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31.
Synthesis, Colour, and Structure of a red Selenium Ultramarine The synthesis conditions for a brilliant red selenium ultramarine with pigment properties are reported. Structural and electron-microscopic investigations indicate, that these compounds possess the nosean structure with underoccupied Na+ and anionic positions, which contain the colour-determining species. It is concluded by applying various spectroscopic methods that the colour is generated by Se2? radicals. Hydrothermally grown single crystals were pink, with only very small amounts of Se2? being present, which were distinctly spectroscopically but not structurally detectable. 相似文献
32.
Sprakel VS Feiters MC Meyer-Klaucke W Klopstra M Brinksma J Feringa BL Karlin KD Nolte RJ 《Dalton transactions (Cambridge, England : 2003)》2005,(21):3522-3534
The copper(I) complexes of diphenylglycoluril basket receptors and , appended with bis(2-ethylpyridine)amine (PY2) and tris(2-methylpyridine)amine (TPA), respectively, and their dioxygen adducts were studied with low-temperature UV-vis and X-ray absorption spectroscopy (XAS). The copper(I) complex of, [.Cu(I)2] or, forms a micro-eta2:eta2 dioxygen complex, whereas the copper(I) complex of, [.Cu(I)2] or, does not form a well defined dioxygen complex, but is oxidized to Cu(II). Dioxygen is bound irreversibly to and the formed complex is stable over time. The coordination geometries of the above complexes were determined by XAS, which revealed that pyridyl groups and amine N-donors participate in the coordination to Cu(I) ions in the complexes of both receptors. The catalytic activities of various metal complexes of and , that were designed as mimics of dinuclear copper enzymes that can activate dioxygen, were investigated. Phenolic substrates that were expected to undergo aromatic hydroxylation, showed oxidative polymerization without insertion of oxygen. The mechanism of this polymerization turns out to be a radical coupling reaction as was established by experiments with the model substrate 2,4-di-tert-butylphenol. In addition to Cu(II), the Mn(III) complex of and the Fe(II) complex of were tested as oxidation catalysts. Oxidation of catechol was observed for the Cu(II) complex of receptor but the other metal complexes did not lead to oxidation. 相似文献
33.
The Structures of the Hexagonal Elpasolite-Type Compounds Ba3NiSb2O9 and Ba3CuSb2O9 The results of an X-ray single crystal study of the hexagonal elpasolite Ba(NiSb2)(6)O9 are given. (Space group: C; a = b = 5.837 Å, c = 14.392 Å; Z = 2). The structure can be described by close-packed BaO3 layers alternating in the sequence c c h c c h … (hex. BaTiO3 type). Groups of two octahedra with common faces are connected by SbO6 octahedra via common corners. They are occupied alternately by Ni and Sb. The final reliability index was R = 3.0%. The Cu2+-compound is of the same structural type. The ligand field and EPR spectra are discussed in comparison with related Ni2+ and Cu2+ compounds. 相似文献
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35.
X-ray absorption spectra at the chromium K-edge are reported for a number of selected chromium compounds of known chemical structure. The spectra were obtained with use of synchrotron radiation available at the
ectron
tretcher
ccelerator ELSA in Bonn. The compounds studied include the tetrahedrally coordinated compounds Ca2Ge0.8Cr0.2O4, Ba2Ge0.1Cr0.9O4, Sr2CrO4, Ca2(PO4)x(CrO4)1−xCl (x=0.25,0.5), Ca5(CrO4)3Cl, CrO3, the octahedrally coordinated compounds Cr(II)-acetate, CrCl3, CrF3, Cr2O3, KCr(SO4)2 · 12H2O, CrO2 and cubic coordinated metallic chromium. In these compounds chromium exhibits a wide range of formal oxidation states (0 to VI). The absorption features in the near edge region are shown to be characteristic of the spatial environment of the absorbing atom. The occurrence of a single pre-edge line easily allows one to distinguish between tetrahedral and octahedral coordination geometry, whereas the energy position of the absorption edge is found to be very sensitive to the valency of the excited chromium atom. Calculations of the ionisation potential of Cr in different oxidation states using the non-relativistic Hartree–Fock method (Froese–Fischer) confirm that the ionisation limit shifts to higher energy with increasing Cr valency. More detailed information on the electronic structure of the different compounds is gained by real-space full multiple scattering calculations using the FEFF8 code. 相似文献
36.
