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排序方式: 共有114条查询结果,搜索用时 15 毫秒
101.
Mustapha El Gouri Abderrahim El Bachiri Salah Eddine Hegazi Mohamed Rafik Ahmed El Harfi 《Polymer Degradation and Stability》2009,94(11):2101-2106
Hexaglycidyl cyclotriphosphazene (HGCP) was synthesized, and characterized by FTIR, 31P, 1H, and 13C-NMR. This compound was used as a reactive flame retardant to blend with commercial epoxy resin DGEBA (Diglycidyl ether of bisphenol A). Its effect on the DGEBA decomposition pathways was characterized by studying both gas and solid phases produced during thermogravimetric analysis (TGA). The gases evolved during TGA in air were studied by means of thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), while the solid residues were analysed by FTIR and scanning electron microscopy (SEM). The results showed that HGCP presents a good dispersion in DGEBA, and the blend thermoset with 4,4′-methylene-dianiline (MDA) curing agent leads to a significant improvement of the thermal stability at elevated temperature with higher char yields compared with pure DGEBA thermoset with the same curing agent. Improvement has also been observed in the fire behaviour of blend sample. 相似文献
102.
Rafik Karaman 《Tetrahedron letters》2010,51(39):5185-142
Using density functional theory (DFT) at the B3LYP level with the 6-31G(d,p) basis set, a general equation is derived relating activation energy with the distance between the two reactive centers (rGM), and the hydrogen-bonding angle (αGM) in an intramolecular proton transfer process. The strong correlation between the values of rGM and αGM with the activation energy, ΔG‡, which reflects the experimental reaction rate, provides an excellent tool to predict reaction rate based on calculated geometrical parameters for a certain system (ΔH‡, ΔG‡ vs rGM and αGM). The slope of the equation can be used as an indicator of the mode by which the two reacting centers orchestrate in an intramolecular process. 相似文献
103.
Abstract 2,2′-Biimidazole complexes of MoO2 +2, MoO2 + and UO2 +2 have been prepared and characterized by elemental analysis, conductance; and 1H NMR, IR and electronic spectra. Two types of complexes have been identified. Those obtained from slightly acidic solutions have the formulae MoO2 (H2bim)Cl2.2H2O 1, UO2(H2bim) (Ac)2 2 and UO2(H2bim)Cl2.2H2O 3; whereas those from alkaline solutions have the formulae Mo2O4(Hbim)2.2H2O 4, and MO2(Hbim)2 (M = Mo(VI) 5, U(VI) 6). The infrared spectra of these complexes show characteristic biimidazole frequencies in the 3200–2500, 1550–1000 and 750 cm?1 regions as well as metal oxygen double bonds in the 900 cm?1 region. The stoichiometries of the acetate complex has been confirmed from 1H NMR signal ratios of bimidazole to acetate protons at 7.3 and 2.3 ppm, respectively. The electronic spectrum of molybdenum(V) complex showed d-d transition band at ?13,500 cm?1 in accord with that reported for copper (d9) imidazole complexes; as well as peaks due to charge transfer bands at 30,000–26,000 cm?1 Peaks assignable to BIM → U(VI) were located at ?26,600 cm?1. The most probable structures of these complexes have been suggested. 相似文献
104.
A PMR analytical procedure is described for the quantitation of isoniazid (4-pyridinecarboxylic acid hydrazide) as a drug entity and in tablets dosage form. The method is accurate and precise with a standard deviation of ± 1.51 and ± 1.34 in the bulk drug and in tablets respectively. The results obtained comply with the official standards required by different pharmacopeias. The PMR spectrum, in addition, provides a very specific mean for identification of isoniazid. 相似文献
105.
Desmarets C Champagne B Walcarius A Bellouard C Omar-Amrani R Ahajji A Fort Y Schneider R 《The Journal of organic chemistry》2006,71(4):1351-1361
Naphthidines 2 were prepared by nickel-catalyzed amination of 1-chloronaphthalene followed by oxidative homocoupling of 1-naphthalene amines 1 using titanium(IV) tetrachloride. The electronic and magnetic properties of materials 2 were investigated by cyclic voltammetry and other electrochemical techniques, EPR and UV-visible spectroscopies, and magnetic susceptibility. It was demonstrated that compounds 2 could be easily and reversibly oxidized via a two-electron-transfer reaction into their bis(radical cation) 2(2.2+), which displays a substantial stability at room temperature (the half-life of 2(2.2+) estimated by EPR at 25 degrees C was 10 days). B3LYP/6-31G optimized structures of N,N'-bis(4-methoxyphenyl)-(1,1'-binaphthyl)-4,4'-diamine 2g shows significant differences in the torsion angle between the naphthalene moieties depending on its oxidation state. Twisted structures are preferred for neutral compounds, whereas more planar are favored for the oxidized forms 2g*+ and 2g(2.2+) to realize spin and/or charge delocalizations over the whole pi-system. Such conformation changes concerted with the electron transfers contribute to explain the unusual two-electron process observed in the electrochemical behavior of 2g instead of the two single-electron transfers that would have been expected in the case of two successive oxidations. It is finally shown that the oxidation of 2g in CH2Cl2 with thianthrenium perchlorate (ThClO4) generates the dication 2g(2.2+) with singlet spin-multiplicity. 相似文献
106.
