全文获取类型
收费全文 | 119156篇 |
免费 | 10191篇 |
国内免费 | 5390篇 |
专业分类
电工技术 | 6981篇 |
技术理论 | 6篇 |
综合类 | 7944篇 |
化学工业 | 19496篇 |
金属工艺 | 7070篇 |
机械仪表 | 8011篇 |
建筑科学 | 9457篇 |
矿业工程 | 3826篇 |
能源动力 | 3318篇 |
轻工业 | 9070篇 |
水利工程 | 2175篇 |
石油天然气 | 7924篇 |
武器工业 | 947篇 |
无线电 | 12814篇 |
一般工业技术 | 13621篇 |
冶金工业 | 5654篇 |
原子能技术 | 1284篇 |
自动化技术 | 15139篇 |
出版年
2024年 | 581篇 |
2023年 | 2165篇 |
2022年 | 3940篇 |
2021年 | 5187篇 |
2020年 | 4086篇 |
2019年 | 3346篇 |
2018年 | 3563篇 |
2017年 | 4115篇 |
2016年 | 3758篇 |
2015年 | 5155篇 |
2014年 | 6135篇 |
2013年 | 7299篇 |
2012年 | 7903篇 |
2011年 | 8379篇 |
2010年 | 7246篇 |
2009年 | 6886篇 |
2008年 | 6708篇 |
2007年 | 6267篇 |
2006年 | 6486篇 |
2005年 | 5574篇 |
2004年 | 3550篇 |
2003年 | 3223篇 |
2002年 | 2968篇 |
2001年 | 2699篇 |
2000年 | 2561篇 |
1999年 | 2811篇 |
1998年 | 2207篇 |
1997年 | 1815篇 |
1996年 | 1780篇 |
1995年 | 1474篇 |
1994年 | 1200篇 |
1993年 | 781篇 |
1992年 | 693篇 |
1991年 | 458篇 |
1990年 | 381篇 |
1989年 | 320篇 |
1988年 | 246篇 |
1987年 | 169篇 |
1986年 | 145篇 |
1985年 | 84篇 |
1984年 | 75篇 |
1983年 | 59篇 |
1982年 | 56篇 |
1981年 | 36篇 |
1980年 | 46篇 |
1979年 | 30篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1974年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
通过分析PHS网络中各寻呼区的统计指标,剖析指标劣化的根本原因,采取修改相应的参数配置、移站、调整天线等措施进行网络优化,优化实施后再次收集统计指标做对比分析,总结经验。 相似文献
72.
73.
This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed. 相似文献
74.
River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory. 相似文献
75.
自动线性跟踪Butterworth有源滤波器研究 总被引:2,自引:0,他引:2
滤波是通信、测试、数据采集和实时控制等领域至关重要的环节。通常的模拟滤波器,由于截止频率固定,在某些宽频率动态范围且有实时性要求的应用场合,往往达不到预期的滤波效果,有时甚至影响整个系统的正常运行。本文从有源滤波器的机理分析入手,提出了一种由单片机参与的滤波系统,它能自动跟踪输入信号频率,线性地选择合适的滤波器截止频率,弥补了原有滤波器的不足。 相似文献
76.
In this article, a new algorithm based on an artificial potential field and hierarchical cell decomposition technique is developed to solve the find-path problem for a mobile robot. The complete map of the workspace including obstacle locations is assumed to be known a priori. The basic cell structure used for decomposition is a hexagon. The artificial potential field is based on an attractive force from the goal position and repelling forces from the obstacles. Computer simulations of the algorithm for various obstacle scenarios are also presented. © 1994 John Wiley & Sons, Inc. 相似文献
77.
78.
Miao Wang Xinluo Zhao Masato Ohkohchi Yoshinori Ando 《Fullerenes, Nanotubes and Carbon Nanostructures》1996,4(5):1027-1039
Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH4 gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH4 gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH4 gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm. 相似文献
79.
80.
WC对Cu/WC_P复合材料性能及组织的影响 总被引:8,自引:0,他引:8
通过WC含量对WC/Cu复合材料性能的影响,确定了冷压-烧结法制备Cu/WC材料的适宜WC含量为10vol%左右。并就WC对该材料组织和再结晶行为的影响进行了有益的探讨。 相似文献