全文获取类型
收费全文 | 139篇 |
免费 | 10篇 |
国内免费 | 55篇 |
专业分类
化学 | 169篇 |
晶体学 | 3篇 |
力学 | 5篇 |
综合类 | 1篇 |
数学 | 2篇 |
物理学 | 24篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 10篇 |
2008年 | 8篇 |
2007年 | 19篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
排序方式: 共有204条查询结果,搜索用时 15 毫秒
81.
以γ-Al2O3为载体,采用等体积浸渍法,制备了不同K2CO3含量的Ni-Cu-Mn-K/Al2O3水煤气变换催化剂,采用低温N2吸附、XRD、TPD和TPR,考察了K2CO3含量对催化剂结构和性能的影响。结果表明:K2CO3的加入使催化剂的还原温度有所提高,适量的K2CO3能增加活性组分的电子密度,从而增强其给电子活化CO的能力,提高催化剂的活性。但过量的K2CO3使得催化剂比表面积和孔容降低,且导致催化剂对CO吸附过强,催化活性降低。当Ni-Cu-Mn-K/γ-Al2O3催化剂中K2CO3的添加量为7.5%时,且催化剂经530 ℃耐热15 h后,在350 ℃时水煤气变换反应中CO转化率达62.29%。 相似文献
82.
Shi-hua Wu Bao-qing Li Wei-ping Huang Shou-min Zhang Juan Shi Xiu-cheng Zheng 《Reaction Kinetics and Catalysis Letters》2003,78(1):49-58
Supported Au catalysts for low-temperature CO oxidation were prepared by solvated metal atom impregnation (SMAI) and conventional
impregnation (CI). X-ray photoelectron spectroscopy investigations indicated that gold in all the samples was in the metallic
state. TEM and XRD measurements showed that the mean diameter of Au particles prepared by SMAI was smaller than that of those
prepared by CI with the same gold content. Catalytic tests showed that SMAI catalysts had higher CO oxidation activity than
CI catalysts with the same compositions. Both SMAI and CI Au/TiO2catalysts exhibited high activities in low temperature CO oxidation. Full CO conversion was obtained at 323 K for 3.1 wt.%
Au/TiO2 (SMAI) catalyst, which displayed higher activity than the 3.1 wt.% Au/D-72(SMAI) and 3.1 wt.% Au/TiO2(CI). Although the sizes of gold particles prepared by the same method and supported on both TiO2 and resin were comparable, the Au/TiO2 catalysts showed significantly higher activities than the Au/resin catalysts with the same Au contents under the same reaction
conditions. These results prove that not only the gold particle size, but also the support plays a key role in CO oxidation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
83.
甲烷/二氧化碳重整反应催化剂的制备及反应性能研究 总被引:9,自引:1,他引:9
采用浸渍法制备载镍CH4/CO2重整反应催化剂,应用ICP,BET,EPMA,SEM,TEM,XPS等手段考察了焙烧温度,浸渍液酸度,助剂等制备条件对催化剂结构及反应性能的影响。结果表明,低温热处理制备的Ni/γ-Al2O3催化剂具有较高的CH4/CO2重整反应活性.经酸或强碱溶液中制备的催化剂尽管活性分布及孔结构等均扔所不同,但二者的反应活性都很高; 相似文献
84.
采用浸渍法和沉积-沉淀法制备了四种不同的Au/Al2O3催化剂,测定了它们在氢气还原前后及催化反应后的金含量及比表面积,结果表明,制备方法明显影响催化剂的金含量,应用X-光粉末衍射技术研究了这些催化剂经还原处理及反应后的物相变化,金以Au^0物相存在,没有发现氧化态的金物相,考察了该催化剂在CH4/CO2重整反应中的催化活性,发现金催化剂的活性取决于金粒子的大小,浸渍法制备的金催化剂具有较大的金晶粒尺寸,催化活性低,沉积-沉淀法制备的金催化剂金晶粒尺寸较小,催化活性较高,以尿素为沉淀剂制备的催化剂给出1073K时的CH4和CO2转化率分别为8.1%和17.6%,高温反应不仅导致金晶粒的聚集,而且存在明显的金流失现象。 相似文献
85.