de Boer JW Brinksma J Browne WR Meetsma A Alsters PL Hage R Feringa BL 《Journal of the American Chemical Society》2005,127(22):7990-7991
The carboxylic acid promoted cis-dihydroxylation and epoxidation of alkenes catalyzed by [MnIV2O3(tmtacn)2]2+ 1 employing H2O2 as oxidant is described. The use of carboxylic acids at cocatalytic levels not only is effective in suppressing the inherent catalase activity of 1, but also enables the tuning of the catalyst's selectivity. Spectroscopic studies and X-ray analysis confirm that the control arises from the in situ formation of carboxylate-bridged dinuclear complexes, for example, 2 {[MnIII2O(CCl3CO2)2(tmtacn)2]2+} and 3 {[MnII2(OH)(CCl3CO2)2(tmtacn)2]+}, during catalysis. For the first time, the possibility to tune, through the carboxylate ligands employed, both the selectivity and activity of dinuclear Mn-based catalysts is demonstrated. To our knowledge, the system 1/2,6-dichlorobenzoic acid (up to 2000 turnover numbers for cis-cyclooctanediol) is the most active Os-free cis-dihydroxylation catalyst reported to date. 相似文献
37.
INDO-LCAO-MO calculations have been performed for the complex cations [TII(NO2)6]4- (TII: Cu2+, Co2+), in order to analyse the T-N bond properties and the Jahn-Teller distortion of the TN6 octahedra as well as the high-spin low-spin behaviour of Co2+. While the essential features of the electronic structure and the coordination geometry of the TN6 polyhedra resulting from the calculations are well in line with the experimental data for nitrocomplexes A2IMIITII(NO2)6, the quantitative agreement is only approximate. 相似文献
38.
39.
Design of a microfluidic device for comprehensive spatial two‐dimensional liquid chromatography 下载免费PDF全文
Bert Wouters Jelle De Vos Gert Desmet Herman Terryn Peter J. Schoenmakers Sebastiaan Eeltink 《Journal of separation science》2015,38(7):1123-1129
This study discusses the design aspects for the construction of a microfluidic device for comprehensive spatial two‐dimensional liquid chromatography. In spatial two‐dimensional liquid chromatography each peak is characterized by its coordinates in the plane. After completing the first‐dimension separation all fractions are analyzed in parallel second‐dimension separations. Hence, spatial two‐dimensional liquid chromatography potentially provides much higher peak‐production rates than a coupled column multi‐dimensional liquid chromatography approach in which the second‐dimension analyses are performed sequentially. A chip for spatial two‐dimensional liquid chromatography has been manufactured from cyclic olefin copolymer and features a first‐dimension separation channel and 21 parallel second‐dimension separation channels oriented perpendicularly to the former. Compartmentalization of first‐ and second‐dimension developments by physical barriers allowed for a preferential flow path with a minimal dispersion into the second‐dimension separation channels. To generate a homogenous flow across all the parallel second‐dimension channels, a radially interconnected flow distributor containing two zones of diamond‐shaped pillars was integrated on‐chip. A methacrylate ester based monolithic stationary phase with optimized macroporous structure was created in situ in the confines of the microfluidic chip. In addition, the use of a photomask was explored to localize monolith formation in the parallel second‐dimension channels. Finally, to connect the spatial chip to the liquid chromatography instrument, connector ports were integrated allowing the use of Viper fittings. As an alternative, a chip holder with adjustable clasp locks was designed that allows the clamping force to be adjusted. 相似文献
40.