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排序方式: 共有138条查询结果,搜索用时 15 毫秒
21.
利用气相色谱法测定了不同色谱柱温度和不同载气流速下,C1~12烷烃在ZSM-5分子筛上的保留时间,并利用相关公式对测试结果进行了线性回归分析,测得了吸附热力学参数和扩散系数;考察了色谱柱温度、烷烃碳链长度和载气流速对烷烃在ZSM-5分子筛上吸附扩散的影响。实验结果表明,回归分析的线性相关性良好,色谱柱温度越高,孔道对吸附质的吸附能力越弱;在不同载气流速下,轴向扩散系数不同;随烷烃碳链长度的增加,吸附焓变呈先增大后减小的趋势,轴向扩散系数呈线性增长;C1~12烷烃在ZSM-5分子筛上的吸附焓变在-1.264~-42.975 k J/mol之间;当载气流速为2.654~4.246 cm/s时,C1~4烷烃的轴向扩散系数在0.328 8~0.551 7 cm2/s之间;当载气流速为5.308~13.270 cm/s时,C1~4烷烃的轴向扩散系数在0.430 2~1.456 4 cm2/s之间。 相似文献
22.
23.
B.S. Liu L. Tian L. Li C.T. Au A.S.‐C. Cheung 《American Institute of Chemical Engineers》2011,57(7):1852-1859
The influence of water in the CH4 feed on the performance of 3%Mo/ZSM‐5 catalyst during methane direct aromatization under supersonic jet expansion (SJE) condition was investigated. We observed that both surface Mo2OxCy and β‐Mo2C species are catalytically active for methane aromatization under SJE condition. The presence of water can promote the removal of surface carbon before the generation of aromatic‐type and/or graphitic carbon. In appropriate amount, water can improve the stability of surface Mo2OxCy, and hence resulting in better catalytic performance. The study provided valuable information relevant to the direct utilization of methane hydrate. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
24.
We have characterized, with emphasis on XAFS spectroscopy, one of the most promising DeNOx catalysts, i.e., Fe/ZSM5 prepared
through the FeCl3sublimation technique. XAFS is a very useful tool for this purpose since it is element specific and can be used in situ, namely,
in the presence of the reactants and at reaction temperature. In this communication it will be pointed out that the as-synthesized
Fe/ZSM5 catalyst contains stable binuclear iron oxo/hydroxo-complexes. The reaction of these complexes with the probe molecule
CO clearly shows that only one of the oxygen shells around iron changes while the iron contribution is not affected, the iron
complex remaining binuclear.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
Internal architecture of coffin‐shaped ZSM‐5 zeolite crystals with hourglass contrast unravelled by focused ion beam‐assisted transmission electron microscopy 下载免费PDF全文
Optical microscopy, focused ion beam and transmission electron microscopy are combined to study the internal architecture in a coffin‐shaped ZSM‐5 crystal showing an hourglass contrast in optical microscopy. Based on parallel lamellas from different positions in the crystal, the orientation relationships between the intergrowth components of the crystal are studied and the internal architecture and growth mechanism are illustrated. The crystal is found to contain two pyramid‐like components aside from a central component. Both pyramid‐like components are rotated by 90° along the common c‐axis and with respect to the central component while the interfaces between the components show local zig‐zag feature, the latter indicating variations in relative growth velocity of the two components. The pyramid‐like intergrowth components are larger and come closer to one another in the middle of the crystal than at the edges, but they do not connect. A model of multisite nucleation and growth of 90° intergrowth components is proposed. 相似文献
26.
The reaction of (NO + C3H8 + O2) can result in selective formation of NO2 over H-ZSM5, Cu,H-ZSM5, Ag,H-ZSM5, and Li,H-ZSM5 catalysts when the concentrations of NO and O2 are 0.1 and 9%, SV > 60,000 h−1 (typical for automotive exhausts), and C3H8/NO > 1. Despite stoichiometric excess of reductant hydrocarbon below this limit, the in situ formed NO2 does not react with C3H8, thus conversion of NO to N2 is negligible. NO can be reduced by C3H8 selectively to N2 only when C3H8/NO ≧ 1. Contrary to many suggestions the reaction temperature, concentration of oxygen, space velocity, and type of exchange
ions have minor influence on the selectivity for N2. These parameters affect the rates of reactions (NO + 2), (C3H8 + NOx) and (C3H8 + O2), therefore they also affect the production of N2 in the HC-SCR process, but only when the ratio of C3H8/NO permits. The metal-exchanged zeolites were prepared in situ by solid-state ion exchange from H-ZSM5. Despite the low degree
of copper exchange (63%), Cu,H-ZSM5 produces substantially more N2 than H-ZSM5, Ag,H-ZSM5, or Li,H-ZSM5. However, the selectivity for N2 is lowest over Cu,H-ZSM5, which also produces considerable NO2 in the reaction of (NO + C3H8 + O2) even at C3H8/NO ≧ 1. Contrary to prior findings, the catalytic activity of Cu,H-ZSM5 for the oxidation of NO by O2 to NO2 in absence of hydrocarbon was comparable to that of H-ZSM5 at high space velocities (2.3 l g−1 min−1). By replacing 30 and 40% of the protons of H-ZSM5 by Ag+ and Li+ ions in Ag,H-ZSM5 and Li,H-ZSM5, respectively, the catalytic activity for this reaction becomes negligible at temperatures
≧100°C. Some mechanistic consequences of these experimental observations are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
27.
