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   179557篇
  免费   8515篇
  国内免费   4145篇
电工技术   5952篇
技术理论   9篇
综合类   7963篇
化学工业   28075篇
金属工艺   9882篇
机械仪表   8935篇
建筑科学   10057篇
矿业工程   2888篇
能源动力   3957篇
轻工业   9197篇
水利工程   2930篇
石油天然气   5352篇
武器工业   683篇
无线电   20946篇
一般工业技术   28229篇
冶金工业   7662篇
原子能技术   1174篇
自动化技术   38326篇
  2024年   290篇
  2023年   1389篇
  2022年   2355篇
  2021年   3450篇
  2020年   2607篇
  2019年   2302篇
  2018年   16577篇
  2017年   15812篇
  2016年   12334篇
  2015年   3999篇
  2014年   4796篇
  2013年   5928篇
  2012年   9049篇
  2011年   15515篇
  2010年   13804篇
  2009年   10877篇
  2008年   11872篇
  2007年   12800篇
  2006年   5480篇
  2005年   5910篇
  2004年   4464篇
  2003年   4395篇
  2002年   3720篇
  2001年   2892篇
  2000年   2821篇
  1999年   2833篇
  1998年   2520篇
  1997年   1996篇
  1996年   1848篇
  1995年   1500篇
  1994年   1261篇
  1993年   921篇
  1992年   683篇
  1991年   583篇
  1990年   419篇
  1989年   369篇
  1988年   327篇
  1987年   173篇
  1986年   160篇
  1985年   107篇
  1984年   93篇
  1983年   62篇
  1982年   59篇
  1981年   53篇
  1980年   40篇
  1968年   45篇
  1966年   43篇
  1965年   45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
991.
992.
焦化汽油加氢试生产重整原料的技术分析   总被引:2,自引:0,他引:2  
在0.6Mt/a柴油加氢精制装置上利用焦化汽油为原料进行重整原料油的试生产,改善了焦化汽油的性质,降低了硫,氮和可导致重整催化剂中毒的金属含量及烯烃含量,提高了饱和烃的含量,生产出了合格的重整原料,该技术拓宽了重整原料来源,较好地解决了焦化汽油的出路问题。  相似文献   
993.
A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained.  相似文献   
994.
互联网是以数字化、网络化、信息化为标志的文化状态,是以交互性、虚拟性、学习性为标志的运作模式,是以多边性、全时性、共享性为标志的机制特质.网络交往的广泛化,对现代社会生活产生重大影响.  相似文献   
995.
An application of Narrative Knowledge Representation Language (NKRL) techniques on (declassified) ‘terrorism in Southern Philippines’ documents has been carried out in the context of the IST Parmenides project. This paper describes some aspects of this work: it is our belief, in fact, that the Knowledge Representation techniques and the Intelligent Information Retrieval tools used in this experiment can be of some interest also in an ‘Ontological Modelling of Legal Events and Legal Reasoning’ context.  相似文献   
996.
In order to develop highly efficient upconversion (UC) material, Er3+-doped oxyfluoride glass ceramics containing BaYF5 nano-crystals were fabricated for the first time. The randomly distributed BaYF5 nano-particles with the size of nearly 25 nm precipitated from the glass matrix at about 700 °C, then tended to aggregate slightly with the increase of heating temperature, resulting in the enhancement of Er3+ UC emission in the wavelength ranging from 500 nm to 700 nm. The UC process was found very sensitive to Er3+ content: with the increase of Er3+ content from 0.5% to 1.0%, the UC intensity behaved with drastic exaltation; while further increasing Er3+ content to 2.0% resulted in a notable fluorescence quenching. Significantly, the UC efficiency of present glass ceramic preponderates notably over that of the previously reported glass ceramic containing LaF3, implying its superior UC potentiality.  相似文献   
997.
Future of energy   总被引:1,自引:0,他引:1  
  相似文献   
998.
Treated was an anti-plane crack perpendicular to the interface of an exponential-type FGM strip bonded to another linear-type FGM substrate with infinite thickness. Through Fourier integral transform, the problem was reduced as a Cauchy singular integral equation, which was further solved numerically by the Lobatto–Chebyshev collocation method. Based on the numerical solution, the effects of the geometrical and physical parameters on the stress intensity factor (SIF) were analyzed and the following conclusions were obtained: (a) A notable discrepancy between the interface-perpendicular crack and the interfacial one is that, to reduce the weak-discontinuity of interface or to make the interface micro-discontinuous will not necessarily decrease the SIF of the former, but will surely decrease that of the latter. (b) When a crack tip is situated very near to the interface (or free surface), its SIF will be high and totally dominated by the interface (or free surface). (c) To increase the stiffness of the FGM on one side of the interface is beneficial to preventing the crack on the other side from growing toward the interface. Besides, some practical suggestions were further given for material design in the field of composites.  相似文献   
999.
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