全文获取类型
收费全文 | 59279篇 |
免费 | 8818篇 |
国内免费 | 5173篇 |
专业分类
电工技术 | 7617篇 |
技术理论 | 2篇 |
综合类 | 6035篇 |
化学工业 | 5060篇 |
金属工艺 | 2162篇 |
机械仪表 | 6167篇 |
建筑科学 | 2799篇 |
矿业工程 | 2046篇 |
能源动力 | 3043篇 |
轻工业 | 3262篇 |
水利工程 | 1586篇 |
石油天然气 | 2605篇 |
武器工业 | 827篇 |
无线电 | 4573篇 |
一般工业技术 | 5213篇 |
冶金工业 | 1704篇 |
原子能技术 | 299篇 |
自动化技术 | 18270篇 |
出版年
2024年 | 292篇 |
2023年 | 1405篇 |
2022年 | 2535篇 |
2021年 | 2672篇 |
2020年 | 2881篇 |
2019年 | 2477篇 |
2018年 | 2197篇 |
2017年 | 2681篇 |
2016年 | 2974篇 |
2015年 | 3326篇 |
2014年 | 4683篇 |
2013年 | 4494篇 |
2012年 | 5152篇 |
2011年 | 5168篇 |
2010年 | 3560篇 |
2009年 | 3780篇 |
2008年 | 3289篇 |
2007年 | 3709篇 |
2006年 | 3062篇 |
2005年 | 2437篇 |
2004年 | 1990篇 |
2003年 | 1568篇 |
2002年 | 1331篇 |
2001年 | 1062篇 |
2000年 | 899篇 |
1999年 | 603篇 |
1998年 | 578篇 |
1997年 | 497篇 |
1996年 | 359篇 |
1995年 | 337篇 |
1994年 | 272篇 |
1993年 | 204篇 |
1992年 | 174篇 |
1991年 | 142篇 |
1990年 | 122篇 |
1989年 | 101篇 |
1988年 | 64篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1959年 | 4篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
利用系统分析方法进行单井措施优选 总被引:1,自引:0,他引:1
油井措施增油一直是油田控制产量递减、含水上升的主要做法,但是随着油田开采程度加深,地下油水分布十分复杂,选择油水井措施难度越来越大。为此,运用系统分析方法进行单井措施优选,通过对区块水驱油、水驱水、井间干扰以及油井的液、油、含水率间关系,综合判断出区块内滞留区、死油区和动用好的区域,指出今后挖潜方向。此方法均应用动态数据,客观性较强、准确性较高,克服了以往选择单井措施的盲目性和主观性。并将该方法在大庆油田杏八、九区基础井网提液试验过程中得到应用,效果较好。 相似文献
113.
Jrgen Sjdin 《国际能源研究杂志》2002,26(6):475-494
Energy taxation in Sweden is complicated and strongly guides and governs district energy production. Consequently, there is a need for methods for accurate calculation and analysis of effects that different energy tax schemes may have on district energy utilities. Here, a practicable method to analyse influence of such governmental policy measures is demonstrated. The Swedish Government has for some years now been working on a reform of energy taxation, and during this process, several interest groups have expressed their own proposals for improving and developing the system of energy taxation. Together with the present system of taxation, four new alternatives, including the proposed directive of the European Commission, are outlined in the paper. In a case study, an analysis is made of how the different tax alternatives may influence the choice of profitable investments and use of energy carriers in a medium‐sized district‐heating utility. The calculations are made with a linear‐programming model framework. By calculating suitable types and sizes of new investments, if any, and the operation of existing and potential plants, total energy costs are minimized. Results of the analysis include the most profitable investments, which fuel should be used, roughly when during a year plants should be in operation, and at what output. In most scenarios, the most profitable measure is to invest in a waste incineration plant. However, a crucial assumption is, with reference to the new Swedish waste disposal act, a significant income from incinerating refuse. Without this income, different tax schemes result in different technical solutions being most profitable. An investment in cogeneration seems possible in only one scenario. It is also found that particular features of some alternatives seem to oppose both main governmental policy goals, and intentions of the district heating company. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
114.
