全文获取类型
收费全文 | 145篇 |
免费 | 6篇 |
国内免费 | 12篇 |
专业分类
化学 | 152篇 |
数学 | 1篇 |
物理学 | 10篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 16篇 |
2012年 | 5篇 |
2011年 | 6篇 |
2010年 | 8篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 11篇 |
2005年 | 3篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
排序方式: 共有163条查询结果,搜索用时 375 毫秒
71.
高分子受阻胺光稳定剂存在下聚丁二烯的单线态氧氧化 总被引:1,自引:0,他引:1
用粘度法、ESR、IR、GPC等方法研究了三种商品高分子受阻胺存在下聚丁二烯的单线态氧氧化,结果表明,高分子受阻胺抑止聚丁二烯的单线态氧氧化,其效率是944>PDS>770>622。用Monroe方法测定了受阻胺对单线态氧的猝灭速率常数,K_q~(-O_2),它们是944(3.2×10~6M~(-1)s~(-1)),PDS(8.2×10~5M~(-1)s~(-1)),622,770为2×10~5M~(-1)s~(-1),ESR研究表明,在本实验条件下,944和PDS能够产生稳定的氮氧自由基No,而622则不产生。用GPC研究还发现,在本实验条件下,PDS具有对聚丁二烯的接枝——交联效应,提出了这种接枝交联效应的机理。 相似文献
72.
A series of new sterically hindered bridged ligand 4,4′-methylene-N,N′-bis(phenyl-2-pyridylmethylene)-bis(2,6-dialkylanil)s was efficiently synthesized by the condensation reaction of 4,4′-methylene-bis(2,6-disubstituted aniline) and benzoyl pyridine. They easily coordinated with Ag(I) to form Ag(I) complexes. The structure of complex [Ag2L42][ClO4]2 was determined by the single X-ray crystallographic analysis, and the double-helical asymmetric unit containing two [Ag2L42] moieties was interconnected with the adjacent unit through hydrogen bonds to form a helical supramolecular architecture. 相似文献
73.
V. I. Kelarev M. A. Silin V. N. Koshelev O. A. Borisova 《Chemistry of Heterocyclic Compounds》2004,40(5):616-621
A series of 2-substituted and 2,3-disubstituted quinazolin-4-ones containing a 3,5-di(tert-butyl)-4-hydroxyphenyl group has been synthesized. They were prepared by the condensation of carboxylic acid imino ester hydrochlorides containing the indicated fragment with ethyl anthranilate and also by the reaction of azomethines, N-acylhydrazones, or the 4-phenylthiosemicarbazone of 3,5-di(tert-butyl)-4-hydroxybenzaldehyde with 2-methyl-4H-2,1-benzoxazin-4-one. 相似文献
74.
Ring opening metathesis polymerization of triazole‐bearing cyclobutenes: Diblock copolymer synthesis and evaluation of the effect of side group size on polymerization kinetics
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jia Wei William Trout Yoan C. Simon Sergio Granados‐Focil 《Journal of polymer science. Part A, Polymer chemistry》2017,55(11):1929-1939
Cyclobutenes containing pendant groups of varying sizes were polymerized via ring opening metathesis polymerization using Grubbs catalyst 2nd generation (G2). The rate of polymerization depended on the size of the pendant groups attached to the cyclobutene rings, with longer side‐chains producing slower polymerization rates and narrower molecular weight distributions. The polymerization of these new molecules proceeded with first order kinetics, consistent with a living polymerization. Chain extension experiments produced cyclobutene‐based diblock copolymers with polydispersity indices below 1.33. The synthetic methods in this report will allow the use of G2 to access new complex polymeric architectures with a higher density of pendant groups than those derived from norbornene analogs and cyclooctene moieties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1929–1939 相似文献
75.
We have correlated data on methods for obtaining sterically hindered ketones, derivatives of furan, thiophene, pyrrole, and pyridine. We examine routes to arylation of chroman-4-ones and synthesis of sterically hindered unsaturated and silicon-containing heteroaromatic ketones. 相似文献
76.
Siziwe Bebe Xinrui Yu Robin A. Hutchinson Linda J. Broadbelt 《Macromolecular Symposia》2006,243(1):179-189
This study explores the application of computational chemistry to estimate free radical polymerization rate coefficients. The Evans-Polanyi relationship is combined with computed heats of polymerization to estimate copolymerization reactivity ratios for many vinyl monomer pairs, focusing on acrylates, methacrylates and styrene, with accuracy assessed by comparison to experimental values. The effect of different optimization approaches on the values of thermodynamic properties is explored, and it is concluded that a combination of conventional optimization and relaxed potential energy scans was most effective at identifying global minima. The difference between thermodynamic properties calculated using the harmonic oscillator treatment and a hindered rotor model is evaluated for methyl methacrylate polymerization. 相似文献
77.
