全文获取类型
收费全文 | 15314篇 |
免费 | 2230篇 |
国内免费 | 1009篇 |
专业分类
电工技术 | 7396篇 |
综合类 | 984篇 |
化学工业 | 252篇 |
金属工艺 | 424篇 |
机械仪表 | 809篇 |
建筑科学 | 98篇 |
矿业工程 | 219篇 |
能源动力 | 347篇 |
轻工业 | 161篇 |
水利工程 | 84篇 |
石油天然气 | 58篇 |
武器工业 | 86篇 |
无线电 | 5134篇 |
一般工业技术 | 647篇 |
冶金工业 | 314篇 |
原子能技术 | 151篇 |
自动化技术 | 1389篇 |
出版年
2024年 | 79篇 |
2023年 | 219篇 |
2022年 | 343篇 |
2021年 | 541篇 |
2020年 | 627篇 |
2019年 | 426篇 |
2018年 | 414篇 |
2017年 | 649篇 |
2016年 | 604篇 |
2015年 | 723篇 |
2014年 | 1035篇 |
2013年 | 983篇 |
2012年 | 1316篇 |
2011年 | 1423篇 |
2010年 | 987篇 |
2009年 | 982篇 |
2008年 | 1036篇 |
2007年 | 1115篇 |
2006年 | 1042篇 |
2005年 | 783篇 |
2004年 | 631篇 |
2003年 | 501篇 |
2002年 | 390篇 |
2001年 | 374篇 |
2000年 | 272篇 |
1999年 | 227篇 |
1998年 | 165篇 |
1997年 | 149篇 |
1996年 | 134篇 |
1995年 | 102篇 |
1994年 | 72篇 |
1993年 | 57篇 |
1992年 | 35篇 |
1991年 | 34篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 6 毫秒
1.
This paper focuses on the design of a 2.3–21 GHz Distributed Low Noise Amplifier (LNA) with low noise figure (NF), high gain (S21), and high linearity (IIP3) for broadband applications. This distributed amplifier (DA) includes S/C/X/Ku/K-band, which makes it very suitable for heterodyne receivers. The proposed DA uses a 0.18 μm GaAs pHEMT process (OMMIC ED02AH) in cascade architecture with lines adaptation and equalization of phase velocity techniques, to absorb their parasitic capacitances into the gate and drain transmission lines in order to achieve wide bandwidth and to enhance gain and linearity. The proposed broadband DA achieved an excellent gain in the flatness of 13.5 ± 0.2 dB, a low noise figure of 3.44 ± 1.12 dB, and a small group delay variation of ±19.721 ps over the range of 2.3–21 GHz. The input and output reflection coefficients S11 and S22 are less than −10 dB. The input compression point (P1dB) and input third-order intercept point (IIP3) are −1.5 dBm and 11.5 dBm, respectively at 13 GHz. The dissipated power is 282 mW and the core layout size is 2.2 × 0.8 mm2. 相似文献
2.
Iqbal Ahmad Syed Mujtaba Shah Muhammad Nadeem Zafar Muhammad Naeem Ashiq Wei Tang Uzma Jabeen 《Ceramics International》2021,47(3):3760-3771
Ferrites are materials of interest due to their broad applications in high technological devices and a lot of research has been focused to synthesize new ferrites. In this regard, an effort has been devoted to synthesize spinel Pr–Ni co-substituted strontium ferrites with a nominal formula of Sr1-xPrxFe2-yNiyO4 (0.0 ≤ x ≤ 0.1, 0.0 ≤ y ≤ 1.0). The cubic structure of pure and Pr–Ni co-substituted strontium ferrite samples calcinated at 1073 K for 3 h has been confirmed through X-ray diffraction (XRD). Average sizes of crystallites (18–25 nm) have been estimated from XRD analysis and nanometer particle sizes of synthesized ferrites have been further verified by scanning electron microscopy (SEM). SEM results have also shown that particles are mostly agglomerated and all the samples possess porosity. It has been observed that at 298 K, the values of resistivity (ρ) increase, while that of AC conductivity, dielectric loss, and dielectric constants decrease with increasing amounts of Pr3+ and Ni2+ ions. The values of dielectric parameters initially decrease with frequency and later become constant and can be explained on the basis of dielectric polarization. Electrochemical impedance spectroscopy (EIS) studies show that the charge transport phenomenon in ferrite materials is mainly controlled via grain boundaries. Overall, synthesized ferrite materials own enhanced resistivity values in the range of 1.38 × 109–1.94 × 109 Ω cm and minimum dielectric losses, which makes them suitable candidates for high frequency devices applications. 相似文献
3.
Mostafa Dellahi Hattab Maker Guillermo Botella Enrique Alameda-Hernandez Azeddine Mouhsen 《International Journal of Circuit Theory and Applications》2020,48(6):887-905
The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD). 相似文献
4.
5.
6.
CMOS光接收机主放大器设计 总被引:1,自引:0,他引:1
利用CMOS工艺设计一种用于SDH STM 4速率级(622 Mb/s)光纤用户网的光接收机放大电路。此电路由输入/输出缓冲、主放大单元、偏置补偿电路4部分组成。通过直接耦合技术提高增益,降低功耗;利用有源电感负载提高系统带宽。采用商用SmartSpice电路仿真软件和CSMC HJ 0.6μm工艺参数对该电路进行仿真。结果表明,该电路在5 V工作电压下中频增益为81 dB,3 dB带宽为470 MHz。 相似文献
7.
概述了电磁干扰(EMI)和电磁兼容(EMC)的基本知识,对DC/DC电源中的电磁干扰进行了综合分析,并给出了各自的解决方案。 相似文献
8.
9.
10.