全文获取类型
收费全文 | 240181篇 |
免费 | 32072篇 |
国内免费 | 18220篇 |
专业分类
电工技术 | 33044篇 |
技术理论 | 11篇 |
综合类 | 23777篇 |
化学工业 | 23227篇 |
金属工艺 | 8499篇 |
机械仪表 | 14684篇 |
建筑科学 | 12590篇 |
矿业工程 | 5982篇 |
能源动力 | 5072篇 |
轻工业 | 10569篇 |
水利工程 | 4553篇 |
石油天然气 | 5455篇 |
武器工业 | 2499篇 |
无线电 | 44014篇 |
一般工业技术 | 19235篇 |
冶金工业 | 6472篇 |
原子能技术 | 1624篇 |
自动化技术 | 69166篇 |
出版年
2024年 | 1521篇 |
2023年 | 4715篇 |
2022年 | 10008篇 |
2021年 | 11052篇 |
2020年 | 9351篇 |
2019年 | 7683篇 |
2018年 | 7102篇 |
2017年 | 8780篇 |
2016年 | 10067篇 |
2015年 | 11640篇 |
2014年 | 16477篇 |
2013年 | 15631篇 |
2012年 | 17294篇 |
2011年 | 17100篇 |
2010年 | 13356篇 |
2009年 | 13927篇 |
2008年 | 13790篇 |
2007年 | 16453篇 |
2006年 | 14652篇 |
2005年 | 12802篇 |
2004年 | 10201篇 |
2003年 | 9004篇 |
2002年 | 7064篇 |
2001年 | 5988篇 |
2000年 | 4986篇 |
1999年 | 3973篇 |
1998年 | 3001篇 |
1997年 | 2478篇 |
1996年 | 2189篇 |
1995年 | 1747篇 |
1994年 | 1384篇 |
1993年 | 1006篇 |
1992年 | 777篇 |
1991年 | 574篇 |
1990年 | 525篇 |
1989年 | 427篇 |
1988年 | 289篇 |
1987年 | 186篇 |
1986年 | 153篇 |
1985年 | 153篇 |
1984年 | 143篇 |
1983年 | 116篇 |
1982年 | 100篇 |
1981年 | 65篇 |
1980年 | 68篇 |
1979年 | 39篇 |
1966年 | 27篇 |
1964年 | 38篇 |
1962年 | 65篇 |
1959年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this paper, symbolic code matrix ,constant matrix and count matrix are defined .The first twomatrices are used to describe the elemental expression of augmented matrix and the nede admittance equa-tion is thus obtained. The third matrix is used to obtain the incoming degree matrix, and according to thematrix all the 1- factors of the Coates graph are given. By using the data code, the determinant is expandedand the same items in the expansion are merged. Thus the symbolic network function in which no term can-cellation occurs is generated. 相似文献
62.
63.
64.
Bandwidth Adaptation Algorithms for Adaptive Multimedia Services in Mobile Cellular Networks 总被引:3,自引:0,他引:3
The fluctuation of available link bandwidth in mobilecellular networks motivates the study of adaptive multimediaservices, where the bandwidth of an ongoing multimedia call can bedynamically adjusted. We analyze the diverse objectives of theadaptive multimedia framework and propose two bandwidth adaptationalgorithms (BAAs) that can satisfy these objectives. The firstalgorithm, BAA-RA, takes into consideration revenue and``anti-adaptation' where anti-adaptation means that a user feelsuncomfortable whenever the bandwidth of the user's call ischanged. This algorithm achieves near-optimal total revenue withmuch less complexity compared to an optimal BAA. The secondalgorithm, BAA-RF, considers revenue and fairness, and aims at themaximum revenue generation while satisfying the fairnessconstraint defined herein. Comprehensive simulation experimentsshow that the difference of the total revenue of BAA-RA and thatof an optimal BAA is negligible. Also, numerical results revealthat there is a conflicting relationship between anti-adaptationand fairness. 相似文献
65.
66.
67.
温熙华 《电信工程技术与标准化》2002,(5):36-39
本主要介绍基于CDMA智能网平台的一种增值业务——“位置服务”,阐述这个业务的网络结构、涉及到的技术问题和解决方案,并将这个整体思路投入到开发业务中去。 相似文献
68.
Multi-valued and universal binary neurons (MVN and UBN) are the neural processing elements with the complex-valued weights and high functionality. It is possible to implement an arbitrary mapping described by partially defined multiple-valued function on the single MVN. An arbitrary mapping described by partially defined or fully defined Boolean function, which can be non-threshold, may be implemented on the single UBN. The quickly converging learning algorithms exist for both types of neurons. Such features of the MVN and UBN may be used for solving the different problems. One of the most successful applications of the MVN and UBN is their usage as basic neurons in the Cellular Neural Networks (CNN). It opens the new effective opportunities in nonlinear image filtering and its applications to noise reduction, edge detection and solving of the super resolution problem. A number of experimental results are presented to illustrate the performance of the proposed algorithms.An erratum to this article can be found at 相似文献
69.
Paul J. Flory 《Polymer International》1985,17(2):96-102
The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters. 相似文献
70.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献