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   164854篇
  免费   15820篇
  国内免费   9737篇
电工技术   12986篇
技术理论   8篇
综合类   20385篇
化学工业   18532篇
金属工艺   8074篇
机械仪表   13039篇
建筑科学   21415篇
矿业工程   8408篇
能源动力   5383篇
轻工业   9243篇
水利工程   6952篇
石油天然气   6824篇
武器工业   2127篇
无线电   10615篇
一般工业技术   19712篇
冶金工业   7258篇
原子能技术   2363篇
自动化技术   17087篇
  2024年   722篇
  2023年   1967篇
  2022年   3866篇
  2021年   4483篇
  2020年   5029篇
  2019年   4204篇
  2018年   4083篇
  2017年   5113篇
  2016年   5749篇
  2015年   5991篇
  2014年   10139篇
  2013年   9284篇
  2012年   12464篇
  2011年   12745篇
  2010年   9873篇
  2009年   10174篇
  2008年   9242篇
  2007年   11649篇
  2006年   10233篇
  2005年   8662篇
  2004年   7158篇
  2003年   6224篇
  2002年   5273篇
  2001年   4422篇
  2000年   3864篇
  1999年   3290篇
  1998年   2576篇
  1997年   2192篇
  1996年   1844篇
  1995年   1638篇
  1994年   1402篇
  1993年   1006篇
  1992年   898篇
  1991年   625篇
  1990年   513篇
  1989年   530篇
  1988年   365篇
  1987年   211篇
  1986年   171篇
  1985年   76篇
  1984年   72篇
  1983年   40篇
  1982年   45篇
  1981年   56篇
  1980年   33篇
  1979年   38篇
  1978年   18篇
  1977年   15篇
  1975年   18篇
  1959年   30篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This study focuses on the relationship between photo-catalytic performance and optical property over Si-incorporated TiO2. The Si-incorporated TiO2 particles exhibited a pure structure of anatase having a particle size of less than 20 nm and surface area of more than 190 m2/g. The absorbance did not shift to a higher wavelength in spite of the incorporation of the Si ions, but the intensity of the photoluminescence (PL) curve was the smallest in the case of the 2.0 mol% Si-TiO2, which was related to the recombination between the excited electrons and holes. Based on these results, the photodecomposition of methyl orange in the liquid reaction was enhanced over the 2.0 mol% Si-incorporated TiO2 compared with that over pure TiO2: Methyl orange at 10.0 ppm was completely decomposed after 100 min when 1.0 g of the 2.0 mol% Si-incorporated TiO2 was used.  相似文献   
62.
闫荣春  许罕多 《山西建筑》2008,34(11):241-242
对"比较法"原理和应用情况进行了分析,说明其在房地产开发中能够科学地预测房地产的价格和收益,从而提高财务分析的科学性和权威性,为项目决策提供科学依据,以促进"比较法"在房地产开发中的应用。  相似文献   
63.
Residual stress as measured quantity in quality assurance The x‐ray method is used in the Volkswagen Automotive Group at different world‐wide locations as a standard procedure to determine residual stress. As an important measured quantity in the quality assurance residual stresses are specified in drawings of different components (e.g. gears, coil springs). Measurements are carried out during quality assurance, production, damage analyse, technical development department and design control of components from suppliers. An optimum efficiency can be achieved, if it exists a unique correlation between residual stress values and loading capacity of components, and if the processes to introduce residual stress can be optimized using residual stress measurements during the production.  相似文献   
64.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施  相似文献   
65.
花小民 《施工技术》2004,33(5):49-51
通过低应变反射波法与钻孔抽芯 2种检测方法的结果对比分析 ,验证低应变反射波法检测基桩的缺陷及位置的准确性 ,积累波形判别的经验。  相似文献   
66.
A method is considered to solve a conditional optimization problem with a linear-fractional objective function over permutations. The performance of sub algorithms to solve this problem is evaluated. The practical efficiency of the algorithm is analyzed by conducting numerical experiments. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 133–146, July–August 2007.  相似文献   
67.
孔颖 《数字社区&智能家居》2007,(3):1429-1429,1438
针对C语言程序设计课程本身的特点,分析学习过程中存在的问题,强调实践的必要性。结合一些学校课程改革和实践的经验.提出面向应用的,科学的学习内容、方法和模式。同时提高学习者的专业动手能力。  相似文献   
68.
The main objective of the present work is to modify the traditional mapping method for the simulation of distributive mixing of multiphase flows in geometries involving moving parts such as, internal mixers or twin-screw extruders without a limitation on their geometrical periodicity. The periodicity condition, limits the results of traditional mapping method to tracking mapping mesh between specific discrete time intervals or distances for that geometry is repeated, hence, result is only for fixed orientation of rotors. Imaginary domain method is introduced to track mapping mesh from one state to the next free of geometrical periodicity limitations. In this work the method is introduced and its applicability and accuracy is discussed in details. A two-dimensional (2D) simulation of mixing of two Newtonian fluids with different viscosities in an intermeshing internal mixer is used as a test case study. In this example the key issues of ability to predict mixing state in details for all orientations of rotors is presented. To reduce diffusion errors of mapping method in the boundaries of the rotors, mapping mesh refinement technique that relies upon one single reference mesh is also presented.  相似文献   
69.
风管摩擦阻力的直接计算方法   总被引:2,自引:1,他引:1  
彭小勇  李惠敏 《暖通空调》2004,34(12):76-77,80
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。  相似文献   
70.
This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab.  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