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   7533篇
  免费   138篇
  国内免费   109篇
电工技术   140篇
综合类   187篇
化学工业   2154篇
金属工艺   339篇
机械仪表   189篇
建筑科学   1137篇
矿业工程   252篇
能源动力   177篇
轻工业   332篇
水利工程   328篇
石油天然气   131篇
武器工业   5篇
无线电   129篇
一般工业技术   313篇
冶金工业   843篇
原子能技术   158篇
自动化技术   966篇
  2024年   4篇
  2023年   47篇
  2022年   76篇
  2021年   100篇
  2020年   113篇
  2019年   110篇
  2018年   114篇
  2017年   105篇
  2016年   173篇
  2015年   170篇
  2014年   284篇
  2013年   314篇
  2012年   283篇
  2011年   506篇
  2010年   451篇
  2009年   520篇
  2008年   409篇
  2007年   493篇
  2006年   512篇
  2005年   409篇
  2004年   403篇
  2003年   380篇
  2002年   278篇
  2001年   211篇
  2000年   173篇
  1999年   146篇
  1998年   104篇
  1997年   116篇
  1996年   103篇
  1995年   113篇
  1994年   80篇
  1993年   82篇
  1992年   62篇
  1991年   67篇
  1990年   53篇
  1989年   36篇
  1988年   34篇
  1987年   35篇
  1986年   41篇
  1985年   27篇
  1984年   12篇
  1983年   5篇
  1982年   6篇
  1981年   3篇
  1980年   14篇
  1978年   1篇
  1977年   1篇
  1973年   1篇
排序方式: 共有7780条查询结果,搜索用时 0 毫秒
21.
介绍射水造墙的接缝原理,并把自己在施工过程中为确保接缝质量达到设计要求而总结出一些经验和处理措施提出为一起探讨。  相似文献   
22.
Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found.  相似文献   
23.
Three ketoacids; glyoxylic acid, pyruvic acid and ketomalonic acid, were identified in ozonated drinking waters and fulvic acid solutions using gas chromatography-mass spectrometry. It was found that the concentrations of ketoacids were much higher than those of aldehydes in ozonated waters. The significance of ketoacids in finished drinking waters is discussed.  相似文献   
24.
通过考察日本的水土保持工作,文中在简明介绍日本水土保持工作的基础上,尤其着重介绍了日本的庭园水土保持,小流域的综合治理,治山绿化工程,水土保持科学研究和滑坡、泥石流防治工程等技术措施和方法。并提出了一些有益的建议;他们的经验有许多值得我们借鉴。  相似文献   
25.
For 30 acid upland and hill soils, with initial pH from 3.5 to 5.8, and loss on ignition from 14% to 94%, cation exchange capacity varied with pH according to the relationship CEC = m pH+C, where m and C are characteristic of each soil. The slope m depended on loss on ignition (LOI), and is given by: m=Δ CEC/Δ=0.22 LOI+1.92. Because of these relationships, CEC measured at the natural pH of the soil (in 0.025 M MgSO4 solution) is more relevant to field conditions than a conventional measurement at pH7. An improved method for estimating lime requirement (LR) of these soils was developed, based on the relationship found between LR and the difference in CEC (ΔCEC) between that at the natural pH of the soil and that at the target pH of 5.5: LR=1.12 ΔCEC+1.48. Lime requirement can therefore also be estimated from loss on ignition using the earlier relationships, and is given by: LR=(0.25 LOI+2.15) Δ+1.48, where Δ is the difference between the natural pH (in 0.025 M MgSO4) and the target pH. Predictions based on this agreed well with results for a further 10 soils.  相似文献   
26.
国内现行规范、标准是以极限变形值作为土钉支护结构水平位移安全监测报警值 ,但没有反映工程进度影响 ,不便指导工程实践。提出“过程控制”概念 ,以反正切函数为基本形式 ,基于历史经验建立“安全时程曲线”控制模型 ,要求施工过程中实测水平位移始终处在“安全时程曲线”之下 ,以确保最终变形在某一适当的阈值之内 ,已有实测结果可以为施工方案调整提供依据。通过实际案例 ,检验模型的可行性 ,表明过程控制模型较极限变形策略更具可操作性  相似文献   
27.
A new technique of using ozone for water treatment is presented. This new technique consists of using a three-step-process composed firstly of ozone adsorption on an appropriate adsorbent, secondly water treatment, and thirdly regeneration of the adsorbent. Results regarding ozone adsorption (the first step) are presented in this paper. Different types of silica gel and a type of TiO2 have been tested for ozone adsorption. It was found that the physical characteristics of the silica gel affect its capacity for ozone. Titanium dioxide has shown ozone decomposition instead of adsorption as it contains Lewis acid sites. An exponential decrease of the silica gel capacity with its moisture content has been found. Linear isotherms in the range of ozone concentrations less than 100?g/m3 NTP have been found. A particle diffusion model with linear equilibrium isotherm has been used to model the breakthrough curves in fixed bed columns.  相似文献   
28.
Equal Strain Consolidation by Vertical Drains   总被引:1,自引:0,他引:1  
This paper shows the development of a series of closed-form solutions of equal strain consolidation in the presence of a vertical drain with smear and well resistance. Using an approach that considers the effects of both the radial and vertical drainage in a fully coupled fashion, solutions are obtained for the excess pore pressure and the degree of consolidation in the compressible soil subjected to a step- or ramp-loading situation. The closed-form solutions in the present paper may be evaluated in an electronic spreadsheet on a standard personal computer.  相似文献   
29.
The Steady radial distribution of chemical species in a wire‐to‐cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, O2 +, O2 ?, O3 ?, O?, O2, O2(1Δg), O2(1g +), O and O3) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poisson's equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by UV spectroscopy.  相似文献   
30.
The effect of gas-liquid contacting conditions in a static mixer on ozone transfer efficiency and reduction of Bacillus subtilis spores was studied in an experimental ozone contactor. An empirical mathematical model was developed that related the transfer efficiency in the experimental system to the superficial liquid velocity in the mixer, the gas-liquid flow rate ratio and the height of the down-stream bubble column. Spore reduction was determined primarily by the dissolved ozone concentration-time (Cavgtm) product in the reactive flow segment and was independent of the gas-liquid contacting conditions in the static mixer. In an integrated ozone contacting system, the static mixer should be designed to maximize ozone mass transfer while the reactive flow segment should be designed for efficient microorganism reduction.  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