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71.
72.
Shevlin SA Guo ZX van Dam HJ Sherwood P A Catlow CR Sokol AA Woodley SM 《Physical chemistry chemical physics : PCCP》2008,10(14):1944-1959
Density Functional Theory calculations are reported on cage structured BN, AlN, GaN and InN sub- and low nanosize stoichiometric clusters, including two octahedral families of T(d) and T(h) symmetry. The structures and energetics are determined, and we observe that BN clusters in particular show high stability with respect to the bulk phase. The cluster formation energy is demonstrated to include a constant term that we attribute to the curvature energy and the formation of six tetragonal defects. The (BN)(60) onion double-bubble structure was found to be particularly unstable. In contrast, similar or greater stability was found for double and single shell cages for the other nitrides. The optical absorption spectra have been first characterised by the one-electron Kohn-Sham orbital energies for all compounds, after which we concentrated on BN where we employed a recently developed Time Dependent Density Functional Theory approach. The one-electron band gaps do not show a strong and consistent size dependency, in disagreement with the predictions of quantum confinement theory. The density of excited bound states and absorption spectrum have been calculated for four smallest BN clusters within the first ionisation potential cut-off energy. The relative stability of different BN clusters has been further explored by studying principal point defects and their complexes including topological B-N bond rotational defects, vacancies, antisites and interstititials. The latter have the lowest energy of formation. 相似文献
73.
K. Ragavendran D. Sherwood D. Vasudevan Bosco Emmanuel 《Physica B: Condensed Matter》2009,404(16):2166-2171
Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn2O4(S) was prepared using starch as the fuel and LiMn2O4(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn2O4(P) compared to LiMn2O4(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (∼25 °C higher) for LiMn2O4(P). The higher formation temperature most likely promotes the oxidation of some Mn3+ to Mn4+ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn4+ in LiMn2O4(P) than that present in LiMn2O4(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn2O4(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn2O4(S). 相似文献
74.
75.
R A Sherwood 《Biomedical chromatography : BMC》1991,5(6):235-239
The measurement of the nucleoside deaminases--cytidine deaminase, guanosine deaminase and adenosine deaminase--by reversed phase high performance liquid chromatography is reviewed. The clinical value of assaying the enzyme activity is discussed for each of these enzymes. Both cytidine deaminase and adenosine deaminase measurements have proven clinical value, although the use of the assay of cytidine deaminase in the diagnosis of pre-eclampsia is probably not helpful. 相似文献
76.
77.
Murray V. Baker Christine Ghitgas Richard K. Haynes Audrey E. Hilliker Gregory J. Lynch Gloria V. Sherwood 《Tetrahedron letters》1984,25(15):1625-1628
The efficient conversion of Hagemann's ester and its t-butyl analogue into dienol ethers and dienol esters, and reactions of the derived dienolates with electrophiles is described. 相似文献
78.
Sherwood JD Risso F Collé-Paillot F Edwards-Lévy F Lévy MC 《Journal of colloid and interface science》2003,263(1):202-212
The swelling of a capsule consisting of salt solution and polyelectrolyte, surrounded by a membrane, is studied. The membrane allows salt and water to pass, but is impermeable to polyelectrolyte molecules. Equilibrium swelling of the capsule is governed by Donnan equilibrium. Transport rates of a salt and water through the membrane are expressed in terms of a Darcy permeability and a salt diffusivity. The governing equations predict that the rate at which equilibrium is attained as the external salt concentration varies is controlled by the timescale for diffusion of salt, rather than by that for Darcy flow. Experiments were performed using capsules with membranes made of covalently linked HSA and alginate. The capsule volume varied with a single relaxation rate when the external salt concentration was changed, as predicted by theory. This constitutes the first step toward a simple method for determining the membrane properties of capsules by measuring rates of change of capsule volume. 相似文献
79.
80.
We exploit the high second-order susceptibility of the organic crystal N-(4-nitrophenyl)-L-prolinol to accomplish, through a cascaded second-order process, wavelength conversion of a signal pulse (from 1.16 to 1.14 microm) under the action of a pump pulse (at 1.15 microm). In a 2.8-mm-thick crystal, wavelength conversion with unit gain was obtained with a pump peak intensity as low as 9 MW/cm(2) . At low intensities, in the limit of negligible conversion where the cascading effect can be described through an effective third-order susceptibility, we derive |(x)((3))(eff) | approximately 2.4 x 10(-17) m(2)/V(2), which is ~10(2) larger than the nonresonant (x)((3)) of conjugated polymers or semiconductors. 相似文献