全文获取类型
收费全文 | 71篇 |
免费 | 0篇 |
专业分类
化学 | 53篇 |
数学 | 14篇 |
物理学 | 4篇 |
出版年
2021年 | 1篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2012年 | 11篇 |
2011年 | 8篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
Interchange reactions involving esters were used in reactive processing with a view to obtaining polymer blends with stabilized morphology. Dibutyltinoxide (DBTO) appeared to be an excellent catalyst for these reactions. In fact, it was shown that the true catalytic entity is a dimeric alkoxy, acyloxy distannoxane entity formed in situ, during processing, by the reaction of the DBTO with the polymer ester groups. This compound was first obtained with model esters and characterized by multinuclear NMR analysis (1H, 13C, 119Sn). The catalytic efficiency of the in situ polymeric distannoxane was compared with other added parent distannoxanes. Later on – still with model compounds – ligand exchanges at the tin sites were investigated and it was shown that these exchanges are not essential to the catalyst activity, but when they take place it increases the catalytic efficiency. Then, this type of catalysis was successfully used for interchange reactions in reactive extrusion of different polymer blends, some applications are briefly presented. To cite this article: M.-F. Llauro and A. Michel, C. R. Chimie 9 (2006). 相似文献
2.
Hureau C Blondin G Charlot MF Philouze C Nierlich M Césario M Anxolabéhère-Mallart E 《Inorganic chemistry》2005,44(10):3669-3683
Two Mn(II) complexes are isolated and X-ray characterized, namely, cis-[(L(2))Mn(II)(Cl)(2)] (1) and [(L(3))Mn(II)Cl(OH(2))](ClO(4)) (2(ClO(4))), where L(2) and L(3) are the well-known tetradentate N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine and N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propane-1,3-diamine ligands, respectively. The crystal structure reveals that whereas the ligand L(2) is in the cis-alpha conformation in complex 1, the ligand L(3) is in the more unusual cis-beta conformation in 2. EPR spectra are recorded on frozen solutions for both complexes and are characteristic of Mn(II) species. Electrochemical behaviors are investigated on acetonitrile solution for both complexes and show that cation 2 exists as closely related Mn(II) species in equilibrium. For both complexes exhaustive bulk electrolyses of acetonitrile solution are performed at oxidative potential in various experimental conditions. In the presence of 2,6-lutidine and after elimination of chloride ligands, the formation of the di-mu-oxo mixed-valent complexes [(L(2))Mn(III)(mu-O)(2)Mn(IV)(L(2))](3+) (3a) and [(L(3))Mn(III)(mu-O)(2)Mn(IV)(L(3))](3+) (4) is confirmed by UV-vis and EPR spectroscopies and cyclic voltammetry. In addition crystals of 4(ClO(4))(3) were isolated, and the X-ray structure reveals the cis-alphaconformation of L(3). In the absence of 2,6-lutidine and without elimination of the exogenous chloride ions, the electrochemical oxidation of 1 leads to the formation of the mononuclear Mn(III) complex, namely, [(L(2))Mn(III)(Cl)(2)](+) (5), as confirmed by UV-vis as well as parallel mode EPR spectroscopy and cyclic voltammetry. In the same conditions, the electrochemical oxidation of complex 2 is more intricate, and a thorough analysis of EPR spectra establishes the formation of the binuclear mono-mu-oxo mixed-valent [(L(3))ClMn(III)(mu-O)Mn(IV)Cl(L(3))](3+) (6) complexes. Electrochemical conversion of Mn(II) complexes into mixed-valent Mn(2)(III,IV) oxo-bridged complexes in the presence of 2,6-lutidine is discussed. The role of the chloride ligands as well as that of L(3) in the building of oxo bridges is discussed. Differences in behavior between L(2) and L(3) are commented on. 相似文献
3.
Synthesis of methylenedioxy-bearing 1-aryl-3-carboxylisoquinolines using a modified Ritter reaction procedure 总被引:1,自引:0,他引:1
This paper describes original approaches aimed at the preparation of electron-rich 1-aryl-3-carboxylisoquinolines. Our first attempt led to an efficient preparation of 1-hydroxyisoquinoline-3-carboxylic acid methyl ester starting from bromophthalide via a rearrangement of 2-acetylamino-2-(3-oxo-1,3-dihydroisobenzofuran-1-yl)-malonic acid dimethyl ester. However, as its eventual application to the synthesis of methylenedioxy-bearing substrates seemed rather long, a second approach involving an extension of the Ritter reaction to safrole was devised. We thus report that, under proper experimental settings, the use of 54% tetrafluoroboric acid in ether enables a Ritter reaction between safrole and 3,4,5-trimethoxybenzonitrile yielding 17% of 7-methyl-5-(3,4,5-trimethoxyphenyl)-7,8-dihydro-[1,3]dioxolo[4,5-g]isoquinoline. This acidic reagent avoids the extensive decomposition seen when using the classical Ritter reaction conditions (i.e.: concentrated sulfuric acid). Further chemical transformations of this methyl-bearing dihydroisoquinoline led to the methylenedioxy-bearing 1-aryl-3-carboxylisoquinoline. These derivatives are related to the peripheral benzodiazepine receptor ligand PK 11195 as well as falcipain-2 inhibitors and other potential antitumor agents. 相似文献
4.
