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   272948篇
  免费   2548篇
  国内免费   297篇
电工技术   4362篇
综合类   129篇
化学工业   45791篇
金属工艺   15514篇
机械仪表   10527篇
建筑科学   5457篇
矿业工程   3857篇
能源动力   4481篇
轻工业   11529篇
水利工程   4308篇
石油天然气   13072篇
武器工业   28篇
无线电   21933篇
一般工业技术   67041篇
冶金工业   36540篇
原子能技术   11325篇
自动化技术   19899篇
  2021年   3303篇
  2019年   3149篇
  2018年   5949篇
  2017年   6162篇
  2016年   6656篇
  2015年   3596篇
  2014年   6047篇
  2013年   11451篇
  2012年   8436篇
  2011年   10382篇
  2010年   8333篇
  2009年   9096篇
  2008年   9287篇
  2007年   8895篇
  2006年   7263篇
  2005年   6294篇
  2004年   6199篇
  2003年   5943篇
  2002年   5677篇
  2001年   5366篇
  2000年   5286篇
  1999年   4645篇
  1998年   7902篇
  1997年   6364篇
  1996年   4843篇
  1995年   4053篇
  1994年   3791篇
  1993年   3977篇
  1992年   3475篇
  1991年   3546篇
  1990年   3742篇
  1989年   3623篇
  1988年   3472篇
  1987年   3474篇
  1986年   3376篇
  1985年   3572篇
  1984年   3469篇
  1983年   3361篇
  1982年   3193篇
  1981年   3232篇
  1980年   3233篇
  1979年   3443篇
  1978年   3649篇
  1977年   3640篇
  1976年   4135篇
  1975年   3366篇
  1974年   3413篇
  1973年   3447篇
  1972年   3078篇
  1971年   2817篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal.  相似文献   
12.
V. G. Deibuk 《Semiconductors》2003,37(10):1151-1155
The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data.  相似文献   
13.
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa.  相似文献   
14.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.  相似文献   
15.
The problem of synthesis of an isotropic reradiator providing for the transparency of a circular perfectly conducting cylinder illuminated by a TE-polarized plane wave is investigated. A general solution to the problem of diffraction from the cylinder with a reradiator is obtained, and a system of nonlinear equations for the synthesis problem is derived. Numerical solution of the synthesis problem is illustrated by a number of examples.  相似文献   
16.
Operation of the dam in a transitional mode is described. __________ Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 1, January 2006, pp. 8–15.  相似文献   
17.
A mathematical model for separation of suspensions with a non-Newtonian disperse medium by dual-stage pressurized flotation in a cylindrical-conical hydrocyclone is developed. A system of differential equations of the convective diffusion and movement of a complex of particles-bubbles is solved by a numerical method. The concentration field is modeled, and integral separation indicators are determined. Values of structural parameters of the hydrocyclone for which the separation indicators depend heavily on the taper angle of the conical section of the housing and the rheological properties of the disperse medium are established. It is demonstrated that dual-stage pressurized flotation makes it possible to reduce considerably the residual concentration of solid-phase particles as compared with single-stage flotation.  相似文献   
18.
19.
Summary.  Quasi-static stress fields for a crack inclined to the direction of property gradation in functionally graded materials (FGMs) are obtained through an asymptotic analysis coupled with Westergaard's stress function approach. The elastic modulus of the FGM is assumed to vary exponentially along the gradation direction. The mode mixity due to the inclination of the property gradient is accommodated in the analysis through superposition of opening and shear modes. The first four terms in the expansion of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field. Using these stress field contours of constant maximum shear stress, constant maximum principal stress, constant first stress invariant and constant out of plane displacement are generated, and the effect of inclination of the property gradation direction on these contours is discussed. Received September 22, 2002 Published online: May 20, 2003 The financial support of National Science Foundation (NSF) under grant no. CMS 99000138 is gratefully acknowledged.  相似文献   
20.
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