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1.
The copolymerization of methyl methacrylate and methacrylic acid in isopropyl alcohol is studied by kinetic, dynamic laser scattering and 13C-NMR methods. Correlations are established between the dependence of the copolymerization rate, the apparent average molecular weight, the diffusion coefficients and the configurational triad composition on the monomer feed. These correlations and the fact that both copolymerization constants are smaller than unity (rMMA = 0.63 ± 0.03; rMA = 0.25 ± 0.05) are in good agreement with the assumption that a comonomer complex takes part in the propagation reaction. A new Markov chain method for the estimation of the configurational triad mole fraction which accounts for the complex participation in a macromolecule formation is developed. Qualitative criteria for evidence the participation of the comonomer complex in copolymerization are proposed using experimental and terminal model calculated mole fractions of the compositional triads and diads. 相似文献
2.
In the present paper the problems of existence and uniqueness of almost periodic solutions for impulsive cellular neural networks with delay are considered. 相似文献
3.
New substrates and reaction conditions which may be expected to yield phenyl cation intermediates have been investigated. The approaches used were: (a) solvolysis of PhX in fluorinated alcohols, where X = ? N (O) = NOTs (tosyloxyazoxy), ? N (O) = NONf (Nf = C4F9SO) and ? OSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document} (CH3)3ōTf (Tf=CF3SO); (b) solvolysis of ArBr, PhOTf and PhOSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document}(CH3)3ōTf (phenyl ‘betylate triflate’) in super-acid solvents (FSO3H · SbF5, SbF5, AgSbF6). Analysis of the product mixtures provided no evidence for the intermediacy of phenyl cations as a major pathway in any of the reactions. This result is remarkable, since the ‘betylate’, for example, is a better leaving group by a factor of at least 105 than the ‘super’ leaving group triflate in the solvolysis of alkyl sulfonates. These results are a further indication of the extremely low stability of phenyl cations, as well as of the very special properties of the nitrogen leaving group in arenediazonium ions. 相似文献
4.
The barycentric method has been applied to determining the thermodynamic potential (the free energy) of a liquid rarefied monodisperse colloid system in which free unstationary diffusion under constant external conditions has been accomplished. Free energy at an arbitrary moment of time has been obtained as a function of horizontal mass center shift toward the cuvette cavity geometrical center of the liquid disperse system investigated. A very good coincidence between the numerical results from the proposed barycentric method and another classical thermodynamic method has been observed. 相似文献
5.
The nonlinear, nonnegative single‐mixture blind source separation problem consists of decomposing observed nonlinearly mixed multicomponent signal into nonnegative dependent component (source) signals. The problem is difficult and is a special case of the underdetermined blind source separation problem. However, it is practically relevant for the contemporary metabolic profiling of biological samples when only one sample is available for acquiring mass spectra; afterwards, the pure components are extracted. Herein, we present a method for the blind separation of nonnegative dependent sources from a single, nonlinear mixture. First, an explicit feature map is used to map a single mixture into a pseudo multi‐mixture. Second, an empirical kernel map is used for implicit mapping of a pseudo multi‐mixture into a high‐dimensional reproducible kernel Hilbert space. Under sparse probabilistic conditions that were previously imposed on sources, the single‐mixture nonlinear problem is converted into an equivalent linear, multiple‐mixture problem that consists of the original sources and their higher‐order monomials. These monomials are suppressed by robust principal component analysis and hard, soft, and trimmed thresholding. Sparseness‐constrained nonnegative matrix factorizations in reproducible kernel Hilbert space yield sets of separated components. Afterwards, separated components are annotated with the pure components from the library using the maximal correlation criterion. The proposed method is depicted with a numerical example that is related to the extraction of eight dependent components from one nonlinear mixture. The method is further demonstrated on three nonlinear chemical reactions of peptide synthesis in which 25, 19, and 28 dependent analytes are extracted from one nonlinear mixture mass spectra. The goal application of the proposed method is, in combination with other separation techniques, mass spectrometry‐based non‐targeted metabolic profiling, such as biomarker identification studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
Daniela Nedeltcheva Vanya Kurteva Ivanka Topalova 《Rapid communications in mass spectrometry : RCM》2010,24(6):714-720
The tautomeric constants of a series of azo dyes were estimated in the gas phase by using electron ionization mass spectrometry. It was shown that the relative amount of the keto tautomer increases from 4‐phenylazo‐1‐phenol to 4‐phenylazo‐anthracen‐1‐ol, thus confirming the quantum‐chemical predictions. The existence of the enol tautomer of 4‐phenylazo‐anthracen‐1‐ol is shown for the first time by mass spectrometry in the gas phase. This finding is supported by flash photolysis measurements in solution. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
8.