Alessandro Fantoni Manuela Viera Rodrigo Martins 《Solar Energy Materials & Solar Cells》2002,73(2):148
In this paper a set of one-dimensional simulations of a-Si:H p–i–n junctions under different illumination conditions and with different intrinsic layer are presented. The simulation program ASCA permits the analysis of the internal electrical behaviour of the cell allowing a comparison among the different internal configurations determined by a change in the input set. Results about the internal electric configuration will be presented and discussed outlining their influence on the current tension characteristic curve. Considerations about the drift–diffusion and the generation–recombination balance distributions, outlined by the simulation, can be used to explain the correlation between the basic device output, the i-layer characteristics (thickness and DOS), the incident radiation intensity and photon energy. 相似文献
115.
William Fornaciari Donatella Sciuto Cristina Silvano Vittorio Zaccaria 《Design Automation for Embedded Systems》2002,7(1-2):7-33
In this paper, we propose a system-level design methodology for the efficient exploration of the architectural parameters of the memory sub-systems, from the energy-delay joint perspective. The aim is to find the best configuration of the memory hierarchy without performing the exhaustive analysis of the parameters space. The target system architecture includes the processor, separated instruction and data caches, the main memory, and the system buses. To achieve a fast convergence toward the near-optimal configuration, the proposed methodology adopts an iterative local-search algorithm based on the sensitivity analysis of the cost function with respect to the tuning parameters of the memory sub-system architecture. The exploration strategy is based on the Energy-Delay Product (EDP) metric taking into consideration both performance and energy constraints. The effectiveness of the proposed methodology has been demonstrated through the design space exploration of a real-world case study: the optimization of the memory hierarchy of a MicroSPARC2-based system executing the set of Mediabench benchmarks for multimedia applications. Experimental results have shown an optimization speedup of 2 orders of magnitude with respect to the full search approach, while the near-optimal system-level configuration is characterized by a distance from the optimal full search configuration in the range of 2%. 相似文献
116.
采用复合形优化法,结合《港口及航道护岸工程设计与施工规范》中推荐的抗滑、抗倾稳定的分项系数计算方法,并考虑了内河航道船形波等作用的影响效应,对重力式护岸断面进行了优化。 相似文献
117.
Transmission of signals, whether on-chip or off-chip, places severe constraints on timing and extracts a large price in energy. New silicon device technologies, such as back-plane CMOS, provide a programmable and adaptable threshold voltage as an additional tool that can be used for low power design. We show that one particularly desirable use of this freedom is energy-efficient high-speed transmission across long interconnects using multi-valued encoding. Our multi-valued CMOS circuits take advantage of the threshold voltage control of the transistors, by using the signal-voltage-to-threshold-voltage span, in order to make area-efficient implementations of 4-PAM (pulse amplitude modulation) transceivers operating at high speed. In a comparison of a variety of published technologies, for signal transmission with interconnects of 10-15 mm length, we show up to 50% improvement in energy for on-chip signal transmission over binary encoding together with higher limits for operating speeds without a penalty in circuit noise margin. 相似文献
118.
119.
The convexity and continuity of fuzzy mappings are defined through a linear ordering and a metric on the set of fuzzy numbers. The local-global minimum property of real-valued convex functions is extended to convex fuzzy mappings. It is proved that a strict local minimizer of a quasiconvex fuzzy mapping is also a strict global minimizer. Characterizations for convex fuzzy mappings and quasiconvex fuzzy mappings are given. In addition, the Weirstrass theorem is extended from real-valued functions to fuzzy mappings. 相似文献
120.
Chunshien Li Roland Priemer Kuo‐Hsiang Cheng 《International journal for numerical methods in engineering》2004,60(7):1301-1315
We give a random optimization (RO) algorithm to optimize a real‐valued function of n real variables. During the optimization process, interpolation points are examined to follow valleys, and jumps to new starting points are executed to avoid numerous iterations in local minima. Convergence with probability one to the global minimum of a function is proved. The proposed RO method is a simple, derivative‐free and computationally moderate algorithm, with excellent performance compared to other RO methods. Seven functions, which are commonly used to test the performance of optimization methods, are used to evaluate the performance of the RO algorithm given here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献