全文获取类型
收费全文 | 62376篇 |
免费 | 9096篇 |
国内免费 | 5493篇 |
专业分类
电工技术 | 7824篇 |
技术理论 | 4篇 |
综合类 | 6355篇 |
化学工业 | 5298篇 |
金属工艺 | 2208篇 |
机械仪表 | 6090篇 |
建筑科学 | 3057篇 |
矿业工程 | 2133篇 |
能源动力 | 3099篇 |
轻工业 | 3733篇 |
水利工程 | 1772篇 |
石油天然气 | 2635篇 |
武器工业 | 875篇 |
无线电 | 5043篇 |
一般工业技术 | 5448篇 |
冶金工业 | 1933篇 |
原子能技术 | 293篇 |
自动化技术 | 19165篇 |
出版年
2024年 | 608篇 |
2023年 | 1552篇 |
2022年 | 2671篇 |
2021年 | 2787篇 |
2020年 | 3092篇 |
2019年 | 2626篇 |
2018年 | 2352篇 |
2017年 | 2870篇 |
2016年 | 3126篇 |
2015年 | 3475篇 |
2014年 | 4886篇 |
2013年 | 4684篇 |
2012年 | 5330篇 |
2011年 | 5369篇 |
2010年 | 3719篇 |
2009年 | 3918篇 |
2008年 | 3477篇 |
2007年 | 3891篇 |
2006年 | 3190篇 |
2005年 | 2574篇 |
2004年 | 2060篇 |
2003年 | 1650篇 |
2002年 | 1370篇 |
2001年 | 1107篇 |
2000年 | 909篇 |
1999年 | 609篇 |
1998年 | 581篇 |
1997年 | 484篇 |
1996年 | 387篇 |
1995年 | 331篇 |
1994年 | 276篇 |
1993年 | 208篇 |
1992年 | 171篇 |
1991年 | 146篇 |
1990年 | 120篇 |
1989年 | 100篇 |
1988年 | 63篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1959年 | 5篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
范忠礼 《电信工程技术与标准化》2002,(4):43-46
本提出了一种标准化的光控制平面。阐明了开了用于光传输网的控制平面所遇到的选择与挑战。光控制平面被分解成邻居发现、服务发现、连接控制和拓扑、资源发现等几个基本的过程。不同的网络组织和分割导致了几个不同的自动配置模型:软性持久链路模型、用户接口模型和对等模型。这是构成以IP为中心的光传输网的控制和管理基础。同时也介绍了基于SDH光交换的新一代CIENA公司智能光网络,它具有大容量光交换能力和网络拓扑结构自动发现、端对端电路配置、带宽动态分配等功能及特点,将大大提高数据、电路业务的服务质量,新一代智能光网络是干线和城域网络交换传输最佳的选择。 相似文献
54.
空间桁架结构拓扑优化设计的线性规划方法 总被引:1,自引:0,他引:1
本文以杆件内力为设计变量,构造了多工况作用下空间桁架结构拓扑优化的线性规划模型,考虑了应力和位移约束,能够避免奇异最优拓扑和不稳定结构的产生。 相似文献
55.
Optimizing of laminar viscous flow through a pipe by two dimensionless values is investigated analytically. Dimensionless entropy generation and pumping power to heat transfer rate ratio are used as basis for constant viscous and the temperature dependence on the viscosity. For this matter we calculate entropy generation and pumping power for a fully developed in a pipe subjected to constant wall temperature for either constant viscosity and the variable viscosity. The variation entropy generation increase along the pipe length for viscous fluid is drawn, either the variation summation dimensionless entropy generation and the pumping power to heat transfer rate ratio are varying the fluid inlet temperature for fixed pipe length and are varying pipe length for fixed fluid inlet temperature are drawn. For low heat transfer conditions the entropy generation due to viscosity friction becomes dominant and the dependence of viscosity with the temperature becomes essentially important to be considered. 相似文献
56.
