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11.
J.M.D. Coey A. Meagher J. Etourneau B. Chevalier P. Hagenmuller 《Solid State Communications》1979,31(12):981-983
151Eu Mössbauer spectra of three compounds in the series EuO1-xNx with x = 0.05, 0.15 and 0.25 show well-resolved Eu2+ and Eu3+ absorbtion lines. The proportion of Eu3+ is just x. There is no evidence for electron hopping. Eu2+ appears to be unstable in environments with more than two nitrogen neighbours. 相似文献
12.
The partial suppression of corrosion of Ag and Cu in concentrated nitric acid solution by a magnetic field of up to 5 T was studied. The corrosion current density of these metals was found to diminish with magnetic field and rotation speed in a rotating disk electrode experiment. The suppression of corrosion is associated with removal of the catalyst HNO(2) from the electrode and passivation of the electrode surface. The Lorentz force was identified as the driving force responsible for the partial suppression of corrosion. A model based on the partial areas associated with active and passive regions on Ag and Cu electrodes is introduced to explain the dependence of the current density on the applied magnetic field. 相似文献
13.
151Eu Mössbauer spectra of fluorozirconate glasses of nominal composition 0.61 ZrF4 · (0.32 ? x) BaF2 · x EuF2 · 0.07 ThF4 with x = 0.10 and 0.20 show that Eu2+ is present in sites with isomer shifts in the range ?15.5 to ?12.9 mm/s, corresponding to EuF bond lengths of 2.3–2.8 Å and a coordination number ranging from 8 to 12. The glasses contain a minor amount (~10%) of Eu3+ in well-defined sites. Effective Debye temperatures deduced from the recoilless fractions for the two ions are θD2+ = 145 K and θD3+ = 261 K. The differences in coordination and bonding indicate that trivalent eurpoium is a network former, whereas the divalent ions are network modifiers. 相似文献
14.
J. M. D. Coey F. M. F. Rhen P. Dunne S. McMurry 《Journal of Solid State Electrochemistry》2007,11(6):711-717
There are suggestions in the electrochemical literature that a body force F
∇c acts when an electrolyte with a non-uniform concentration c of paramagnetic ions is subject to a uniform magnetic field. We demonstrate, experimentally and theoretically, that no such
magnetic body force exists, to first order. A second-order correction associated with the demagnetizing field does lead to
a very small concentration-dependent body force, which is not expected to produce any observable effect in electrochemistry.
Contribution to special issue on Magnetic field effects in Electrochemistry.
相似文献
J. M. D. CoeyEmail: |
15.
R.D. Gunning Karsten Rode Sumesh R.G. Sofin M. Venkatesan J.M.D. Coey Igor V. Shvets James G. Lunney 《Applied Surface Science》2009,255(10):5245-5247
Thin films of lithium ferrite (Li0.5Fe2.5O4) have been deposited on (0 0 1) Al2O3 by pulsed laser deposition, with substrate deposition temperatures ranging between 500 and 800 °C, and oxygen pressures between 1 × 10−1 and 4 × 10−7 mbar. X-ray diffraction shows that films grow with a (1 1 1) orientation. Conversion electron Mössbauer spectra for the high-pressure films show a single sextet with a hyperfine field of 49 T, while the low-pressure films show two sextets with hyperfine fields of 47 and 49 T. The spectra also reveal paramagnetic ferric iron in both types of films. Magnetization measurements of the films show a saturation magnetization of between 1.7 and 3.1μB per formula unit and a coercivity of between 10 and 44 mT. The films prepared under the lower oxygen pressures are semiconducting with resistivities of 2 × 10−2 to 8 × 10−2 Ω cm. They exhibit an anomalous Hall effect with p-type conduction at 175 K. 相似文献
16.
The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm?2. A 1/f2 variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force. 相似文献
17.
Co1−xCrx alloy nanowires with 0.01<x<0.93 were fabricated by electrodeposition in a porous alumina membrane from an electrolyte containing Co and Cr ions. The composition, structure and magnetic properties of the nanowires have been characterized. Cobalt-rich nanowires were electrodeposited at a potential of −1.0 V relative to Ag/AgCl and chromium-rich nanowires were deposited beyond −3.5 V. The optimized processing conditions include hydrogen annealing to give hysteresis loops for the Co80Cr20 nanowires with coercivity of up to 200 mT and squareness of up to 0.95. Magnetization of the Co80Cr20 nanowire is 77 A m2 kg−1 and the energy product of the arrays is 35 kJ m−3. 相似文献
18.
57Fe Mössbauer spectra are reported for the ThMn12 structure series of intermetallic compounds R(Fe11Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient αJ of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe11Ti) compound, which may find applications as a permanent magnet. 相似文献
19.
J.D. Fabris W. da N. Mussel J.M.D. Coey M.F. de Jesus Filho A.T. Goulart 《Hyperfine Interactions》1997,110(1-2):33-40
Powdered crystals of an iron-rich spinel separated from tuffite were examined by chemical analysis, X-ray diffractometry (XRD), magnetometry, scanning electron microscopy and Mössbauer spectroscopy. They are found to contain mainly 48 mass% Fe2O3; 16.9% FeO; 14.3% TiO2; 9% MgO and 3% Al2O3. The magnetization is 29 J T-1 kg-1 at B0 ~ 0.9 T. XRD pattern reveals two cubic phases with α0 = 0.8382(5) and 0.8412(5) nm, respectively. Mössbauer spectra are very complex, but the hyperfine field distribution patterns can be decomposed in two relatively well-resolved Gaussian distributions for the Fe3+ block (averaged isomer shift relative to α-Fe, δ = 0.27 mm s-1) with Bhf = 43.6 T (14.6% of the whole spectral area, WSA) and Bhf = 47.3 (27.7% WSA). A second less resolved distribution block (δ = 0.63 mm s-1) shows two main maxima in the P(Bhf) curve at 35.3 T (25.7% WSA) and 45.2 T (19.7% WSA), respectively. The Mg-rich maghemite (lower α0) appears to be a direct alteration product of a Mg-rich magnetite (higher α0), via an oxidation process of structural Fe2+ to Fe3+ proceeding from the outer to the inner part of the crystal. 相似文献
20.
J.D. Fabris M.F. de Jesus Filho J.M.D. Coey W. da N. Mussel A.T. Goulart 《Hyperfine Interactions》1997,110(1-2):23-32
Tropical soils often contain high amounts of iron oxides. Hematite (αFe2O3) and goethite (αFeOOH) are the most widespread iron oxides, but magnetite (Fe3O4) and maghemite (γFe2O3) occur in magnetic pedons. A wide range of spinel compositions in the Fe3O4-γFe2O3 series has been identified in magnetic Brazilian soils. Isomorphic substitution of mainly Ti4+, Al3+ and Mg2+, but also of Cr3+ and Mn2+ and other minor elements for iron are related to changes in their structural stability and magnetic properties. Magnetic
iron oxides of selected Brazilian pedodomains are discussed, distinguishing those produced from mafic rocks (tuffite, basalt),
where primary magnetite transforms to maghemite, from those produced in non-mafic lithologies (such as steatite), where inherited
magnetite may be exceptionally stable in the soil.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献