全文获取类型
收费全文 | 38819篇 |
免费 | 2984篇 |
国内免费 | 1811篇 |
专业分类
电工技术 | 901篇 |
综合类 | 1778篇 |
化学工业 | 19199篇 |
金属工艺 | 1743篇 |
机械仪表 | 618篇 |
建筑科学 | 433篇 |
矿业工程 | 317篇 |
能源动力 | 2300篇 |
轻工业 | 1261篇 |
水利工程 | 70篇 |
石油天然气 | 7004篇 |
武器工业 | 242篇 |
无线电 | 1973篇 |
一般工业技术 | 2116篇 |
冶金工业 | 1268篇 |
原子能技术 | 528篇 |
自动化技术 | 1863篇 |
出版年
2024年 | 155篇 |
2023年 | 664篇 |
2022年 | 1431篇 |
2021年 | 1614篇 |
2020年 | 1332篇 |
2019年 | 1109篇 |
2018年 | 951篇 |
2017年 | 1079篇 |
2016年 | 1254篇 |
2015年 | 1185篇 |
2014年 | 1923篇 |
2013年 | 1993篇 |
2012年 | 2140篇 |
2011年 | 2645篇 |
2010年 | 1955篇 |
2009年 | 2167篇 |
2008年 | 1933篇 |
2007年 | 2276篇 |
2006年 | 2234篇 |
2005年 | 1889篇 |
2004年 | 1615篇 |
2003年 | 1521篇 |
2002年 | 1341篇 |
2001年 | 1296篇 |
2000年 | 1111篇 |
1999年 | 929篇 |
1998年 | 758篇 |
1997年 | 566篇 |
1996年 | 529篇 |
1995年 | 421篇 |
1994年 | 375篇 |
1993年 | 284篇 |
1992年 | 238篇 |
1991年 | 173篇 |
1990年 | 157篇 |
1989年 | 82篇 |
1988年 | 58篇 |
1987年 | 48篇 |
1986年 | 21篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1974年 | 5篇 |
1959年 | 3篇 |
1951年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
大庆蜡油在酸性催化剂上反应机理的研究 总被引:11,自引:5,他引:6
以大庆蜡油为原料,采用两种不同类型的催化剂,在流化床反应器实验装鬣上进行催化裂化反应。结果表明,大庆蜡油在酸性催化剂上反应所产生的干气组成与高烯烃催化裂化汽油相同,干气的产生主要是单分子裂化反应所造成的。从干气产率、组成以及液化气组成可以看出,大庆蜡油在不同类型的催化剂上明显地表现出裂化反应类型的差异。 相似文献
82.
In this research, Ni/SiO2 catalyst was modified with different amount of Gd2O3 and characterized with temperature-programmed desorption of CO2 (CO2-TPD) and NH3 (NH3-TPD), temperature-programmed reduction with H2 (H2-TPR) and X-ray diffraction (XRD). It was found that Gd2O3-modified Ni/SiO2 catalysts possessed higher CO2 adsorption and activation ability due to the formation of surface carbonate species. H2-TPR and XRD characterizations found that the strong interaction among nickel, Gd2O3 and SiO2 took place, which improved the dispersion of Ni. Gd2O3-modified Ni/SiO2 catalysts exhibited higher activity and stability for the combined oxy-CO2 reforming of methane in fluidized-bed reactor. The H2/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO2/O2 ratio in feed. 相似文献
83.
Ahmad Nozad Golikand Elaheh Lohrasbi Mohammad Ghannadi Maragheh Mehdi Asgari 《Journal of Applied Electrochemistry》2008,38(6):869-874
The effect of carbon surface oxidation on platinum supported carbon particles (Pt/C) with nitric acid was investigated by
cyclic voltammetry, electrochemical impedance spectroscopy, polarization experiments and chronoamperometry. Cyclic voltammograms,
polarization curves and electrochemical impedance spectra showed that the treated catalyst had much larger active surface
area and higher ionic conductivity than the untreated catalyst, and provided enhanced performance for oxygen reduction. The
formation of acidic groups was examined by IR spectra. The Pt/C surface oxidation had a large effect on the performance of
a gas diffusion electrode for oxygen reduction reaction. 相似文献
84.
