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41.
Karl Hensen Alexander Lemke Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(10):1196-1197
The reaction of 2,6‐dimethylpyridine with TiBr4 affords the title compound, [TiBr4(C7H9N)], which is the first example of a neutral TiBr4L complex (L is a singly bonded ligand). The environment around the Ti atom can be described as a somewhat distorted trigonal bipyramid, with the nitrogen base occupying an equatorial position. The crystal was a non‐merohedral twin. 相似文献
42.
van Grootel PW Hensen EJ van Santen RA 《Langmuir : the ACS journal of surfaces and colloids》2010,26(21):16339-16348
Three different pathways toward CO formation from adsorbed CH and O are compared by quantum-chemical density functional theory (DFT) calculations for planar and stepped Rh surfaces. The conventional pathway competes with the pathway involving a formyl (CHO) species. This holds for both types of surfaces. The barrier for carbon-oxygen bond formation for the planar surface (180 kJ/mol) is substantially higher than that for the stepped surface (90 kJ/mol). The reaction path through intermediate formyl formation competes with direct formation of CO from recombination via adsorbed C and O atoms. Calculations are used as a basis for the analysis of the overall kinetics of the methane steam reforming reaction as a function of the particle size and the metal. 相似文献
43.
Hensen Karl Achatz Manfred Müller Rolf Tröbs Ulrich 《Theoretical chemistry accounts》1974,34(4):327-337
Using a one-center-method, treating the inner shells statistically, the valence-shell, however, by quantum mechanics, the equilibrium internuclear distances and total molecular energies have been computed for CH4, SiH4, GeH4, SnH4, PbH4, BH 4 ? , AlH 4 ? , GaH 4 ? , InH 4 ? , TlH 4 ? , NH 4 + , PH 4 + , AsH 4 + , SbH 4 + , and BiH 4 + . The results are in good agreement with experimental data as well as with theoretical values. 相似文献
44.
I. A. Ledenev R. V. Prikhod’ko I. V. Stolyarova E. J. M. Hensen J. A. R. van Veen M. V. Sychev V. V. Goncharuk 《Kinetics and Catalysis》2006,47(3):451-459
The mesostructured silica SBA-15, γ-Al2O3, and amorphous silica-alumina are modified with Ni(acac)2 in the liquid and gas phases. This process depends crucially on the nature of active sites on the support surface. In the modification of materials containing weakly acidic or weakly basic hydroxyl groups, it is necessary to use low-polarity solvents. The dominant Ni(acac)2 chemisorption sites on amorphous silica-alumina are the acid hydroxyls of ≡Si-OH-Al= bridges. The covalent bonding resulting from the replacement of the acetylacetonate ligand favors the fixation of the adsorbed complex on the support surface. The coordinatively unsaturated sites formed by Al3+ ions play an insignificant role in Ni(acac)2 chemisorption. The degree of dispersion of the oxide phase in the resulting catalysts depends strongly on the strength of the interaction between the modifier molecules and the active sites of the support. This is not the case with the aluminum acetylacetonate complexes that form upon the modification of the Al-containing supports. Gas-phase modification affords finer NiO particles than liquid-phase modification. 相似文献
45.
Kazansky VB Subbotina IR Rane N van Santen RA Hensen EJ 《Physical chemistry chemical physics : PCCP》2005,7(16):3088-3092
The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid-base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Br?nsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Br?nsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation. 相似文献
46.
The crystal structures of trans-tetrabromobis(pyridine)silicon (1) and trans-tetrabromobis(3,5-dimethylpyridine)silicon (2) have been determined: (1) crystallizes in the monoclinic space group C2/m with cell dimensions a = 14.4250(2) Å, b = 7.3055(1) Å, c = 7.2839(1) Å, = 117.660(1)°, (2) crystallizes in the monoclinic space group C2/m with cell dimensions a = 16.013(3) Å, b = 7.316(1) Å, c = 8.179(2) Å, = 113.19(1)°. Both molecules, with D2h symmetry, have crystallographic C2h site symmetry. The environment about the Si atoms can be described as a slightly distorted octahedron with the pyridyl ligands occupying axial positions and the four bromo ligands in the equatorial plane. 相似文献
47.
Ohne Zusammenfassung 相似文献
48.
Yi Zhang D.A.J.Michel Ligthart Peng Liu Lu Gao Tiny M.W.G.M.Verhoeven Emiel J.M.Hensen 《催化学报》2014,(12)
Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and sol-id-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photo-catalytic water splitting, CO oxidation, and H2 oxidation. Mixed Ga–Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2–9 nm. These catalysts had negligible activity in photocatalytic H2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga–Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The in-fluence of particle size on Rh-catalyzed oxidation of CO and H2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The op-posite holds for H2 oxidation. 相似文献
49.
50.
Hao Zhang Aleksei Bolshakov Raghavendra Meena Gustavo A. Garcia A. Iulian Dugulan Alexander Parastaev Guanna Li Emiel J. M. Hensen Nikolay Kosinov 《Angewandte Chemie (International ed. in English)》2023,62(32):e202306196
Non-oxidative coupling of methane is a promising route to obtain ethylene directly from natural gas. We synthesized siliceous [Fe]zeolites with MFI and CHA topologies and found that they display high selectivity (>90 % for MFI and >99 % for CHA) to ethylene and ethane among gas-phase products. Deactivated [Fe]zeolites can be regenerated by burning coke in air. In situ X-ray absorption spectroscopy demonstrates that the isolated Fe3+ centers in zeolite framework of fresh catalysts are reduced during the reaction to the active sites, including Fe2+ species and Fe (oxy)carbides dispersed in zeolite pores. Photoelectron photoion coincidence spectroscopy results show that methyl radicals are the reaction intermediates formed upon methane activation. Ethane is formed by methyl radical coupling, followed by its dehydrogenation to ethylene. Based on the observation of intermediates including allene, vinylacetylene, 1,3-butadiene, 2-butyne, and cyclopentadiene over [Fe]MFI, a reaction network is proposed leading to polyaromatic species. Such reaction intermediates are not observed over the small-pore [Fe]CHA, where ethylene and ethane are the only gas-phase products. 相似文献