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T.-C. Chung Y. Schlesinger S. Etemad A. G. Macdiarmid A. J. Heeger 《Journal of Polymer Science.Polymer Physics》1984,22(7):1239-1246
The results of measurements of the optical absorption spectra, IR absorption spectra, thermogravimetric analysis, and elementary analysis of pyrolyzed polyacrilonitrile are presented as a function of the pyrolysis temperature Tp and of the duration of pyrolysis. At Tp ~ 200°C, an intermediate phase was discovered, containing conjugated CN sequences and a completely unreacted carbon backbone. The optical absorption data imply that the resulting polymer is a semiconductor with a delocalized π-electron system and an energy gap Eg ? 2.5 eV. For Tp > 260°C, the weight loss rapidly increases, and the absorption edge gradually broadens and shifts to lower energies. The resulting polymer (after higher-temperature pyrolysis) contains CN and C?C? C conjugation sequences, but appears to be a complex structure consisting of a mixture of different chemical species. 相似文献
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Some nitrogen screening constants and their anisotropies are calculated within the CNDO/S level of approximation. Satisfactory agreement is found with available experimental data in most cases. In general the reported results are in closer agreement with experiment than are those found from ab initio calculations. The calculated data for the isoelectronic molecules N2O and CH2N2 would be in better agreement with experiment if the assignments of the two nitrogen nuclei were reversed in both cases. A reasonable correlation is obtained with some observed nitrogen chemical shifts. Contributions arising from electronic transitions are reported for N2, HCN, CH3CN, CH3NC, NO2+ and NO2?. 相似文献
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X‐ray absorption near‐edge structure (XANES) spectroscopy was used to examine the oxidation state of Zn, Fe and Cu in 22 normal and 23 tumour regions spread over 30 formalin‐fixed, paraffin‐embedded tissue samples of human primary invasive breast cancer. A micro‐mapping analysis of the metal distribution in the tissue was performed prior to the XANES analysis to identify and localise the metals in the tumour and normal tissue regions. The aim of this study was to identify the oxidation state of Zn, Fe and Cu in normal and tumour tissues of the breast, in order to correlate the oxidation state of these elements with the carcinogenesis process. The position of the Zn K‐edge in normal and tumour tissues suggests that Zn exists in a bounded form. The shape of the Cu K‐edge XANES spectra and the first derivative spectra of normal and tumour tissues shows that a significant portion of the total copper is present as Cu (I). Nevertheless, the position of the edges in the normal and tumour tissue spectra does not exclude the presence of Cu (II). The shape and position of both normal and tumour regions of the tissue suggest that they contain mixtures of Fe (II) and Fe (III) ions with a significant fraction being Fe (III). However, normal tissue regions were found to have a higher fraction of Fe (II) compared to the tumour tissues. In order to estimate the best target for therapy, more information is required about the relative abundance of Zn, Fe and Cu binding proteins, their oxidation state and their localisation at the subcellular level. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Experimental measurements were carried out on the boiling heat transfer characteristics of γ-Al2O3/water and SnO2/water Newtonian nanofluids. Nanofluids are liquid suspensions containing nanoparticles with sizes smaller than 100 nm. In
this research, suspensions with different concentrations of γ-Al2O3 and SnO2 nanoparticles in water were studied under nucleate pool boiling heat transfer conditions. Results show that nanofluids possess
noticeably higher boiling heat transfer coefficients than the base fluid. The boiling heat transfer coefficients depend on
the type and concentration of nanoparticles. 相似文献
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Zahra JA el-Abadelah MM Nazer MZ Ebraheem KA Boese R 《Organic & biomolecular chemistry》2003,1(10):1798-1801
The tautomerism of 4-methyldihydro-1,3,4-benzotriazepin-5-ones (2,3) is re-investigated by means of X-ray diffraction and quantum chemical calculations. The data revealed that the model compound (2a) exists in the amidrazone 1,4-dihydro tautomeric form (A), but not in the alternate 3,4-dihydro tautomer (B) as was previously reported. 相似文献