全文获取类型
收费全文 | 8836篇 |
免费 | 791篇 |
国内免费 | 511篇 |
专业分类
电工技术 | 1040篇 |
技术理论 | 1篇 |
综合类 | 838篇 |
化学工业 | 577篇 |
金属工艺 | 512篇 |
机械仪表 | 824篇 |
建筑科学 | 766篇 |
矿业工程 | 1265篇 |
能源动力 | 344篇 |
轻工业 | 243篇 |
水利工程 | 165篇 |
石油天然气 | 346篇 |
武器工业 | 48篇 |
无线电 | 936篇 |
一般工业技术 | 515篇 |
冶金工业 | 1049篇 |
原子能技术 | 156篇 |
自动化技术 | 513篇 |
出版年
2024年 | 24篇 |
2023年 | 100篇 |
2022年 | 206篇 |
2021年 | 289篇 |
2020年 | 316篇 |
2019年 | 193篇 |
2018年 | 150篇 |
2017年 | 150篇 |
2016年 | 231篇 |
2015年 | 308篇 |
2014年 | 566篇 |
2013年 | 451篇 |
2012年 | 718篇 |
2011年 | 742篇 |
2010年 | 559篇 |
2009年 | 585篇 |
2008年 | 495篇 |
2007年 | 598篇 |
2006年 | 592篇 |
2005年 | 491篇 |
2004年 | 414篇 |
2003年 | 371篇 |
2002年 | 331篇 |
2001年 | 273篇 |
2000年 | 209篇 |
1999年 | 149篇 |
1998年 | 108篇 |
1997年 | 86篇 |
1996年 | 81篇 |
1995年 | 83篇 |
1994年 | 55篇 |
1993年 | 41篇 |
1992年 | 35篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 27篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1966年 | 2篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
在全国天然气管道“主干互联、区域成网”(以下简称“互联互通”)基础格局逐渐形成的背景下,天然气管网规模日益扩大、管道分支和气源增加,并且分布不集中、输送方向可变,使得输气方案更加灵活,可以更好地解决某些地域的供气紧张问题;但受现有站场和设备的限制,暂不能满足某些多线组合极限工况,使得“互联互通”的初衷难以全部实现。为了使得现有的各输气干线在实现“互联互通”之后可以满足更多的多线组合工况,在分析“互联互通”背景下M管网工况变化的基础上,研发了可以进行水力仿真和压气站方案制订的计算软件,并对3种极限工况下的不同输气量情况进行了可行性试算,进而基于试算结果提出了相应的管网改进建议。研究结果表明:(1)经验证,软件计算误差满足要求;(2)在M管道某处增设压气站或在某些输气站场配置压缩机组;(3) M管网改进调整后,可以完成大部分的多线组合极限工况,真正实现“互联互通”的输气方案。结论认为,该研究成果有助于推进全国天然气管网早日实现“互联互通”。 相似文献
2.
3.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors. 相似文献
4.
Hierarchical micro-nanostructured albite-based glass-ceramic for high dielectric strength insulators
V. Fuertes M.J. Cabrera J. Seores D. Muñoz J.F. Fernández E. Enríquez 《Journal of the European Ceramic Society》2018,38(7):2759-2766
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications. 相似文献
5.
为解决21000工作面采空区及顶板涌水问题,根据工作面出水点的不同情况,采取了集水器导水、老塘设挡水堰截水、挖排水沟疏水等多项治水措施,经统计排水量达33~42m3/h,有效控制了水情,确保了工作面正常生产。 相似文献
6.
Electrical Breakdown Properties and Space Charge Formation in High Temperature Region in Ultraviolet Ray Irradiated PVC
下载免费PDF全文
![点击此处可从《Electrical Engineering in Japan》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Polyvinyl chloride (PVC) is the most popular insulating material for electric wiring instruments. However, an exothermic reaction above 150 °C may cause deterioration of the insulating properties of PVC. Therefore, it is important to clarify the heat degradation in PVC, not only to investigate the ignition of electrical wiring products but also to use electrical products safely. It is known that ultraviolet (UV) irradiation causes chemical deterioration of PVC and an increase in its conductivity. Generally, it has been thought that the electrical breakdown properties, electrical conduction, and insulating performance are affected by space charge accumulation in an insulating material. A high temperature pulsed electroacoustic (PEA) system usable up to 250 °C has been developed, and the PEA system can measure the space charge distribution and conduction current in the high temperature range simultaneously. In this investigation, the space charge distribution and conduction current were measured up to electrical breakdown in a non‐UV irradiated sample (normal PVC) and in 353 nm and 253 nm UV‐irradiated PVC samples in the range from room temperature to 200 °C in a DC electric field. In the short wavelength UV irradiated PVC sample (253 nm, 300 h), a deterioration of breakdown strength at 90 °C to 150 °C and negative packet‐like charges were observed at 60 °C and 100 °C, a positive charge accumulated in front of both the anode and cathode above 90 °C, and a higher electric field near the cathode side because the positive charge of the cathode side was greater. 相似文献
7.
Defects are often present in rolled products, such as wire rod. The market demand for wire rod without any defects has increased. In the final wire rod products, defects originating from steel making, casting, pre‐rolling of billets and during wire rod rolling can appear. In this work, artificial V‐shaped longitudinal surface cracks have been analysed experimentally and by means of FEM. The results indicate that the experiments and FEM calculations show the same tendency except in two cases, where instability due to fairly “round” false round bars disturbed the experiment. FE studies in combination with practical experiments are necessary in order to understand the behaviour of the material flows in the groove and to explain whether the crack will open up as a V‐shape or if it will be closed as an I‐shape. 相似文献
8.
迷宫螺旋泵和密封工作特性研究 总被引:1,自引:1,他引:0
介绍了一种实测迷宫螺旋泵和密封工作特性的实验方法,通过该方法可以测得迷宫螺旋泵的泵送特性曲线、迷宫螺旋端面组合密封的最大密封压力以及端面开启的开始转速,具有一定的实用价值。 相似文献
9.
10.
无线监测示功仪的研制与应用 总被引:2,自引:0,他引:2
针对常规示功仪资料储存的容量有限和对油井不能长时间连续监测的不足,研制了无线监测示功仪。该示功仪将载荷和位移传感器、无线传输以及太阳能供电等多种技术集于一体(1)采用加速度传感器,实现了光杆无线位移检测,解决了常规位移传感器寿命短、可靠性差的问题;(2)应用CC1000无线模块,实现了油井示功图短距离数据无线交换,屏弃了常规仪器电缆通讯的方式;(3)通过增加仪器储存容量和移植USB接口,解决了常规示功仪储存数据量少的问题,极大地方便了数据交换;(4)将太阳能电池与充电电池有机结合,圆满解决了仪器供电问题。 相似文献