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   295209篇
  免费   3861篇
  国内免费   1047篇
电工技术   5364篇
综合类   828篇
化学工业   41571篇
金属工艺   10145篇
机械仪表   8475篇
建筑科学   7018篇
矿业工程   1272篇
能源动力   7806篇
轻工业   23316篇
水利工程   2789篇
石油天然气   3291篇
武器工业   20篇
无线电   36217篇
一般工业技术   53915篇
冶金工业   66884篇
原子能技术   5307篇
自动化技术   25899篇
  2022年   1668篇
  2021年   2399篇
  2020年   1670篇
  2019年   2042篇
  2018年   3869篇
  2017年   4116篇
  2016年   4594篇
  2015年   3101篇
  2014年   4540篇
  2013年   12238篇
  2012年   8448篇
  2011年   11097篇
  2010年   7744篇
  2009年   8824篇
  2008年   9169篇
  2007年   9047篇
  2006年   8040篇
  2005年   9791篇
  2004年   8832篇
  2003年   8624篇
  2002年   6934篇
  2001年   7281篇
  2000年   6299篇
  1999年   6947篇
  1998年   21658篇
  1997年   14619篇
  1996年   10916篇
  1995年   7820篇
  1994年   6842篇
  1993年   6808篇
  1992年   4364篇
  1991年   4266篇
  1990年   4127篇
  1989年   3904篇
  1988年   3816篇
  1987年   3219篇
  1986年   3116篇
  1985年   3373篇
  1984年   3014篇
  1983年   2910篇
  1982年   2764篇
  1981年   2732篇
  1980年   2641篇
  1979年   2376篇
  1978年   2206篇
  1977年   3174篇
  1976年   4744篇
  1975年   1863篇
  1974年   1770篇
  1973年   1721篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Single-polarization single-mode photonic crystal fibers   总被引:5,自引:0,他引:5  
A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 /spl mu/m, where only the slow-axis mode exists and the confinement loss is less than 0.1 dB/km.  相似文献   
82.
A binary extended 1-perfect code of length n + 1 = 2/sup t/ is additive if it is a subgroup of /spl Zopf//sub 2//sup /spl alpha// /spl times/ /spl Zopf//sub 4//sup /spl beta//. The punctured code by deleting a /spl Zopf//sub 2/ coordinate (if there is one) gives a perfect additive code. 1-perfect additive codes were completely characterized and by using that characterization we compute the possible parameters /spl alpha/, /spl beta/, rank, and dimension of the kernel for extended 1-perfect additive codes. A very special case is that of extended 1-perfect /spl Zopf//sub 4/-linear codes.  相似文献   
83.
Parameterisation of slant-Haar transforms   总被引:1,自引:0,他引:1  
A parameterisation of the slant-Haar transform is presented, which includes an existing version of the slant-Haar transform. An efficient algorithm for the slant-Haar transform is developed and its computational complexity is estimated. The parametric slant-Haar transforms are compared to the Karhunen-Loeve transform. The parametric slant-Haar is shown to perform better than the commonly used slant-Haar and slant-Hadamard transforms for the first-order Markov model and also performs better than the discrete cosine transform for images approximated by the generalised image correlation model  相似文献   
84.
85.
The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented  相似文献   
86.
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance  相似文献   
87.
Crosstalk between microstrip transmission lines   总被引:1,自引:0,他引:1  
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk  相似文献   
88.
89.
An instrument is proposed for continuously tracking the Sun and measuring its height by the use of a laser gyrometer as measuring converter. The accuracy in photoelectric sighting on the Sun is improved by greatly reducing the light fluxes to be compared by screening out the central part of the Sun's image in the focal plane. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 7–9, March, 1994.  相似文献   
90.
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval.  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