全文获取类型
收费全文 | 34377篇 |
免费 | 3572篇 |
国内免费 | 1625篇 |
专业分类
电工技术 | 10451篇 |
综合类 | 2950篇 |
化学工业 | 2354篇 |
金属工艺 | 1626篇 |
机械仪表 | 2234篇 |
建筑科学 | 1309篇 |
矿业工程 | 1054篇 |
能源动力 | 865篇 |
轻工业 | 443篇 |
水利工程 | 319篇 |
石油天然气 | 530篇 |
武器工业 | 327篇 |
无线电 | 8196篇 |
一般工业技术 | 2351篇 |
冶金工业 | 1019篇 |
原子能技术 | 327篇 |
自动化技术 | 3219篇 |
出版年
2024年 | 138篇 |
2023年 | 421篇 |
2022年 | 651篇 |
2021年 | 880篇 |
2020年 | 914篇 |
2019年 | 705篇 |
2018年 | 663篇 |
2017年 | 1032篇 |
2016年 | 1140篇 |
2015年 | 1315篇 |
2014年 | 2399篇 |
2013年 | 1905篇 |
2012年 | 2618篇 |
2011年 | 2708篇 |
2010年 | 2054篇 |
2009年 | 2088篇 |
2008年 | 2051篇 |
2007年 | 2528篇 |
2006年 | 2224篇 |
2005年 | 1788篇 |
2004年 | 1577篇 |
2003年 | 1371篇 |
2002年 | 1122篇 |
2001年 | 1031篇 |
2000年 | 826篇 |
1999年 | 623篇 |
1998年 | 446篇 |
1997年 | 391篇 |
1996年 | 360篇 |
1995年 | 300篇 |
1994年 | 286篇 |
1993年 | 182篇 |
1992年 | 170篇 |
1991年 | 125篇 |
1990年 | 140篇 |
1989年 | 107篇 |
1988年 | 78篇 |
1987年 | 45篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 423 毫秒
11.
12.
An alternative Equivalent Electrical Circuit for Proton Exchange Membrane Fuel Cells is modelled in this study. Both I–V characteristics and H2 consumptions corresponding to generated power under load and no-load conditions are investigated. For this purpose, H2 consumptions and I–V characteristics of three different sized PEMFCs are tested. There is a very good harmony between the model results and measured values (relative error %0.7, %6.4 and %2.5 for FC-A, FC-B and FC-C respectively). In the proposed model current passes only on parallel resistance and not on serial resistance at no-load condition. Thus, a FC with higher parallel resistance should be preferred. Another key output of this study is that based on the proposed model, performance comparison of FCs can be performed with the parameters defined in this work. Proposals made in this study can easily be used for performance analysis of FCs under for both steady state and transient analysis. 相似文献
13.
Yafei Liu Zhilong Fu Xingyu Chen Yaxin Wei Bo Zhang Aimin Chang 《Journal of the American Ceramic Society》2021,104(5):2134-2142
Rare-earth ions doped Ca0.9R0.1CeNbMoO8 (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce3+ ions and promote the conductivity of ceramics. Except for Sm3+-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm2+ ions in Sm3+-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics. 相似文献
14.
针对高可靠度机载多余度EWIS各组成部分寿命服从指数分布但参数未知的情况,提出采用无失效数据可靠度分析方法评估EWIS的可靠度水平。通过Monte-Carlo仿真方法对连接形式为“先并联、后串联”EWIS各组成部分寿命进行抽样,利用“最小最大值”方法获得系统寿命的抽样值,用概率纸检验法初步判断EWIS寿命是否服从威布尔分布,再用Pearson拟合优度检验法判断EWIS寿命是否服从威布尔分布。结合无故障飞行时间的样本值与EWIS寿命服从威布尔分布的假设,采用无失效数据分析方法评估EWIS的可靠度水平。研究方法对机载多余度EWIS无失效数据可靠度分析有一定的贡献。 相似文献
15.
The 3D structure electromagnetic computation presents several difficulties related to the volume mesh. In fact, the entire volume space must be taken into account even the smallest details. In this article, we propose a formulation based on the reciprocity theorem combined with the generalized equivalent circuit method to model a planar 3D structure with both coaxial and planar excitation. The major advantage of this formulation is the fact to reduce the computational volume into 2D ones in the discontinuity plane. In addition, we focused on the calculation of the discontinuity between the excitation source and the planar structure to determine the exact behavior of the electric coaxial excitation model. The obtained current density, electric field distributions, and the input impedance are presented and discussed in the following sections. An approximately good agreement of input impedance with those obtained by the simulator and measurement is shown. 相似文献
16.
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
17.
Polarity Effect and Electromagnetic Radiation of Partial Discharge Accompanying Growth of Electrical Tree
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)
Tatsuya Mutakamihigashi Yoshito Kuroishi Hideki Ueno 《Electrical Engineering in Japan》2015,192(3):19-26
We have investigated the characteristics of radiated electromagnetic (EM) waves from positive and negative partial discharges (PD) in epoxy resin and cross‐linked polyethylene. We found that there is a correlation among the EM level from PD, the positive PD current, and electrical trees. Therefore, the growth of an electrical tree produces a lot of positive PD. We have also investigated the characteristics of the frequency region of EM waves from PD in air, insulating oil, and liquid epoxy in addition to the above insulators. EM waves were detected in the frequency region of 40 MHz to 300 MHz from positive and negative PD in epoxy resin and cross‐linked polyethylene. EM waves were also detected in the frequency region of 40 MHz to 150 MHz from positive and negative PD in air. In the case of insulating oil and liquid epoxy, EM waves were detected in the frequency regions of 40 MHz to 150 MHz from positive PD, and 40 MHz to 250 MHz from negative PD. The frequency region differed depending on the material and the discharge polarity. Our investigation indicates that the cause is differences in electric field strength at the time of PD occurrence. 相似文献
18.
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
19.
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
20.