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101.
102.
A successful route to prepare zeolites with controlled crystal size from the millimeter range down to nanometer scale by simulating the natural formation conditions is presented. Water is used as the solution and reaction medium at high temperatures and pressures (T=120-400°C, p=1 kbar); aluminosilicate glasses with identical chemical composition as the zeolite products are used as precursors. The synthesis of heulandite is reported as representative example. 相似文献
103.
Based on previously developed solution phase chemistry, an effective general approach to the synthesis of heparin-like oligosaccharides on a soluble polymer support is reported. 相似文献
104.
Griselda Corro M. Paz Elizalde Angeles Velasco 《Reaction Kinetics and Catalysis Letters》2002,76(1):117-122
NO oxidation was investigated over Pt-Sn/g-Al2O3. The addition of Sn to 1%Pt/g-Al2O3 enhances NO oxidation to NO2. This effect is related to the enhancement of chemisorbed oxygen on the metallic surface produced by Sn. 相似文献
105.
Javier Cataln Marta Snchez-Cabezudo Jos Luis G. De Paz Jos Elguero Robert W. Taft Frederick Anvia 《Journal of computational chemistry》1989,10(3):426-433
The annular tautomerism of 1,2,3-triazole and 3(5)-methylpyrazole is discussed by means of a combination of theoretical calculations and experimental (ICR) gas-phase basicities and acidities. In the gas phase 1,2,3-triazole exists as the 2H-tautomer, whereas both tautomers of 3(5)-methylpyrazole are of similar energy. The solvent effects on these prototropic equilibria are discussed taking into account solvent properties as polarity/polarizability, acidity, and basicity. In nonhydrogen bonding solvents, the difference in dipole moments between both tautomers plays a role that has usually been underestimated. 相似文献
106.
Julio Casado J. Ramón Leis Manuel Mosquera L. Carlos Paz M. Elena Peña 《Monatshefte für Chemie / Chemical Monthly》1984,115(2):155-163
Acetic acid/acetate ion buffer acts catalytically upon the nitrosation of amines under conditions in which the only nitrosating agents are N2O3 and NOBr, but inhibits nitrosation by H2NO
2
+
. The kinetic characteristics of these phenomena have been analysed quantitatively and compared with similar effects caused by the solventsTHF, DMSO and dioxane. The experimental results show that this behaviour is an effect of the medium.
Kinetische Untersuchungen zur Bildung von N-Nitroso-Verbindungen, 8. Mitt.: Nachweis eines Medium-Effekts von Essigsäure/Acetat-Puffer auf die Geschwindigkeitskonstante der Nitrosierung
Zusammenfassung Essigsäure/Acetat-Puffer wirkt bei der Nitrosierung von Aminen katalytisch, unter Bedingungen, wo die alleinigen nitrosierenden Agentien N2O3 und NOBr sind; andererseits wird die Nitrosierung durch H2NO 2 + unterbunden. Die kinetischen Charakteristika dieses Phänomens wurden quantitativ analysiert und mit ähnlichen Effekten der LösungsmittelTHF, DMSO und Dioxan verglichen. Die experimentellen Ergebnisse zeigen, daß dieses Verhalten auf einen Mediumeffekt zurückzuführen ist.相似文献
107.
Kinetics of the hydrolysis of bisphenol A diglycidyl ether (BADGE) in water-based food simulants 总被引:1,自引:0,他引:1
P. Paseiro Losada J. Simal Lozano S. Paz Abuín P. López Mahía J. Simal Gándara 《Fresenius' Journal of Analytical Chemistry》1993,345(7):527-532
Summary The first-order degradation kinetics of bisphenol A diglycidyl ether (BADGE; CAS No. 1675-54-3) has been studied in three water-based food simulants (3% (W/V) acetic acid, distilled water and 15% (V/V) ethanol) at various temperatures. BADGE and its first and second hydrolysis products were determined by reversed-phase high-performance liquid chromatography with fluorescence detection. Nonlinear regression was used to fit the experimental data at 40, 50 and 60°C with the proposed kinetic equations; Arrhenius' equation was then fitted to the rate constants obtained and the kinetic models were tested by comparing experimental data obtained at 70°C with the kinetic curves calculated using the rate constants predicted for this temperature. The half-life of BADGE was longest in ethanol and shortest in acetic acid. The rings opening in acetic acid appears to happen by means of active hydrogens whereas in the other simulants it is mainly influenced by the formation of acid/base adducts. The results imply that resins which comply with existing legislation on the migration of unreacted monomer may still contaminate foodstuffs. 相似文献
108.
M. M. Mato S. M. Cebreiro P. V. Verdes J. L. Legido M. I. Paz Andrade 《Journal of Thermal Analysis and Calorimetry》2005,80(2):245-251
Summary Experimental excess molar enthalpies and densities have been measured for the ternary mixture x1MTBE+x21-propanol+(1-x1-x2)octane and the involved binary mixtures at 298.15 K and atmospheric pressure. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. A standard Calvet microcalorimeter was employed to determine the excess molar enthalpies. Densities were measured using a DMA 4500 Anton Paar densimeter. The UNIFAC group contribution model (in the versions of Larsen et al., and Gmehling et al.) has been used to estimate excess enthalpies values. Experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results. 相似文献
109.
M. M. Mato S. M. Cebreiro J. L. Legido M. I. Paz Andrade 《Journal of Thermal Analysis and Calorimetry》2006,84(1):279-283
Experimental
excess molar volumes for the ternary system {x1MTBE+x21-propanol+(1–x1–x2)nonane}
and the three involved binary mixtures have been determined at 298.15 K and
atmospheric pressure. Excess molar volumes were determined from the densities
of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter.
The ternary mixture shows maximum values
around the binary mixture MTBE+nonane and minimum values for the mixture MTBE+propanol.
The ternary contribution to the excess molar volume is negative, with the
exception of a range located around the rich compositions of 1-propanol.
Several empirical equations predicting ternary mixture properties from
experimental binary mixtures have been applied. 相似文献
110.
Pina J Seixas de Melo J Pina F Lodeiro C Lima JC Parola AJ Soriano C Clares MP Albelda MT Aucejo R García-España E 《Inorganic chemistry》2005,44(21):7449-7458
A new fluorescent macrocyclic structure (L1) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal. 相似文献