全文获取类型
收费全文 | 9135篇 |
免费 | 544篇 |
国内免费 | 546篇 |
专业分类
电工技术 | 350篇 |
综合类 | 404篇 |
化学工业 | 641篇 |
金属工艺 | 222篇 |
机械仪表 | 936篇 |
建筑科学 | 381篇 |
矿业工程 | 48篇 |
能源动力 | 175篇 |
轻工业 | 408篇 |
水利工程 | 37篇 |
石油天然气 | 77篇 |
武器工业 | 56篇 |
无线电 | 868篇 |
一般工业技术 | 873篇 |
冶金工业 | 204篇 |
原子能技术 | 38篇 |
自动化技术 | 4507篇 |
出版年
2024年 | 14篇 |
2023年 | 66篇 |
2022年 | 100篇 |
2021年 | 118篇 |
2020年 | 142篇 |
2019年 | 210篇 |
2018年 | 196篇 |
2017年 | 269篇 |
2016年 | 346篇 |
2015年 | 312篇 |
2014年 | 510篇 |
2013年 | 531篇 |
2012年 | 509篇 |
2011年 | 820篇 |
2010年 | 529篇 |
2009年 | 577篇 |
2008年 | 654篇 |
2007年 | 597篇 |
2006年 | 524篇 |
2005年 | 480篇 |
2004年 | 447篇 |
2003年 | 358篇 |
2002年 | 318篇 |
2001年 | 198篇 |
2000年 | 187篇 |
1999年 | 198篇 |
1998年 | 181篇 |
1997年 | 104篇 |
1996年 | 110篇 |
1995年 | 105篇 |
1994年 | 77篇 |
1993年 | 71篇 |
1992年 | 66篇 |
1991年 | 63篇 |
1990年 | 45篇 |
1989年 | 41篇 |
1988年 | 36篇 |
1987年 | 18篇 |
1986年 | 27篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper has two main objectives. The first is to examine the influence of membrane stresses on postbuckled deformations
of nonlinear elastic isotropic rectangular plates. The second is to further examine the accuracy of a new 3-D Cosserat eight
noded brick element (Nadler and Rubin in Int J Solids Struct 40: 4585–4614, 2003) which was developed within the context of
the theory of a Cosserat point. The equations of the Cosserat element include both material and geometric nonlinearities.
A number of example problems are considered which examine predictions of the Cosserat element for beams and plates and comparison
has been made with results from the commercial codes ANSYS and ADINA. Also, the approximate nonlinear postbuckling solution
described in Timoshenko and Gere (Theory of elastic stability, Mc Graw-Hill, New York) is shown to be more limited than originally
expected. These results suggest that the Cosserat element is robust, can perform well under extreme conditions and is capable
of modeling combinations of three-dimensional bodies with attached thin structures. 相似文献
62.
M. Guignard V. Nazabal F. Smektala J.‐L. Adam O. Bohnke C. Duverger A. Moréac H. Zeghlache A. Kudlinski G. Martinelli Y. Quiquempois 《Advanced functional materials》2007,17(16):3284-3294
High second‐order susceptibilities are created by thermal poling in bulk germanium disulfide based chalcogenide glasses. Experimental conditions of the poling treatment (temperature, voltage, time) were optimized for each glass composition. The second‐order nonlinear signals were recorded by using the Maker fringes experiment and a second‐order coefficient χ(2) up to 8 pm V–1 was measured in the Ge25Sb10S65 glass. This value is obtained using a simulation based on accurate knowledge of the thickness of the nonlinear layer. Two mechanisms are proposed to explain the creation of a nonlinear layer under the anode: the formation and the migration of charged defects towards the anode may mainly occur in Ge20Ga5Sb10S65 and Ge25Ga5S70 glasses, whereas the migration of Na+ ions towards the cathode may be responsible for the accumulation of negative charges under the anode in Ge33S67 and Ge25Sb10S65 glasses. Different electronic conductivity behaviors seem to be at the origin of the phenomenon. In parallel, the potential effect of the poling treatment on the structural and electronic properties is studied using Raman spectroscopy and secondary ion mass spectroscopy measurements. 相似文献
63.
Heat convection in ballast mass in railway embankments is a problem of heat convection in porous media. In order to calculate the temperature distribution of the Qing-Tibet railway embankment from the governing equations used to study forced convection for incompressible fluids porous media, detailed finite-element formulas for heat convection in porous media are derived using Galerkin’s method. The temperature distributions on central lines of the traditional railway embankment, the ripped-rock embankment, and the ripped-rock revetment embankment that were constructed on July 15, 2002 have been analyzed and compared on July 15, October 15 in the 24th year after construction, and January 15 in the 25th year after construction under the climatic and geological conditions on the Qing-Tibet Railway. The calculated results indicate that the traditional railway embankment will raise the permafrost temperature under the embankment base and make the permafrost embankment thermally unstable. The ripped-rock embankment and the ripped-rock revetment embankment will reduce the permafrost temperature under the embankment base in cold regions, therefore maintaining the thermal stability of permafrost. However, the ripped-rock embankment needs more rock mass while the ripped-rock revetment embankment need less rock mass, and its construction cost is lower than that of the former. Therefore, it is highly recommended that the ripped-rock revetment embankment be used for the Qing-Tibet railway embankment structure in high temperature permafrost regions so that the permafrost embankment can be protected as much as possible. 相似文献
64.
