001年 | 415篇 |
2000年 | 348篇 |
1999年 | 277篇 |
1998年 | 228篇 |
1997年 | 226篇 |
1996年 | 212篇 |
1995年 | 166篇 |
1994年 | 132篇 |
1993年 | 93篇 |
1992年 | 81篇 |
1991年 | 42篇 |
1990年 | 28篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
何明一 《电子科学学刊(英文版)》1994,11(1):1-10
A new concept, the generalized inverse group (GIG) of signal, is firstly proposed and its properties, leaking coefficients and implementation with neural networks are presented. Theoretical analysis and computational simulation have shown that (1) there is a group of finite length of generalized inverse signals for any given finite signal, which forms the GIG; (2) each inverse group has different leaking coefficients, thus different abnormal states; (3) each GIG can be implemented by a grouped and improved single-layer perceptron which appears with fast convergence. When used in deconvolution, the proposed GIG can form a new parallel finite length of filtering deconvolution method. On off-line processing, the computational time is reduced to O(N) from O(N2). And the less the leaking coefficient is, the more reliable the deconvolution will be. 相似文献
132.
133.
Energy minimization and design for testability 总被引:6,自引:0,他引:6
Srimat T. Chakradhar Vishwani D. Agrawal Michael L. Bushnell 《Journal of Electronic Testing》1994,5(1):57-66
The problem of fault detection in general combinational circuits is NP-complete. The only previous result on identifying easily testable circuits is due to Fujiwara who gave a polynomial time algorithm for detecting any single stuck fault inK-bounded circuits. Such circuits may only contain logic blocks with no more thanK input lines and the blocks are so connected that there is no reconvergent fanout among them. We introduce a new class of combinational circuits called the (k, K)-circuits and present a polynomial time algorithm to detect any single or multiple stuck fault in such circuits. We represent the circuit as an undirected graphG with a vertex for each gate and an edge between a pair of vertices whenever the corresponding gates have a connection. For a (k, K)-circuit,G is a subgraph of ak-tree, which, by definition, cannot have a clique of size greater thank+1. Basically, this is a restriction on gate interconnections rather than on the function of gates comprising the circuit. The (k, K)-circuits are a generalization of Fujiwara'sK-bounded circuits. Using the bidirectional neural network model of the circuit and the energy function minimization formulation of the fault detection problem, we present a test generation algorithm for single and multiple faults in (k, K)-circuits. This polynomial time aggorithm minimizes the energy function by recursively eliminating the variables. 相似文献
134.
一种基于神经网络的模糊推理方法 总被引:4,自引:1,他引:3
对于Zadeh的模糊关系合成法则(简称CRI方法),选择一个适宜蕴涵关系矩阵是至关重要的。通常蕴涵关系矩阵的元素值是通过一个所构造的数学表达式计算的,或是由领域专家凭经验直接给出。然而,有时,特别是对于后一种情形,CRI法不能满足模糊推理最基本的一致性要求。文章构造了一个神经网络用于模糊推理,新方法不仅是CRI方法的推广,而且远比CRI方法易于满足推理的一致性要求。得益于神经网络的长处,新方法具有灵活性、可调性。文章给出了权值的具取值法。 相似文献
135.
Horst W. Hamacher Martine Labbé Stefan Nickel Anders J.V. Skriver 《Annals of Operations Research》2002,110(1-4):33-53
Locating a facility is often modeled as either the maxisum or the minisum problem, reflecting whether the facility is undesirable (obnoxious) or desirable. But many facilities are both desirable and undesirable at the same time, e.g., an airport. This can be modeled as a multicriteria network location problem, where some of the sum-objectives are maximized (push effect) and some of the sum-objectives are minimized (pull effect).We present a polynomial time algorithm for this model along with some basic theoretical results, and generalize the results also to incorporate maximin and minimax objectives. In fact, the method works for any piecewise linear objective functions. Finally, we present some computational results. 相似文献
136.
Distribution of melamine in polyester–melamine surface coatings cured under nonisothermal conditions
N. J. W. Gamage D. J. T. Hill C. A. Lukey P. J. Pomery 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):83-91
The influence of experimental cure parameters on the diffusion of reactive species in polyester–melamine thermoset coatings during curing has been investigated with X‐ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared. The diffusion of melamine plays a vital role in the curing process and, therefore, in the ultimate properties of coatings. At a low (<20%) hexamethoxymethylmelamine (HMMM) crosslinker concentration, the matrix composition is uniform, but at high HMMM concentrations, excess HMMM rapidly segregates to the air–coating interface. The rate of migration is governed by the difference in the surface free energies of polyester and HMMM and the concentration gradient of HMMM between the bulk and the surface. An increased rate of energy absorption also increases the rate of migration of HMMM to the surface. A physical model has been proposed to explain this surface segregation phenomenon in terms of cocondensation and self‐condensation reactions. It suggests that an appropriate amount of melamine can be segregated on the surface and allowed to self‐condense to form a desired thickness of a melamine topcoat through the control of the binder composition and cure conditions. This technique can be implemented to apply a melamine topcoat during cure. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 83–91, 2004 相似文献
137.
ZHANG Zu-fan DU Hui-ping JIANG Ze Chongqing University of Posts Telecommunications Chongqing China University of Electronic Science Technology of China Chengdu China 《中国邮电高校学报(英文版)》2006,13(4):29-33
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar… 相似文献
138.
In this paper, we develop call admission control algorithms for SIR-based power-controlled DS-CDMA cellular networks. We consider networks that handle both voice and data services. When a new call (or a handoff call) arrives at a base station requesting for admission, our algorithms will calculate the desired power control setpoints for the new call and all existing calls. We will provide necessary and sufficient conditions under which the power control algorithm will have a feasible solution. These conditions are obtained through deriving the inverse of the matrix used in the calculation of power control setpoints. If there is no feasible solution to power control or if the desired power levels to be received at the base station for some calls are larger than the maximum allowable power limits, the admission request will be rejected. Otherwise, the admission request will be granted. When higher priority is desired for handoff calls, we will allow different thresholds (i.e., different maximum allowable power limits) for new calls and handoff calls. We will develop an adaptive algorithm that adjusts these thresholds in real-time as environment changes. The performance of our algorithms will be shown through computer simulation and compared with existing algorithms. 相似文献
139.
本文描述一种采用BP神经网络对雷达辐射源体制和用途进行智能识别的方法 ,包括理论分析、神经网络结构设计、推理和学习算法设计、编程算法设计、实验结果比较与分析等。实验表明 ,该方法有着良好的识别效果 相似文献
140.
The self-organizing map (a neural network) was applied to the spectral pattern recognition of voice quality in 34 subjects: 15 patients operated on because of insufficient glottal closure and 19 subjects not treated for voice disorders. The voice samples, segments of sustained /a/, were perceptually rated by six experts. A self-organized acoustic feature map was first computed from tokens of /a/ and then used for the analysis of the samples. The locations of the samples on the map were determined and the distances from a normal reference were compared with the perceptual ratings. The map locations corresponded to the degree of audible disorder: the samples judged as normal were overlapping or close to the normal reference, whereas the samples judged as dysphonie were located further away from it. The comparison of pre- and postoperative samples of the patients showed that the perceived improvement of voice quality was also detected by the map. 相似文献