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131.
L.E. Valiente-Banuet G. Majer K. Müller 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):280-284
Advanced nuclear magnetic resonance (NMR) techniques were applied to study the local environments of hydrogen in NaAlH4. Through a combined application of the magic echo (ME) and the magic Hahn echo (MHE) sequences the hetero- and homonuclear contributions to the dipolar second moment (M2) were determined separately. The obtained values are compared with the second moments calculated by the van Vleck formulae, using structural data determined by neutron scattering on NaAlD4. This comparison indicates structural differences between NaAlH4 and NaAlD4. A model is suggested for the orientation of the [AlH4]− tetrahedra in NaAlH4, for which the calculated second moments are in good agreement with the experimentally observed values. 相似文献
132.
133.
Positive mouns in iron: Dipolar fields at tetrahedral sites and jump frequencies at low temperatures
M. Schmolz K. -P. Döring K. Fürderer M. Gladisch N. Haas D. Herlach G. Majer J. Rosenkranz W. Schäfer L. Schimmele W. Schwarz A. Seeger E. Yagi 《Hyperfine Interactions》1986,31(1-4):199-204
On polycrystalline and monocrystalline iron muon-spin precession frequencies and transverse relaxation rates have been measured
down to 0.5 K. In the polycrystalline sample two distinct precession frequencies were observed at and below 1.4 K. They are
attributed to the different dipolar fields at magnetically inequivalent tetrahedral interstices seen by muons moving locally
around impurities. By contrast, in monocrystalline iron we observed only one precession frequency in monocrystalline iron
with a damping rate which increased with decreasing temperature down to 0.5 K. We attribute the difference between the monocrystalline
and the polycrystalline sample to different impurity contents. The single-crystal data are discussed in terms of μ+ diffusion by hopping between interstitial sites of tetragonal symmetry. The answer to several open questions is expected
from an extension of the measurements to lower temperatures. 相似文献
134.
135.
Tóth GK Holly S Majer Z Hollósi M Rajnavölgyi E Laczkó I 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(1):215-223
Circular dichroism and Fourier-transform infrared spectroscopies were used to compare the conformational mobility of 13-mer peptides covering the 317-329 region of the envelope protein hemagglutinin of human influenza A virus subtypes H1, H2 and H3 with that of their truncated deca- and nonapeptide analogs. These peptides were demonstrated to bind to the murine I-Ed major histocompatibility complex encoded class II and human HLA-B*2705 class I molecules. Despite the amino acid substitutions in the three 13-mer subtype sequences, no significant differences in the conformational properties could be shown. Deletion of the N-terminal three residues resulted in a shift to an increased alpha-helical conformer population in the 317-329 H1 peptide and the breakage of the 3(10) or weakly H-bonded (nascent) alpha-helix in the H2 and H3 peptides. The conformational change observed upon deletion did not influence the efficiency of I-Ed peptide interaction, however, the C-terminal Arg had a beneficial effect both on MHC class II and class I binding without causing any remarkable change in solution conformation. 相似文献
136.
137.
H Pledger JR. G.-S. Wu T. S. Young T. E. Hogen-esch G. B. Butler 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):1297-1307
Graft copolymers of acrylamide and yellow dextrin were prepared using cerium(IV) as initiator. The yellow dextrin had a very broad molecular weight distribution but was fractionated utilizing dialysis and ultrafiltration membranes. Initiator efficiencies were determined using size exclusion chromatography and were found to be between 2.4 and 34%. Initiator efficiency increased with acrylamide concentration at constant cerium (IV) and yellow dextrin concentrations, and decreased with increasing cerium(IV) concentration at constant acrylamide and yellow dextrin concentrations. Plots of acrylamide conversion and intrinsic viscosity vs initial acrylamide concentration at constant yellow dextrin and ceric ion concentrations showed a maximum at about 2.0 M. 相似文献
138.
The novel monomer, π-(2, 4-hexadiene- l-yl acrylate) tricarbonyliron (HATI), has been prepared by two routes. It was homopolymerized and copolymerized with acrylonitrile, vinyl acetate, styrene, and methyl acrylate in benzene solutions. In all cases azobisisobutyronitrile was the initiator. The relative reactivity ratios, where HATI is defined as M1, were determined: r1 = 0.34, r2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = 0.74, M2 = acrylonitrile; r1 = 2.0, r2 = 0.05, M2 = vinyl acetate; r1 = 0.26, r2 = 1.81, M2 = styrene; and r1 = 0.30, r2 = 0.74, M2 = methyl acrylate. The homo-and copolymers had high values of Tg. When polymerizations are carried out at high concentrations, a very high molecular weight tail is observed in HATI hompolymerizations and in HATI-methyl acrylate copolymerizations. The polymers were characterized by IR, gel permeation chromatography, viscosity, and differential scanning calorimetry studies. Finally, thermal decompositions carried out in air resulted in decomposition of the Fe(CO)3 group, producing Fe2O3 as a fine powder. Thermal decomposition under nitrogen (in solution and on solids ground into KBr pellets) resulted in slow destruction of the Fe(CO)3 groups but the resulting polymer mass was insoluble, and the question of what form the iron exists in (Fe metal, oxides, carbides, etc.) has not been answered. 相似文献
139.
Mixtures of methane and olefins (ethylene, propylene, butenes, butadiene, and styrene) have been polymerized over HSO3 F-SbF3 to yield an oily oligomer with a molecular weight ranging from 100 to 700. The NMR spectra of each polymer showed a sharp peak at or near 1.25 &, suggesting the presence of block methylene in the polymer. The formation of block methylene is surprising considering the fact that the polymerization reaction is carbonium ion in nature. A primary cation has been invoked to explain the results. The formation of this primary cation must involve some extraordinary stabilization by some component in the acid. 相似文献
140.
G.W. SWENSON JR 《Journal of sound and vibration》2002,255(3):519-529
A directional microphone system for field recording of sounds in the air often involves a parabolic reflector to focus the sound waves on the microphone (transducer) element. Some deficiencies of such a system are noted with respect to reproduction of spectra. The reflector system, involving as it does a structure comparable to a wavelength in linear dimension, is not susceptible to traditional high- or low-frequency approximate methods of computation. Modern numerical techniques now permit precise calculation of the directional responses of small reflectors of various shapes. One result is a proposal for a very economical and effective system involving a plane reflector. Other baffle shapes are also investigated, which may be of interest in special applications. 相似文献