全文获取类型
收费全文 | 1093篇 |
免费 | 178篇 |
国内免费 | 104篇 |
专业分类
电工技术 | 50篇 |
综合类 | 82篇 |
化学工业 | 68篇 |
金属工艺 | 12篇 |
机械仪表 | 61篇 |
建筑科学 | 19篇 |
矿业工程 | 7篇 |
能源动力 | 3篇 |
轻工业 | 18篇 |
水利工程 | 7篇 |
石油天然气 | 13篇 |
武器工业 | 11篇 |
无线电 | 363篇 |
一般工业技术 | 72篇 |
冶金工业 | 10篇 |
原子能技术 | 12篇 |
自动化技术 | 567篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 27篇 |
2019年 | 26篇 |
2018年 | 27篇 |
2017年 | 23篇 |
2016年 | 38篇 |
2015年 | 41篇 |
2014年 | 73篇 |
2013年 | 70篇 |
2012年 | 85篇 |
2011年 | 108篇 |
2010年 | 82篇 |
2009年 | 80篇 |
2008年 | 91篇 |
2007年 | 92篇 |
2006年 | 93篇 |
2005年 | 54篇 |
2004年 | 58篇 |
2003年 | 38篇 |
2002年 | 43篇 |
2001年 | 30篇 |
2000年 | 19篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有1375条查询结果,搜索用时 15 毫秒
1.
影响雷电通道产生的水平电场因素众多,分析其影响因素对电力系统的雷电防护具有重要意义。文中利用运动电荷电磁场方程求解得到闪电回击通道的水平电场和方位磁场,并结合C-R 算法,得到了有限电导率地面上方的水平电场。依据运动电荷电磁场方程的特征分析了不同回击速度、不同距离、不同电导率对雷击产生的水平电场的影响。得出以下结论:水平电场随回击速度增大而减小;水平电场波形呈双极性特征且水平距离越大或电导率越小负向偏移越明显。这些研究结论为输电线路雷电过电压计算打下良好的基础。与其他方法相比,本文方法可以避免远距离电磁场计算中的震荡问题和积分方程的奇异问题。 相似文献
2.
Qibing Jin Zeyu Wang Wu Cai Yuming Zhang 《International Journal of Adaptive Control and Signal Processing》2021,35(5):811-827
In this paper, the parameter estimation issue of Wiener system with random time delay and missing output data is studied. The linear part of Wiener system is described by Finite Impulse Response (FIR) model. The mathematical formula of the Expectation Maximum algorithm to identify Wiener-FIR system that contains the random time delay and the nonlinear output data in missing completely at random mechanism is derived, which is never considered before. To obtain the unmeasurable intermediate variable in Wiener-FIR system, the idea of auxiliary model is adopted. The time delay and system parameters can be estimated simultaneously by this method. Numerical example and the identification of water tank system example are carried out, the effectiveness of the algorithm is proved. 相似文献
3.
《Ceramics International》2022,48(15):21268-21282
Mullite-Al2O3-SiC composites were in-situ synthesized through carbothermal reduction reaction of fly ash (FA) with a high alumina content and activated carbon (AC). The effects of sintering temperature, holding time, and amount of AC on the β-SiC yield, microstructure, dielectric properties, and electromagnetic (EM) absorption performance of the composites in the 2–18 GHz frequency range were studied. The results show that increasing the AC improves the porosities of the composites, with the highest porosity of 56.17% observed. The β-SiC yield varies considerably as the sintering parameters were altered, with a maximum yield of 23% achieved under conditions of 12 wt% AC, 1400 °C sintering temperature, and 3 h holding time. With a thickness of 3.5 mm, this composite has excellent EM absorption performance, exhibiting a minimum reflection loss (RLmin) of -51.55 dB at 7.60 GHz. Significantly, the maximum effective absorption bandwidth (EAB) reaches 3.39 GHz when the thickness is 3.0 mm. These results demonstrate that the composite prepared under ideal conditions can absorb 99.99% of the waves passing through it. Because of the interfacial polarization, conductive loss, and impedance matching of the heterostructure, the synthesized mullite-Al2O3-SiC composites with densities ranging from 1.43 g/cm3 to 1.62 g/cm3 demonstrate outstanding EM attenuation capabilities. Therefore, this study presents a remarkable way of utilizing fly ash to fabricate inexpensive, functional ceramic materials for EM absorption applications. 相似文献
4.
结合工程实例,介绍了磁通量传感器在吉安赣江大桥V墩体外索检测中的应用.磁通量传感器可以对体外预应力索、悬索桥和斜拉桥的预应力索以及其他磁性材料结构进行无接触应力监控.由于钢结构本身可作为传感器,并且通过磁导率的变化来反映应力变化,磁通量传感器可以安全准确地测定索力. 相似文献
5.
In July 2015 Professor K.T. Tokuyasu passed away in San Diego giving us the opportunity to reflect on the contribution this electron microscopist made to the field of immunocytochemistry. His work provided a sensitive, minimally invasive approach to producing thin sections of biological material for labeling with antibodies. His approach has been applied to a wide range of biological applications and provided important information on cellular processes. 相似文献
6.
随着薄膜体声波谐振器(FBAR)工作频率及FBAR器件集成度的不断提高,FBAR器件的电磁干扰问题显得尤为突出。常用电学模型和有限元模型都假定FBAR中的电磁场为无源准静态场,无法仿真模型的相关电磁特性。使用HFSS高频电磁仿真软件建立了FBAR的三维电磁仿真模型,采用一个包含声场特性的等效介电常数,实现了FBAR电磁场分布、电磁场耦合与压电效应的一体化仿真。分析了高频电磁场分布及电磁场耦合对谐振特性的影响,通过优化FBAR与临近元件的间距及采用不同介电常数的基板材料,减小了电磁场耦合的干扰。 相似文献
7.
8.
9.
Despite the fact that a radio frequency (RF) shielding box affects a coil inductance used in matching network, RF engineers have used a coil inductance measured in open space on designing matching networks since it is difficult to precisely measure the coil inductance within the RF shielding box. In this work, we investigate the influences of the RF shielding box on the coil inductance via a 3D full electromagnetic wave simulation. Simulation results shows that the coil inductance decreases from -6.0% to -11.9% compared with its ideal inductance depending on coil positions within the RF shielding box. Both inductive and capacitive coupling between the coil and surfaces of the RF shielding box contribute to the reduction of the coil inductance. We expect that these results would be useful for those who design RF matching networks. 相似文献
10.
在分析低压配电监控需求的基础上,提出了基于MCF51EM256单芯片SOC的解决方案,该方案利用其片内高精度16位ADC和高速32位COLDFIRE-V1核较好地实现了保护、测量、控制、管理和通讯功能,从而经济高效地满足了低压测控装置的完整需求,具有较高的参考价值. 相似文献