全文获取类型
收费全文 | 30358篇 |
免费 | 890篇 |
国内免费 | 281篇 |
专业分类
电工技术 | 481篇 |
综合类 | 33篇 |
化学工业 | 4774篇 |
金属工艺 | 1063篇 |
机械仪表 | 708篇 |
建筑科学 | 448篇 |
矿业工程 | 48篇 |
能源动力 | 1497篇 |
轻工业 | 1213篇 |
水利工程 | 169篇 |
石油天然气 | 100篇 |
武器工业 | 1篇 |
无线电 | 2787篇 |
一般工业技术 | 4686篇 |
冶金工业 | 1672篇 |
原子能技术 | 276篇 |
自动化技术 | 11573篇 |
出版年
2024年 | 103篇 |
2023年 | 431篇 |
2022年 | 1003篇 |
2021年 | 1183篇 |
2020年 | 928篇 |
2019年 | 979篇 |
2018年 | 1253篇 |
2017年 | 996篇 |
2016年 | 966篇 |
2015年 | 628篇 |
2014年 | 1080篇 |
2013年 | 1768篇 |
2012年 | 1695篇 |
2011年 | 4180篇 |
2010年 | 2036篇 |
2009年 | 1875篇 |
2008年 | 1434篇 |
2007年 | 1191篇 |
2006年 | 943篇 |
2005年 | 955篇 |
2004年 | 822篇 |
2003年 | 830篇 |
2002年 | 494篇 |
2001年 | 199篇 |
2000年 | 192篇 |
1999年 | 211篇 |
1998年 | 423篇 |
1997年 | 287篇 |
1996年 | 263篇 |
1995年 | 199篇 |
1994年 | 180篇 |
1993年 | 169篇 |
1992年 | 127篇 |
1991年 | 158篇 |
1990年 | 125篇 |
1989年 | 113篇 |
1988年 | 103篇 |
1987年 | 109篇 |
1986年 | 101篇 |
1985年 | 102篇 |
1984年 | 110篇 |
1983年 | 93篇 |
1982年 | 74篇 |
1981年 | 81篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 45篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Data fitting with a spline using a real-coded genetic algorithm 总被引:2,自引:0,他引:2
Fujiichi Yoshimoto Author Vitae Toshinobu Harada Author Vitae Author Vitae 《Computer aided design》2003,35(8):751-760
To obtain a good approximation for data fitting with a spline, frequently we have to deal with knots as variables. The problem to be solved then becomes a continuous nonlinear and multivariate optimization problem with many local optima. Therefore, it is difficult to obtain the global optimum. In this paper, we propose a method for solving this problem by using a real-coded genetic algorithm. Our method can treat not only data with a smooth underlying function, but also data with an underlying function having discontinuous points and/or cusps. We search for the best model among candidate models by using the Bayes Information Criterion (BIC). With this, we can appropriately determine the number and locations of knots automatically and simultaneously. Five examples of data fitting are given to show the performance of our method. 相似文献
42.
In the modeling of the gas metal-arc (GMA) welding process, heat inputs to the workpiece by the arc and the metal transfers
have been considered separately. The heat energy delivered due to the metal transfer has been approximated in the form of
a cylindrical volumetric heat source, whose dimensions of the radius and the height are dependent on the molten metal droplet
characteristics. The pinch instability theory (PIT) and the static force balance theory (SFBT) of drop detachment have independently
been used to obtain the expressions for various characteristics of the drop,i.e., the drop radius, the drop velocity, and the drop frequency at various welding parameters. The occurrence or the nonoccurrence
of finger penetration, routinely found in the GMA welding at high welding currents, has been satisfactorily explained by the
cylindrical heat source model. The effect of various welding parameters,e.g., the welding current, the wire radiusetc., on the weld bead penetration characteristics has been investigated. In this modeling effort, the heat conduction equation
has been solved in three dimensions. 相似文献
43.
The efficient, economical and often elegant transformation from a design schema to an embodied design solution containing real components is essential for the commercial success of a product. More often the ability of the designer to explore an optimum solution is severely frustrated by the analytically intensive and time-consuming aspects of embodying a concept. This paper presents a computer based system-modelling tool that is to be used by designers during the transformation of a concept to an embodied solution particularly to deal with standard components. This environment provides for the representation of conceptual schemas and subsequent embodiment from computer based component selection modules. These selection modules encompass the full range of electronic representations for standard mechanical components. The strategy for representing a mechanical system, its included components and their associated representations is discussed. The process of constructing a system model, specifying the desired performance characteristics and system resolution are also described. 相似文献
44.
Backlash is one of the most important non-linearities that limit the performance of speed and position control in industrial, robotics, automotive, automation and other applications. The control of systems with backlash has been the subject of study since the 1940s. This survey reveals that surprisingly few control innovations have been presented since the early path breaking papers that introduced the describing function analysis of systems with backlash. Promising developments are however taking place using adaptive and non-linear control strategies. 相似文献
45.
46.
H.A. Barker Author Vitae A.H. Tan Author Vitae K.R. Godfrey Author Vitae 《Automatica》2003,39(1):127-133
Analysis of systems with direction-dependent dynamics is currently limited to cases in which the dynamics in the two directions of the output are first order; results for such systems have been published for both pseudo-random maximum-length binary (MLB) and inverse-repeat maximum-length binary (IR-MLB) inputs. These relatively limited analytical results make it useful to examine alternative ways of modelling such systems and in this paper, Wiener models are considered for this purpose. Methods for optimising the Wiener model parameters by matching the system and model cross-correlation functions, outputs, and discrete Fourier transforms of the outputs are considered, and the results are compared. These methods are also applied to a first-order direction-dependent system with a maximum-length ternary (MLT) input, for which no analytical results are currently available, and to a second-order system with an IR-MLB input. 相似文献
47.
Terry WindeattAuthor Vitae 《Pattern recognition》2003,36(12):2743-2756
Various measures, such as Margin and Bias/Variance, have been proposed with the aim of gaining a better understanding of why Multiple Classifier Systems (MCS) perform as well as they do. While these measures provide different perspectives for MCS analysis, it is not clear how to use them for MCS design. In this paper a different measure based on a spectral representation is proposed for two-class problems. It incorporates terms representing positive and negative correlation of pairs of training patterns with respect to class labels. Experiments employing MLP base classifiers, in which parameters are fixed but systematically varied, demonstrate the sensitivity of the proposed measure to base classifier complexity. 相似文献
48.
In the present work Taguchi's approach has been applied to the V-process castings of Al-11 per cent Si alloy to acertain the most influential control factors which will provide better and consistent surface finish to the castings regardless of the noise factors present. The control factors of the V-process that may affect the quality of the castings are the molding sand, vibration frequency, vibrating time, degree of vacuum imposed, and pouring temperature. In order to understand how these factors affect the surface roughness of the V-process castings, response surface methodology has been applied, and to obtain the optimal setting of the control factors Taguchi's method has been used. It is found that the pouring temperature has a significant effect on the surface roughness of Al-11 per cent Si alloy castings made by a V-process. Thus the pouring temperature must be kept at the lower level. All other factors are insignificant. Therefore, any setting of the insignificant factors/variables that give the minimum cost can be used. 相似文献
49.
50.