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71.
The small organic molecule electro-oxidation (OMEO) and the hydrogen evolution (HER) are two important half-reactions in direct liquid fuel cells (DLFCs) and wa... 相似文献
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Ricardo Amorim 《General Relativity and Gravitation》1985,17(6):525-533
A consistent set of equations of motion for classical charged particles with spin and magnetic dipole moment in a Riemann-Cartan space-time is generated from a constrained Lagrangian formalism. The equations avoid the spurious free helicoidal solutions and at the same time conserve the canonical condition of normalization of the 4-velocity. The 4-velocity and the mechanical moment are parallel in this theory, where the condition of orthogonality between spin and 4-velocity is treated as a nonholonomic constraint. A generalized BMT precession equation is obtained as one of the results of the formalism. 相似文献
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Lima CS De Amorim EL Nascimento SC De Araújo CF Agra MF Barbosa-Filho JM Silva MS Da-Cunha EV Vieira IJ Braz-Filho R 《Natural product research》2005,19(3):217-222
Three new pyranonaphthoquinones: 5-hydroxy-6-methoxy-alpha-lapachone, 5,6-dihydroxy-a-lapachone and 4',5-dihydroxy-6-methoxy-alpha-lapachone, and two known compounds: lapachol and 5,5'-dihydroxy-3',4',7-trimethoxyflavanone, were isolated from the stem bark of Melloa quadrivalvis. Their structures were established by spectrometric data, mainly 1D- and 2D-NMR and mass spectra. The methylazoetetrazolium (MTT) method using viable cells of the strain Hep2 and the strain NCIH-292 demonstrated cytotoxic activity. The CI50 was also calculated. The chloroform extract and 5-hydroxy-6-methoxy-alpha-lapachone inhibited cell growth. 相似文献
77.
E. A. N. Fernandes N. Nepomuceno A. B. Trevizam H. V. Amorim 《Journal of Radioanalytical and Nuclear Chemistry》1998,236(1-2):113-119
A chemical and radiochemical neutron activation analysis (CNAA/RNAA) method has been developed for the determination of three
calcium isotopes (48Ca,46Ca, and44Ca) in a single sample derived from urine. This method was developed in support of clinical research using a dual enriched
stable isotope methodology to study bone mineralization in premature infants, juvenile rheumatoid arthritics, and cystic fibrosis.
In these studies, one enriched isotope of calcium is administered orally, and one is administered intravenously. By making
determinations of three isotopes (two enriched, one unenriched) within the same sample, the perturbation from natural isotopic
ratios can be determined and used to calculate true absorption of calcium. In our method,48Ca is determined via the48Ca(n,γ)49Ca reaction and 3084 keV gamma-ray,46Ca via the46Ca(n,γ)47Ca reaction and 1296 keV gamma-ray, and44Ca via the44Ca(n,γ)45Ca reaction and 256 keV (max) beta-particle. A pair of chemical separation steps are employed to separate calcium from urine
as calcium oxalate with a yield in the range of 80–90%, and a radiochemical step is employed prior to the measurement of45Ca to remove interfering radionuclides. 相似文献
78.
In the present paper, a simultaneous pre-concentration procedure for the sequential determination of cadmium and lead in table salt samples using flame atomic absorption spectrometry is proposed. This method is based on the liquid-liquid extraction of cadmium(II) and lead(II) ions as dithizone complexes and direct aspiration of the organic phase for the spectrometer. The sequential determination of cadmium and lead is possible using a computer program. The optimization step was performed by a two-level fractional factorial design involving the variables: pH, dithizone mass, shaking time after addition of dithizone and shaking time after addition of solvent. In the studied levels these variables are not significant. The experimental conditions established propose a sample volume of 250 mL and the extraction process using 4.0 mL of methyl isobutyl ketone. This way, the procedure allows determination of cadmium and lead in table salt samples with a pre-concentration factor higher than 80, and detection limits of 0.3 ng g−1 for cadmium and 4.2 ng g−1 for lead. The precision expressed as relative standard deviation (n = 10) were 5.6 and 2.6% for cadmium concentration of 2 and 20 ng g−1, respectively, and of 3.2 and 1.1% for lead concentration of 20 and 200 ng g−1, respectively. Recoveries of cadmium and lead in several samples, measured by standard addition technique, proved also that this procedure is not affected by the matrix and can be applied satisfactorily for the determination of cadmium and lead in saline samples. The method was applied for the evaluation of the concentration of cadmium and lead in table salt samples consumed in Salvador City, Bahia, Brazil. 相似文献
79.
Luis Amorim Dolores Díaz Jesús Jiménez-Barbero Yves Blériot 《Tetrahedron letters》2006,47(50):8887-8891
The synthesis of a β-d-mannopyranoside analog, fully identical to the naturally occurring d-mannopyranose in terms of hydroxyl pattern, and displaying a skew-boat conformation close to a B2,5 boat strongly believed to be adopted by the oxycarbenium transition state during glycosidic bond cleavage of β-mannane by family 26 β-mannanase, is described. The conformationally locked analog has been obtained by tethering the C-2 and C-5 carbon atoms of the sugar ring with a three carbon bridge using RCM methodology. Conformation of the mannose analog has been confirmed by NMR and molecular modelling. 相似文献
80.
Castro AL Madeira PJ Nunes MR Costa FM Florêncio MH 《Rapid communications in mass spectrometry : RCM》2008,22(23):3761-3766
The use of inorganic species as assisting materials in matrix-assisted laser desorption/ionization (MALDI) analysis is an alternative approach to avoid interfering matrix ions in the low-mass region of the mass spectra. Reports of the application of inorganic species as matrices in MALDI analysis of small molecules are, however, scarce. Nevertheless, titanium dioxide (TiO(2)) powder has been reported to be a promising matrix medium. In this study we further explore the use of TiO(2) as a matrix for the MALDI analysis of low molecular weight compounds. We present results showing that nanosized TiO(2) anatase and TiO(2) rutile perform better as MALDI matrices than a commercial TiO(2) anatase/rutile mixture. Moreover, when using nanosized TiO(2) anatase as a matrix, high-quality mass spectra can be obtained with strong analyte signals and weak or non-existing matrix interference ions. Furthermore, our results show that the phase type plays an important role in the application of TiO(2) as a MALDI matrix. 相似文献