S. Bidault L. Viau O. Maury S. Brasselet J. Zyss E. Ishow K. Nakatani H. LeBozec 《Advanced functional materials》2006,16(17):2252-2262
The bottom‐up design of polymer films exhibiting quadratic nonlinear optical properties that can be tuned optically and chemically is described. The polymer matrices are doped with metal‐containing chromophores built around a ZnII core and photoisomerizable ligands with two different geometries. These molecules possess specifically designed photophysical and nonlinear optical properties to be used towards all‐optical poling, an interference process between one‐ and two‐photon excitations that locally induces macroscopic second‐order effects in polymer films. It is shown that grafting the molecules onto the polymer chains improves the stability of the macroscopic photoinduced nonlinearity in the films. 相似文献
65.
反复荷载下钢筋混凝土剪力墙的非线性有限元分析 总被引:1,自引:0,他引:1
本文介绍了反复荷载下非线性有限元分析程序,该程序针对钢筋混凝土剪力墙类结构的特点,采用了钢筋与混凝土复合单元计算模型,考虑混凝土裂面接触效应的反复加载混凝土应力-应变关系。在钢筋应力-应变关系中,还同时考虑了混凝土开裂后钢筋的拉伸强化效应及反复荷载下钢筋的Bausinger效应。本文还介绍了作者利用该程序对反复荷载试验的试件及Ger-venka的剪力墙板进行的计算分析。结果表明,本文所采用的分析模型是合理、准确的;和国内外以往的分析比较,本文的方法成功地消去了力-位移滞回曲线中的拐点现象,而且计算的混凝土裂缝开闭也能和实测较好地吻合。表明本文方法能为分析反复荷载下钢筋混凝土剪力墙类结构性能提供一个准确、有力的工具。 相似文献
66.
Marco Dalai Author Vitae 《Automatica》2007,43(8):1418-1425
In this paper we consider the problem of constructing confidence regions for the parameters of nonlinear dynamical systems. The proposed method uses higher order statistics and extends the LSCR (leave-out sign-dominant correlation regions) algorithm for linear systems introduced in Campi and Weyer [2005, Guaranteed non-asymptotic confidence regions in system identification. Automatica 41(10), 1751-1764. Extended version available at 〈http://www.ing.unibs.it/∼campi〉]. The confidence regions contain the true parameter value with a guaranteed probability for any finite number of data points. Moreover, the confidence regions shrink around the true parameter value as the number of data points increases. The usefulness of the proposed approach is illustrated on some simple examples. 相似文献
67.
It is stated in the above-mentioned comment that the main result of the paper Xiong, Zhang, et al. [(2006). Performance evaluation of UKF-based nonlinear filtering. Automatica 42(2), 261-270] can be extended to a class of filters, such as the extended Kalman filter (EKF). As we show here, this belief can be justified in a rigorous way, even for the nonlinear stochastic system with a nonlinear measurement equation. 相似文献
68.
本文针对目前热能表中大量存在的计算器准确度较低的问题,提出了使用高次曲线拟合的非线性修正方法,提高了准确度. 相似文献
69.
70.
Jonas Sjberg Qinghua Zhang Lennart Ljung Albert Benveniste Bernard Delyon Pierre-Yves Glorennec Hkan Hjalmarsson Anatoli Juditsky 《Automatica》1995,31(12):1691-1724
A nonlinear black-box structure for a dynamical system is a model structure that is prepared to describe virtually any nonlinear dynamics. There has been considerable recent interest in this area, with structures based on neural networks, radial basis networks, wavelet networks and hinging hyperplanes, as well as wavelet-transform-based methods and models based on fuzzy sets and fuzzy rules. This paper describes all these approaches in a common framework, from a user's perspective. It focuses on what are the common features in the different approaches, the choices that have to be made and what considerations are relevant for a successful system-identification application of these techniques. It is pointed out that the nonlinear structures can be seen as a concatenation of a mapping form observed data to a regression vector and a nonlinear mapping from the regressor space to the output space. These mappings are discussed separately. The latter mapping is usually formed as a basis function expansion. The basis functions are typically formed from one simple scalar function, which is modified in terms of scale and location. The expansion from the scalar argument to the regressor space is achieved by a radial- or a ridge-type approach. Basic techniques for estimating the parameters in the structures are criterion minimization, as well as two-step procedures, where first the relevant basis functions are determined, using data, and then a linear least-squares step to determine the coordinates of the function approximation. A particular problem is to deal with the large number of potentially necessary parameters. This is handled by making the number of ‘used’ parameters considerably less than the number of ‘offered’ parameters, by regularization, shrinking, pruning or regressor selection. 相似文献