全文获取类型
收费全文 | 113篇 |
免费 | 1篇 |
专业分类
化学 | 83篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 3篇 |
物理学 | 25篇 |
出版年
2023年 | 1篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 6篇 |
1972年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有114条查询结果,搜索用时 234 毫秒
41.
The rate of alkylation of (2-N,N-dimethylaminophenyl)diphenylphosphine with benzyl bromide in chloroform is faster than that of the corresponding reaction of (4-N,N-dimethylaminophenyl)diphenylphosphine. This result is discussed in terms of a through-space N2p–P(IV) interaction for the former. The rate of alkaline cleavage of benzyl(4-N,N-dimethylaminophenyl)diphenylphosphonium bromide, which gives toluene, is slower than the rate of alkaline cleavage of benzyl(2-N,N-dimethylaminophenyl)diphenylphosphonium bromide, which gives dimethylaniline. This result is also discussed in terms of the through-space N2p–P(IV) interaction. The 31P NMR spectra of a series of ortho-dimethylamino-substituted triarylphosphines and benzyltriarylphosphonium halides show that the phosphorus atom is more shielded than in the corresponding para-dimethylamino compounds, as anticipated on the basis of an N2p–P(IV) interaction for the former. 相似文献
42.
J. M. G. Cowie Guangxian Li R. Ferguson I. J. McEwen 《Journal of Polymer Science.Polymer Physics》1992,30(12):1351-1358
The miscibilities of ternary copolymer blends prepared from poly(styrene-stat-acrylonitrile), poly(styrene-stat-methyl methacrylate), and poly(methyl methacrylate-stat-acrylonitrile) were predicted by calculating the interaction parameter, χblend, for various blend combinations, from the corresponding binary segmental interaction parameters estimated from previous work. Binodal and spinodal curves were calculated using the Flory-Huggins theory and it was observed that the most accurate estimate of the boundary between miscible and immiscible blends was given by the spinodal. It has also been demonstrated that in some of the ternary blends with fixed copolymer compositions the miscibility of the blend can be altered by changing the ratio of the three components in the mixture. Conditions for miscibility in this ternary system, and possibly a general feature of all such systems, are (a) that at least two of the binary interaction parameters χij are less than the critical value χcrit, while the third should not be too much larger, that is, one of the copolymers may act as a compatibilizer for the other two copolymers, (b) that the difference Δχ = /χ12 ? χ13/ is small. © 1992 John Wiley & Sons, Inc. 相似文献
43.
The ternary system nitromethane (1) +diethyl ether (2) +polystyrene (3) has been examined by determining the demixing behavior of the polymer in the temperature–solvent composition plane. Enhanced solvation of the polymer is evidenced by the ability of the mixture to dissolve very high molecular weight (107 g/mol) polystyrene at intermediate solvent compositions compared with the behavior in the two solvents separately. The cosolvent action of the mixture is analyzed in terms of modern theories of polymer solution free volume. 相似文献
44.
CI mass spectra of the five isomeric vicinal d2-decanes have been recorded using methane and d4-methane as reagent gases. In contrast to earlier suggestions, we find that a large fraction of the alkyl fragment ions from n-decane are formed by elimination of olefins from the abundant [M – 1] ion. Only the C9 and C8 fragment ions are produced completely by a one-step reaction between the decanes and the methane reagent ions. Isotope exchange does not occur between the hydrocarbon and the reagent ions derived from d4-methane but extensive scrambling of the deuterium label in the d2-decanes does take place in the [M – 1] ion. 相似文献
45.
A. Larrínaga E.M. Elexpuru L.M. Len J.M.G. Cowie I.J. McEwen 《European Polymer Journal》1994,30(12):1347-1350
The copolymerisation of the monomers 2,4-dicyanobut-1-ene and N-vinyl carbazole has been studied. The presence of a charge transfer complex from these two monomers with a 1:1 stoichiometry has been established, and a value of 0.22 dm3 mol−1 at 298 K for the equilibrium constant for complex formation has been obtained from NMR measurements. The copolymer composition data have been analyzed allowing for the participation of the complex in the propagation reactions; the results have been compared with the predictions of two simpler terminal models and with the penultimate model. 相似文献
46.
Two series of ring substituted poly(di-phenyl itaconate)s have been prepared and characterized. The 2-, 3-, and 4-methylphenyl and chlorophenyl derivatives were studied and the glass transition temperatures (Tg) of the 3-substituted polymers were found to be lower than those of the 2- or 4-substituted polymers in each series. Some suggestion of polar effects contributing to Tg was evident in the poly(di-(4-chlorophenyl)itaconate). Dynamic mechanical studies revealed prominent damping peaks in the glassy state of the poly(di(methylphenyl)itaconate)s which can be attributed to methyl group relaxation. The chloro-derivatives showed fewer features, although in the 4-chloro compound there is evidence of restricted ring oscillation in the glass. 相似文献
47.
Ionkin AS Marshall WJ Fish BM Schiffhauer MF McEwen CN 《Chemical communications (Cambridge, England)》2008,(42):5432-5434
The first stable enols in 1,2-dihydrophosphetes and were synthesized and structurally characterized with intermolecular hydrogen bonds to phosphoryl groups in 10-membered dimeric structures; in contrast, trivalent analogue exists in keto-form, where such stabilization by hydrogen bonds is not feasible. 相似文献
48.
49.
50.