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   85131篇
  免费   1010篇
  国内免费   411篇
电工技术   886篇
综合类   2322篇
化学工业   11697篇
金属工艺   4847篇
机械仪表   3049篇
建筑科学   2184篇
矿业工程   563篇
能源动力   1160篇
轻工业   3647篇
水利工程   1275篇
石油天然气   345篇
无线电   9402篇
一般工业技术   16544篇
冶金工业   2967篇
原子能技术   313篇
自动化技术   25351篇
  2021年   25篇
  2019年   20篇
  2018年   14463篇
  2017年   13391篇
  2016年   9972篇
  2015年   606篇
  2014年   262篇
  2013年   264篇
  2012年   3178篇
  2011年   9462篇
  2010年   8311篇
  2009年   5589篇
  2008年   6820篇
  2007年   7830篇
  2006年   161篇
  2005年   1254篇
  2004年   1167篇
  2003年   1217篇
  2002年   573篇
  2001年   131篇
  2000年   212篇
  1999年   90篇
  1998年   178篇
  1997年   128篇
  1996年   107篇
  1995年   53篇
  1994年   51篇
  1993年   53篇
  1992年   23篇
  1991年   41篇
  1989年   21篇
  1988年   26篇
  1986年   24篇
  1985年   22篇
  1982年   20篇
  1977年   20篇
  1969年   24篇
  1968年   43篇
  1967年   34篇
  1966年   42篇
  1965年   44篇
  1963年   29篇
  1962年   22篇
  1960年   30篇
  1959年   35篇
  1958年   37篇
  1957年   37篇
  1956年   34篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Ultrasonic wave velocities were determined at parallel and perpendicular to manufacturing direction and at the interval angles of 15° in clockwise and counterclockwise directions of particleboard and fiberboard. The experimental results were compared with the predicted values using some empirical formulae such as Hankinson and Jacoby equations. The results showed that the ultrasonic wave velocity were the highest in parallel direction in particleboard and fiberboard and decreases with increase of angle and the lowest values occurred in perpendicular direction. The predicted ultrasonic velocity using Hankinson and Jacoby equations are in close agreement with the measured values. Relationship between ultrasonic wave velocities and particles and fibers angle could be successfully presented by cubic and quadratic regression equations as well.  相似文献   
83.
84.
85.
A new method is proposed to produce gold nanoparticles (GNP) by in situ reduction of a gold salt dissolved in water. The reducing agent used is Tiron instead of the citrate anion most often mentioned in literature. The influence of various parameters has been investigated, such as the content of Tiron with respect to that of the precursor of gold HAuCl4, or the initial pH of the solution after mixing of reactants. It is shown that Tiron also exerts a positive influence as a dispersant, which impedes agglomeration of gold nanoparticles. The typical average size of GNP synthesized in the present work is close to 7 nm.  相似文献   
86.
87.
Reduction of flash generated in a gas vent is of great concern for manufacturers of electronic parts. The present study proposes a theoretical model for flash generation through consideration of flow characteristics in a gas vent. The model predicts the factors controlling flash, i.e., material parameters such as zero‐shear viscosity, crystallization temperature, thermal conductivity, and heat capacity, and process parameters such as injection and mold wall temperatures, packing pressure, and the clearance of a gas vent. On the other hand, we measure the amount of flash generated in the molding of poly(phenylene sulfide) (PPS) composites containing glass fiber and spherical fillers (CaCO3 or Al2O3). Flash reduces with decreasing size of spherical fillers. These experimental data are successfully interpreted using the flash model. Polym. Eng. Sci., 45:198–206, 2005. © 2005 Society of Plastics Engineers  相似文献   
88.
It is experimentally ascertained that light stimulates the negative magnetoresistance observed in a high electric field in silicon doped with boron and manganese. The optimum conditions (the electric field, temperature, illumination, and resistivity of the material) for observation of the largest magnitude of negative magnetoresistance in (Si:B):Mn are determined. The dependence of the negative magnetoresistance on the concentration of compensating impurity is established.  相似文献   
89.
Some approximate solutions for predicting the stress intensity factor of a short crack penetrating an inclusion of arbitrary shape have been developed under mode I and mode II loading conditions. The derivation of the fundamental formula is based on the transformation toughening theory. The transformation strains in the inclusion are induced by the crack-tip field and remotely applied stresses, and approximately evaluated by the Eshelby equivalent inclusion theory. As validated by detailed finite element (FE) analyses, the developed solutions have good accuracy for different inclusion shape and for a wide range of modulus ratio between inclusion and matrix material.  相似文献   
90.
An overview of nondestructive evaluation methods   总被引:1,自引:0,他引:1  
ondestructive evaluation is described as nondestructive testing (NDT), nondestructive inspection (NDI), and nondestructive examination (NDE). The activities associated with the evaluation include testing, inspection, and examination and primarily involve looking at (or through) and/or measuring some characteristic of an object. Frequently there is a desire to determine some characteristic of the object or to determine whether the object contains irregularities, discontinuities, or flaws. These examinations, inspections, or tests are used to determine the physical soundness of a material without impairing its usefulness. Nondestructive evaluation is a powerful tool that can help assure safety, quality, and reliability; increase productivity; decrease liability; protect the environment; and save money. In this article, nondestructive evaluation is represented by the acronym NDE.  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