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   25125篇
  免费   1719篇
  国内免费   1173篇
电工技术   255篇
综合类   1194篇
化学工业   10405篇
金属工艺   4303篇
机械仪表   354篇
建筑科学   719篇
矿业工程   541篇
能源动力   1460篇
轻工业   2836篇
水利工程   136篇
石油天然气   1355篇
武器工业   92篇
无线电   558篇
一般工业技术   2256篇
冶金工业   1242篇
原子能技术   225篇
自动化技术   86篇
  2024年   107篇
  2023年   519篇
  2022年   646篇
  2021年   797篇
  2020年   850篇
  2019年   815篇
  2018年   747篇
  2017年   824篇
  2016年   744篇
  2015年   704篇
  2014年   1123篇
  2013年   1334篇
  2012年   1383篇
  2011年   1717篇
  2010年   1276篇
  2009年   1513篇
  2008年   1299篇
  2007年   1599篇
  2006年   1444篇
  2005年   1232篇
  2004年   1050篇
  2003年   923篇
  2002年   786篇
  2001年   728篇
  2000年   649篇
  1999年   424篇
  1998年   399篇
  1997年   323篇
  1996年   344篇
  1995年   220篇
  1994年   212篇
  1993年   201篇
  1992年   183篇
  1991年   164篇
  1990年   142篇
  1989年   81篇
  1988年   58篇
  1987年   59篇
  1986年   52篇
  1985年   49篇
  1984年   48篇
  1983年   21篇
  1982年   42篇
  1981年   36篇
  1980年   31篇
  1979年   20篇
  1978年   24篇
  1977年   18篇
  1976年   17篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
针对微等离子体氧化技术的特点,利用IGBT和峰值电流控制模式设计了一种高频大功率微等离子体氧化电源,它可以克服目前普遍使用的晶闸管整流式电源的缺陷,并能满足微等离子体氧化技术对电源的要求。  相似文献   
112.
In this article, we report fabrication of 5 wt% of Dy as DyVO4 supported ZnO by template-free hydrothermal-thermal decomposition method and its photocatalytic activity towards degradation of azo dyes Rhodamine-B (Rh-B) and Trypan Blue (TB) in solar light, Electrocatalytic activity in methanol oxidation and Self-cleaning properties. The as prepared DyVO4-ZnO was characterized by surface analytical and spectroscopic techniques. The results suggested that Dysprosium vanadate doping on ZnO has increased its photocatalytic efficiency with high reusability. DyVO4-ZnO exhibits higher electrocatalytic activity than prepared ZnO for methanol electrooxidation in alkaline medium, revealing its promising potential as the anode in direct methanol fuel cells. Hydrophobicity of ZnO increases by doping of DyVO4.  相似文献   
113.
使用X射线衍射仪(XRD)、紫外-可见吸收光谱仪(UV-VIS)与拉曼光谱仪,对进行氧化气氛热处理前后的紫色翡翠样品进行光谱测试。XRD分析结果显示,紫色翡翠样品中95%以上是硬玉成分。热处理前后的紫外-可见吸收光谱对比结果显示,样品热处理后的光谱和热处理前相比,437nm处尖峰以及580nm处吸收包基本消失;而拉曼光谱图对比结果显示,热处理后黄褐色部位拉曼峰值基线整体呈上升趋势。分析结果表明,紫色翡翠样品主要致色离子为Fe2+,在经过热处理后,Fe2+氧化成为Fe3+,生成Fe2O3,从而致使热处理后的紫色翡翠样品呈现出黄褐色。  相似文献   
114.
研究镁合金微弧氧化膜的表面层与致密层界面处的组织形态。在磷酸盐碱性电解液(5~20g/LNaH2PO4,1~5g/LNaOH,5~8g/LKF,0.5~2g/LNa3C6H5O7,0.5~2g/LEDTA)中,以AZ91镁合金为基体制备出微弧氧化陶瓷薄膜,制备时采用恒电流控制模式,电流密度为10~30A/dm2。采用透射电镜(TEM)和扫描电镜(SEM)研究氧化薄膜界面及附近区域的微观结构。结果表明:微弧氧化膜的表面层靠近表面层与致密层界面处的组织以微晶和纳米晶为主,含有少量非晶态物质;微弧氧化膜的表面层与致密层界面处的组织以非晶态物质为主;微弧氧化膜的致密层靠近表面层与致密层界面处的组织为混晶组织,主要为MgO晶粒,少量为MgAlO4晶粒,并含有少量非晶态物质。  相似文献   
115.
通过射频反应溅射,在氧化铝基板上制备了TaN薄膜电阻。研究了TaN薄膜电阻在不同加载功率密度下表面温度的变化,研究了高温下TaN薄膜氧化所造成的电阻失效。按照混合集成电路规范的测试条件,在环境温度为70℃,TaN薄膜电阻的厚度为0.1μm,氧化铝基板厚度为0.125mm的条件下,TaN薄膜电阻可以耐受4W/mm2的功率密度,或者9.4W/mm2的1min瞬时功率密度冲击。  相似文献   
116.
