全文获取类型
收费全文 | 1623篇 |
免费 | 91篇 |
国内免费 | 148篇 |
专业分类
化学 | 526篇 |
晶体学 | 6篇 |
力学 | 39篇 |
综合类 | 1篇 |
数学 | 190篇 |
物理学 | 402篇 |
无线电 | 698篇 |
出版年
2024年 | 2篇 |
2023年 | 32篇 |
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 46篇 |
2019年 | 24篇 |
2018年 | 29篇 |
2017年 | 52篇 |
2016年 | 47篇 |
2015年 | 50篇 |
2014年 | 98篇 |
2013年 | 103篇 |
2012年 | 63篇 |
2011年 | 116篇 |
2010年 | 72篇 |
2009年 | 125篇 |
2008年 | 114篇 |
2007年 | 114篇 |
2006年 | 105篇 |
2005年 | 79篇 |
2004年 | 64篇 |
2003年 | 65篇 |
2002年 | 46篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 36篇 |
1998年 | 40篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 22篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 7篇 |
1982年 | 2篇 |
1978年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1862条查询结果,搜索用时 468 毫秒
1.
《Microelectronics Journal》2015,46(11):1012-1019
This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm2 and 0.08 mm2, respectively. 相似文献
2.
3.
4.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献
5.
6.
Theory of a novel voltage-sustaining layer for power devices 总被引:3,自引:0,他引:3
The theory of a novel voltage-sustaining layer for power devices, called a Composite Buffer layer (CB-layer for short) is proposed. The CB-layer can be implemented in several ways, one particular implementation is used here, which consists of alternating n- and p-type regions, that are parallel to the direction of the applied electric field. In the off-state, the fields induced by the depletion charges of both region types compensate each other to allowing the doping in both n-regions and p-regions to be very high without causing a reduction of the breakdown voltage. In the onstate the heavy doping ensures the voltage drop is very low and that the saturation current density high. A simple relationship between the specific on-resistance and Ron and the sustaining voltage VB can be shown to be Ron=2.53 × 10−7bVB1.23 ωcm2, where the breadth b (in μm) of each region is much smaller than the thickness W. The design method of the CB-layer is discussed in some detail. The simulation results are shown to be in perfect agreement with the theory. The structure has application to a wide variety of different power devices. An RMOST structure has been used to demonstrate the benefits of the technique in the paper, for which excellent performance is demonstrated. 相似文献
7.
We observe that a term of the WZW-type can be added to the Lagrangian of the Poisson σ-model in such a way that the algebra of the first class constraints remains closed. This leads to a natural generalization of the concept of Poisson geometry. The resulting “WZW–Poisson” manifold M is characterized by a bivector Π and by a closed three-form H such that 1/2[Π,Π]Schouten=H,ΠΠΠ. 相似文献
8.
In this paper the modelling, analysis and optimization of millimeter wave oscillatorsare investigated by using the a frequency-domain harmonic balance technique (FDHB), where theexternal-circuit impedances looking outside from the active device are calculated with a combinedtechnique of modes expansion, Galerkin, and collocation methods. The optimization results arein agreement with the experimental ones, which show the reliability of the presented model andoptimization. 相似文献
9.
本文介绍一种适用于散射通讯用的前馈抛物面宽频带正交器双线极化馈源设计,该馈源工作于0.8GHz频段。实践证明,该馈源在20%的工作带宽内基本上具有近似于旋转对称的波束,且系统VSWR<1.3。因此,对工作于较低频段的天线,该馈源是很好的选型。 相似文献
10.
王福臣 《固体电子学研究与进展》1992,(4)
对WC76型S频段大功率振荡用砷化镓场效应晶体管的微波性能作了介绍。文中给出了测试振荡器的设计。测试结果表明,WC76型振荡管在s频段的微波性能良好,振荡频率在3GHz左右时,输出功率可达3.5w,直流—射频转换效率可达44%,而且在2~4GHz的整个S频段均能满意地工作。 相似文献