全文获取类型
收费全文 | 51篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学 | 23篇 |
晶体学 | 20篇 |
数学 | 3篇 |
物理学 | 6篇 |
出版年
2020年 | 1篇 |
2013年 | 2篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1995年 | 1篇 |
1992年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有52条查询结果,搜索用时 390 毫秒
1.
Preparation and Properties of Formed Aluminium Oxide. I. Influence of the Precipitation Conditions of the Boehmite Hydrogel on the Pore Structure of Formed Aluminium Oxide A report is given on the influence of the precipitation conditions of boehmite (pH value, temperature, concentration and residence time in the precipitation suspension) on the cavity structure of aluminium oxide spheres, made by coagulation of boehmite hydrosol in ammonia liquor and subsequent thermal treatment at 110 and 600°C. The boehmite hydrogel was obtained at continuous precipitation conditions by neutralisation of sodium aluminate solution with nitric acid. It is shown that the difference in the pore structure of the formed aluminium oxide obtained by varying the precipitation conditions were caused by the special morphological features of the boehmite crystallization in the precipitation process. 相似文献
2.
Esna Killian Kevin Blann Annette Bollmann John T. Dixon Sven Kuhlmann Munaka C. Maumela Hulisani Maumela David H. Morgan Palesa Nongodlwana Matthew J. Overett Mari Pretorius Karola Hfener Peter Wasserscheid 《Journal of molecular catalysis. A, Chemical》2007,270(1-2):214-218
A systematic study was conducted on the Cr catalysed tri- and tetramerisation of ethylene using bis(diphenylphosphino)amine ligands with N-aryl functionality. This study revealed that the oligomerisation reaction product selectivity is primarily dependent on the structure and size of the N-aryl groups.
Addition of sufficient steric bulk to the N-phenyl group via ortho-alkyl substitution increased the combined 1-hexene and 1-octene selectivity (overall alpha selectivity) to above 82% at an overall 1-octene selectivity of 56%. The introduction of a single carbon spacer between the N-atom and the aryl-moiety, as well as the addition of branching on this carbon, resulted in further selectivity improvements, achieving an overall 1-octene selectivity of 64% and an overall alpha selectivity of 84%. This was obtained at catalyst productivities in excess of 1,000,000 g/g Cr/h. 相似文献
3.
Overett MJ Blann K Bollmann A Dixon JT Haasbroek D Killian E Maumela H McGuinness DS Morgan DH 《Journal of the American Chemical Society》2005,127(30):10723-10730
The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation. Both 1-octene and higher 1-alkenes are formed by further ethylene insertion into a metallacycloheptane intermediate, whereas 1-hexene is formed by elimination from this species as in other reported trimerisation reactions. This is supported by deuterium labeling studies, analysis of the molar distribution of 1-alkene products, and identification of secondary co-oligomerization reaction products. In addition, the formation of two C6 cyclic products, methylenecyclopentane and methylcyclopentane, is discussed, and a bimetallic disproportionation mechanism to account for the available data is proposed. 相似文献
4.
Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities 总被引:11,自引:0,他引:11
Bollmann A Blann K Dixon JT Hess FM Killian E Maumela H McGuinness DS Morgan DH Neveling A Otto S Overett M Slawin AM Wasserscheid P Kuhlmann S 《Journal of the American Chemical Society》2004,126(45):14712-14713
Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system. 相似文献
5.
6.
W. Bollmann 《Crystal Research and Technology》1978,13(8):1001-1007
The electrical conductivity σ of CaMoO4 crystals was investigated between room temperature and 850°C. The mobility vv and the diffusion coefficient Dv of the O− ion vacancies have been derived from σ: vvT = 3300 exp (−1.52 eV/kT) cm2 K/Vs, Dv = (0.1…1) × exp (−1.52 eV/kT) cm2/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo5+ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1. 相似文献
7.