纯硅ZSM—35沸石的合成及特性研究 总被引:1,自引:0,他引:1
利用吸附态模板剂在Na2O-SiO2-EDA(乙二胺)的干粉体系中合成了纯硅ZSM-35沸石,并采用XRD、SEM、IR等手段对产物的物化特性进行了表征。考察了无机碱及乙二胺用量对纯硅ZSM-35沸石合成的影响。通过稳定性实验发现,纯硅ZSM-35沸石的热稳定性及耐酸性较好,而耐碱性较差。 相似文献
28.
改性HZSM—5上正己烷,正庚烷和甲基环戊烷芳构化反应规律的研究 总被引:6,自引:0,他引:6
通过不同的方法对HZSM-5分子筛改性,用脉冲微反装置和连续流动固定床积分微反装置考察了硅铝化、载铂量、水热处理、高温焙烧对HZSM-5分子筛催化剂性能的影响,系统研究了催化剂的表面酸性质、载铂量和反应气氛对反应的影响。通过TPD、XRD、^27Al MASNMR等方法测试催化剂的物理性质,研究了水热处理、高温焙烧和载铂前后HZSM-5分子筛的结构、表面酸性质及其变化的规律,并与反应性能关联,总结 相似文献
29.
Currently microporous oxidic materials including zeolites are attracting interest as potential hydrogen storage materials. Understanding how molecular hydrogen interacts with these materials is important in the rational development of hydrogen storage materials and is also challenging theoretically. In this paper, we present an incoherent inelastic neutron scattering (INS) study of the adsorption of molecular hydrogen and hydrogen deuteride (HD) in a copper substituted ZSM5 zeolite varying the hydrogen dosage and temperature. We have demonstrated how inelastic neutron scattering can help us understand the interaction of H2 molecules with a binding site in a particular microporous material, Cu ZSM5, and by implication of other similar materials. The H2 molecule is bound as a single species lying parallel with the surface. As H2 dosing increases, lateral interactions between the adsorbed H2 molecules become apparent. With rising temperature of measurement up to 70 K (the limit of our experiments), H2 molecules remain bound to the surface equivalent to a liquid or solid H2 phase. The implication is that hydrogen is bound rather strongly in Cu ZSM5.
Using the simple model for the anisotropic interaction to calculate the energy levels splitting, we found that the measured rotational constant of the hydrogen molecule is reduced as a consequence of adsorption by the Cu ZSM5.
From the decrease in total signal intensity with increasing temperature, we were able to observe the conversion of para-hydrogen into ortho-hydrogen at paramagnetic centres and so determine the fraction of paramagnetic sites occupied by hydrogen molecules, ca. 60%. 相似文献
30.
Zn/H-ZS M-5轻烃芳构化催化剂中Zn与分子筛协同作用的研究 总被引:1,自引:0,他引:1
分析了Al2 O3 的加入引起Zn/H ZSM 5催化剂芳构化活性和选择性下降以及稳定性有所改善的原因在于高温焙烧或水热处理 ,使掺有粘结剂氧化铝的Zn/H ZSM 5催化剂表面锌组元的再分布 ,即Al2 O3 上的锌含量增加 ,而处于H ZSM 5沸石上的锌浓度降低。较为系统地探讨了Al2 O3 和ZnO/Al2 O3 的芳构化催化作用以及锌组元和ZnO/Al2 O3的引入对HZSM 5性能的影响。论证了在Zn/H ZSM 5催化剂中只有处于分子筛表面的Zn组元才能同分子筛B酸中心产生协同作用 ,从而改善H ZSM 5分子筛的芳构化活性与选择性 ,而在经过焙烧和水热处理的混有Al2 O3 的Zn/H ZSM 5催化剂中 ,分布在Al2 O3 上的锌组元几乎不与分子筛发生协同作用 ,因而对催化剂的活性与芳构化选择性影响甚小 相似文献