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   290716篇
  免费   3340篇
  国内免费   1326篇
电工技术   4983篇
综合类   531篇
化学工业   42996篇
金属工艺   11338篇
机械仪表   8655篇
建筑科学   7013篇
矿业工程   1666篇
能源动力   7323篇
轻工业   23305篇
水利工程   3156篇
石油天然气   5940篇
武器工业   44篇
无线电   34262篇
一般工业技术   58279篇
冶金工业   53904篇
原子能技术   7617篇
自动化技术   24370篇
  2021年   2304篇
  2019年   2204篇
  2018年   3744篇
  2017年   3833篇
  2016年   4088篇
  2015年   2644篇
  2014年   4550篇
  2013年   12711篇
  2012年   7442篇
  2011年   10247篇
  2010年   7897篇
  2009年   9134篇
  2008年   9598篇
  2007年   9625篇
  2006年   8287篇
  2005年   7640篇
  2004年   7527篇
  2003年   7290篇
  2002年   7055篇
  2001年   7063篇
  2000年   6687篇
  1999年   6992篇
  1998年   16508篇
  1997年   11790篇
  1996年   9130篇
  1995年   7063篇
  1994年   6233篇
  1993年   6307篇
  1992年   4615篇
  1991年   4348篇
  1990年   4264篇
  1989年   4247篇
  1988年   3901篇
  1987年   3586篇
  1986年   3582篇
  1985年   3969篇
  1984年   3673篇
  1983年   3404篇
  1982年   3192篇
  1981年   3219篇
  1980年   3181篇
  1979年   3005篇
  1978年   3042篇
  1977年   3273篇
  1976年   4239篇
  1975年   2580篇
  1974年   2509篇
  1973年   2519篇
  1972年   2102篇
  1971年   1848篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Comments on R. L. Woolfolk and F. C. Richardson's (see record 1985-12614-001) discussion of the ideology of behavior therapy and their argument that behavior therapy cannot develop a conception of what might be appropriate goals of treatment. The present author contends that goals are as much a scientific question as are questions of technique. A scientific approach to the study of goal selection is presented that can be applied to any type of adjustment problem. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
Heat conduction in an electronic device is commonly modeled as a discretized thermal system (e.g., finite element or finite difference models) that typically uses large matrices for solving complex problems. The large size of electronic-system heat transfer models can be reduced using model reduction methods and the resulting reduced-order models can yield accurate results with far less computational costs. Electronic devices are typically composed of components, like chips, printed circuit boards, and heat sinks that are coupled together. There are two ways of creating reduced-order models for devices that have many coupled components. The first way is to create a single reduced-order model of the entire device. The second way is to interconnect reduced-order models of the components that constitute the device. The second choice (which we call the "reduce then interconnect" approach) allows the heat transfer specialist to perform quick simulations of different architectures of the device by using a library of reduced-order models of the different components that make up the device. However, interconnecting reduced-order models in a straightforward manner can result in unstable behavior. The purpose of this paper is two-fold: creating reduced-order models of the components using a Krylov subspace algorithm and interconnecting the reduced-order models in a stable manner using concepts from control theory. In this paper, we explain the logic behind the "reduce then interconnect" approach, formulate a control-theoretic method for it, and finally exhibit the whole process numerically, by applying it to an example heat conduction problem  相似文献   
993.
Summary Recently, the hypoelastic-idealplastic solid under simple shear has been studied. As an unexpected result, the slope of the stress-strain curve at the beginning of the plastic range turned out to be negative. While all other assumptions remained the same, this effect was recognized for all objective stress rates, which have been used for the hypoelastic constitutive law.The main objective of this paper is an interpretation of this remarkable result, where this interpretation should be given in an acceptable and rational form. To this end, we apply the constitutive assumption of the elastic-idealplastic body for comparison.With 1 Figures  相似文献   
994.
Indoor test methods for solar collectors are widely accepted and recommended by ASHRAE. The development of a solar simulator for indoor testing and the certification procedure for photo-thermal solar devices is discussed in this paper. The system consists of 14 quartz halogen lamps and provides a testing area of about 1 × 1 m. The irradiance can be varied from 400 to 1500 W/m2. This is achieved by varying the input power supplied to individual lamps. The radiation output characteristics of a single lamp have been studied. The distribution of intensity over the covered area of 1·20 × 1·20 m has been recorded using a precision Eppley pyranometer.A variety of collectors—evacuated tubular collectors and flat-plate collectors of both liquid and air heating types—has been tested under sufficiently stable insolation conditions. Results for a conventional solar air heater are presented together with suggestions for further improvements.  相似文献   
995.
Self-organizing communication networks   总被引:3,自引:0,他引:3  
  相似文献   
996.
We have performed tribotechnical tests of carbonaceous filled polytetrafluoroethylene in a wide range of loads with the recording of acoustic emission signals. Based on a spectral analysis of the sequence of rms deviations of acoustic emission signals using a discrete Fourier transform, we have constructed a normalized energy spectrum. We show that the mass wear of the material can be determined from the power of the high-frequency component of the spectrum obtained.  相似文献   
997.
998.
999.
A new type of radiative cooling system is described. The radiator makes use of nonimaging optics and evacuated-tube technology to radiate significant amounts of heat to the 3 K environment of outer space. The nonimaging optics are used to direct the radiation overhead, through the most transparent part of the 8–13 μm atmospheric window. The required optical concentration is small, and relatively simple mirror geometries are possible. The evacuated-tube technology is used to attain storage temperatures at or below the freezing point, even when dewpoint temperatures are well above the freezing point.  相似文献   
1000.
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