McGuinness DS Wasserscheid P Keim W Morgan D Dixon JT Bollmann A Maumela H Hess F Englert U 《Journal of the American Chemical Society》2003,125(18):5272-5273
Cr(III) complexes of tridentate SNS ligands have been prepared and evaluated as catalysts for ethylene trimerization, with several giving very high activity and excellent selectivity toward 1-hexene when activated with methylaluminoxane. The new complexes illustrate the potential of sulfur-based ligands on early transition metals for catalysis. 相似文献
8.
The quantum-size effect (QSE) driven growth of Bi film structures on Ni(111) was studied in situ using low energy electron microscopy and selective area low energy electron diffraction (μLEED). Domains with a (3×3), [(3)(1)(-1)(2)], and (7×7) film structure are found with a height of 3, 5, and 7 atomic layers, respectively. A comparison of I/V-μLEED curves with tensor LEED calculations shows perfectly accommodated Fermi wavelengths, indicative that not only the quantized height, but also the film structure is driven by QSE. 相似文献
9.
U. Steinike H. Geissler H.-P. Hennig K. Jancke J. Jedamzik U. Kretzschmar U. Bollmann 《无机化学与普通化学杂志》1990,590(1):213-221
Influence of Mechanical Activation on Thermal Decomposition of Gibbsite The influence of mechanical activation on structure and reactivity of gibbsite in dependence on stress mechanism (pressure stress and shearing in vibration-mills, shock stress in disintegrators) is investigated. With increasing mechanical treatment the degree of order is decreased. Mechanically disturbed gibbsite shows changed decomposition series. After mechanical activation and short-time heating there are formed nearly X-ray amorphous Al2O3 with high spec. surfaces. It is possible to transform these alumina into pseudo-boehmite with a very low alkali content. The transformation into pseudo-boehmite is dependent on the degree of order of the mechanically pretreated gibbsite and is independent of the spec. surface of X-ray amorphous Al2O3. The products can be used for the preparation of adsorbents and catalyser components. 相似文献
10.
Urade VN Bollmann L Kowalski JD Tate MP Hillhouse HW 《Langmuir : the ACS journal of surfaces and colloids》2007,23(8):4268-4278
The double-gyroid phase of nanoporous silica films has been shown to possess facile mass-transport properties and may be used as a mold to fabricate a variety of highly ordered inverse double-gyroid metal and semiconductor films. This phase exists only over a very small region of the binary phase diagram for most surfactants, and it has been very difficult to synthesize metal oxide films with this structure by evaporation-induced self-assembly (EISA). Here, we show the interplay of the key parameters needed to synthesize these structures reproducibly and show that the interfacial curvature may be systematically controlled. Grazing angle of incidence small-angle X-ray scattering (GISAXS) is used to determine the structure and orientation of nanostructured silica films formed by EISA from dilute silica/(poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl) surfactant solutions. Four different highly ordered film structures are observed by changing only the concentration of the surfactant, the relative humidity during dip-coating, and the aging time of the solution prior to coating. The highly ordered films progress from rhombohedral (Rm) to 2D rectangular (c2m) to double-gyroid (distorted Iad) to lamellar systematically as interfacial curvature decreases. Under all experimental conditions investigated, increasing the aging time of the coating solution was found to decrease the interfacial curvature. In particular, this parameter was critical to being able to synthesize highly ordered, pure-phase double-gyroid films. The key role of the aging time is shown via processing diagrams that map out the interplay between the aging time, composition, and relative humidity. 29Si nuclear magnetic resonance (NMR) spectroscopy and solution-phase small-angle X-ray scattering (SAXS) of the aged coating solutions presented in part I of this series are then used to interpret the effects of aging prior to dip-coating. Specifically, it was found that a predictive model based on volume fractions and the silica cluster stoichiometry obtained from 29Si NMR qualitatively explains the trends observed with composition and aging. However, apart from the effects of relative humidity, a quantitative comparison of the predicted phase with the experimental processing diagram suggests that less-condensed silica clusters are more effective at swelling the EO blocks at early aging times. This enhanced swelling decreases with aging time and results in lower-curvature nanostructures such as the double-gyroid. The decrease in swelling is attributed to the decreased thermodynamic driving force for the more-condensed silica clusters to mix with the EO block of the surfactant. 相似文献