Rafik W. Bassily Rimon H Youssef Ramadan I. El-Sokkary Mina A Nashed 《Journal of carbohydrate chemistry》2013,32(6):653-663
ABSTRACT The 13C NMR spectra of a range of di-O-isopropylidene acetals of α,α-trehalose and its analogues 1, 2, 4-7 have been studied Attention has been focussed on the chemical shifts of the acetal carbon and methyl groups of the acetals. These parameters are characteristic of ring-size (1,3-dioxolane and 1,3-dioxane). Di-n-butylstannylene and cyclic orthoester intermediates 9 and 12 of 2,6-di-O-benzoyl-α-D-galactopyranosyl 2,6-di-O-benzoyl-α-D-galactopyranoside (8) were used to synthesize the partially protected trehalose analogue having chain extension at positions 4,4′ and 3,3′ (10 and 13) respectively. Acetonation of the synthetic trehalose type disaccharide yielded mainly 3,4:3′,4′-di-O-isopropylidene derivative 4. The benzoylation of 4 followed by acid hydrolysis gave 8 in 85% yield, which was the key intermediate for the synthesis of 10 and 13 相似文献
107.
Pandozzi F Vetrone F Boyer JC Naccache R Capobianco JA Speghini A Bettinelli M 《The journal of physical chemistry. B》2005,109(37):17400-17405
The spectroscopic behavior of gadolinium gallium garnet (Gd3Ga5O12, GGG) nanocrystals codoped with 1% each of Tm3+ and Yb3+ prepared via a solution combustion synthesis procedure was investigated. Initial excitation of the codoped nanocrystals with 465.8 nm (into the 1G4 state) showed a dominant blue-green emission ascribed to the 1G4-3H6 transition as well as red and NIR emissions from the 1G4-3F4 and 1G4-3H5/3H4-3H6 transitions, respectively. Excitation at this wavelength (465.8 nm) showed the existence of a Tm3+ --> Yb3+ energy transfer process evidenced by the presence of the 2F5/2-2F7/2 Yb3+ emission in the NIR emission spectrum. The decay time constants proved that the transfer of energy occurred via the 3H4 state. Following excitation of the Yb3+ ion with 980 nm, intense upconverted emission was observed. Emissions in the UV (1D2-3H6), blue (1D2-3F4), blue-green (1G4-3H6), red (1G4-3F4), and NIR (1G4-3H5/3H4-3H6) were observed and were the direct result of subsequent transfers of energy from the Yb3+ ion to the Tm3+ ion. Power dependence studies showed a deviation from expected values for the number of photons involved in the upconversion thus indicating a saturation of the upconversion process. An energy transfer efficiency of 0.576 was determined experimentally. 相似文献
108.
Rafik Gharbi Anis Romdhane Zine Mighri Marie‐Thrse Martin 《Journal of heterocyclic chemistry》2005,42(1):169-172
New tetracyclic 6H‐[1]benzopyrano[3,4‐e]pyrazolo[1,5‐a]pyrimidin‐6‐ones ( 4a‐e ) have been synthesized through the condensation under acidic conditions of [1]benzopyrano[4,3‐c][1,5]‐benzodiazepin‐7(8H)‐one ( 1 ) and a series of 3,4‐disubsituted 5‐amino‐1H‐pyrazoles 3a‐e . 相似文献
109.
110.
Loutfy H. Madkour Amera M. Hassanein Mohamed M. Ghoneim Safwat A. Eid 《Monatshefte für Chemie / Chemical Monthly》2001,40(7):245-258
The inhibition of corrosion of iron in 2 M nitric acid and 2 M sulfuric acid solutions by substituted phenylhydantoin, thiohydantoin, and dithiohydantoin compounds was measured using thermometric, weight loss, and polarization methods. The three methods gave consistent results. The polarization curves indicated that the hydantoin compounds act as mixed-type inhibitors. The adsorption of the inhibitors were found to obey the Temkin adsorption isotherm. The higher inhibition efficiency of the additives in nitric with respect to sulfuric acid solution may be attributed to the reduced formation of soluble quaternary nitrogen salts in nitric acid medium, favouring adsorption of the parent additive on the metal surface. The obtained results indicate that the corrosion rate of iron in both acids increases with increasing temperature, both in absence and presence of the tested inhibitors. Kinetic-thermodynamic model functions and Temkin isotherm data are compared and discussed. The synergistic effect of halide anions on the inhibition efficiency of the hydantoin compounds was also investigated. 相似文献