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101.
102.
The thermal and operational stabilities ofDesulfovibrio gigas periplasmic hydrogenase were studied at 30 and 50°C in aqueous and micellar media. At the lower temperature the hydrogenase
was more stable in reverse micelles of a cationic surfactant. No inactivation was detected over almost 16 d of incubation
of the hydrogenase in the reverse micellar solution, during which the enzyme lost around 50% of the initial enzymatic activity
in the aqueous solution. At 50°C the hydrogenase was more stable in aqueous medium, because of the changes that occur with
the temperature in the organic phase—precipitation of surfactant and solvent evaporation. It was found that only micellar
solutions of this enzyme can be repeatedly used, since the hydrogenase is inactivated after the first cycle of oxireduction
in aqueous medium. The effect of glycerol and the electron carrier methylviologen as stabilizers of hydrogenase activity was
also investigated. The results are interpreted on the grounds of hydrogenase and surfactant electrostatic properties. 相似文献
103.
Neusa M.T. Pires Fernanda M.B. Coutinho Marcos A.S. Costa 《European Polymer Journal》2004,40(11):2599-2603
This paper reports the study of the dependence of reaction conversion, catalyst activity, polymer microstructure, molecular weight, molecular weight distribution curves and Mooney viscosity on reaction temperature and monomer concentration in the reaction medium used in the synthesis of high cis-polybutadiene. A ternary catalyst system composed by neodymium versatate, trans-butyl chloride and diisobutylaluminum hydride was used in its synthesis. The highest molecular weights were obtained at polymerization temperatures in the range from 70 to 80 °C. The highest content of cis-1,4 repeating units (about 99%) was observed when the polymerization was carried out at the lowest initial monomer concentration (0.56 mol/l). 相似文献
104.
De Oliveira MF Saczk AA Okumura LL Fernandes AP De Moraes M Stradiotto NR 《Analytical and bioanalytical chemistry》2004,380(1):135-140
A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% (v/v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-m thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10–9–10–8 mol L–1 for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples. 相似文献
105.
C. H. Collins C. A. Bertran A. L. Pires Valente Priscila de A. Leone A. L. M. Murta K. E. Collins 《Chromatographia》1988,26(1):168-170
Summary Separation of perhalogenated compounds resulting from thermolysis, photolysis or radiolysis of mixtures of halogens in carbon tetrachloride was carried out by programmed temperature gas chromatography. Plots of relative retentions (to CBr4) vs the number of bromine atoms present for known compounds of the general formula CxBryClz (x=1 and 2; y+z=4 or 6) gave three linear correlations (all with r>0.99). These correlations permitted projections of the identities of reaction products for which no standards were available. These projections were later confirmed by CG-MS. *** DIRECT SUPPORT *** A0732166 00010 相似文献
106.
Susana?Shimizu Paulo?Augusto?R.?Pires Watson?Loh Omar?A.?El SeoudEmail author 《Colloid and polymer science》2004,282(9):1026-1032
The enthalpies of micellization of the following surfactant series have been determined by calorimetry: benzyl (2-acylaminoethyl)dimethylammonium chlorides, RABzMe2Cl, and alkyldimethylbenzylammonium chlorides, RBzMe2Cl, where A, Bz and Me refer to amide, benzyl, and methyl groups, respectively and the acyl (for RABzMe2Cl) and/or the alkyl (for RBzMe2Cl) groups C10, C12, C14, and C16, respectively. For both series, the shapes of the calorimetric titration curves (enthalpograms) depend on the following micellar parameters: critical micelle concentration, aggregation number, and degree of counterion binding. The calorimetric-based critical micelle concentrations are in excellent agreement with those determined by conductivity. The Gibbs free energy, the enthalpy and the entropy of micellization were calculated, and divided into contributions from the CH2 groups of the hydrophobic tail, and the terminal CH3 plus head group of the surfactant. For both surfactant series, all thermodynamic parameters per CH2 group were found to be similar, since their transfer (from bulk solution to the micelle) is independent of the surfactant head-group structure. The Gibbs free energy, the enthalpy, and the entropy of transfer of the head group of RABzMe2Cl are more favorable than their counterparts for RBzMe2Cl, because of direct and/or water mediated hygrogen bonding of the amide groups in the micelle. 相似文献
107.
Rinaldo A. M. Vieira Leticia S. V. S. Su?é Carlos A. M. Pires Antonio O. S. Silva Marcelo J. B. Souza Antonio S. Araujo 《Reaction Kinetics and Catalysis Letters》2006,88(1):119-126
Summary The catalytic oxidation of phenol over CuZSM-12 (SAR = 200) has been studied using a semi-batch slurry reactor at temperatures
of 110; 120 and 130oC, and acidic neutral and basic pH. At 130oC, the phenol undergoes total conversion to carbon dioxide and water in 1.5 h. The kinetic parameters were evaluated using
a modified homogeneous-heterogeneous model for the experimental data. Using this modified model, the activation energy for
the catalytic oxidation process was ca. 90 kJ mol-1. 相似文献
108.
E.A. Benjamim A. Lépine-Szily D.R. Mendes Junior R. Lichtenthäler V. Guimarães P.R.S. Gomes L.C. Chamon M.S. Hussein A.M. Moro A. Arazi I. Padron J. Alcantara Nuñez M. Assunção A. Barioni O. Camargo Jr. R.Z. Denke P.N. de Faria K.C.C. Pires 《Physics letters. [Part B]》2007
The elastic scattering of the radioactive halo nucleus 6He on 27Al target was measured at four energies close to the Coulomb barrier using the RIBRAS (Radioactive Ion Beams in Brazil) facility. The São Paulo Potential (SPP) was used and its diffuseness and imaginary strength were adjusted to fit the elastic scattering angular distributions. Reaction cross-sections were extracted from the optical model fits. The reduced reaction cross-sections of 6He on 27Al are similar to those for stable, weakly bound projectiles as 6,7Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al. 相似文献
109.
The dynamics of the strong-anisotropic Ising model in a transverse field is used with the purpose to explain the dielectric critical slowing down observed experimentally in the quasi-one-dimensional hydrogen-bonded ferroelectric crystal CsH2PO4. A good agreement with the experimental data of the temperature dependence of the dielectric constant and the relaxation time is obtained. 相似文献
110.