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31.
A series of ternary compounds RECu9Mg2 (RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb) have been synthesized via induction melting of elemental metal ingots followed by annealing at 400 °C for 4 weeks. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for examining microstructure and phase composition. These phases crystallize with an ordered version of the binary hexagonal structure type first reported for CeNi3. The crystal structure was solved for TbCu9Mg2 from single crystal X-ray counter data (TbCu9Mg2-structure type, P63/mmc-space group, hP24-Pearson symbol, a=0.49886 (7) nm, c=1.61646 (3) nm, RF=0.0474 for 190 unique reflections). The Rietveld refinement of the X-ray powder diffraction patterns of RECu9Mg2 confirmed the same crystal structure for the reported rare earth metals. The unit cell volumes for RECu9Mg2 smoothly follow the lanthanide contraction. The existence of a RECu9Mg2 phase was excluded for RE=Er and Tm under the investigated experimental conditions.  相似文献   
32.
The effect of static and pulsed magnetic fields (~1 T) on the electrical conductivity of CdTe crystals has been revealed. With a delay after the magnetic exposure of crystals, the effect is observed in the form of two peaks of their conductivity with the subsequent relaxation return. The first peak at both types of magnetic treatment is observed ~1 h after exposure and its amplitude exceeds the background value by ~23–36% (the larger value corresponds to the static field). The second peak appears in both cases also at commensurate but much larger delays of ~50–60 h, and its amplitudes are much different for the two types of exposure, exceeding the background by ~60% for the static field and only by ~11% for the pulsed field. Possible mechanisms of the observed effects have been discussed.  相似文献   
33.
A phase transition from the cubic CsCl-type structure (Pm-3m space group) into a tetragonal UPb-type structure (I41/amd) is observed for the LiAg binary compound at ambient conditions. The crystal structure of the tetragonal modification of the LiAg binary compound was solved by direct methods in SHELXS on the base of structure factors which were extracted from a powder diffraction pattern and refined by SHELXL and the Rietveld method (a = 3.9605(1), c = 8.2825(2) Å, Bragg R-factor = 4.81, Rf-factor = 4.87). Elevated temperatures and/or a small Li-excess versus the equimolar composition favour the cubic structure whereas ambient and lower temperatures and/or a small Li-deficiency stabilize the tetragonal structure. This reconstructive transition is reversible but proceeds slowly.  相似文献   
34.
Binuclear Rh(II) compounds [Rh2(μ-OOCCH3)2(dbbpy)2(H2O)2](CH3COO)2 (1) (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine), [Rh2(μ-OOCCH3)2(dbbpy)2(H2O)2](BF4)2·H2O·CH3CN (2), [Rh2(CH3COO)2(C18H24N2)2(CH3CN)2](BF4)2·4CH3CN (3) and {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n (4) have been synthesized and characterized with spectroscopic methods. Structure of complex 3 has been determined using X-ray crystallography. Rhodium atoms in compound 3 have distorted octahedral coordination with O and N atoms in equatorial positions and Rh atom and CH3CN molecule in axial coordination sites. Reduction of rhodium(II) compounds with aqueous 2-propanol leads to the formation of polymetallic compound {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n (4) containing [Rh2]3+ core. Compound 4 shows strong antiferromagnetic properties, μ = 0.18–1.73 M.B. in the range 1.8–300 K, J = −597 cm−1. Electrochemistry of compounds 3 and 4 in CH3CN has been investigated. Compound 4 exhibits a poorly reversible oxidation system at E1/2 = −0.92 V (ΔEp = 0.19 V) and in solution in DMF is slowly oxidized to 3 even in total absence of oxygen. Complex 3 is irreversibly oxidized to Rh(III) compound at Epa = 1.48 V and irreversibly reduced at Epc = −1.02 V to lead to the unstable polynuclear complex 4 in CH3CN.  相似文献   
35.
Icosacerium nonadecamagnesium henoctacontazinc, Ce20Mg19Zn81, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F3m, a = 21.1979 (8) Å] and represents a new structure type among the technologically important family of ternary rare earth–transition metal–magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce20Mg19Zn81 structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz.A (Zn+Zn4+Zn4+Zn12+Ce6), B (Mg+Zn12+Ce4+Zn24+Ce4), C (Zn4+Zn12+Mg6) and D (Zn4+Zn4+Mg12+Ce6), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic‐type bonding.  相似文献   
36.
CdWO4 crystals grown by the Czochralski method at the low-temperature gradient were investigated with electron spin resonance (ESR) spectroscopy. ESR spectra did not contain the spectra of impurity ions typical for the CdWO4 structure, i.e., Fe3+, Mn2+, and Cr3+. At the same time, in the studied crystals a complex ESR spectrum having the hyperfine structure due to two nonequivalent tungsten atoms was observed (W183;I=1/2; natural abundance, 14.28%). Angular dependence analysis and simulation of ESR spectra have shown that this novel spectrum is described by a spin-Hamiltonian with the following parameters:D=839 G,E=80 G,g xx=2.01,g yy=1.97,g zz=1.987 and electron spinS=7/2. There is one magnetically nonequivalent position of the center in the crystal structure and the direction ofD zz andg zz corresponds to the direction of Wn-Wn+2 (or Cdn-Cdn+2) in the crystal structure. Because of the fact that it is in principle impossible to achieve the electron stateS=7/2 for the d-shell of one transition metal ion and taking into account the fact that such electron state is realized for two nonequivalent tungsten atoms, we suppose the defect structure to be the chain W2+-M+-W3+. In the structure of this defect the ion M+ is diamagnetic, the ions W2+ and W3+ have electron spinS=2 andS=3/2, respectively. The necessary condition for such defect to exist is to place this chain of ions in cadmium positions for the charge compensation. the reason for such defects to form is supposed to be the incorporation of M+ ions into the CdWO4 lattice. The presence of W2+ and W3+ in Cd positions in the defect structure provides the charge compensation and the lowering of the lattice stress.  相似文献   
37.
The creep strains in linear viscoelastic materials under nonstationary loading of various types (incremental loading, complete unloading, and cyclic loading) are determined. Boltzmann–Volterra hereditary theory with fractional exponential kernel is used. Nonstationary loads are specified by Heaviside functions. The calculated results are validated by experimentally determining nonstationary creep strains of glass-reinforced plastic, plastic laminate, polymer concrete, duralumin, and nylon  相似文献   
38.
39.
Stereospecific behavior of allyl derivatives and acetylenes in CuX -complexes (X = Cl-, Br-, NO3 -, BF4 -, 1/2SiF6 2-, 1/2SO4 2-) is studied by X-ray diffraction analysis. The influence of donor atoms N, S, and O and of the Cu-X bond polarization on the -complex formation is considered. The efficiency of Cu-(C=C) and Cu-(CC) -interaction and specific behavior of mono- and disubstituted acetylenes with respect to Cu(I) are compared.  相似文献   
40.
In this review an exhaustive crystallochemical analysis of copper(I) π-complexes with allyl derivatives of heterocyclic compounds has been performed. Structural genesis of inorganic constituents starting from the simplest units to the most complicated aggregates was considered taking into account the specific role of Cu-(C=C) interaction, the construction of the organic ligands, the basicity and nucleophilic activity of their heteroatoms, as well as olefin Cu(I) π-complex preparation route.   相似文献   
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