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排序方式: 共有87条查询结果,搜索用时 15 毫秒
1.
Prachur Bhargava Joseph X. Zheng Roderic P. Quirk Stephen Z. D. Cheng 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):3605-3611
We report the formation of a highly entangled and interconnected, self-assembled, wormlike-cylinder network of polystyrene-block-poly(ethylene oxide) in N, N-dimethylformamide/water. In this system, N,N-dimethylformamide was a common solvent and water was a selective solvent for the poly(ethylene oxide) blocks. The degrees of polymerization of the polystyrene and poly(ethylene oxide) blocks were 962 and 227, respectively. The network was formed at copolymer concentrations higher than 0.4 wt % and consisted of self-assembled, wormlike cylinders that were interconnected by Y-shaped, T-shaped, and multiple junctions. The network morphology was visualized with transmission electron microscopy. Capillary viscometry measurements revealed an order-of-magnitude increase in the inherent viscosity of the colloidal system upon the formation of the network. A similar effort to obtain a wormlike-cylinder network in an N,N-dimethylformamide/acetonitrile system, in which acetonitrile was a selective solvent for the poly(ethylene oxide) blocks, was unsuccessful even at high copolymer concentrations; instead, the wormlike cylinders showed a tendency to align. The viscosity measurements also did not show a substantial increase in the inherent viscosity. Thus, the solvent played a critical role in determining the formation of the self-assembled, wormlike-cylinder network. This formation of the network resulted from an interplay between the end-capping energy, bending energy (curvature), and configurational entropy of the self-assembled, wormlike-cylinder micelles that minimized the free energy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3605–3611, 2006 相似文献
2.
Kim Henrick Mary McPartlin Glen B. Deacon Roderic J. Phillips 《Journal of organometallic chemistry》1980,204(3):287-294
An X-ray crystallographic study has shown that the complex (C6H5)2TlO2CC6F5(OPPh3) has a dimeric structure with unsymmetrical pentafluorobenzoate bridging (TlO 2.531 and 2.789 Å) but an exact crystallographic centre of symmetry. The pentafluorobenzoate groups are also unsymmetrically chelated to thallium (TlO 2.389 and 2.531 Å.), which overall has irregular six coordination. 相似文献
3.
The experimental evidence supporting the involvement of enolate anions in group transfer polymerization(GTP) is reviewed. The results of silyl group exchange studies between living silyl ketene acetal-ended oligomers under typical GTP conditions are discussed. It is concluded that the observations of significant amounts of silyl group exchange in the presence of polymerizing monomer are not consistent with the originally proposed “associative mechanism” based on the GTP Criterion which precludes intermolecular silyl group exchange. 相似文献
4.
A living functionalization method has been investigated for group transfer polymerization (GTP) of poly(alkyl methacrylates) using ethyl 2-phenyl-2-butenoate (EPB). The end-capping reactions of EPB to living trimethylsilyl ketene acetal-ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by SEC, VPO, UV-visible spectrosocopy, 1H and 13c NMR spectroscopy. The results of sequential monomer addition, varying stoichiometry and copolymerization indicate that EPB effects efficient chain end functionalization only at stoichiometric concentrations; chain transfer reactions (chain transfer constant = 0.4) occur with excess EPB and during copolymerization with MMA. Chain transfer reactions (chain transfer constant = 0.1) also occur when copolymerizing ethyl 2-methyl-2-butenoate with MMA. 相似文献
5.
Three disparate food systems (gummy candy, Mozzarella cheese, and cooked ham) were characterized for their viscoelastic behavior
under isothermal conditions over an extended frequency range of 10−3 to 104 Hz using broadband viscoelastic spectroscopy (BVS). The materials were tested for any stress-induced fluid flow. However,
no evidence of fluid flow was found under the tested frequency range. Validity of time–temperature superposition for the selected
materials was also tested and compared with data from BVS. 相似文献
6.
NI LiXiao HAO XiangYang LI ShiYin CHEN ShiJin REN GaoXiang & ZHU Liang Key Laboratory of Integrated Regulation Resource Development on Shallow Lakes Ministry of Education College of Environmental Science Engineering Hohai University Nanjing China 《中国科学B辑(英文版)》2011,(7)
The algicidal activity of the terrestrial plants is a novel and promising means for alga control of eutrophic waters.In this study,three compositae plants — Artemisia annua(A.annua),Conyza canadensis(C.canadensis),and Erigeron annuus(E.annuus) were selected and antialgal activity of petroleum ether(PE),ethyl acetate(EA) and ethanol extracts of these plants on blue algae Microcystis aeruginosa was investigated.The result shows the EA extracts of these plants present the stronger inhibitory effects.The result... 相似文献
7.
Roderic P. Quirk Young J. Kim Ya Guo Chrys Wesdemiotis Mark A. Arnould 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2684-2693
Hydroxyl chain‐end functionalizations of polymeric organolithium compounds with oxetane (trimethylene oxide) were studied in benzene at 25 °C. Functionalizations of poly(styryl)lithium and polystyrene‐oligo‐butadienyllithium proceed efficiently to form the corresponding ω‐hydroxypropyl‐functionalized polymers in 98 and 97% isolated yields, respectively. No nonfunctional polymer (≤1–2%) was detected by thin layer chromatography (TLC) analysis for either polymer. All functionalized polymers were characterized by 13C and 1H NMR analyses; no evidence for oxetane oligomerization at the chain end was observed. The MALDI‐TOF mass spectrum of ω‐hydroxypropylpolystyrene was consistent with the expected structure without any detectable oligomerization of oxetane. A small, but detectable series of peaks corresponding to nonfunctional polystyrene was also observed in the MALDI‐TOF mass spectrum. The functionalization of the adduct of 1,1‐diphenylethylene and PSLi produced the corresponding ω‐hydroxypropyl‐functionalized polymer in only 86% isolated yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2684–2693, 2006 相似文献
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10.
Gabriel J. Summers Roderic P. Quirk 《Journal of polymer science. Part A, Polymer chemistry》1998,36(8):1233-1241
The novel syntheses of N,N-diisopropyl-4-benzoylbenzamide, N,N-diisopropyl-4-(1-hydroxy-1-phenylethyl)benzamide, and N,N-diisopropyl-4-(1-phenylethenyl)benzamide ( 1 ) are described. ω-Amidopolystyrene ( 2 ) was synthesized in quantitative yields by the reaction of poly(styryl)lithium with stoichiometric amounts of N,N-diisopropyl-4-(1-phenylethenyl)benzamide ( 1 ) in toluene/tetrahydrofuran (4 : 1 v/v) at −78°C. Deblocking of the amide protecting group by acid hydrolysis quantitatively provides the corresponding aromatic carboxyl chain-end functionalized polystyrene ( 3 ). The functionalization agent and functionalized polymers were characterized by HPLC, thin-layer chromatography, size exclusion chromatography, vapor phase osmometry, spectroscopy (1H-NMR, 13C-NMR, and FTIR), potentiometry, and elemental analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1233–1241, 1998 相似文献