全文获取类型
收费全文 | 487篇 |
免费 | 16篇 |
国内免费 | 40篇 |
专业分类
电工技术 | 71篇 |
综合类 | 25篇 |
化学工业 | 69篇 |
金属工艺 | 25篇 |
机械仪表 | 4篇 |
建筑科学 | 85篇 |
矿业工程 | 3篇 |
能源动力 | 2篇 |
水利工程 | 2篇 |
武器工业 | 3篇 |
无线电 | 146篇 |
一般工业技术 | 80篇 |
冶金工业 | 15篇 |
原子能技术 | 2篇 |
自动化技术 | 11篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 35篇 |
2011年 | 15篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 18篇 |
2007年 | 36篇 |
2006年 | 47篇 |
2005年 | 48篇 |
2004年 | 47篇 |
2003年 | 24篇 |
2002年 | 15篇 |
2001年 | 19篇 |
2000年 | 28篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有543条查询结果,搜索用时 15 毫秒
1.
Pin Yang Carolina A. Gomez Samantha Andrews Josef D. Sorenson Ken S. Chen 《Journal of the American Ceramic Society》2021,104(7):3247-3259
The electric discharge across a varistor granule filled air gap under a fast-rising voltage pulse was investigated for surge protection applications. The effects of temperature and pressure on the arc and the electrical conduction were analyzed by the characteristic changes in voltage waveforms triggered by a fast-rising high voltage pulse. In addition to the gap size, experimental results show that competing mechanisms among arc conduction, conduction through the varistor granule network, thermionic emission from Joule heating at granule-to-granule contact points, and the magnitude of the switching voltage dictate the maximum surge protection voltage for the filled air gap. Experimental evidence indicated that accumulated degradation was created at small contact points between varistor granules by repetitive assaults from longer duration, high voltage pulses. The uniqueness of using varistor over other dielectric granules in an air gap for surge protection is identified and discussed. 相似文献
2.
以ZnO粉末为主要原料,添加TiO2、Bi2O3、MnO2、Co2O3、Sb2O3为组元,在不同烧结温度(1100~1250℃)与保温时间(1.0~2.5h)下制备ZnO压敏陶瓷。采用SEM观察陶瓷形貌,利用压敏电阻直流参数仪测试陶瓷的电学性能,研究烧结温度与保温时间对陶瓷结构和性能的影响。结果表明,随烧结温度升高,压敏电压、漏电流逐渐降低,而非线性系数先减小后增加。制备ZnO压敏陶瓷的适宜烧结温度与保温时间分别为1250℃、1h,压敏电压为17.0V/mm、漏电流为0.014mA、非线性系数为14.2,陶瓷内部晶粒可长大至128.7μm。 相似文献
3.
An investigation was made into the effect of doping with the elemental crystal Ge or/and GeO2 on the TiO2-V2O5-Y2O3 varistor ceramics. The result shows that as the doping contents of V2O5 and Y2O3 are 0.5 mol%, respectively, co-doping with 0.3 mol% Ge and 0.9 mol% GeO2 makes the highest α value (α = 12.8), the lowest breakdown voltage V1mA (V1mA = 15.8 V/mm) and the highest grain boundary barrier ΦB (ΦB = 1.48 eV), which is remarkably superior to the TiO2-V2O5-Y2O3 varistor ceramics undoped with Ge and GeO2 and mono-doped with Ge or GeO2. The TiO2-V2O5-Y2O3-Ge-GeO2 ceramic has the prospect of becoming a novel varistor ceramic with excellent electrical properties. 相似文献
4.
Abstract—To reduce the negative effects of wind farms connection on power system stability, many countries have elaborated grid code requirements. Low-voltage ride through (LVRT) capability is the core of these requirements. This paper presents a framework to design and apply the series resonance fault current limiter (SRFCL) with a metal oxide varistor (MOV) for LVRT performance enhancement of doubly fed induction Machine (DFIG)-based wind farms. The main advantages of the SRFCL are simplicity, high reliability and automatically operation during fault condition for enhancing the LVRT performance. To demonstrate the capability of the SRFCL, a comparative study of the SRFCL and the bridge-type fault current limiter (BFCL) is performed. The study wind farm has been modeled with equivalent aggregated DFIG. Simulations were carried out in PSCAD/EMTDC environment. Simulation results demonstrate that the SRFCL provides a simple and effective solution to enhance the LVRT and reduce the fault current contribution of wind farms. 相似文献
5.
Choon-Woo Nahm 《中国稀土学报(英文版)》2013,31(3):276-280
The effect of Tb4O7 on electrical behavior of the ZnO-Pr6O11-based varistor ceramics was investigated.Microstructural analysis indicated that the addition of Tb4O7 decreased average grain size from 3.6 to 3.2 μm and increased the sintered density from 5.58 to 5.68 g/cm3.As the amount of Tb4O7 increased,the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65.The varistor ceramics added with 0.5 mol.% in the amount of Tb4O7 exhibited an excellent stability by exhibiting-0.1% in the variation rate of the breakdown field,0% in the variation rate of the nonlinear coefficient,and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115℃/24 h. 相似文献
6.
仪器仪表产品的脉冲耐压试验是产品型式试验、例行试验中的基本内容。通过对GB4793.1标准的整理,归纳了仪器仪表产品的脉冲耐压试验要求。通过对试验方法和设备特性的梳理,总结了特性参数,并介绍了应对脉冲耐压试验可采取的保护器件的类别及选用方法。 相似文献
7.
MOV(金属氧化锌压敏电阻)常以多片并联的形式应用于限压型SPD(电涌保护器)中,由于其性能的优劣直接影响器件的整体保护效果,遂对MOV多片并联方法及性能进行分析,通过并联后MOV电气特性的理论与试验分析,得出MOV产生电流偏差IL的主因是由于U_(1mA)和R_d的不一致性。同时基于ATP-EMTP(电磁暂态分析软件),考虑在大电流作用下MOV的响应特性和全电流区的伏安特性,并构建电路模型,利用2 ns上升速率的方波回路和8/20μs脉冲电流发生回路进行实测,仿真MOV在不同片数下的残压与通流特性,得到多片并联后MOV的特性参数变化趋势,得出MOV 5片并联其效果相对最佳。 相似文献
8.
开展兼具非线性电导和介电特性的复合材料的理论基础和应用研究,有助于更有效、广泛地解决高电压等级电力系统绝缘设备或部件电场分布不均匀的难题。为此,制备了ZnO压敏陶瓷-硅橡胶复合材料并测量了其非线性压敏介电特性。结果表明:制备的复合材料具有良好的分散性和非线性电导及介电特性;当ZnO压敏陶瓷填料体积分数10%时,复合材料可以表现出明显的非线性介电特性,可以起到更显著的电场均匀作用;当ZnO压敏陶瓷填料体积分数20%时,复合材料呈现出明显的非线性电导特性,电导非线性系数可以达到10以上,当电场强度超过压敏电压梯度时电导率可以提高100倍以上,而电场强度达到1.5倍压敏电压梯度时,可在对不均匀电场起抑制作用的同时,避免较大的损耗。 相似文献
9.