全文获取类型
收费全文 | 12383篇 |
免费 | 1907篇 |
国内免费 | 409篇 |
专业分类
电工技术 | 582篇 |
技术理论 | 1篇 |
综合类 | 1083篇 |
化学工业 | 261篇 |
金属工艺 | 525篇 |
机械仪表 | 923篇 |
建筑科学 | 1536篇 |
矿业工程 | 359篇 |
能源动力 | 148篇 |
轻工业 | 74篇 |
水利工程 | 519篇 |
石油天然气 | 177篇 |
武器工业 | 228篇 |
无线电 | 5319篇 |
一般工业技术 | 652篇 |
冶金工业 | 144篇 |
原子能技术 | 66篇 |
自动化技术 | 2102篇 |
出版年
2024年 | 65篇 |
2023年 | 193篇 |
2022年 | 339篇 |
2021年 | 300篇 |
2020年 | 480篇 |
2019年 | 501篇 |
2018年 | 407篇 |
2017年 | 442篇 |
2016年 | 434篇 |
2015年 | 549篇 |
2014年 | 964篇 |
2013年 | 841篇 |
2012年 | 1093篇 |
2011年 | 1061篇 |
2010年 | 810篇 |
2009年 | 779篇 |
2008年 | 701篇 |
2007年 | 857篇 |
2006年 | 720篇 |
2005年 | 552篇 |
2004年 | 478篇 |
2003年 | 443篇 |
2002年 | 362篇 |
2001年 | 283篇 |
2000年 | 216篇 |
1999年 | 141篇 |
1998年 | 124篇 |
1997年 | 98篇 |
1996年 | 101篇 |
1995年 | 80篇 |
1994年 | 63篇 |
1993年 | 49篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
基于列队竞争算法的变权值树状管网优化布置 总被引:3,自引:2,他引:1
根据树状输配水管网的特点,提出一种简化的灌溉输配水管网优化布置模型及求解方法。该模型的目标函数仅有各个管段的长度和流量,既考虑了流量的变化,实现变权值的管网优化布置,又摒除了管材的价格、规格型号等因素的影响,使得优化计算更简便。用列队竞争算法对该模型进行求解,首先用图论的有关理论建立管网系统的连接矩阵、流量向量等,并根据邻接矩阵表示的树图的特点设计了相应的适应度函数、编码方法和变异算子。通过算例表明该算法能够获得费用最小的布置方案,与单亲遗传算法和模拟退火遗传算法相比,该方法模型简单,控制参数少,收敛速度快,有较高的搜索效率和稳定性。 相似文献
992.
993.
Faulty planning will result in project failure, whereas high-quality project planning increases the project's chances of success. The paper reports on the successful development and implementation of a model aimed at evaluating the quality of project planning. The model is based on both the abilities required of the project manager and the organizational support required for a proper project management infrastructure. The model was validated and applied by 282 project managers in nine organizations, where strong and weak planning processes were identified and analysed. 相似文献
994.
The material flow is a major focus point in improving productivity in today’s product diversified manufacturing organizations. Nevertheless, there is still a lack of efficient methods to control material flow through manufacturing processes in cases where multi-item tracking is difficult to achieve. This paper presents an RFID-based RTLS (Real-Time Location System) solution for obtaining multi-item work-in-process visibility within a manufacturer. It delivers detailed performance metrics through RTLS data analysis in order to evaluate workflow performance and to obtain a lean process. We pre-filter the RTLS data through the development of a middleware data collection method to acquire near real-time performance evaluation. A case study illustrates the complete process including measurements before and after a workflow redesign. The increased level of detail from RFID measurements yields new insights into shop floor actions and the real effects of redesign efforts. 相似文献
995.
996.
针对分流制排水管道的特点,结合排水设计经验,吸纳管理部门及施工单位意见,对分流制排水管道设计中存在的管道布置、最小管径选择、分流管道与合流管道衔接、管道交叉、管道穿河渠、管道穿道路等关键性问题进行分析。同时,提出优化方法及解决方案,为更加合理地设计分流制排水管道提供参考与借鉴。 相似文献
997.
HE XiaoWei ZHANG MinXuan & LI JinWen PDL School of Computer National University of Defense Technology Changsha China 《中国科学:信息科学(英文版)》2011,(4)
In this paper,a 2-mm long on-chip dipole antenna pair on silicon substrate is simulated to investigate the transmission characteristics.A novel technique is proposed by employing a 0.35-mm thick diamond layer between silicon substrate and heat sink to improve antenna performance.The simulated transmission gain of this antenna pair with 1 mm separation on a 10-Ω cm silicon substrate increases by 9 dB at 20 GHz.A modified plane wave model involving diamond layer is also presented to explain gain improvement.E... 相似文献
998.
This letter proposes an open‐ended waveguide antenna with a single split‐ring resonator. In contrast to the waveguide antennas incorporating multiple rings reported in a previous study, which exhibited narrow bandwidth, the proposed antenna uses only one ring to achieve broader bandwidth while keeping the aperture small. A single ring has a relatively low quality factor compared to multiple rings. The simulated and measured fractional bandwidth was 4.13% and 4.03%, respectively, which is much broader than the fractional bandwidth of about 1% demonstrated in a previous study. This simple technique can be used in many applications that require small apertures including near‐field probes and array elements. 相似文献
999.
Madhurika Mahajan T. Chakarvarty Sunil Kumar Khah 《AEUE-International Journal of Electronics and Communications》2011,65(11):954-957
A numerical model for resonant frequency using asymmetric loading is presented using cavity model. In asymmetric loaded antenna, the posts are not equispaced on annular ring antenna and resonant frequency is independent of the angular location of posts. The posts are located away from the centre of patch. The diameter of post is thin as compared to the diameter of annular ring antenna. The first few dominant modes calculated for asymmetric loading are compared to symmetric loading where the posts are to be located at specific angular locations. The theoretical model is compared to the simulated results of IE3D based on Method of Moments. The numerical model developed can also be verified further by the full wave analysis. 相似文献
1000.
裂缝性气藏转换波3D3C地震采集观测系统优选 总被引:3,自引:1,他引:2
川西坳陷深层须家河组气藏具有埋藏深、岩性致密、非均质性强、储层类型多样、气水关系复杂等特点,采用常规油气藏地震勘探技术难以取得很好的效果。转换波三维三分量(3D3C)勘探综合了纵波勘探和转换波勘探的优势,对于解决川西深层致密裂缝性储层的裂缝检测及含气性预测问题具有良好的应用前景。为此,针对深层气藏特点及裂缝检测的需要,对接收线距、束间滚动距、宽窄方位角、观测系统类型及覆盖次数等观测系统参数进行了分析论证,认为斜交方式、小接收线距、小滚动距、全方位、高覆盖次数等是决定采集数据随方位角和偏移距分布均匀的主要因素,可以更好地满足纵横波方位各向异性分析及横波分裂裂缝检测要求。设计了3个斜交砖墙式观测系统方案,并结合XC地区3D3C转换波勘探观测系统分析进行了优选。 相似文献