首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4725篇
  免费   125篇
  国内免费   5篇
化学   2847篇
晶体学   56篇
力学   63篇
数学   437篇
物理学   1090篇
无线电   362篇
  2021年   35篇
  2020年   36篇
  2019年   39篇
  2016年   67篇
  2015年   68篇
  2014年   77篇
  2013年   149篇
  2012年   146篇
  2011年   176篇
  2010年   120篇
  2009年   91篇
  2008年   158篇
  2007年   165篇
  2006年   162篇
  2005年   163篇
  2004年   150篇
  2003年   147篇
  2002年   129篇
  2001年   124篇
  2000年   131篇
  1999年   76篇
  1998年   51篇
  1997年   68篇
  1996年   96篇
  1995年   79篇
  1994年   87篇
  1993年   70篇
  1992年   69篇
  1991年   69篇
  1990年   65篇
  1989年   48篇
  1988年   54篇
  1987年   69篇
  1986年   63篇
  1985年   68篇
  1984年   67篇
  1983年   53篇
  1982年   60篇
  1981年   63篇
  1980年   46篇
  1979年   50篇
  1978年   54篇
  1977年   60篇
  1976年   63篇
  1975年   59篇
  1974年   60篇
  1973年   47篇
  1968年   27篇
  1967年   25篇
  1957年   30篇
排序方式: 共有4855条查询结果,搜索用时 859 毫秒
1.
2.
This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS).  相似文献   
3.
Maes  W. de Meyer  K. Dupas  L. 《Electronics letters》1985,21(11):490-491
Classical parameter-extraction programs rely on the minimisation of the relative current deviation. However, since, especially for analogue applications, the slope of the IDS/VDS curve in the saturation region is at least equally important, a new fit strategy has been developed. This new fit strategy extracts a parameter set which optimises the current residual as well as the slope residual at every point.  相似文献   
4.
5.
6.
A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm2. The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature.  相似文献   
7.
Geerk  J.  Linker  G.  Meyer  O.  Politis  C.  Ratzel  F.  Smithey  R.  Strehlau  B.  Xiong  G. C. 《Zeitschrift für Physik B Condensed Matter》1987,67(4):507-511
Thin superconducting films of La1.8Sr0.2CuO4 have been prepared by magnetron sputter deposition and subsequent temperature treatment. The composition of the films has been determined by Rutherford backscattering and the structure by thin film X-ray diffraction. The onset of superconductivity was about 32 K and the midpoint near 28 K. Defect production in the films by He ion bombardment revealed a drasticT c reduction with a sensitivity similar to that observed in the Chevrel phases. Oxygen implantation and subsequent annealing led to an enhancement of theT c onset.  相似文献   
8.
Silicon integrated circuit spiral inductors and transformers are analyzed using electromagnetic analysis. With appropriate approximations, the calculations are reduced to electrostatic and magnetostatic calculations. The important effects of substrate loss are included in the analysis. Classic circuit analysis and network analysis techniques are used to derive two-port parameters from the circuits. From two-port measurements, low-order, frequency-independent lumped circuits are used to model the physical behavior over a broad-frequency range. The analysis is applied to traditional square and polygon inductors and transformer structures as well as to multilayer metal structures and coupled inductors. A custom computer-aided-design tool called ASITIC is described, which is used for the analysis, design, and optimization of these structures. Measurements taken over a frequency range from 100 MHz to 5 GHz show good agreement with theory  相似文献   
9.
The possibility to directly modulate widely tunable lasers up to several gigahertz is desirable in telecom applications. We discuss the dynamic properties of the recently proposed widely tunable twin-guide laser concept. It has promising prospects with a maximum theoretical bandwidth above 20 GHz and the 3-dB bandwidth at 250 mA indicates that an actual bandwidth of 12 GHz should be possible. The current lasers were not designed for high-speed modulation, so only 1-GHz modulation can be reached at the moment.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号