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41.
L L Elliott S Connors E Kille S Levin K Ball D Katz 《The Journal of the Acoustical Society of America》1979,66(1):12-21
A four-alternative, forced choice adaptive procedure was used to measure the lowest intensity at which children could identify monosyllabic nouns that had been standardized to be understandable (at comfortable listening levels) to inner city, 3-year-old children. Results showed no age-related performance changes when the words were presented against a 12-talker babble or against filtered noise. In quit, however, performance improved between the ages of 5 and 10 years. Performance of children with learning problems was poorer than performance of children achieving normal school progress, even though clinical measures of auditory sensitivity showed no differences. Results are discussed in terms of "semantic closure" skills of children. 相似文献
42.
The kinetics of decarboxylative dechlorination of N-chloroalanine were studied at 25° in aqueous HCl solutions covering the pH range 1.4 to 2.8. These data were compared with literature results, and were interpreted in terms of first-order reactions of the cationic, uncharged, and anionic forms of the reactant. Pressure effect studies on the reaction of the anionic species yielded a volume of activation estimate of + 50 ± 3 cm3 mol−1. This result is consistent with a concerted fragmentation process. © 1996 John Wiley & Sons, Inc. 相似文献
43.
Yen Wei Edward J. Connors Xinru Jia Ce Wang 《Journal of polymer science. Part A, Polymer chemistry》1998,36(5):761-771
Free radical ring-opening polymerization of 2-methylene-1,3-dioxepane (MDP) in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) has been achieved to afford a chain polyester (PMDP) with di-t-butyl peroxide (DTBP) as an initiator at 125°C. The polydispersity of the polymers decreases as the concentration of TEMPO is increased. At high TEMPO concentrations, the polydispersity as low as 1.2 was obtained, which is below the theoretical lower limit for a conventional free radical polymerization. A linear relationship between the number-average molecular weight (Mn) and the monomer conversion was observed with the best-fit line passing very close to the origin of the Mn-conversion plot. The isolated and purified TEMPO-capped PMDP polymers have been employed to prepare chain extended polymers upon addition of more MDP monomer. These results are suggestive of the “living” polymerization process. A possible polymerization mechanism might involve thermal homolysis of the TEMPO-PMDP bonds followed by the addition of the monomers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 761–771, 1998 相似文献
44.
Spectroscopic properties for a series of 2,5-diarylidenecyclopentanones in weak and strong acid environments are reported. Electronic absorption and fluorescence spectra have been measured for the all-E configurations of 2,5-dibenzylidenecyclopentanone (1), 2,5-bis(3-phenylallylidene)cyclopentanone (2), and 2,5-bis(5-phenylpenta-2,4-dienylidene)cyclopentanone (3) in acetic acid and sulfuric acid solutions. The spectroscopic evidence indicates that in 96% sulfuric acid 1, 2, and 3 are protonated both in the ground state and on the S1 potential energy surface. This assignment is supported by Zerner's intermediate neglect of differential overlap (ZINDO) and time-dependent density functional theory (TD-DFT) calculations. In glacial acetic acid, 1, 2, and 3 are unprotonated in the ground state. The absence of observable fluorescence from 1 in glacial acetic acid indicates that S1 is npi, whereas the observation of fluorescence from 2 and 3 in acetic acid is consistent with S1 being pipi. A combination of spectroscopic data, molecular orbital calculations, and fluorescence lifetime measurements indicate that 2 and 3 undergo intermolecular excited-state proton transfer in glacial acetic acid and diluted sulfuric acid solutions. Photochemical studies reveal that, unlike its behavior in organic solvents, 1 does not undergo efficient E,E --> E,Z photoisomerization in 96% sulfuric acid. 相似文献
45.
The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using
the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative
morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted
for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating
the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated
by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the
observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc
tris(thiourea) ions and sulphate ions. 相似文献
46.
47.
Based on an emission study of xanthone at ≈2 and 77°K it is concluded that the “dual” phosphorescence at 77°K in a 3-methylpentane glass matrix is due to emission from two n, triplet states of xanthone. The two triplet states and their respective ground states are distinguished by their different molecular geometries. 相似文献
48.
Richard H. Clarke Robert E. Connors Harry A. Frank Jeffrey C. Hoch 《Chemical physics letters》1977,45(3):523-528
Properties expected of the triplet state of a pair of interacting pigment molecules in photosynthetic systems are described in terms of the triplet state properties of the monomer pigment. The triplet state zero-field splittings and intersystem crossing rate constants measured in isolated chlorophylls and the same properties measured in vivo are utilized to elucidate the geometry of the eraction center in photosynthetic systems. 相似文献
49.
[structure: see text]. Reported here is the synthesis of oligonucleotides containing a 2'-acylamido-2'-deoxyuridine residue at their 3'-terminus. Compared to control sequences bearing a thymidine residue, the quinolone-capped duplexes give higher UV melting points. In the case of (5'-ACGCGU-NA-2')2, where NA denotes a nalidixic acid residue, the melting point increase is up to 22 degrees C over that of (ACGCGT)2. 相似文献
50.