选择性氧化工艺已经成为制备高性能垂直腔面发射激光器(VCSEL)的关键技术,氧化后形成的氧化层提供了良好的电限制和折射率导引,但选择性氧化速率是呈线性规律还是抛物线规律仍存在很大的争议.在多种温度条件下,做了环形沟槽和环形分布孔的氧化实验,这是在垂直腔面发射激光器中采用的两种结构.实验结果表明,氧化窗口形状对氧化速率的影响也依赖温度条件,并对这种实验现象给出了定性解释.  相似文献   
117.
The electrocatalytic production of hydrogen from seawater provides a low-cost way to realize energy conversion, but is restricted by high potential for seawater electrolysis and the chlorine oxidation reaction (ClOR) at the anode. Here, the self-growth of Mo-doped Ni2P nanosheet arrays with rich P vacancies on molybdenum-nickel foam (MNF) (Mo-Ni2Pv@MNF) is reported as bifunctional catalyst for Cl-free hydrogen production by coupling hydrogen evolution reaction (HER) with hydrazine oxidation reaction (HzOR) in seawater. Impressively, the Mo-Ni2Pv@MNF electrode as bifunctional catalyst has an excellent activity for overall hydrazine splitting (OHzS) with an ultralow voltage of only 571 mV at 1000 mA cm−2 and can maintain stability for an ultra-long time of 1000 h at 100 mA cm−2. Moreover, integration of OHzS into self-assembled hydrazine fuel cells (DHzFC) or solar cells can enable the self-powered H2 production. The industrial hydrazine sewage as feed for the above eletrolysis system can be degraded to ≈5 ppb rapidly. Density functional thoery calculations demonstrate that the electronic structure modulation induced by P vacancies and Mo doping can not only achieve thermoneutral ΔGH* for hydrogen evolution reaction but also enhance dehydrogenation kinetics from *N2H4 to *NHNH2 for HzOR, achieving enhanced dehydrogenation kinetics.  相似文献   
118.
K17镍基铸造高温合金环境损伤的研究   总被引:1,自引:0,他引:1  
本文研究了镍基铸造高温合金K17在真空、空气和热腐蚀环境中热暴露前后持久性能和高温拉伸性能的变化.结果表明,真空中热暴露对K17合金的持久寿命没有影响,但降低高温瞬时拉伸强度,提高持久塑性和高温瞬时拉伸塑性;空气和热腐蚀环境中热暴露明显降低持久性能和高温瞬时拉伸性能,其中尤以热腐蚀环境最严重,空气环境暴露造成晶界氧化并贫Cr,热腐蚀环境暴露引起晶界严重硫化,晶界两侧贫Cr富S,因而弱化晶界,降低性能.  相似文献   
119.
The effect of 0.1 at.% Zr (0.2 wt.% Zr) on the cyclic oxidation of hipped -NiAl was studied. Oxidation testing was performed in static air at 1100–1200 °C, using 1-hr exposure cycles for test times up to 3000 hr. The weight change versus time data were modeled with the COSP computer program to analyze and predict cyclic-oxidation behavior. Zr additions significantly change the nature of the scale-spalling process during cooling so that the oxide spalls near the oxide-air interface at a relatively low depth within the scale. Without Zr, the predominantly -Al2O3 scale tends to spall randomly to bare metal at relatively high effective-scale-loss rates, particularly at 1150°C and 1200°C. This leads to higher rates of Al consumption for the Zr-free aluminide and much earlier depletion of Al, leading to eventual breakaway (i.e., failure).  相似文献   
120.
The oxidation behavior in air of Fe-19.6Cr-15.1Mn was studied from 700 to 1000°C. Pseudoparabolic kinetics were followed, giving an activation energy of 80 kcal/mole. The scale structure varied with temperature, although spinel formation occurred at all temperatures. At both 700 and 800°C, a thin outer layer of -Mn2O3 formed. The inner layer at 700°C was (Fe,Cr,Mn)3O4, but at 800°C there was an intermediate layer of Fe2O3 and an inner layer of Cr2O3 + (Fe, Cr,Mn)3O4. Oxidation at 900°C produced an outer layer of Fe3O4 and an inner layer of Cr2O3+(Fe,Cr,Mn)3O4. Oxidation at 1000°C caused some internal oxidation of chromium. In addition, a thin layer of Cr2O3 formed in some regions with an intermediate layer of Fe3O4 and an outer layer of (Fe,Mn)3O4. A comparison of rates for Fe3O4 formation during oxidation of FeO as well as for the oxidation of various stainless steels, which form spinels, gave good agreement and strongly suggests that spinel growth was rate controlling. The oxidation rate of this alloy (high-Cr) was compared with that of an alloy previously studied, Fe-9.5Cr-17.8Mn (low-Cr) and was less by about a factor of 12 at 1000°C and by about a factor of 100 at 800°C. The marked differences can be ascribed to the destabilization of wustite by the higher chromium alloy. No wustite formation occurred in the high-Cr alloy, whereas, extensive wustite formed in the low-Cr alloy. Scale structures are explained by the use of calculated stability diagrams. The mechanism of oxidation is discussed and compared with that of the low-Cr alloy.  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