全文获取类型
收费全文 | 28171篇 |
免费 | 3468篇 |
国内免费 | 2340篇 |
专业分类
电工技术 | 2429篇 |
技术理论 | 7篇 |
综合类 | 3816篇 |
化学工业 | 1041篇 |
金属工艺 | 302篇 |
机械仪表 | 1548篇 |
建筑科学 | 8398篇 |
矿业工程 | 400篇 |
能源动力 | 455篇 |
轻工业 | 529篇 |
水利工程 | 281篇 |
石油天然气 | 629篇 |
武器工业 | 277篇 |
无线电 | 3989篇 |
一般工业技术 | 2210篇 |
冶金工业 | 373篇 |
原子能技术 | 260篇 |
自动化技术 | 7035篇 |
出版年
2024年 | 67篇 |
2023年 | 393篇 |
2022年 | 705篇 |
2021年 | 804篇 |
2020年 | 888篇 |
2019年 | 731篇 |
2018年 | 710篇 |
2017年 | 870篇 |
2016年 | 1048篇 |
2015年 | 1170篇 |
2014年 | 2004篇 |
2013年 | 1731篇 |
2012年 | 2215篇 |
2011年 | 2383篇 |
2010年 | 2004篇 |
2009年 | 1972篇 |
2008年 | 1943篇 |
2007年 | 2094篇 |
2006年 | 1874篇 |
2005年 | 1457篇 |
2004年 | 1172篇 |
2003年 | 966篇 |
2002年 | 780篇 |
2001年 | 679篇 |
2000年 | 612篇 |
1999年 | 510篇 |
1998年 | 369篇 |
1997年 | 292篇 |
1996年 | 240篇 |
1995年 | 242篇 |
1994年 | 203篇 |
1993年 | 167篇 |
1992年 | 141篇 |
1991年 | 104篇 |
1990年 | 79篇 |
1989年 | 72篇 |
1988年 | 57篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 25篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
101.
This paper derives the admissible decompositions for a time series dynamic linear model, assuming only that the model is observable. The decompositions depend on factorizations of the characteristic polynomial of the state evolution matrix G into relatively prime factors. This generalizes the method of West (1997 ) which considers one decomposition in the particular case where G is diagonalizable. Conditions are derived for a decomposition to be independent. These results show that no autoregressive process of order d has an independent decomposition for any integer d . Two illustrations of this procedure are discussed in detail. 相似文献
102.
103.
Sarrazin Jean-Christophe; Giraudo Marie-Dominique; Pailhous Jean; Bootsma Reinoud J. 《Canadian Metallurgical Quarterly》2004,30(3):411
In 3 experiments, the authors studied the organization of spatiotemporal information in memory. Stimuli consisted of configurations of dots, presented sequentially. The stimuli were either proportional, with interdot distances corresponding to interdot durations, or not proportional, with interdol distances not corresponding to interdot durations. After a learning phase, participants reproduced the spatial (Experiment 1), temporal (Experiment 2), or spatial and temporal (Experiment 3) characteristics of the target 60 times in succession. In the nonproportional conditions, effects of variable interdot durations or distances on the reproduction of, respectively, constant distances (tau effect) or durations (kappa effect) were observed, whereas no such effects were observed when variable distances or durations were to be produced. Tau and kappa effects influenced the accuracy but not the variability of responses. The results are discussed in light of the distinction between properties of the stabilized mental image and the process of stabilization. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
105.
T. Bag 《Information Sciences》2006,176(19):2910-2931
In this paper, definitions of strongly fuzzy convergent sequence, l-fuzzy weakly convergent sequence and l-fuzzy weakly compact set are given in a fuzzy normed linear space. The concepts of fuzzy normal structure, fuzzy non-expansive mapping, uniformly convex fuzzy normed linear space are introduced and fixed point theorems for fuzzy non-expansive mappings are proved. 相似文献
106.
利用自行研制的“光电阴极多信息量测试系统”首次对国产三代微光管中的GaAs光电阴极的均匀性进行了光谱响应测试 ,结果表明该国产三代微光管存在明显的非均匀性。利用曲线拟合方法估算了GaAs光电阴极的材料性能参数 ,发现表面逸出概率不一致是非均匀性的主要原因 ,GaAs材料的少子扩散长度 (1 1 2~ 1 82 ) μm ,与阴极厚度相当 ,后界面复合速率在 (1× 1 0 5~ 1× 1 0 6 )cm/s之间 ,它限制了阴极灵敏度的提高 相似文献
107.
