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181.
A goal of modern biology is to understand the molecular mechanisms underlying cellular function. The ability to manipulate and analyze single cells is crucial for this task. The advent of microengineering is providing biologists with unprecedented opportunities for cell handling and investigation on a cell-by-cell basis. For this reason, lab-on-a-chip (LOC) technologies are emerging as the next revolution in tools for biological discovery. In the current discussion, we seek to summarize the state of the art for conventional technologies in use by biologists for the analysis of single, mammalian cells, and then compare LOC devices engineered for these same single-cell studies. While a review of the technical progress is included, a major goal is to present the view point of the practicing biologist and the advances that might increase adoption by these individuals. The LOC field is expanding rapidly, and we have focused on areas of broad interest to the biology community where the technology is sufficiently far advanced to contemplate near-term application in biological experimentation. Focus areas to be covered include flow cytometry, electrophoretic analysis of cell contents, fluorescent-indicator-based analyses, cells as small volume reactors, control of the cellular microenvironment, and single-cell PCR. 相似文献
182.
Gary E. Martin Russell H. Robins Phil B. Bowman Wayne K. Duholke Kathleen A. Farley Brian D. Kaluzny Jane E. Guido Sandra M. Sims Thomas J. Thamann Brian E. Thompson Toshihide Nishimura Yukimi Noro Tsutoma Tahara 《Journal of heterocyclic chemistry》1999,36(1):265-270
Parenteral formulations of linezolid (PNU-100766), a novel (S)-3-(4′-fluorophenyl)-5-N-acetamidomethyloxazolidin-2-one antibiotic, were subjected to photo-stability testing as required by ICH guidelines. Direct, reversed phase chromatographic evaluation of the photo-irradiated solutions revealed two chromatographically broad degradants. Following preparative chromatographic isolation, the structures of both degradants were determined by mass spectrometric, nmr, and vibrational spectroscopic methods. The degradant structures formed by decomposition involving photo-oxidation of the morpholine, followed by a carbon-carbon bond scission to a formyloxyethylformamide-containing degradant. Facile hydrolytic cleav age of the formate ester in acidic media gave the second chromatographically broad degradant containing a N-2-hydroxyethylformamide group. The formamide substituent underwent further hydrolysis in acidic media to the corresponding secondary amine. 相似文献
183.
Carty D Goddard A Köhler SP Sims IR Smith IW 《The journal of physical chemistry. A》2006,110(9):3101-3109
The kinetics of the reaction between O atoms and OH radicals, both in their electronic ground state, have been investigated at temperatures down to ca. 39 K. The experiments employed a CRESU (Cinétique deRéaction en Ecoulement Supersonique Uniforme) apparatus to attain low temperatures. Both reagents were created using pulsed laser photolysis at 157.6 nm of mixtures containing H2O and O2 diluted in N2 carrier gas. OH radicals were formed by both direct photolysis of H2O and the reaction between O(1D) atoms and H2O. O(3P) atoms were formed both as a direct product of O2 photolysis and by the rapid quenching of O(1D) atoms formed in that photolysis by N2 and O2. The rates of removal of OH radicals were observed by laser-induced fluorescence, and concentrations of O atoms were estimated from a knowledge of the absorption cross-section for O2 at 157.6 nm and of the measured fluence from the F2 laser at this wavelength. To obtain a best estimate of the rate constants for the O + OH reaction, we had to correct the raw experimental data for the following: (a) the decrease in the laser fluence along the jet due to the absorption by O2 in the gas mixture, (b) the increase in temperature, and consequent decrease in gas density, as a result of energy released in the photochemical and chemical processes that occurred, and (c) the formation of OH(v = 0) as a result of relaxation, particularly by O2, of OH radicals formed in levels v > 0. Once these corrections were made, the rate constant for reaction between OH and O(3P) atoms showed little variation in the temperature range of 142 to 39 K and had a value of (3.5 +/- 1.0) x 10(-11) cm3 molecule(-1) s(-1). It is recommended that this value is used in future chemical models of dense interstellar clouds. 相似文献
184.
Two fixed point theorems for uniformly lipschitzian mappings in metric spaces, due respectively to E. Lifšic and to T.-C. Lim and H.-K. Xu, are compared within the framework of the so-called CAT(0) spaces. It is shown that both results apply in this setting, and that Lifšic’s theorem gives a sharper result. Also, a new property is introduced that yields a fixed point theorem for uniformly lipschitzian mappings in a class of hyperconvex spaces, a class which includes those possessing property (P) of Lim and Xu. 相似文献
185.
Berteloite C Lara M Bergeat A Le Picard SD Dayou F Hickson KM Canosa A Naulin C Launay JM Sims IR Costes M 《Physical review letters》2010,105(20):203201
We report combined studies on the prototypical S(1D2) + H2 insertion reaction. Kinetics and crossed-beam experiments are performed in experimental conditions approaching the cold energy regime, yielding absolute rate coefficients down to 5.8 K and relative integral cross sections to collision energies as low as 0.68 meV. They are supported by quantum calculations on a potential energy surface treating long-range interactions accurately. All results are consistent and the excitation function behavior is explained in terms of the cumulative contribution of various partial waves. 相似文献
186.
We say that a quantum spin system is dynamically localized if the time-evolution of local observables satisfies a zero-velocity Lieb-Robinson bound. In terms of this definition we have the following main results: First, for general systems with short range interactions, dynamical localization implies exponential decay of ground state correlations, up to an explicit correction. Second, the dynamical localization of random xy spin chains can be reduced to dynamical localization of an effective one-particle Hamiltonian. In particular, the isotropic xy chain in random exterior magnetic field is dynamically localized. 相似文献
187.
We establish locality estimates, known as Lieb–Robinson bounds, for the Toda lattice. In contrast to harmonic models, the
Lieb–Robinson velocity for these systems do depend on the initial condition. Our results also apply to the entire Toda as
well as the Kac-van Moerbeke hierarchy. Under suitable assumptions, our methods also yield a finite velocity for certain perturbations
of these systems. 相似文献
188.
189.
I.G. Hassan H.M. Soliman G.E. Sims J.E. Kowalski 《International Journal of Multiphase Flow》1996,22(6):1123-1142
Experimental data are presented for the mass flow rate and quality of two-phase (air-water) discharge from a stratified region through two side branches (6.35 mm W.) with their parallel centrelines located in a vertical plane. These data correspond to different values of the interface level between the onset of gas entrainment at the upper branch to the onset of liquid entrainment at the lower branch for test-section pressures of 316 and 517 kPa, test-section-to-separators pressure difference ranging from 40 to 235 kPa, branch separating distance to diameter ratio ranging from 1.5 to 8 and different hydraulic resistances of the lines connecting the test section to the separators. Normalized plots are shown to be capable of absorbing the effects of some independent variables within the tested range of operating conditions. Empirical relations were developed for the prediction of the two-phase mass flow rate and quality in terms of normalized parameters. These relations represent the data with a high degree of correlation. 相似文献
190.
The effect of a microwave discharge on the rae of production of HBr in the H2/Br2 system was found to be similar to that observed for the H2/Cl2 system. The interpretation of a large vibrational enhancement on the X(=Cl, Br) + H2 reactions is in agreement with trajectory calculations for these reactions. The criteria of endothermicity and of activation energy as a measure of the role of internal excitation are examined and shown to be useful under different reaction conditions. 相似文献