《Analytical letters》2012,45(9):589-595
Abstract The speed of trimethylsilylation of sterically hindered phenols was increased by promoting the reaction with a small amount of trifluoroacetic acid. Promotion was successful with hexamethyldisilazane, trimethylchlorosilane, bis-(trimethylsilyl)-trifluoroacetamide, bis-(trimethylsilyl)-acetamide, and trimethylsilylimidazole. 相似文献
78.
Jan Romanski Piotr NowakKrzysztof Kosinski Janusz Jurczak 《Tetrahedron letters》2012,53(39):5287-5289
A mild, rapid, and efficient method for the solvolysis of sterically hindered esters under high pressure is described. Transesterification is carried out in the presence of DBU at room temperature and at a pressure of 10 kbar to give quantitative conversions within short reaction times. The substrates examined included aromatic and aliphatic esters of sterically hindered alcohols and phenols. An optically pure benzyl ester of phenylalanine was chosen to study racemization of the amino acid esters under high-pressure reaction conditions. 相似文献
79.
Ashok K.S. Chauhan Puspendra Singh Ray J. Butcher 《Journal of organometallic chemistry》2010,695(18):2118-3656
Elemental tellurium inserts into the Csp3-Br bond of α-bromomesitylmethyl ketone and due to its strong carbophilic character affords the crystalline C-tellurated derivative of 2,4,6-trimethylacetophenone, (MesCOCH2)2TeBr2, 1b in over 80% yield. Electrophilic substitution of the parent ketone with aryltellurium trichlorides, at room temperature, gives nearly quantitative yields of unsymmetrical alkylaryltellurium dichlorides (MesCOCH2)ArTeCl2 (Ar = mesityl, Mes, 2a; 1-naphthyl, Np, 3a; anisyl, Ans, 4a). Fairly stable mesitoylmethyltellurium(II) derivatives, (MesCOCH2)2Te, 1 and (MesCOCH2)ArTe (Ar = Mes, 2; Np, 3 and Ans, 4) obtained as the reduction products of their dihalotellurium(IV) analogues, readily undergo oxidative addition of dihalogens to afford the corresponding (MesCOCH2)2TeX2 (X = Cl, 1a; Br 1b; I, 1c) and (MesCOCH2)ArTeX2 (X = Cl, Br, I, Ar = Mes, 2a, 2b, 2c; Np, 3a, 3b, 3c and Ans, 4a, 4b, 4c). Crystallographic structural characterization of 1, 1b, 2, 2a, 2b, 2c, 3, 3a and 4c illustrates that the steric demand of mesityl group appreciably influences primary geometry around the 5-coordinate Te(IV) atom when it is bound directly to it. It also makes the Te atom inaccessible for the ubiquitous Te?X intermolecular secondary bonding interactions that result in supramolecular structures. In the crystal lattice of symmetrical telluroether 1, an interesting supramolecular synthon based upon reciprocatory weak C-H?O H-bonding interaction gives rise to chains via self-assembly. 相似文献
80.
Troy A. Lowe Martin R. L. Paine David L. Marshall Larry A. Hick Jenny A. Boge Philip J. Barker Stephen J. Blanksby 《Journal of mass spectrometry : JMS》2010,45(5):486-495
Hindered amine light stabilisers (HALS) are the most effective antioxidants currently available for polymer systems in post‐production, in‐service applications, yet the mechanism of their action is still not fully understood. Structural characterisation of HALS in polymer matrices, particularly the identification of structural modifications brought about by oxidative conditions, is critical to aid mechanistic understanding of the prophylactic effects of these molecules. In this work, electrospray ionisation tandem mass spectrometry (ESI‐MS/MS) was applied to the analysis of a suite of commercially available 2,2,6,6‐tetramethylpiperidine‐based HALS. Fragmentation mechanisms for the [M + H]+ ions are proposed, which provide a rationale for the product ions observed in the MS/MS and MS3 mass spectra of N‐H, N‐CH3, N‐C(O)CH3 and N‐OR containing HALS (where R is an alkyl substituent). A common product ion at m/z 123 was identified for the group of antioxidants containing N‐H, N‐CH3 or N‐C(O)CH3 functionality, and this product ion was employed in precursor ion scans on a triple quadrupole mass spectrometer to identify the HALS species present in a crude extract from of a polyester‐based coil coating. Using MS/MS, two degradation products were unambiguously identified. This technique provides a simple and selective approach to monitoring HALS structures within complex matrices. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献