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   261987篇
  免费   31310篇
  国内免费   9061篇
电工技术   13110篇
技术理论   24篇
综合类   14245篇
化学工业   54601篇
金属工艺   13442篇
机械仪表   15285篇
建筑科学   19086篇
矿业工程   7461篇
能源动力   7252篇
轻工业   20135篇
水利工程   3868篇
石油天然气   16482篇
武器工业   1650篇
无线电   31208篇
一般工业技术   37287篇
冶金工业   13113篇
原子能技术   2283篇
自动化技术   31826篇
  2024年   799篇
  2023年   3612篇
  2022年   6343篇
  2021年   9139篇
  2020年   8154篇
  2019年   8639篇
  2018年   9345篇
  2017年   10483篇
  2016年   10178篇
  2015年   12421篇
  2014年   14819篇
  2013年   17870篇
  2012年   16745篇
  2011年   17632篇
  2010年   15885篇
  2009年   15046篇
  2008年   14288篇
  2007年   13627篇
  2006年   13913篇
  2005年   12072篇
  2004年   8602篇
  2003年   7563篇
  2002年   6867篇
  2001年   6103篇
  2000年   6519篇
  1999年   6874篇
  1998年   5463篇
  1997年   4462篇
  1996年   4175篇
  1995年   3491篇
  1994年   2808篇
  1993年   1959篇
  1992年   1531篇
  1991年   1219篇
  1990年   930篇
  1989年   730篇
  1988年   532篇
  1987年   332篇
  1986年   271篇
  1985年   192篇
  1984年   132篇
  1983年   102篇
  1982年   119篇
  1981年   100篇
  1980年   69篇
  1979年   39篇
  1978年   27篇
  1977年   22篇
  1976年   38篇
  1973年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
基于i860的存储器子系统设计   总被引:1,自引:0,他引:1  
微处理机系统中的存储器子系统设计对整个系统性能的高低有重要的影响,尤其当微处理器的主频越来越高时。本文结合实际例子,给出了一个基于i860处理器(40MHz)的主存设计方案,讨论了实际中需仔细考虑的因素。该设计可为其它高性能RISC系统设计提供参考。  相似文献   
992.
刘洪岭 《炼铁》1995,14(5):22-24
天津钢管公司DRC直接还原厂将采用英国戴维国际工程公司的DRC煤基直接还原技术,以铁矿石、煤、石灰石为原燃料,用回转窑来生产直接还原铁(DRI)。该厂将由两条回转窑生产线组成,每条生产线的生产能力为15万tDRI/年,回转窑规格为φ5.0m×80m。工厂生产主线将采用计算机集散控制系统(DCS)以实现对生产过程的自动控制。  相似文献   
993.
在语音时域挑选剩余可懂度低的可用置换集合,置换集合是语音TDS系统中不可缺少的重要环节,本文给出了可用置换选取的条件、客观评价标准和方法。  相似文献   
994.
本文应用有初始几何缺陷的壳体非线性应变分量公式及内时本构理论,对冷却塔在重力作用下的内力进行了弹塑性大变形计算,分析了常见的几种缺陷对冷却塔内力分布的影响。对于工程实际中有缺陷的冷却塔的整体性能分析具有重要意义,可以为工程设计提供理论基础。  相似文献   
995.
Porous silica glass was prepared by sol-gel process from tetraethoxysilane (TEOS). The effects of solvents (water, ethanol), drying condition, heat treatment temperature on specific surface area and pore size distribution of porous silica were investigated. Gelation process accelerates with an increase of H2O content, while retards with the increase of ethanol amount. Structure changes during heat treatment were studied by means of DTA, XRD. TEM micrographs show that the gel particles shrink after heated at 500°C, thus the average pore size decreases.  相似文献   
996.