Quantitative determination of Closantel residues in milk by high-performance liquid chromatography with fluorescence detection. 总被引:1,自引:0,他引:1
A HPLC method with fluorescence detection for quantitative determination of Closantel residues in milk has been developed and validated. The proposed cleaning procedure with acetonitrile and acetone extraction, and solid-phase clean-up with Florisil enables concentrations of Closantel below 50 micrograms/l to be determined. The method was shown to be sufficient, precise, accurate, selective and rugged. The method was applied in the regular monitoring of Closantel residues in milk and of the pharmacokinetic behavior of Closantel in sheep. 相似文献
9.
Ivanka Antovic Nevenka M. Antovic 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(1):31-37
226Ra activity concentration in the mullet (Mugilidae) species Mugil cephalus whole individuals, and some organs (gills, gastrointestinal system, fins, muscle and bones), was measured by the γ-coincidence
spectrometer PRIPYAT-2M. 226Ra transfer parameters [concentration factors (CFs)] from seawater, sediment and mud with detritus to fish tissues, and annual
intake by humans consuming this fish species, have been estimated. Minimum detected radium activity concentration in whole
M. cephalus individuals was found to be 0.89 ± 0.42 to 3.09 ± 0.41 Bq kg−1, with arithmetic mean of 1.65 ± 0.39 Bq kg−1. An average concentration in muscles is found to be 2.28 ± 0.84 Bq kg−1, in gills—5.02 ± 1.85 Bq kg−1, in gastrointestinal system—12.88 ± 1.71 Bq kg−1, and in bones—14.72 ± 3.75 Bq kg−1. No one fins showed radium activity above minimum detectable one. Annual intake of 226Ra by human consumers of this fish species is estimated to provide an effective dose of 0.006 mSv year−1. CFs for 226Ra indicating transfer from seawater to whole individuals ranged from 8.9 to 30.9, and those indicating transfer from the
sediment and mud with detritus—from 0.11 to 0.39 and from 0.08 to 0.3, respectively. The seawater to bones CFs varied from
97.9 to 197.3, to gastrointestinal system—from 59 to 178.8, to gills—from 22.5 to 68.3, to muscles—from 17 to 30.8. 相似文献
10.
L. M. Kovachev L. I. Pavlov L. M. Ivanov D. Y. Dakova 《Journal of Russian Laser Research》2006,27(3):185-203
We have investigated the evolution of picosecond and femtosecond optical pulses governed by the amplitude vector equation
in the optical and UV domains. We have written this equation in different coordinate frames, namely, in the laboratory frame,
the Galilean frame, and the moving-in-time frame and have normalized it for the cases of different and equal transverse and
longitudinal sizes of optical pulses or modulated optical waves. For optical pulses with a small transverse size and a large
longitudinal size (optical filaments), we obtain the well-known paraxial approximation in all the coordinate frames, while
for optical pulses with relatively equal transverse and longitudinal sizes (so-called light bullets), we obtain new non-paraxial
nonlinear amplitude equations. In the case of optical fields with low intensity, we have reduced the nonlinear amplitude vector
equations governing the light-bullet evolution to the linear amplitude equations. We have solved the linear equations using
the method of Fourier transform. An unexpected new result is the relative stability of light bullets and the significant decrease
in the diffraction enlargement of light bullets with respect to the case of long pulses in the linear propagation regime. 相似文献