Peichun Li Amar Zerroukhi Jianding Chen Yvan Chalamet Thomas Jeanmaire Zhean Xia 《应用聚合物科学杂志》2008,110(6):3990-3998
Chemical shrinkage was used for the in situ measurement of the progressing chemical stabilization reactions and the influence of ozone during the stabilization of polyacrylonitrile. A method for evaluating the activation energy through the sensitivity temperature is presented. The calculated results show that the activation energies were 161.57 kJ/mol in air and 181.23 kJ/mol in ozone-enriched air. Therefore, the chemical reactions were postponed during stabilization in ozone-enriched air. Ozone seemed to act in three ways: first, ozone promoted the formation of the serious skin–core structure. Second, ozone accelerated the chemical reactions and shortened the stabilization time at lower heating rates. Third, ozone postponed the chemical reactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
85.
Reda Karoum Antonio de Lucas-Consuegra Fernando Dorado Jose Luis Valverde Alain Billard Philippe Vernoux 《Journal of Applied Electrochemistry》2008,38(8):1083-1088
The electrochemical promotion of catalysis (EPOC) of propene combustion was investigated using Pt sputtered thin film on an
O2− conductor, 8 mol% Y2O3-stabilized-ZrO2 (YSZ). In order to separate the influence of the thermal migration of the O2− oxide ions from the electrolyte to the catalyst surface and the impact of an electrical polarization on the catalytic activity,
several light-off experiments (cool down and heat up procedures) were successively performed under different polarizations,
i.e. OCV, +2 and −2 V. These experiments have clearly shown that the presence of O2− (thermally or electrochemically induced) inhibits the catalytic activity of the platinum for the propene deep oxidation.
These results demonstrate the importance to define a normalized rate enhancement ratio, ρ
n
, from a reference value of the catalytic rate corresponding to a Pt surface state free of O2− ions. 相似文献
86.
丁辛醇装置丁醛加氢催化剂在装置扩能投产以后热点上移 (失活 )的速率较快 ,针对催化剂老化的原因进行分析、判断 ,找出原因 ,采用相应的解决措施 ,可延长催化剂使用寿命 ,增加装置效益 相似文献
87.
硫含量对钴钼型耐硫脱氧剂的脱氧活性影响 总被引:2,自引:0,他引:2
研究了工艺气中硫含量对钴钼型耐硫脱氧剂脱氧活性的影响。通过常压微反 -色谱装置测定脱氧剂的本征脱氧活性 ,加压原粒度反应器测定脱氧剂的表观脱氧活性 ,结合实际经验确定了耐硫脱氧剂所需的最低硫含量。还讨论了温度、压力、空速对耐硫脱氧剂脱氧活性的影响。结果表明 ,耐硫脱氧剂完全能满足耐硫变换工艺的要求 ,而且有耐硫变换的作用 ,并对耐硫变换催化剂起到保护作用 相似文献
88.
Performance of the polymer- and oxide-supported triphase catalysts and effect of ultrasound on their stabilities 总被引:1,自引:0,他引:1
Hsieh-Ting Chung Hung-Shan Weng 《Journal of the Chinese Institute of Chemical Engineers》2008,39(5):449-455
In this study, several trialkylamines were immobilized on chloromethylated polystyrene (CMPS), silica gel, and alumina to prepare triphase catalysts for catalyzing the etherification reaction of allyl bromide (the organic reactant) and sodium phenolate (the aqueous reactant). The reactor was agitated mechanically or with the aid of ultrasonic vibration. Performances of the prepared catalysts were compared, and the effect of imposing ultrasound was investigated based on the activity, selectivity, and stability of the catalyst. Experimental results show that tri-n-propylamine is the best active species when CMPS is used as the support, while tri-n-butylamine is the best when SiO2 and Al2O3 are employed as the supports. The CMPS-supported catalyst is far better than the SiO2- and Al2O3-supported catalysts in activity and selectivity but not in stability. Imposing the ultrasound can effectively increase the reaction rate. Mechanical agitation at a low speed with the imposition of ultrasonic vibration not only results in a conversion slightly higher than the case with a high mechanical agitation speed without ultrasonic vibration, but also gives a constant stability for the CMPS-supported catalyst. 相似文献
89.
The continuous production of hydrogen from cyclohexanes is achieved effectively using Pt/ACF (ACF = activated carbon fiber) catalysts in a fixed-bed flow reactor. The Pt catalysts are more effective than a Pd/ACF catalyst for the reaction. Besides cyclohexane, methylcyclohexane, 1,4-dimethylcyclohexane, and p-menthane can also be employed as hydrogen source in the reaction system. 相似文献
90.