Brigitte Florin-Michel Marie-France Llauro R. Spitz Q.-T. Pham 《European Polymer Journal》1979,15(3):277-283
Ethylene 1-hexene copolymers obtained by catalytic polymerization have been examined by 1H and 13C NMR. Copolymer compositions have been determined by 1H NMR and i.r. and the sequence distributions for 1-hexene by 13C NMR. Variations of the copolymer microstructure have been related to the experimental conditions for copolymerization. 相似文献
5.
Christian Pichot Marie-France Llauro Quang-Tho Pham 《Journal of polymer science. Part A, Polymer chemistry》1981,19(10):2619-2633
The compositions and sequence distributions of vinyl acetate–butyl acrylate copolymers obtained with batch and semicontinuous emulsion polymerizations have been studied by 1H and 13C NMR. The batch process gives heterogeneous copolymers while with the semicontinuous one the sequence distribution is statistical. These differences in sequence distributions have been related to the physical properties of the copolymers. 相似文献
6.
Abdirahman Elmi Fatouma Mohamed Abdoul-Latif Rosella Spina Franois Dupire Stphanie Philippot Champy Marie-France Hugues Jacobs Dominique Laurain-Mattar 《Molecules (Basel, Switzerland)》2021,26(10)
For the first time, the study of the antioxidant activity, the characterization of the phytoconstituants, and the evaluation of in vitro and in vivo toxicity of A. djiboutiensis leave and latex are performed. The antioxidant activity of both latex (ADL) and the methanolic extract of leaves (ADM) is determined using 1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) scavenging radical methods and ferric reducing/antioxidant power (FRAP) assay. The phytochemical study of latex is done using Liquid Chromatography-Mass Spectrometry (LC-MS/MS) and a molecular networking-based approach. The evaluation of in vivo toxicity is performed on mice by oral gavage with a suspension of ADL. Our results show that weak antioxidant activity of ADL and ADM in opposition to their high polyphenol, 83.01 mg and 46.4 mg expressed in gallic acid equivalent (GAE)/g of dry weight (DW), respectively, and flavonoid contents 13.12 mg and 4.25 mg expressed in quercetin equivalent (QE)/g dry weight (DW), respectively. Using the Global Natural Products Social Molecular Networking (GNPS) website, nine (9) anthraquinones derivatives, ten (10) chromones derivatives, two (2) flavonols/ chromones isomers are annotated in the molecular network. The treated mice do not display abnormalities in their general physical appearance and biochemistry parameters, compared to the controls. Only glucose and calcium levels are slightly higher in male treated mice compared to the vehicles. 相似文献
7.
Marie-France Llauro-Darricades Naima Bensemra Alain Guyot Roger Petiaud 《Macromolecular Symposia》1989,29(1):171-184
High resolution 1H and 13C NMR data were obtained on PVC and PVC reduced with Bu3SnH. The reduction is never complete and CH2Cl groups preferentially remain. It causes almost complete formation of cyclopentane structures from both internal and chain end unsaturation. 1H NMR gives total unsaturation as well as chain end unsaturation except if there are interferences with initiator residues; in that case, its combination with 13 C NMR of reduced PVC gives the chain end unsaturation. By the last method short branches and long ends are determined. Residual primary chlorine in all kinds of branches (methyl, ethyl, butyl, long ends) is taken into account. Long end contents are to be corrected (factor around 1.5), due to incomplete relaxation in standard analysis conditions. 1H NMR of reduced PVC can be used to get the total non-reduced structures, both -CH2Cl and -CHCl-. PVC was prepared by suspension or solution (trichlorobenzene) polymerization at 55° C, using dicetyl peroxydicarbonate as an initiator. The initiator residue content is higher in suspension PVC at very low conversion, and then levels off at a low value; in solution polymerization, it chiefly depends on the monomer/initiator ratio. At low conversion, more chain end and less short branches are present in suspension polymerization. Otherwise, only the butyl branch content shows a definite trend to increase with conversion. In solution polymerization, the number of defects is chiefly dependent on the initial monomer concentration; it is generally much higher than in suspension, except for the chloromethyl branches where both processes give about the same results. 相似文献
8.
Alicia Henry Marie-France Vallat Gauthier Schrodj Philippe Fioux Vincent Roucoules Gregory Francius Jalal Bacharouche 《Plasma Chemistry and Plasma Processing》2016,36(2):627-650
Surface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of ~60 W and exposure time of ~30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase. 相似文献
9.
10.