Damiana Chinese Antonella Meneghetti Gioacchino Nardin Patrizia Simeoni 《国际能源研究杂志》2007,31(9):829-848
A mixed integer linear programming model combined with a more traditional design by scenarios is proposed to optimize facilities size and operation mode of a municipal energy system involving significant civil centres and a hospital. Moving from the need of a new heat and power station for the local hospital due to the construction of new pavilions, the opportunity of involving other centres in the neighbourhood in a distributed cogeneration system is analysed, increasing system complexity step by step. Smaller cogeneration units tailored to hospital needs are rewarding ventures with relatively low risks but, in a country whose traditional power generation systems heavily rely on fossil fuels and where energy policy and market conditions can make it profitable to sell surplus power, district heating systems foster the installation of larger cogenerators and lead thereby to higher profits and to better performance as for primary energy savings and greenhouse gases emission reduction. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
57.
蒙特卡洛法速度谱的自动拾取 总被引:3,自引:3,他引:0
蒙特卡洛速度谱的自动拾取采用一种非线性优化的快速方法,所得叠加速度的精度可以满足常规地震资料处理中叠加的要求,转换为层速度后可用于叠前深度偏移成象,在给定初始速度模型前提下建立优化目标函数。采用蒙特卡洛非线性优化算法,以最大相似度量准则在考虑实际地质条件前提下给出速度约束条件,对初始速度模型加以扰动,自动寻找速度谱中叠加能量的全局最优解,从而获得合理的速度模型。实际地震资料处理的应用结果表明,自动拾取速度谱比常规的人工速度谱解释工作的效率大幅度提高。在SUN Ultra60机上,仅需1h即可完成2000km的地震资料的速度谱拾取任务,而且所获得的速度模型不受人为因素影响,转换所得的层速度模型用于叠前深度偏移后,获得了满意的成象效果。 相似文献
58.
59.
A. VAN LOEY A. FRANSIS M. HENDRICKX G. MAESMANS J. de NORONHA P. TOBBACK 《Journal of food science》1994,59(4):828-832
Based on thermal degradation kinetics and heat transfer expressed as the Ball formula method, a simplified approach was used to optimize sterilization processes for thermal softening of white beans (Phaseolus vulgaris, subsp. nanus Metz., variety Manteca de Leon) Constant retort profiles in a still and end-over-end rotary water cascading retort (Barriquand Steriflow) were used. Quality attributes of beans processed at the optimum were evaluated by a trained taste panel and by a tenderometer. Both approaches could distinguish (P<0.01) between attributes of products from optimal rotary and still processes. End-over-end rotation resulted in faster heat penetration and better quality retention of beans. Texture of white beans processed at 4° or 8°C from the optimal temperature could be distinguished (P<0.01) by the sensory panel and by the tenderometer. 相似文献
60.
G. Dong 《Annals of Mathematics and Artificial Intelligence》1993,7(1-4):107-127
LDL is one of the recently proposed logical query languages, which incorporate set, for data and knowledge base systems. Since LDL programs can simulate negation, they are not monotonic in general. On the other hand, there are monotonic LDL programs. This paper addresses the natural question of “When are the generally nonmonotonic LDL programs monotonic?” and investigates related topics such as useful applications for monotonicity. We discuss four kinds of monotonicity, and examine two of them in depth. The first of the two, called “ω-monotonicity”, is shown to be undecidable even when limited to single-stratum programs. The second, called “uniform monotonicity”, is shown to implyω-monotonicity. We characterize the uniform monotonicity of a program (i) by a relationship between its Bancilhon-Khoshafian semantics and its LDL semantics, and (ii) with a useful property called subset completion independence. Characterization (ii) implies that uniformly monotonie programs can be evaluated more efficiently by discarding dominated facts. Finally, we provide some necessary and/or sufficient, syntactic conditions for uniform monotonicity. The conditions pinpoint (a) enumerated set terms, (b) negations of membership and inclusion, and (c) sharing of set terms as the main source for nonuniform monotonicity. 相似文献