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1.
Colour Effects in Oxidic and Other Mn2+ Compounds – the Ligand Field Spectra of Mixed Crystals MgO/MnO, CaO/MnO, and of MnAl2O4 The colour intensity and the shift of the hue is examined for mixed crystals Mg1?xMnxIIO and Mn1?yIICayO in dependence of the Mn2+-concentration and interpreted in terms of Mn2+? Mn2+ pair interactions and variations of the Mn? O bond length, respectively. The experimental band positions (sextet-quartet transitions) could be fitted quantitatively – also in case of Mn2+ in tetrahedral (MnAl2O4) and dodecahedral oxygen coordination (Mn3Al2Ge3O12, MnY2Mg2Ge3O12) – by means of crystal field calculations. The obtained ligand field parameters are discussed in comparison with data for octahedral Mn2+ ions with H2O, F? and Cl? as ligands. 相似文献
2.
The structure of the perovskite compound Sr NiIITeVI (6)O6 (1:1 order in the octahedral sites) is described in detail. The obtained Ni? O distance (2.04 Å aTe–O = 1.91 Å) together with that one within the corresponding tungsten perovskite (part II) will be analyzed quantitatively with respect to the connection between structure and ligand-field as well as EPR data. The comparison of this distance and the spectroscopic results of the tellurium perovskite with corresponding data of NiII-doped MgO however shows already now that an interpretation on the basis of an ionic model is impossible 相似文献
3.
Structure and Bonding in Transitition Metal Fluorides MIIMeIVF6 A. Phase Transitions A summary outline of the structure types of all compounds MIIMeIVF6 known so far is given. Compounds with a 3d transition metal ion in the MII site crystallize in the cubic ordered ReO3 lattice and the hexagonal LiSbF6 structure. For cations with a Jahn- Teller unstable Eg ground state we have found a symmetry reduction to tetragonal and triclinic variants of those two lattice types in addition. Phase transitions between the different structures could be observed by Guinier techniques in the temperature range 80 K < T < 800 K in many cases. The relative stability of the hexagonal low temperature phases in comparison to the cubic high temperature modifications is extensively discussed on the basis of geometric parameters and the electronic properties of the MeIV and MII ions. Quite a number of compounds MIIMeIVF6 was prepared and characterized for the first time. The results of the spectroscopic investigation will be published later. 相似文献
4.
Dirk Reinen 《Monatshefte für Chemie / Chemical Monthly》1965,96(2):730-739
Zusammenfassung Für das oktaedrisch koordinierte Co2+-Ion werden ein Termschema und Energiegleichungen für zwei charakteristischeDq/B-Werte angegeben und mit deren Hilfe aus den Spektren der Co2+-haltigen Ilmenite MgTiO3 und CdTiO3
1 die Zuordnung des intensitätsstärksten Quartett-Dublett-Überganges (
a
4
T1g
b
2
T1g) auf eindeutige Weise ermöglicht.Weiter wird das spektrale Verhalten der Mg1–x
CO
x
O-Mischkristalle (0,05x1,0) in Abhängigkeit von der Co2+-Konzentration untersucht. Die Änderungen der Bandenintensitäten und desRacah-ParametersB werden wie in der analogen MgO-NiO-Mischkristallreihe2 auf Spin-Spin-Wechselwirkungen der über Sauerstoff benachbarten Co2+-Ionen zurückgeführt.
Mit 3 Abbildungen 相似文献
The energy levels of the octahedrally coordinated Co2+-ion and energy equations for two characteristicB-values are given, which allow to identify the quartet-doublet-transition ( a 4 T1g b 2 T1g) of the highest intensity from the spectrum of the Co2+ containing ilmenites MgTiO3 and CdTiO3 1.In addition, the variation of the spectra of the Mg1–x Co x O-mixed crystals (0.05x1.0) with the Co2+ concentration is investigated. The changes in the intensities of the absorption bands and of theRacah-parameterB are (as for the corresponding MgO-NiO-mixed crystals2 interpreted as being caused by spin-spin-interactions between Co2+ ions bonded to the same oxygen.
Mit 3 Abbildungen 相似文献
5.