A finite element formulation and the solution of a set of nonlinear coupled heat and mass transfer equations for a two-phase system with a moving evaporation interface is presented. The interface condition takes into account the moisture transfer balance at the moving boundary. The finite element results were compared with existing results for a single phase system for model validation. In the two-phase system, the movement of evaporation front has an appreciable effect on the temperature and moisture distribution inside the porous medium during drying. The effect of the nondimensional heat of vapourization parameter γ on the evaporation front, temperature and moisture distribution in porous medium was studied. The higher the value of γ, the slower is the movement of the evaporation front. The temperature decreased and the moisture content increased as the nondimensional vapourization parameter γ increased. This model has potential applications in studying the heat and mass transfer characteristics in food and biomaterials.  相似文献   
997.
Dynamic oxide voltage relaxation spectroscopy   总被引:3,自引:0,他引:3  
A new method for trap characterization of oxidized silicon is described. The Dynamic Oxide Voltage Relaxation Spectroscopy (DOVRS) is an improved version of the formerly proposed Oxide Voltage Relaxation Spectroscopy (OVRS) technique which applies a periodic long duration constant current for tunneling injection. It has been demonstrated that the new technique can be used not only to separate and identify the oxide trap from interface trap, but also to separate and determine the centroid from the oxide trap density generated in the MOS system by the tunneling current stress. In the pulse constant current mode, the OVRS measurement can be completed instead of using the double current-voltage technique. Thus the new method results in more accurate and quicker measurements of the oxide trap centroid. Analytical expressions for computing the paramaters of the interface and oxide traps are derived. The effect of the channel carrier mobility on the spectroscopy is also considered. Two types of oxide and two types of interface traps were observed at a pulse constant Fowler-Nordheim current stress by the new method of DOVRS  相似文献   
998.
The Fe-Ag granular metal solid samples with 10% and 30% weight iron have been successfully fabricated using a sol-gel method, which are characterized by X-ray diffraction and transmission electron micrography. The average diameters of iron particles are from about a few nanometres to a few tens of nanometres controlled by the reducing temperature. The evolution of magnetic properties and microstructure during heat treating are described in detail and explained by using the superparamagnetism, single domain and multi domain theories. The magnetic anisotropy of the Fe-Ag granular solid is studied by using the law of approach to saturation. It is found that the magnetic anisotropy constant is in the order of 105 J m–3 which is higher than the value of the bulk iron and increases with the increase of reducing temperature.  相似文献   
999.
A series of Fe-C-X and Fe-C-X1-X2 alloys in which X, X1 and X2 either raise or depress the activity of C iny were investigated by autodilatometer, optical microscopy, and transmission electron microscopy (TEM) to reveal the relations among the chemical composition, transformation kinetics, and morphology of ferrite plates. The incubation time of austenite decomposition at the nose temperature in the time-temperature-transformation (TTT) diagrams, the concentration of C in y in contact with theα/gg boundary, and the growth rate of ferrite were evaluated to estimate the magnitude of the solute drag-like effect (SDLE) for the different alloying elements used. All the results are consistent qualitatively with the SDLE hypothesis. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.  相似文献   
1000.
In this paper, the stochastic boundary element method, which combines the mixed boundary integral equations method explored in Reference 1 with the first-order reliability method, is developed to study probabilistic fatigue crack growth. Due to the high degree of complexity and non-linearity of the response, direct differentiation coupied with the response-surface method is employed to determine the response gradient. Three random processes, the mode I and mode II. stress intensity factors and the crack direction angle, are included in the expression of the response gradient. The sensitivity of these random processes is determined using a first-order response model. An iteration scheme based on the HL-RF method2 is applied to locate the most probable failure point on the limit-state surface. The accuracy and efficiency of the stochastic boundary element method are evaluated by comparing the cumulative distribution function of the fatigue life obtained with Monte Carlo simulation. The reliability index and the corresponding probability of failure are calculated for a fatigue crack growth problem with randomness in the crack geometry, defect geometry, fatigue parameters and external loads. The response sensitivity of each primary random variable at the design point is determined to show its role in the fatigue failure. The variation of each primary random variable at the design point with the change of probability of failure is also presented in numerical examples.  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