全文获取类型
收费全文 | 17354篇 |
免费 | 2474篇 |
国内免费 | 1675篇 |
专业分类
电工技术 | 3098篇 |
技术理论 | 1篇 |
综合类 | 2320篇 |
化学工业 | 1282篇 |
金属工艺 | 418篇 |
机械仪表 | 1192篇 |
建筑科学 | 889篇 |
矿业工程 | 405篇 |
能源动力 | 523篇 |
轻工业 | 920篇 |
水利工程 | 445篇 |
石油天然气 | 737篇 |
武器工业 | 244篇 |
无线电 | 1883篇 |
一般工业技术 | 1561篇 |
冶金工业 | 463篇 |
原子能技术 | 143篇 |
自动化技术 | 4979篇 |
出版年
2024年 | 68篇 |
2023年 | 229篇 |
2022年 | 448篇 |
2021年 | 533篇 |
2020年 | 614篇 |
2019年 | 582篇 |
2018年 | 512篇 |
2017年 | 706篇 |
2016年 | 800篇 |
2015年 | 869篇 |
2014年 | 1160篇 |
2013年 | 1253篇 |
2012年 | 1491篇 |
2011年 | 1432篇 |
2010年 | 1102篇 |
2009年 | 1173篇 |
2008年 | 1057篇 |
2007年 | 1248篇 |
2006年 | 967篇 |
2005年 | 856篇 |
2004年 | 713篇 |
2003年 | 549篇 |
2002年 | 497篇 |
2001年 | 413篇 |
2000年 | 322篇 |
1999年 | 315篇 |
1998年 | 207篇 |
1997年 | 201篇 |
1996年 | 177篇 |
1995年 | 189篇 |
1994年 | 171篇 |
1993年 | 136篇 |
1992年 | 94篇 |
1991年 | 72篇 |
1990年 | 74篇 |
1989年 | 52篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 29篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1962年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The catalytic partial oxidation of CH4 to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH4 into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl2O4 spinel phase had a positive effect on the stability of the catalyst. 相似文献
112.
Abstract. The simultaneous switching autoregressive (SSAR) model proposed by Kunitomo and Sato (A non-linearity in economic time series and disequilibrium econometric models. In Theory and Application of Mathematical Statistics (ed. A. Takemura). Tokyo:University of Tokyo Press (in Japanese), 1994; Asymmetry in economic time series and simultaneous switching autoregressive model. Struct. Change Econ. Dyn. , forthcoming (1994).) is a Markovian non-linear time series model. We investigate the finite sample as well as the asymptotic properties of the least squares estimator and the maximum likelihood (ML) estimator. Due to a specific simultaneity involved in the SSAR model, the least squares estimator is badly biased. However, the ML estimator under the assumption of Gaussian disturbances gives reasonable estimates. 相似文献
113.
《Automatica》2014,50(12):3276-3280
This paper proposes a continuous-time framework for the least-squares parameter estimation method through evolution equations. Nonlinear systems in the standard state space representation that are linear in the unknown, constant parameters are investigated. Two estimators are studied. The first one consists of a linear evolution equation while the second one consists of an impulsive linear evolution equation. The paper discusses some theoretical aspects related to the proposed estimators: uniqueness of a solution and an attractive equilibrium point which solves for the unknown parameters. A deterministic framework for the estimation under noisy measurements is proposed using a Sobolev space with negative index to model the noise. The noise can be of large magnitude. Concrete signals issued from an electronic device are used to discuss numerical aspects. 相似文献
114.
115.
116.
《自动化学报》2014,(11)
A linear transformation is proposed to deal with the consensus problem of high-order linear multi-agent systems(LMASs).In virtue of the linear transformation, the consensus problem is equivalently translated into a partial stability problem. We discuss three issues of the LMASs under a generalized linear protocol: 1) to find criteria of consensus convergence; 2) to calculate consensus function; 3) to design gain matrices in the linear consensus protocol. Precisely, we provide a necessary and sufficient criterion of consensus convergence in terms of Hurwitz stability of a matrix and give an analytical expression of the consensus function. In addition, we set up a relation between the gain matrices in the protocol and the convergence time and consensus accuracy of the agents, and then design the gain matrices with respect to a pre-specified convergence time and a required consensus accuracy. 相似文献
117.
R. J. Bhansali 《时间序列分析杂志》1993,14(2):125-146
Abstract. For predicting the future values of a stationary process { xt } ( t = 0, pL 1, pL 2,…) on the basis of its past, two key parameters are the variance V ( h ), h ≥ 1, of the h -step prediction error and Z ( h ) ={ R (0) - V ( h )}/ R (0), the corresponding measure, in an R 2 sense, of the predictability of the process from its past, where R (0) denotes the process variance. The estimation of V ( h ) and Z ( h ) from a realization of T consecutive observations of { xt } is considered, without requiring that the process follows a finite parameter model. Three different autoregressive estimators are examined and are shown to be asymptotically equivalent in the sense that as T ∝ they have the same asymptotic normal distribution. The question of bias in estimating these parameters is also examined and a bias correction is proposed. Finite sample behaviour is investigated by a simulation study. 相似文献
118.
Data reconciliation consists in modifying noisy or unreliable data in order to make them consistent with a mathematical model (herein a material flow network). The conventional approach relies on least-squares minimization. Here, we use a fuzzy set-based approach, replacing Gaussian likelihood functions by fuzzy intervals, and a leximin criterion. We show that the setting of fuzzy sets provides a generalized approach to the choice of estimated values, that is more flexible and less dependent on oftentimes debatable probabilistic justifications. It potentially encompasses interval-based formulations and the least squares method, by choosing appropriate membership functions and aggregation operations. This paper also lays bare the fact that data reconciliation under the fuzzy set approach is viewed as an information fusion problem, as opposed to the statistical tradition which solves an estimation problem. 相似文献
119.
The partial oxidation of methane to synthesis gas was studied at atmospheric pressure and in the temperature range of 550–800°C over -Al2O3-supported bimetallic Pt–Co, and monometallic Pt and Co catalysts, respectively. Both methane conversion and CO selectivity over a bimetallic Pt0.5Co1 catalyst were higher than those over monometallic Pt0.5 and Co1 catalysts. Furthermore, the addition of platinum in Pt–Co bimetallic catalysts effectively improved their resistance to carbon deposition with no coking occurring on Pt0.5Co1 during 80 h reaction. The FTIR study of CO adsorption observed only linearly bonded CO on bimetallic Pt–Co catalysts. TPR and XPS showed enhanced formation of a cobalt surface phase (CSP) in bimetallic Pt–Co catalysts. The origins of the good coking resistivity of bimetallic Pt–Co catalysts were discussed. 相似文献
120.
ExPosition is a new comprehensive R package providing crisp graphics and implementing multivariate analysis methods based on the singular value decomposition (svd). The core techniques implemented in ExPosition are: principal components analysis, (metric) multidimensional scaling, correspondence analysis, and several of their recent extensions such as barycentric discriminant analyses (e.g., discriminant correspondence analysis), multi-table analyses (e.g.,multiple factor analysis, Statis, and distatis), and non-parametric resampling techniques (e.g., permutation and bootstrap). Several examples highlight the major differences between ExPosition and similar packages. Finally, the future directions of ExPosition are discussed. 相似文献