全文获取类型
收费全文 | 18855篇 |
免费 | 1616篇 |
国内免费 | 1274篇 |
专业分类
电工技术 | 1765篇 |
综合类 | 2406篇 |
化学工业 | 761篇 |
金属工艺 | 485篇 |
机械仪表 | 1294篇 |
建筑科学 | 520篇 |
矿业工程 | 295篇 |
能源动力 | 471篇 |
轻工业 | 272篇 |
水利工程 | 400篇 |
石油天然气 | 228篇 |
武器工业 | 164篇 |
无线电 | 1285篇 |
一般工业技术 | 1590篇 |
冶金工业 | 231篇 |
原子能技术 | 55篇 |
自动化技术 | 9523篇 |
出版年
2024年 | 42篇 |
2023年 | 159篇 |
2022年 | 246篇 |
2021年 | 312篇 |
2020年 | 424篇 |
2019年 | 464篇 |
2018年 | 385篇 |
2017年 | 584篇 |
2016年 | 597篇 |
2015年 | 702篇 |
2014年 | 1008篇 |
2013年 | 1469篇 |
2012年 | 1125篇 |
2011年 | 1212篇 |
2010年 | 954篇 |
2009年 | 1071篇 |
2008年 | 1165篇 |
2007年 | 1244篇 |
2006年 | 1091篇 |
2005年 | 963篇 |
2004年 | 810篇 |
2003年 | 720篇 |
2002年 | 664篇 |
2001年 | 556篇 |
2000年 | 511篇 |
1999年 | 437篇 |
1998年 | 356篇 |
1997年 | 360篇 |
1996年 | 302篇 |
1995年 | 267篇 |
1994年 | 273篇 |
1993年 | 198篇 |
1992年 | 189篇 |
1991年 | 150篇 |
1990年 | 113篇 |
1989年 | 103篇 |
1988年 | 92篇 |
1987年 | 57篇 |
1986年 | 53篇 |
1985年 | 39篇 |
1984年 | 57篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 12篇 |
1977年 | 21篇 |
1976年 | 14篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
基于二阶矩阵微分方程的机械振动系统线性二次型调节器设计 总被引:1,自引:0,他引:1
本文讨论机械振动系统线性二次型状态调节器(LQR)问题,直接针对系统二阶运动微分方程,性能指标为一个依赖于二阶导数的泛函。由欧拉-拉格朗日方程得出一个系统矩阵增广的二阶线性微分方程,指出该方程稳定的特征对就是最优控制振动系统闭环特征对,并给出求解最优控制状态反馈矩阵的方法,另外,由本文方法还可得出基于速度和加速度反馈的最优控制反馈矩阵。这里不涉及求解代数矩阵Riccati方程。 相似文献
82.
杨怀义 《数字社区&智能家居》2006,(14)
网格袋布局管理器是java布局中最有用、最灵活、最复杂、最难掌握的一种布局管理器,实际上,如果我们明白了在布局时它利用了单元格相对坐标定位这一点,以及各个约束条件在布局中的作用,网格袋布局也会变得很轻松。 相似文献
83.
Label printing finds many applications in industry. However, this task is still labor intensive in many printing factories. Since each template can only accommodate a fixed number of labels, an important task is to work out the compositions of templates by allocating suitable labels to each template in order to fulfill the order requirements effectively. The template design could be rather arbitrary, which usually ends up with a lot of excessive printed labels. Enhancing the template design will significantly improve the efficiency of the printing process, and, at the same time, reduce the waste of resources. This motivates the study of more automatic design methods. In this paper, the problem is first formulated as a nonlinear integer programming problem. The main variables in the formulation are the compositions and the printing frequencies of templates. For practical purpose, each type of label is confined to one template only which allows automated packing and handling. The structure of the problems is carefully analyzed and a new algorithm is proposed. Numerical results show that the proposed method is a simple but effective way of generating good template designs. 相似文献
84.
An adaptive product platform offers high customizability for generating feasible product variants for customer requirements. Customization takes place not only to product platform structure but also to its relevant parameters. Structural and parametric optimization processes are interwoven with each other to achieve the total optimality. This paper presents an evolutionary method dealing with interwoven structural and parametric optimization of adaptive platform product customization. The method combines genetic programming and genetic algorithm for handling structural and parametric optimization, respectively. Efficient genetic representation and operation schemes are carefully adapted. While designing these schemes, features specific to structural and parameter customization are considered for the simplification of platform product management. The experimental results show that the performance of the proposed algorithm outperforms that of the tandem evolutionary algorithm in which a genetic algorithm for parametric optimization is totally nested in a genetic programming for structural optimization. 相似文献
85.
