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31.
Elim HI Cai B Sugihara O Kaino T Adschiri T 《Physical chemistry chemical physics : PCCP》2011,13(10):4470-4475
We have experimentally carried out a Rayleigh scattering study of a high refractive index TiO(2) nanohybrid polymer. By employing the Rayleigh scattering technique with at least three different wavelengths, we can obtain the Rayleigh ratio of the TiO(2) nanohybrid polymer at each utilized wavelength. These measured Rayleigh ratios are then used to estimate the size of the nanoparticle and determine the number of nanoparticles per unit volume or particle density. Furthermore, this technique can be used to evaluate the dominant size of nanoparticles in the nanohybrid polymer mainly contributed to Rayleigh scattering. 相似文献
32.
Bruyneel C Chandra AK Uchimaru T Zeegers-Huyskens T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(3):591-602
The energies, vibrational frequencies and IR intensities of cis- and trans-N-acetyl-L-alanine (NAAL) are computed using the density functional theory (B3LYP) combined with the 6-311G(d, p) basis set. The trans conformer is characterized by an intramolecular NH ... O hydrogen bond leading to the formation of a five-membered ring and is by 23 kJ mol(-1) more stable than the cis conformer. The difference between the vibrational frequencies and IR intensities computed for the two conformers is discussed. The IR spectra at different temperatures and the Raman spectra of solid NAAL and its deuterated counterpart are investigated and discussed. The frequencies of the v(OH) vibration and the isotopic ratio suggest the formation of short OH ... O hydrogen bonds in the solid state. The NH group seems also to be involved in a weak hydrogen bond. 相似文献
33.
Bin Wen Seiichi Takami Yoshiyuki Kawazoe Tadafumi Adschiri 《Journal of Physics and Chemistry of Solids》2012,73(11):1264-1267
The mechanical stabilities of K4 carbon and K4-like NaC2 have been studied by performing first-principle calculations. Total energies as functions of isotropic deformations and volume-conserving tetragonal and trigonal deformations have been calculated. For K4 carbon, the total energy shows a minimum for isotropic and trigonal deformations, but exhibits maxima for tetragonal deformation. In contrast, the total energy of K4-like NaC2 shows a minimum under all three deformations. These results indicate that K4 carbon is not a metastable phase, but that K4-like NaC2 is a metastable phase. In addition, the heat of formation of K4-like NaC2 is discussed. 相似文献
34.
Zbignew Pawelka Asit K Chandra Tadafumi Uchimaru Thérèse Zeegers-Huyskens 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(1):17-31
The conformation and vibrational properties of 2-methoxy-1,2-diphenylethanone (MDPE) are investigated in the gas phase and in organic solvents. Ab initio calculations carried out at the B3LYP/6-31G(d) level demonstrate that three stable conformers having cisoid, skewed and transoid structures are present in the gas phase. In the gas phase, the conformers are separated by a low energy barrier and their relative energies do not differ by more than 7.2 kJ mol (-1) Like in crystalline MDPE 'Acta Crystallogr. Sect. C 44 (1988) 894', weak CH...O hydrogen bonds are present in the cisoid conformation. The IR and Raman spectra of solid MDPE are discussed. Several vibrational modes are split in organic solvents. A comparison between the theoretical data and the experimental dipole moments indicates that two conformers are present in solution, the population of the cisoid form increasing with the permittivity of the medium. 相似文献
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37.
Rate constants for the gas‐phase reactions of CH3OCH2CF3 (k1), CH3OCH3 (k2), CH3OCH2CH3 (k3), and CH3CH2OCH2CH3 (k4) with NO3 radicals were determined by means of a relative rate method at 298 K. NO3 radicals were prepared by thermal decomposition of N2O5 in a 700–750 Torr N2O5/NO2/NO3/air gas mixture in a 1‐m3 temperature‐controlled chamber. The measured rate constants at 298 K were k1 = (5.3 ± 0.9) × 10?18, k2 = (1.07 ± 0.10) × 10?16, k3 = (7.81 ± 0.36) × 10?16, and k4 = (2.80 ± 0.10) × 10?15 cm3 molecule?1 s?1. Potential energy surfaces for the NO3 radical reactions were computationally explored, and the rate constants of k1–k5 were calculated according to the transition state theory. The calculated values of rate constants k1–k4 were in reasonable agreement with the experimentally determined values. The calculated value of k5 was compared with the estimate (k5 < 5.3 × 10?21 cm3 molecule?1 s?1) derived from the correlation between the rate constants for reactions with NO3 radicals (k1–k4) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH3OCH2CF3 and CHF2CF2OCH2CF3 to be 240 and >2.4 × 105 years, respectively, with respect to reaction with NO3 radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009 相似文献
38.
