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201.
The binding of 7-aminocoumarins, substituted in the 3-position with heterocyclic benzimidazole or benzothiazole groups by domain-forming polymers in water has been studied. The acrylic polyelectrolyte, poly(methacrylic) acid (PMAA) was used as a solubilizing agent for coumarin dyes 6, 7, and 30 in water. The acid-base properties of these bound coumarin dyes were monitored spectroscopically on titration of aqueous solutions. Alterations in the fluorescence wavelength and intensity, quantum yields, lifetimes, and polarization are consistent with the preferential binding of the dyes in compact hydrophobic domains that form at a pH regime in which the polymer is in its protonated (uncharged) state. In this pH range (<4.0), coumarins 7 and 30 are bound as monocations, whereas coumarin 6 remains in its neutral form. Reduced quantum yields and lifetimes of fluorescence for cationic coumarins can be understood in terms of the imposition of a low-lying electron transfer state, an example of a twisted intramolecular charge transfer (TICT) intermediate. Effects of polymer microenvironment on the rate of TICT state decay (a reverse electron transfer) are observed. Coumarins of the azole type may find use as fluoroprobes of the microenvironments of proteins and other biological macromolecules and as agents for pH sensing. 相似文献
202.
Sergio A. Jimenez‐Lam Zenaido Martinez‐Ramirez Iván A. Santos‐López Prof. Brent E. Handy Prof. María G. Cárdenas‐Galindo Prof. Juan C. Fierro‐Gonzalez 《Chemphyschem》2012,13(18):4173-4179
Iron oxide‐supported gold samples were prepared by co‐precipitation from HAuCl4 and Fe(NO3)3. The activities of the samples as CO oxidation catalysts were tested without thermal treatment and following treatments in flows of He and O2 at various temperatures. It was found that the untreated samples and those treated in a flow of He at 150 °C were more active than samples that had been treated at 400 °C in either a flow of O2 or of He. Infrared spectra recorded during CO oxidation catalysis indicate the presence of bonded CO molecules to cationic gold on all samples, whereas spectra of the least active catalysts indicate a predominant presence of Fe2+ carbonyls, which were highly stable under the conditions of our experiments. Our results indicate that in the least active samples the Fe2+‐bound CO blocks sites that would otherwise be available for oxygen activation. 相似文献
203.
204.
A. Duran J. L. Perez-Rodriguez M. C. Jimenez de Haro 《Analytical and bioanalytical chemistry》2009,394(6):1671-1677
This work describes the use of a new dedicated laboratory-made micro X-ray diffraction system for detecting the phases present
in cross-sections of artworks. As an example, the phases present in samples from gilding ceramics and stone sculptures from
the heritage of Seville (Spain) were successfully detected using this new system, which takes advantage of various devices
developed for synchrotron radiation, and is complemented by the information provided by other techniques. 相似文献
205.
Carmen M. Romero Eulogio Jiménez Felipe Suárez 《The Journal of chemical thermodynamics》2009,41(4):513-516
The influence of temperature on the behavior of surface properties of aqueous solutions has often been used to obtain information about solute structural effects on water.In this work, we present experimental results for surface tension of aqueous solutions of n-pentanol, n-hexanol, n-heptanol, and n-octanol at T = (283.15, 288.15, 293.15, 298.15, 303.15, and 308.15) K at several concentrations. The results were used to evaluate the limiting experimental slopes of surface tension with respect to mole fraction and the hydrophobicity constant of the Connors model at each temperature. The thermodynamic behavior of aqueous alcohol solutions is discussed in terms of the effect of the hydrocarbon chain on water structure.The temperature dependence of the limiting slopes of surface tension with respect to mole fraction, as well as the hydrophobicity constant derived from surface measurements, is interpreted in terms of alcohol hydration. 相似文献
206.
A new series of intermolecular hydrogen-bonded complexes has been obtained using mesogenic 4- n -nonyloxybenzoic acid and mesogenic 5-(4-pyridyl)-2-(4- n -alkoxy) benzylideneamino-1,3,4-thiadiazole moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Intermolecular hydrogen bonding was studied by FTIR spectroscopy, from crystalline to the isotropic state. A study by PM3 semi-empirical calculations is also described. 相似文献
207.
L. J. Alemany M. C. Jimenez E. Pardo J. Machek S. vachula 《Reaction Kinetics and Catalysis Letters》1993,51(2):383-388
The physicochemical characterization of V–Mo–Ox/SiO2 catalysts with different contents of the active phase VMo3O11 has been carried out by means of UV-VIS DR, FT-IR and Laser Raman spectroscopy. 相似文献
208.
209.
Francisco Sanchez Maria J. Nasarre Maria M. Graciani Ragael Jimenez Maria L. Moya John Burgess Michael J. Blandamer 《Transition Metal Chemistry》1988,13(2):150-154
Summary Rate constants are reported for the oxidation by peroxodisulphate ions of octacyanomolybdate(IV) in concentrated aqueous salt solutions containing up to 6 mol dm–3 salt including mixed salt solutions. The dependence of the logarthm of rate constant on salt concentration is discussed in terms of ionic hydration enthalpies and B-viscosity coefficients. The analysis confirms that ion-pairs play a key role in determining reactivities in these systems. 相似文献
210.
Gas chromatography with electron-capture detection was used in the determination of diaminopimelic acid (as the N-heptafluorobutyryl isobutyl derivative) and 3-hydroxymyristic acid (as the O-pentafluorobenzoyl methyl derivative) in Gram-negative bacterial cells in infected human urine. Use of the column-switching (two-dimensional gas chromatography) technique greatly enhanced the selectivity of the detection and simplified the processing of samples. The system described should prove useful for trace detection of specific bacterial constituents in complex environments. 相似文献