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排序方式: 共有98条查询结果,搜索用时 62 毫秒
81.
Mariana Cristea Stela Dragan Demetra Dragan Bogdan C. Simionescu 《Macromolecular Symposia》1998,126(1):143-155
Interpolyelectrolyte complexes (PECs) were obtained starting from polycations with (N,N-dimethyl-2-hydroxypropylenammonium chloride) units in the main chain and sodium salts of the poly(acrylic acid), on one hand, and poly (2-acrylamido-2-methylpropane sulfonic acid), on the other hand, as polyanions. The polycations were different as concerns both the content of the quaternary ammonium salt groups and the degree of branching. The polyanions were different both by their structure and molecular weight. The complex formation was followed through the variation of the reduced viscosity and of the conductivity of the reaction medium vs. the unit molar ratio polyanion/polycation in two ranges of concentration. 相似文献
82.
Kreibik Stefan Coman Virginia Marutoiu Constantin Mihailescu Gheorghe Pruneanu Stela 《平面色谱法杂志一现代薄层色谱法》2001,14(5):355-359
JPC – Journal of Planar Chromatography – Modern TLC - In normal TLC practice, migration of the mobile phase through the layer is controlled by capillary forces. Under these conditions... 相似文献
83.
Maria Cazacu Luminita Ghimici Ecaterina Stela Dragan 《Journal of polymer science. Part A, Polymer chemistry》2004,42(15):3720-3728
Siloxane‐modified cationic polyelectrolytes were synthesized through the quaternization reaction of a poly(ethylene glycol)‐based polymer containing tertiary amine groups in the chain with chloroalkyl‐functionalized siloxanes. Linear or crosslinked structures were obtained, depending on the functionality of the siloxane: a chloroalkyl‐monofunctionalized or ‐polyfunctionalized siloxane was used. The reaction occurred in solution with n‐propanol as a solvent and NaI as a catalyst. All products were characterized with elemental analysis and IR and 1H NMR spectrometry. Viscometric measurements of the linear polymer in dilute aqueous solutions revealed typical polyelectrolyte behavior. The swelling capacities in various solvents of the crosslinked structures were determined. The thermal stability of the crosslinked cationic structures obtained with a polyfunctional siloxane as a quaternization agent was much higher than that of the parent polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3720–3728, 2004 相似文献
84.
Cornelia Luca Stela DrÎgan V. BÎrboiu M. Dima 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):449-454
A multifunctional crosslinked polymer resulted from a chloromethylated polystyrene reaction with tris(2-hydroxyethyl)amine. A benzyl chloride reaction (chosen as a structural unit model) with tris(2-hydroxyethyl)amine was investigated to explain the reasons for the crosslinking. Amino-ethers and tris(2-hydroxyethyl)amine hydrochloride in addition to ammonium quaternary salt were isolated from this reaction. The formation of amino-ethers proved that an ammonium quaternary salt rearrangement also takes place during the quaternization reaction. This rearrangement leads to chloromethylated polystyrene during its reaction with tris(2-hydroxyethyl)amine. 相似文献
85.
The extraction of chelate and ion-association complexes formed by various metal ions and two new organic reagents (derivatives of benzoxazolylacrolein) has been investigated in order to evaluate the possibilities for analytical application. The composition of the extracted species and their conditional extraction constants are given. Two simple extraction procedures for flame atomic absorption analysis of high purity lead salts have been developed. The proposed methods permit determination of (a) 1 × 10–5% Co, Fe and Ni and 5 × 10–6% Cu and Zn and (b) 1 × 10–5% Pd and 5 × 10–6% Ag and Au, with relative standard deviations in the range 4–8%. 相似文献
86.
Ecaterina Stela Dragan Maria Cazacu Alexandra Nistor 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):6801-6813
Ionic organic/siloxane networks containing quaternary ammonium salt (QAS) sequences in the cross‐linking bridges were obtained by the Menshutkin reaction of oligo(N,N‐dimethylaminoethylmethacrylate) (ODMAEM) with a telechelic chloroalkylated siloxane (CAS), such as 1,3‐bis‐(chloromethyl)‐1,1,3,3‐tetramethyldisiloxane, 1,3‐bis‐(chloropropyl)‐1,1,3,3‐tetramethyldisiloxane, and α,ω‐bis(chloromethyl) oligodimethylsiloxane. The resulted structures were investigated by Fourier transform infrared spectroscopy emphasizing the presence of both organic and siloxane moieties. The thermogravimetric analysis under inert atmosphere of the networks, besides the thermal stability, gave also information on the composition of hybrid hydrogels. The morphology of the lyophilized networks was evidenced by environmental scanning electron microscopy, as a function of CAS structure and CAS: ODMAEM feed molar ratio. The swelling response of the ionic networks in water as a function of pH and counterion nature and concentration as well as the water vapors sorption capacity in dynamic regime were evaluated. The properties of the ionic hybrid hydrogels were correlated with the reactants feed molar ratio and concentration of the reaction mixture, CAS type, and the presence of a catalyst. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 相似文献
87.
Chain microstructure and conformation of partially quaternized poly(dimethylaminoethyl methacrylate)
Virgil Barboiu Gabriela Liliana Ailiesei Anca Giorgiana Grigoras Elena Rusu Ecaterina Stela Dragan 《International Journal of Polymer Analysis and Characterization》2019,24(7):610-618
1H-NMR spectroscopy was used to establish the chain microstructure and conformation produced by the quaternization reaction of syndiotactic poly[2-(dimethylamino)ethyl methacrylate], a polymer with tertiary amino groups in the side chains. A chain microstructure with mini blocks of modified units was found by analyzing the N+CH3 signal that was proved to be split in accordance with the composition triads. The macromolecular backbone changes its form by quaternization, from a close to an expanded coil, was confirmed by light scattering measurements and NOE spectra modifications. The two linked processes, the block formation and chain expansion can be the key in developing a reaction mechanism explaining both positive and negative deviations from a second-order kinetic model. 相似文献
88.
We give the general spherically symmetric perfect fluid or dust solution with flat three-spaces orthogonal to the four-velocity. The case of dust corresponds to a subset of the Tolman solution. The shear-free case corresponds to the Friedmann line element. 相似文献
89.
This preliminary study was designed to determine the extent to which the carbon isotope ratio in four species of lichens was influenced by such features as humidity, rainfall, radioactivity, and air quality. The sampling sites were selected to be at a great distance from any pollution. At the time of sampling, field data (temperature, relative humidity, average monthly precipitation, and radioactivity) were recorded. delta(13)C in whole lichen specimens were determined using standard mass spectrometric techniques with a standard deviation of+/-0.3 per thousand. We have found a weak but negative correlation between delta(13)C and relative humidity, and a positive correlation between delta(13)C and average monthly precipitation at the studied sites. The effects were minor, of the order of 1.5 per thousand for all the lichens. We have examined the correlation between (137)Cs activity concentration of the studied lichens and delta(13)C of these lichens, and we have suggested that fixation of radiocesium does not alter photosynthesis rate. There was a delta(13)C variation with the altitude gradient with less negative delta(13)C values at higher altitude. It is possible that this difference is caused by the ozone and occurred at the high elevations. 相似文献
90.