G. Münninghoff W. Treutmann E. Hellner G. Heger D. Reinen 《Journal of solid state chemistry》1980,34(3):289-299
The structures of single crystals Rb2Cr1?xMnxCl4 (0 ? x ? 1) have been studied by neutron diffraction. A crystal of composition x = 0.01 shows a superstructure of the K2NiF4 type [space group Bbcm; a = b = 7.262Å, c = 15.733Å]. The structural refinement [R = 0.043] yields an antiferrodistortive order of tetragonally elongated octahedra (superimposed by a small orthorhombic component) with CrCl bond lengths of 2.43 Å (∥[001]) and 2.40 Å, 2.74 Å (⊥[001]). Structural results for x = 0.01/0.08/0.53/0.63/0.83/0.91/0.97 in space group [K2NiF4 type]—in particular the anomalous ms displacements of Cl(1) in the (001) plane—give evidence that the distortion of the (Mn, Cr)Cl6 octahedra decreases with increasing x. AOM calculations based on experimental ligand field energies indicate that the individual CrCl6 polyhedra are more strongly distorted than the (Jahn-Teller stable) MnCl6 octahedra in mixed crystals with larger x values. 相似文献
6.
The EPR single-crystal and powder spectra of mixed crystals of (3-chloroanilinium)(8)(Cd(1-x)Cu(x)Cl(6))Cl(4) are measured as a function of temperature and x and analyzed with respect to the geometry and bonding properties of the CuCl(6) polyhedra. These undergo strong distortions due to vibronic Jahn-Teller coupling, with the resulting tetragonal elongation being superimposed by a considerable orthorhombic symmetry component induced by a host site strain acting as a compression along the crystallographic a axis. This strain becomes apparent in the cadmium compound (x = 0), whose crystal structure is also reported [a = 8.701(2) ?, b = 13.975(2) ?, c = 14.173(2) ?, alpha = 81.62(1) degrees, beta = 72.92(1) degrees, gamma = 77.57(1) degrees, triclinic P&onemacr;, Z = 1]. A calculation of the ground state potential surface and its vibronic structure nicely reproduces the g values, Cu-Cl spacings, and ligand field data. At high copper concentrations (including x = 1), the CuCl(6) polyhedra are coupled elastically, with the long axes of neighboring polyhedra having perpendicular orientations. The elastic correlation presumably is not of the long-range antiferrodistortive type, however. Above about 55 K, the angular Jahn-Teller distortion component becomes dynamically averaged within the time scale of the EPR experiment, leading to local tetragonally compressed CuCl(6) octahedra. 相似文献
7.
8.
9.
Jelle E. Stumpel Dr. Danqing Liu Prof. Dirk J. Broer Dr. Albertus P. H. J. Schenning 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):10922-10927
Herein, we describe the preparation of patterned photoresponsive hydrogels by using a facile method. This polymer‐network hydrogel coating consists of N‐isopropylacrylamide (NIPAAM), cross‐linking agent tripropylene glycol diacrylate (TPGDA), and a new photochromic spiropyran monoacrylate. In a pre‐study, a linear NIPAAM copolymer (without TPGDA) that contained the spiropyran dye was synthesised, which showed relatively fast photoswitching behaviour. Subsequently, the photopolymerisation of a similar monomer mixture that included TPGDA afforded freestanding hydrogel polymer networks. The light‐induced isomerisation of protonated merocyanine into neutral spiropyran under slightly acidic conditions resulted in macroscopic changes in the hydrophilicity of the entire polymer film, that is, shrinkage of the hydrogel. The degree of shrinkage could be controlled by changing the chemical composition of the acrylate mixture. After these pre‐studies, a hydrogel film with spatially modulated cross‐link density was fabricated through polymerisation‐induced diffusion, by using a patterned photomask. The resulting smooth patterned hydrogel coating swelled in slightly acidic media and the swelling was higher in the regions with lower cross‐linking densities, thus yielding a corrugated surface. Upon exposure to visible light, the surface topography flattened again, thus showing that a hydrogel coating could be created, the topography of which could be controlled by light irradiation. 相似文献
10.