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71.
Lebeugle D Colson D Forget A Viret M Bataille AM Gukasov A 《Physical review letters》2008,100(22):227602
Bismuth ferrite, BiFeO3, is the only known room-temperature magnetic ferroelectric material. We demonstrate here, using neutron scattering measurements in high quality single crystals, that the antiferromagnetic and ferroelectric order parameters are intimately coupled. Initially in a single ferroelectric state, our crystals have a canted antiferromagnetic structure describing a unique cycloid. Under electrical poling, polarization reorientation induces a spin flop. We argue here that the coupling between the two orders may be stronger in the bulk than in thin films where the cycloid is absent. 相似文献
72.
With the industrial scale, the synthesis of zeolites must imperatively be made out of agitated reactor. However a significant parameter of agitation must be taken into account: shearing. Shearing seems to have a harmful effect (when one seeks has a metastable form) on the stability of the zeolite thus synthesized on its purity. 相似文献
73.
M. Cazayous A. Sacuto D. Lebeugle D. Colson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):209-212
We have performed Raman measurements on high energy excitations in BiFeO3 single crystals as a function of both temperature and laser excitation lines. A strong feature observed at 1250 cm-1 in the Raman spectra has been previously assigned to two phonon overtone. This peak exhibits an unusual frequency shift with
the laser lines and the temperature dependence of its Fano lineshape shows two singularities at 150 K and 200 K which can
be related to magnetic excitations. In the same energy range, we have also identified the two-magnon excitation with a temperature
dependence very similar to the one measured for the one-magnon modes. 相似文献
74.
Jérôme Colson Wolfgang Bauer Melanie Mayr Wolfgang Fischer Wolfgang Gindl-Altmutter 《Cellulose (London, England)》2016,23(4):2439-2448
The rheological behaviour of homogenised fibres originally having different lengths was evaluated. For this purpose, mixtures of pulp fibres and fines were fibrillated mechanically without pre-treatment and characterised with regard to morphology and viscosity. It was found that, for all samples, a similar number of homogenisation passes was needed to reach a viscosity plateau. However, the value of the final viscosity differed significantly: homogenised suspensions derived from fines achieved only about 60 % of the viscosity of suspensions derived from pulp. Already after a few homogenisation cycles, no differences between the samples could be measured using optical devices, indicating that fibrillation on the nanometre scale was responsible for the distinct rheological behaviours. Atomic force microscopy measurements indicated significantly reduced fibril lengths for the suspensions derived from fines, which explains their reduced viscosity. 相似文献
75.
John W. Colson Jason A. Mann Catherine R. DeBlase William R. Dichtel 《Journal of polymer science. Part A, Polymer chemistry》2015,53(2):378-384
Two-dimensional covalent organic frameworks (COFs) are polymer networks that organize molecular building blocks into porous, layered structures of interest for organic optoelectronic and energy storage devices. Current synthetic methods produce these materials as either insoluble, microcrystalline powders or as oriented thin films on various substrates, including single-layer graphene (SLG). Under these conditions, COF thin films form on both the graphene-coated and bare regions of the substrate, suggesting uncontrolled nucleation processes that occur either in solution or nonselectively on different surfaces. Here, we describe modified polymerization conditions that provide COF films selectively on SLG. This finding enables COF films to be grown on lithographically patterned SLG substrates, which provide insight into the uniformity of film growth across the substrate and factors relevant to their nucleation and growth. The ability to grow COF films selectively on lithographically patterned SLG will facilitate their integration into devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 378–384 相似文献
76.
A survey of many crystal structures shows that short intermolecular chlorine-chlorine contacts are anisotropic. This observation challenges the currently used potential function models which allow only for isotropic exp-6 and coulomb interactions. In this study the polymorphic p-dichlorobenzene DCB system is used to illustrate the difficulties encountered by relying on the isotropic atom-atom approximation. It is found that exp-6 potential functions cannot be extrapolated beyond the range of contacts used in their derivation. Addition of coulomb terms provides needed additional flexibility to the potential function but the derived C-Cl bond polarization is not found to be a constant of the molecule, i.e. the optimum value is not the same for each phase of DCB. Furthermore, no single exp-6 potential function could satisfy the structural constraints provided by the three phases of crystalline DCB and by hexachlorobenzene. These findings are typical of curve-fitting methods which employ an incorrect mathematical form for the curve and indicate the necessity of including anisotropic terms in the interaction potential. 相似文献
77.
We show that a laser can efficiently accelerate charged particles if a magnetic field is introduced to improve the coupling
between the particle and the wave. Solving the relativistic equations of motion for an electron in a uniform magnetic field
and superposed, circularly polarized electromagnetic wave, we find that in energy-position phase space an electron traces
out a curtate cycloid: it alternately gains and loses energy. If, however, the parameters are chosen so that the electron's
oscillations in the two fields are resonant, it will continually accelerate or decelerate depending on its initial position
within a wavelength of light.
A laboratory accelerator operating under these resonant conditions appears attractive: in a magnetic field of 105 Gauss, and the fields of a 5×1012 W, 10 μm wavelength laser, an optimally positioned electron would accelerate to 700 MeV in only 10m.
Supported by NASA Grant NSG-7490 相似文献
78.
A. Bertinotti D. Colson J. Hammann J. -F. Marucco D. Luzet A. Pinatel V. Viallet 《Physica C: Superconductivity and its Applications》1995,250(3-4):213-221
X-ray diffraction analyses of good-quality single crystals of HgBa2Ca2Cu3O8+δ, synthetized by a closed-vessel technique at low pressure, have lead to more definite results with respect to previous structural studies. Samples with Tc = 135 K showed a Cu occupancy of 16.1% on the Hg site at the origin of the unit cell. Excess oxygen appears to be present only in the basal plane at the interstitial site
, 0 with an occupancy δ = 0.190 ± 0.015. This compound has the shortest copper oxygen apical distance within the mercury family (2.696(3) Å) together with an almost complete planarity of the CuO2 planes. Variations in the excess oxygen content upon different heat treatments were analyzed by thermogravimetry and magnetic-susceptibility measurements. A correlation between δ and Tc could be derived, showing in particular that superconductivity exists down to a very low interstitial oxygen content. 相似文献
79.
80.
Deanne L. Snavely Valerie A. Walters Steven D. Colson Kenneth B. Wiberg 《Chemical physics letters》1984,103(5):423-429
The 700 and 3050 cm?1 region of benzene seeded in argon is studied using Fourier-transform infrared absorption spectroscopy. Analysis of the sequence band structure in the 700 cm?1 region gave new anharmonic constants and values of Trot (79 ± 15 K) and Tvib (/2~160 K) which indicate a disequilibrium between the rotational and vibrational degrees of freedom. A band contour analysis of the 3050 cm?1 Fermi triad is used to obtain new values of the Coriolis coupling constants and band origins. 相似文献