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1.
Anionic polymerization of methyl methacrylate in THF and toluene at ?70° was studied by means of i.r. spectroscopy. The reaction mixtures show characteristic absorption at 1600–1750 cm?1 caused by the stretching vibrations of the propagating centre as well as by the groups obtained in side reactions (metal splitting, addition to a carbonyl group, cyclization). Sec-butyllithium is more effective in THF than n-butyllithium, ethyllithium and fluorenyllithium. When polymerizing in toluene, small amounts of a donor (THF or HMPT) cause formation of active centres similar to those in pure THF. The “living” ends of oligo-MMA form 1:1 complexes with electron acceptors such as trialkylaluminium and triethylboron. 相似文献
2.
L.V. Vinogradova V.N. Zgonnik N.I. Nikolaev Kh.B. Tsvetanov 《European Polymer Journal》1979,15(6):545-550
The electric conductivity of polybutadienyl-lithium and polyisoprenyl-lithium has been investigated in tetrahydrofuran and dimethoxyethane solutions over wide temperature and concentration ranges (0 to ?70°; 7·10?2 to 1·10?7 and 5·10?3 to 1·10?7 mol/l). Dissociation constants, enthalpy and entropy of dissociation of ion pairs, relative constants for formation of ion triplets, and interionic distances were calculated for each system investigated. The nature of “living” chains under these conditions is considered. 相似文献
3.
Ch.B. Tsvetanov 《European Polymer Journal》1979,15(5):503-507
It is shown by i.r. spectroscopy that the anionic polymerization of methacrylonitrile using organomagnesium compounds as initiators leads to two types of “living” ends i.e. and The active centres form complexes with the monomer, as well as with the nitrile groups of the monomer units in the polymer chain, in a hydrocarbon medium. The complexes are characterized by bands in the 2250–2280 cm?1 region. Addition of donors destroys the complexes and in some cases (hexamethylphosphorous triamide) converts the complex of organomagnesium compound with monomer into a “living” end. In ethers as solvent, the dominant side-reaction is addition of the initiator to the nitrile group of the monomer. 相似文献
4.
L.V. Vinogradova N.I. Nikolaev V.N. Sgonnik B.L. Erussalimsky G.V. Sinitsina Ch.B. Tsvetanov I.M. Panayotov 《European Polymer Journal》1981,17(5):517-520
The parallel changes in the electric conductivity and u.v. spectra of polybutadienyl- and polyisoprenyl-lithium (MnLi) have been investigated in tetrahydrofuran and dimethoxyethane solutions during prolonged storage at 0 and 25°. A considerable dependence of the rate of these changes on the nature of the medium and Mn Li concentration was found. The decrease in the initiating activity during storage has been estimated for the PBLi-THF system. 相似文献
5.
T. Tsanov K. Vassilev R. Stamenova C. Tsvetanov 《Journal of polymer science. Part A, Polymer chemistry》1995,33(15):2623-2628
Radiation crosslinked poly(ethylene oxide)s (PEO) modified with two tetraalkylammonium salts: allyldimethyldodecylammonium bromide and ethylmethacrylate dimethyldodecylammonium bromide were prepared. They have been characterized by elemental analysis, IR, 1H-NMR spectra, and DSC measurements. Their activity as phase transfer catalysts (PTC) in the model displacement reaction of 1-bromooctane with aqueous sodium cyanide were studied. The reaction kinetics were followed under pseudo-first-order conditions. Small amounts of onium salt inserted into the PEO network gave rise to a five time increase in the rate constant. The recovered catalysts could be re-used without loss of activity. © 1995 John Wiley & Sons, Inc. 相似文献
6.
The anionic polymerization of methyl methacrylate was carried out in the presence of t-BuOK/Quaternary ammonium salt (QAS) and α-lithio-ethylisobutyrate/QAS in toluene and THF. Seven QAS and one quaternary phosphonium salt of different size and shape were used as modifiers. With the aid of the model system alkali picrate/QAS, it was found that the interaction between the picrate salt and QAS in toluene does not proceed as a pure cation exchange reaction. Two types of adducts were distinguished: Initiator/QAS with a very long hydrocarbon chain (>C12) promote isotactic placement, while the adducts t-BuOK/QAS with two or more bulky substituents produce a highly syndiotactic polymer with high conversion and comparatively low polydispersity in pure toluene. 相似文献
7.
Ohne Zusammenfassung 相似文献
8.
Andrzej Dworak Barbara Trzebicka Wojciech Wałach Alicja Utrata Christo Tsvetanov 《Macromolecular Symposia》2004,210(1):419-426
A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed. 相似文献
9.
10.
AW Hilkert CB Douthitt HJ Schlüter WA Brand 《Rapid communications in mass spectrometry : RCM》1999,13(13):1226-1230
Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd. 相似文献