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   8708篇
  免费   119篇
  国内免费   451篇
电工技术   133篇
综合类   208篇
化学工业   2413篇
金属工艺   2596篇
机械仪表   356篇
建筑科学   371篇
矿业工程   66篇
能源动力   353篇
轻工业   208篇
水利工程   26篇
石油天然气   483篇
武器工业   11篇
无线电   204篇
一般工业技术   1239篇
冶金工业   377篇
原子能技术   131篇
自动化技术   103篇
  2024年   8篇
  2023年   89篇
  2022年   143篇
  2021年   197篇
  2020年   147篇
  2019年   161篇
  2018年   174篇
  2017年   183篇
  2016年   158篇
  2015年   225篇
  2014年   449篇
  2013年   592篇
  2012年   363篇
  2011年   653篇
  2010年   504篇
  2009年   517篇
  2008年   555篇
  2007年   621篇
  2006年   501篇
  2005年   400篇
  2004年   379篇
  2003年   358篇
  2002年   337篇
  2001年   239篇
  2000年   241篇
  1999年   205篇
  1998年   212篇
  1997年   157篇
  1996年   137篇
  1995年   109篇
  1994年   87篇
  1993年   50篇
  1992年   40篇
  1991年   30篇
  1990年   22篇
  1989年   10篇
  1988年   11篇
  1987年   4篇
  1986年   4篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
排序方式: 共有9278条查询结果,搜索用时 0 毫秒
1.
Through improved synthesis process, resistance reduction effect of (K0.5Bi0.5)TiO3 (KBT) doping in Y–Mn co-doped BaTiO3 (BT) lead free ceramics was investigated. By different doping methods (doping K2O, Bi2O3 and TiO2 or synthesized KBT), medium Curie temperature (around 130 °C) lead free BT ceramics were obtained with ultra-low resistivity (13.84 Ωcm) with a temperature maintaining process at 700 °C. In this contribution, effect of sintering process and doping methods is discussed in detail.  相似文献   
2.
在实验室条件下对用丙烯腈-苯乙烯共聚物在硫酸存在下的水解磺化产物(HSAS)处理的泥浆性能进行了评定。HSAS处理的泥浆有较小的滤失性,较好的耐盐和抗高温性。  相似文献   
3.
长距离油、气、水混输管道内壁流动腐蚀的研究进展   总被引:13,自引:0,他引:13  
就近几十年来,多相流管线的流动腐蚀(CO2腐蚀,H2S腐蚀,腐蚀/冲蚀协同作用),腐蚀/冲蚀数学模型和设计准则,腐蚀检测,腐蚀防护与控制技术等方面的研究进展进行了综述。指出了当前研究中所存在的一些问题,就多相流的研究方向提出了相应的建议。  相似文献   
4.
Based on an idea introduced by Benjamin and Cornell (1970. Probability, statistics and decision for civil engineers. New York: McGaw Hill) and previous works by the authors it is demonstrated how condition indicators may be formulated for the general purpose of quality control and for assessment and inspection planning in particular. The formulation facilitates quality control based on sampling of indirect information about the condition of the considered components. This allows for a Bayesian formulation of the indicators whereby the experience and expertise of the inspection personnel may be fully utilized and consistently updated as frequentistic information is collected. The approach is illustrated on an example considering a concrete structure subject to corrosion. It is shown how half-cell potential measurements may be utilized to update the probability of excessive repair after 50 years. Furthermore in the same example it is shown how the concept of condition indicators might be applied to develop a cost optimal maintenance strategy composed of preventive and corrective repair measures.  相似文献   
5.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.  相似文献   
6.
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.  相似文献   
7.
槽孔式水力驱动控制棒槽孔阻力系数实验研究   总被引:2,自引:0,他引:2  
对槽孔式水力驱动控制棒槽对孔阻力系数进行了大量实验研究,获得了槽孔式水力驱动控制棒槽对孔阻力系数和其随槽对孔位移的变化规律,分析了槽对孔阻力系数与控制棒槽对孔结构参数之间的关系。结果表明:随槽对孔位移的增加,槽对孔阻力系数从某一较大的定值迅速降低到某一较小的定值,然后再迅速反回到初始的定值,形成一个对称的宽幅波谷;槽高使阻力系数曲线波谷幅宽发生变化,也使完全不重合段的阻力系数发生变化;随内套孔径的增大,阻力系数有所降低,其对阻力系数的影响也进一步减弱。孔径增大到一定程度,阻力系数基本不受孔径参数的影响。  相似文献   
8.
水溶性涂料使用性能研究   总被引:1,自引:0,他引:1  
龚光福 《电讯技术》1998,38(2):49-52
本文通过试验对水溶性涂料的耐盐雾腐蚀性能,耐热性能,高低温冲击性能,耐油性能,涂膜与铁基体,面漆的给合力及涂膜表面电阻进行研究,同时指出了该涂料在军用电子产品上的应用前景。  相似文献   
9.
A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds.  相似文献   
10.
I.L. Lehr 《Corrosion Science》2007,49(5):2210-2225
This work is a study of the electropolymerisation of pyrrole onto iron electrodes in the presence of sodium bis(2-ethylhexyl) sulfosuccinate in a wide pH interval. The characterisation of the films was done using electrochemical techniques, SEM/EDX and IR spectroscopy. We show that it is possible to synthesise homogeneous, adherent and very compact films in the pH range between 7 and 12 under potentiodynamic, galvanostatic and potentiostatic conditions without substrate dissolution. The effects of various parameters on electrodeposition were investigated. The new procedure for the electrochemical synthesis of polypyrrole results in improved anticorrosion properties. The inhibition is proposed to be due to the sum of a repulsion of chloride ions because AOT remains entrapped in the polymer matrix and the presence of the iron oxide. Advantages of the use of surfactants in the electropolymerisation solution are discussed.  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