Dieter Seebach Ryan Gilmour Uro Groelj Gildas Deniau Christof Sparr Marc‐Olivier Ebert AlbertK. Beck LynneB. McCusker Dubravka iak Tadafumi Uchimaru 《Helvetica chimica acta》2010,93(4):603-634
The structures of iminium salts formed from diarylprolinol or imidazolidinone derivatives and α,β‐unsaturated aldehydes have been studied by X‐ray powder diffraction (Fig. 1), single‐crystal X‐ray analyses (Table 1), NMR spectroscopy (Tables 2 and 3, Figs. 2–7), and DFT calculations (Helv. Chim. Acta 2009 , 92, 1, 1225, 2010 , 93, 1; Angew. Chem., Int. Ed. 2009 , 48, 3065). Almost all iminium salts of this type exist in solution as diastereoisomeric mixtures with (E)‐ and (Z)‐configured +NC bond geometries. In this study, (E)/(Z) ratios ranging from 88 : 12 up to 98 : 2 (Tables 2 and 3) and (E)/(Z) interconversions (Figs. 2–7) were observed. Furthermore, the relative rates, at which the (E)‐ and (Z)‐isomers are formed from ammonium salts and α,β‐unsaturated aldehydes, were found to differ from the (E)/(Z) equilibrium ratio in at least two cases (Figs. 4 and 5, a, and Fig. 6, a); more (Z)‐isomer is formed kinetically than corresponding to its equilibrium fraction. Given that the enantiomeric product ratios observed in reactions mediated by organocatalysts of this type are often ≥99 : 1, the (E)‐iminium‐ion intermediates are proposed to react with nucleophiles faster than the (Z)‐isomers (Scheme 5 and Fig. 8). Possible reasons for the higher reactivity of (E)‐iminium ions (Figs. 8 and 9) and for the kinetic preference of (Z)‐iminium‐ion formation are discussed (Scheme 4). The results of related density functional theory (DFT) calculations are also reported (Figs. 10–13 and Table 4). 相似文献
39.
Dr. Hayato Ishikawa Takaki Suzuki Dr. Hideo Orita Dr. Tadafumi Uchimaru Prof. Dr. Yujiro Hayashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(42):12616-12626
The efficient asymmetric total synthesis of (?)‐oseltamivir, an antiviral reagent, has been accomplished by using two “one‐pot” reaction sequences, with excellent overall yield (60 %) and only one required purification by column chromatography. The first one‐pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/Horner–Wadsworth–Emmons reaction combined with retro‐aldol/Horner–Wadsworth–Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base‐catalyzed isomerization. Six reactions can be successfully conducted in the second one‐pot reaction sequence; these are deprotection of a tert‐butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column‐free synthesis of (?)‐oseltamivir has also been established. 相似文献
40.
Rate constants for the reactions of OH and NO3 radicals with CH2?CHF (k1 and k4), CH2?CF2 (k2 and k5), and CHF?CF2 (k3 and k6) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k1 = (1.20 ± 0.37) × 10?12 exp[(410 ± 90)/T], k2 = (1.51 ± 0.37) × 10?12 exp[(190 ± 70)/T], and k3 = (2.53 ± 0.60) × 10?12 exp[(340 ± 70)/T] cm3 molecule?1 s?1. The rate constants for NO3 radical reactions at 298 K were k4 = (1.78 ± 0.12) × 10?16 (CH2?CHF), k5 = (1.23 ± 0.02) × 10?16 (CH2?CF2), and k6 = (1.86 ± 0.09) × 10?16 (CHF?CF2) cm3 molecule?1 s?1. The rate constants for O3 reactions with CH2?CHF (k7), CH2?CF2 (k8), and CHF?CF2 (k9) were determined by means of an absolute rate method: k7 = (1.52 ± 0.22) × 10?15 exp[?(2280 ± 40)/T], k8 = (4.91 ± 2.30) × 10?16 exp[?(3360 ± 130)/T], and k9 = (5.70 ± 4.04) × 10?16 exp[?(2580 ± 200)/T] cm3 molecule?1 s?1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH2?CHF, CH2?CF2, and CHF?CF2 with respect to reaction with OH radicals, NO3 radicals, and O3 were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010 相似文献