碱金属碳酸盐改性对Au/TS催化剂的丙烯气相环氧化活性和稳定性的提升作用研究 《燃料化学学报》2003,48(10):1256-1262
制备了不同碱金属碳酸盐(Na2CO3、K2CO3、Rb2CO3和Cs2CO3)超声浸渍改性的Au/TS-1催化剂,采用XRD、ICP、XPS、UV-vis、NH3-TPD、FT-IR和HAADF-STEM等手段对催化剂结构性质进行了表征,研究了碱金属碳酸盐改性对Au/TS-1催化剂的丙烯气相环氧化活性和稳定性的影响。结果表明,碱金属碳酸盐改性可以降低Au/TS-1催化剂的表面酸性,减缓环氧丙烷(PO)在催化剂表面吸附引起的积炭失活,抑制金颗粒粒径的增大;此外,Cs2CO3和Rb2CO3改性还可减少Au/TS-1催化剂上的骨架外Ti含量。碱金属碳酸盐改性后的Au/TS-1的催化活性和稳定性都得到明显的改善,其中,Cs2CO3改性的Au/TS-1表现出最佳的催化活性,丙烯转化率为6.2%,环氧丙烷选择性为86.2%,氢气利用效率为26.2%。相关研究为提高Au/TS-1催化剂的丙烯气相环氧化活性和稳定性提供了新的思路。 相似文献
86.
真空浸渍是通过负压作用和浸渍作用,改善材料性能或满足某种特定要求的工艺技术.侧重介绍了真空浸渍技术在铸件后续处理、混凝土改性和聚合物辅助成型等材料加工制备中的应用,其中包括它们的基本原理、技术优势、浸渍剂种类、浸渍设备与装置以及工艺流程等,展望了其应用前景. 相似文献
87.
《Comptes Rendus Chimie》2016,19(4):423-432
The catalytic properties of raw biomass chars and Ni-loaded biomass chars prepared at a high-heating-rate were assessed in the methane decomposition reaction. The raw chars exhibited a moderated catalytic activity in methane cracking while the Ni-loaded chars showed a catalytic activity 10 times higher than the raw chars. The deposited carbon was a highly ordered one as evidenced by XRD, Raman analysis and oxygen reactivity tests. The activation energy in the combustion reaction was estimated to be 300 kJ/mol. These results indicate that biomass char can be an effective low-cost and active support for metal impregnation to be used in catalytic cracking of hydrocarbons for hydrogen production. 相似文献
88.
Based on the analysis of the isotherms of N2 adsorption, the fractal dimension and other texture geometric parameters were determined for silica gel, modified silica
gel, and relevant composite materials. The correlations between the texture parameters were found. A criterion for the estimation
of the efficiency of using the composite adsorbent volume was proposed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 781–785, May, 2000. 相似文献
89.
Maria Ochsenkühn-Petropoulou Angeliki Lampropoulou Hansjürgen Becker Wolfgang Spyra 《Mikrochimica acta》2001,136(3-4):185-191
An analytical technique for the simultaneous determination of PAHs (polycyclic aromatic hydrocarbons) in wooden railway beams,
impregnated with coal tar for their protection, has been developed, based on the effective extraction of the PAHs and their
determination by GC-MS. Two extraction techniques, the Soxhlet and the ultrasonic one, using two different solvents, hexane
and toluene have been compared for their efficiency for PAHs which can be determined in ppb-ppt range after optimised clean
up and enrichment. Several parameters, such as the degree of impregnation of the wooden beams, the effect of sun radiation
on the degradation of the PAHs and their migration to the soil have been investigated by following the concentration of the
PAHs and that of their methylated products found at various sampling positions. The results are useful for the decision about
recycling procedure or their further disposal. 相似文献
90.
采用共沉淀法制备了一系列ZrxTi1-xO2(x=0.0,0.1,0.5,0.9,1.0)复合氧化物,并以此为载体,用等孔体积浸渍H2PtCl6制得Pt/ZrxTi1-xO2柴油车氧化催化剂.运用N2吸附-脱附,X射线多晶粉末衍射,X射线光电子能谱,H2程序升温还原和NH3程序升温脱附等手段对催化剂进行了表征.结果表明,在系列催化剂样品中,Zr0.1Ti0.9O2复合氧化物主要以锐钛矿形式存在,具有较好的织构性能,样品的比表面积达94m2/g,孔体积为0.33cm3/g.相应地,Pt/Zr0.1Ti0.9O2催化剂表现出优异的催化氧化性能,HC和CO的起燃温度(T50)分别为185和174oC,完全转化温度(T90)分别为197和201oC;且具有较低的SO2氧化活性,350oC时SO2仅转化25.5%. 相似文献