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   701107篇
  免费   5904篇
  国内免费   1842篇
化学   319818篇
晶体学   9077篇
力学   30330篇
综合类   20篇
数学   78736篇
物理学   190976篇
无线电   79896篇
  2021年   6176篇
  2020年   6822篇
  2019年   7693篇
  2018年   10018篇
  2017年   10114篇
  2016年   14093篇
  2015年   7599篇
  2014年   12836篇
  2013年   29203篇
  2012年   22604篇
  2011年   26928篇
  2010年   20481篇
  2009年   21314篇
  2008年   27148篇
  2007年   27459篇
  2006年   25499篇
  2005年   23172篇
  2004年   21645篇
  2003年   19695篇
  2002年   19349篇
  2001年   21192篇
  2000年   16926篇
  1999年   13499篇
  1998年   11600篇
  1997年   11368篇
  1996年   10569篇
  1995年   9723篇
  1994年   9762篇
  1993年   9323篇
  1992年   9979篇
  1991年   10424篇
  1990年   9886篇
  1989年   9572篇
  1988年   9182篇
  1987年   8405篇
  1986年   7921篇
  1985年   9910篇
  1984年   10155篇
  1983年   8481篇
  1982年   8672篇
  1981年   8046篇
  1980年   7777篇
  1979年   8298篇
  1978年   8629篇
  1977年   8416篇
  1976年   8318篇
  1975年   7932篇
  1974年   7736篇
  1973年   8029篇
  1972年   5791篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
61.
Integrated chaos generators   总被引:4,自引:0,他引:4  
This paper surveys the different design issues, from mathematical model to silicon, involved in the design of analog CMOS integrated circuits for the generation of chaotic behavior  相似文献   
62.
63.
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films.  相似文献   
64.
V. A. Steklov Mathematics Institute, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 347–358, June, 1989.  相似文献   
65.
The effect of secondary scattering that is produced by the induced current in an infinitely long, finitely conducting wire over a plane, finitely conducting earth from an incident electromagnetic pulse is investigated. This is accomplished by finding the field of a Hertzian dipole over the earth and identifying the part that is due to secondary scattering. Frequency-domain results for the overall induced current require that certain infinite integrals be numerically evaluated. Fourier inversion to the time domain in turn requires the numerical evaluation of another infinite integral. When the results are compared to those obtained when secondary scattering is ignored, it is found that secondary scattering slightly increases the current for the case of broadside incidence and reduces it for the case of grazing incidence by as much as two orders of magnitude. Peak currents are much smaller than previously thought. These general results hold for all of the earth parameters that were used in the study  相似文献   
66.
We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.  相似文献   
67.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 46–50, January, 1991.  相似文献   
68.
69.
A systematic study on the electrochemical behavior of diosmin in Britton-Robinson buffer (pH 2.0-10.0) at a glassy carbon electrode (GCE) was made. The oxidation process of the drug was found to be quasi-reversible with an adsorption-controlled step. The adsorption stripping response was evaluated with respect to various experimental conditions, such as the pH of the supporting electrolyte, the accumulation potential and the accumulation time. The observed anodic peak current at +0.73 V vs. Ag/AgCl reference electrode increased linearly over two orders of magnitude from 5.0x10(-8) M to 9.0x10(-6) M. A limit of detection down to 3.5x10(-8) M of diosmin at the GCE was achieved with a mean recovery of 97+/-2.1%. Based on the electrochemical data, an open-circuit accumulation step in a stirred sample solution of BR at pH 3.0 was developed. The proposed method was successfully applied to the determination of the drug in pharmaceutical formulations. The results compared favorably with the data obtained via spectrophotometric and HPLC methods.  相似文献   
70.
Ionic conductivity of dry quaternary ammonium polymer, polydiallyldimethylammonium with Cl and H2PO4 counter ions was studied in a wide range of frequencies (10−2-107 Hz) and temperatures (300-470 K). The data were analysed within the formalism of permittivity. WAXS, and thermal properties of this polymer were investigated prior to conductivity measurements.  相似文献   
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