In this article, we are combining minimization criteria in the colorant separation process for spectral color reproduction. The colorant separation is performed by inverting a spectral printer model: the spectral Yule‐Nielsen modified Neugebauer model. The inversion of the spectral printer model is an optimization operation in which a criterion is minimized at each iteration. The approach we proposed minimizes a criterion defined by the weighted sum of a spectral difference and a perceptual color difference. The weights can be tuned with a parameter α ∞ [0, 1]. Our goal is to decrease the spectral difference between the original data and its reproduction and also to consider perceptual color difference under different illuminant conditions. In order to find the best α value, we initially compare a pure colorimetric criterion and a pure spectral criterion for the reproduction, then we combine them. We perform four colorant separations: the first separation will minimize the 1976 CIELAB color difference where four illuminants are tested, the second separation will minimize an equally weighted summation of 1976 CIELAB color difference with the four illuminants tested independently, the third colorant separation will minimize a spectral difference, and the fourth colorant separation will combine a weighted sum of a spectral difference and one of the two first colorimetric differences previously introduced. This last colorant separation can be tuned with a parameter in order to emphasize on spectral or colorimetric difference. We use a six colorants printer with artificial inks for our experiments. The prints are simulated by the spectral Yule‐Nielsen modified Neugebauer model. Two groups of data are used for our experiments. The first group describes the data printed by our printing system, which is represented by a regular grid in colorant space of the printer and the second group describes the data which is not originally produced by our printing system but mapped to the spectral printer gamut. The Esser test chart and the Macbeth Color Checker test chart have been selected for the second group. Spectral gamut mapping of this data is carried out before performing colorant separation. Our results show improvement for the colorant separations combining a sum of 1976 CIELAB color difference for a set of illuminants and for the colorant separation combining a sum of 1976 CIELAB color difference and spectral difference, especially in the case of spectral data originally produced by the printer. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 494–504, 2008 相似文献
108.
Bullwhip reduction for ARMA demand: The proportional order-up-to policy versus the full-state-feedback policy 总被引:1,自引:0,他引:1
Gerard Gaalman Author Vitae 《Automatica》2006,42(8):1283-1290
A ‘proportional’ order-up-to policy reacting to ARMA demand is analyzed using stochastic optimal control theory. This policy is compared with a full-state-feedback order-up-to policy. Necessary conditions for an optimum of a weighted sum of the inventory and the ordering variances for both policies are formulated. Based on this a relatively simple expression for the ‘full-state’ policy is derived. The comparison between the two policies demonstrates that the ‘intuitively’ designed proportional policy does not fulfill the objective of controlling both the inventory and ordering variance for all parameter values of the demand model as well as the full-state-feedback policy. The full-state-feedback policy outperforms the proportional policy in several aspects. 相似文献
109.
G. N. Lilis A. Halder S. Telukunta S. Servetto 《International journal for numerical methods in engineering》2007,71(3):277-312
Many problems in geophysics, acoustics, elasticity theory, cancer treatment, food process control and electrodynamics involve study of wave field synthesis (WFS) in some form or another. In the present work, modelling of wave propagation phenomena is studied as a static problem, using finite element method and treating time as an additional spatial dimension. In particular, WFS problems are analysed using discrete methods. It is shown that a fully finite element-based scheme is very natural and effective method for the solution of such problems. Distributed WFS in the context of two-dimensional problems is outlined and incorporation of any geometric or material non-linearities is shown to be straightforward. This has significant implications for problems in geophysics or biological media, where material inhomogeneities are quite prevalent. Numerical results are presented for several problems referring to media with material inhomogeneities and predefined absorption profiles. The method can be extended to three-dimensional problems involving anisotropic media properties in a relatively straightforward manner. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
110.
Generalized null space uncorrelated Fisher discriminant analysis for linear dimensionality reduction
We propose a generalized null space uncorrelated Fisher discriminant analysis (GNUFDA) technique integrating the uncorrelated discriminant analysis and weighted pairwise Fisher criterion. The GNUFDA can effectively deal with the small sample-size problem and perform satisfactorily when the dimensionality of the null space decreases with increase in the number of training samples per class and/or classes, C. The proposed GNUFDA can extract at most C-1 optimal uncorrelated discriminative vectors without being influenced by the null-space dimensionality. 相似文献