P. I. Stetsyuk 《Cybernetics and Systems Analysis》2006,42(1):54-64
New quadratic models are proposed to improve the upper-bound estimates in the maximum weighted cut problem. They are found
by two original methods for deriving redundant quadratic constraints. A well-known linear model is shown to follow from the
models proposed. Recommendations on how to develop its strengthened analogs are given.
This study is partially sponsored from the grant UM2-2574-KV-03 (CRDF Cooperative Grants Program).
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 63—75, January–February 2006. 相似文献
86.
U. Amato G. Amodeo V. Brandi V. Cuomo D. Ruggi C. Serio V. Silvestrini G. C. Tosato 《国际能源研究杂志》1985,9(1):33-51
In Italy solar thermal energy and energy from biogas are two possible means of reducing dependence on energy imports. Using a multiperiod LP model (MARKAL) the authors assessed the likely potential of both technologies under various circumstances. The study covered the period 1980–2005, in five segments of five years. It focused only on the subsystem of the energy end-uses which can be substituted for by solar thermal and biogas technologies. The overall non-renewable sources which can be saved in 20 years by these technologies total 450 PJ (1 PJ = 101 5 J) if the fuel prices rise at 0 per cent average annual, 1450 PJ if the fuel prices rise at 4.2 per cent average annual, 1860 PJ if the fuel prices rise at 7.2 per cent average annual and 3780 PJ if the fuel prices rise at 15 per cent average annual. However the most competitive technologies appear to be solar water heaters used mainly in the private and commercial sectors and biogas systems used mainly in the agricultural sector. The study was carried out by APRE under ENEA (formerly CNEN) contract and was intended to serve as an analytical basis for establishing an overall development and demonstration strategy for end-use renewable technologies in Italy. 相似文献
87.
The objective, strategy, and implementation details of a new undergraduate course, Internet-based Instrumentation and Control, are presented. The course has a companion laboratory that is supported by the National Science Foundation and industry. The combination is offered to senior-level undergraduate engineering students interested in sensing, instrumentation, control, and web programming that want to learn more about the integration of these technologies for solving real-world engineering problems. The course will also be offered to gifted high school seniors with similar interests and can serve as a vehicle to attract them to engineering disciplines. Preliminary assessment of the first offering of the course is encouraging and has shown that the course has achieved success in helping students understand concepts and master basic technologies for developing Internet-based automatic systems. 相似文献
88.
T.J. Adye R. Dubitzky S.J. Gowdy G.Hamel de Monchenault R.G. Jacobsen S. Kluth E. Leonardi L. Wilden 《Computer Physics Communications》2003,150(3):197-214
A system based on ROOT for handling the micro-DST of the BaBar experiment is described. The purpose of the Kanga system is to have micro-DST data available in a format well suited for data distribution within a world-wide collaboration with many small sites. The design requirements, implementation and experience in practice after three years of data taking by the BaBar experiment are presented. 相似文献
89.
90.
An Interval Fuzzy Multiobjective Watershed Management Model for the Lake Qionghai Watershed, China 总被引:4,自引:0,他引:4
Lijing Wang Wei Meng Huaicheng Guo Zhenxing Zhang Yong Liu Yingying Fan 《Water Resources Management》2006,20(5):701-721
Integrated watershed management is required to ensure the reasonable use of resources and reconcile interactions among natural and human systems. In the present study, an interval fuzzy multiobjective programming (IFMOP) method was used to solve an integrated watershed management problem. Based on system analysis, an IFMOP model suitable for a lake watershed system {IFMOPLWS} was developed and applied to the Lake Qionghai watershed in China. Scenario analysis and an interactive approach were used in the solution process. In this manner, various system components were incorporated into one framework for holistic consideration and optimization. Integrality and uncertainty, as well as the multiobjective and dynamic characteristics of the watershed system, were well addressed. Using two scenarios, two planning schemes were generated. Agriculture, tourism, macroeconomics, cropland use, water supply, forest coverage, soil erosion, and water pollution were fully interpreted and compared to identify a preferable planning alternative for local agencies. This study showed that the IFMOPLWS is a powerful tool for integrated watershed management planning and can provide a solid base for sustainable watershed management. 相似文献