全文获取类型
收费全文 | 219篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 161篇 |
力学 | 1篇 |
数学 | 40篇 |
物理学 | 23篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 14篇 |
2011年 | 17篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 19篇 |
2007年 | 17篇 |
2006年 | 22篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1891年 | 2篇 |
1890年 | 2篇 |
排序方式: 共有225条查询结果,搜索用时 206 毫秒
101.
Koshevoy IO Lin CL Hsieh CC Karttunen AJ Haukka M Pakkanen TA Chou PT 《Dalton transactions (Cambridge, England : 2003)》2012,41(3):937-945
A family of the diphosphines PPh(2)C(2)(C(6)H(4))(n)C(2)PPh(2) (n = 0-3), which possess a dialkynyl-arene spacer between the phosphorus atoms, was used for the synthesis of a series of bimetallic gold(I) complexes 1-7. Unlike the corresponding polynuclear Au(i) clusters, which show unique phosphorescence, 1-7 reveal dual emissions consisting of fluorescence and phosphorescence. The results are rationalized, in a semi-quantitative manner, by the trace (1-3) to zero (4-7) contribution of MLCT varying with the number of conjugated phenylene rings. As a result, unlike typical polynuclear Au(I) clusters with 100% triplet state population, the rate constant of the S(1)→T(1) intersystem crossing is drastically reduced to 10(9) s(-1) (4-7)-10(10) s(-1) (1-3), so that the fluorescence radiative decay rate can compete or even dominates. The drastic O(2) quenching of phosphorescence demonstrates the unprotected nature of the emission chromophores in 1-7, as opposed to the well protected, O(2) independent phosphorescence in most multimetallic Au(I) clusters. 相似文献
102.
103.
Moberg V Homanen P Selva S Persson R Haukka M Pakkanen TA Monari M Nordlander E 《Dalton transactions (Cambridge, England : 2003)》2006,(1):279-288
The chiral clusters [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] have been synthesized by derivatizing the parent carbonyl cluster [H(4)Ru(4)(CO)(12)] with the appropriate mono- or didentate chiral phosphine ligand. The phosphine-substituted clusters were found to be able to catalyze the (asymmetric) hydrogenation of tiglic acid albeit with relatively low selectivity (enantiomeric excesses varying from 0 to 23%). It was found that the stability of the chiral ruthenium hydride clusters and the product distribution obtained in the catalytic reactions are dependent on the nature of the chiral phosphine. The crystal structures of [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, O-DUPHOS (partially oxygenated ligand), DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] are presented. 相似文献
104.
In this paper we study several kinds of maximal almost disjointfamilies. In the main result of this paper we show that forsuccessor cardinals , there is an unexpected connection betweeninvariants ae(), b() and a certain cardinal invariant md(+)on +. As a corollary we get for example the following result.For a successor cardinal , even assuming that < = and 2= +, the following is not provable in ZermeloFraenkelset theory. There is a +-cc poset which does not collapse andwhich forces a() = + < ae() = ++ = 2. We also apply the ideasfrom the proofs of these results to study a = a() and non(M).2000 Mathematics Subject Classification 03E17 (primary), 03E05(secondary). 相似文献
105.
Kubicka D Kumar N Venäläinen T Karhu H Kubicková I Osterholm H Murzin DY 《The journal of physical chemistry. B》2006,110(10):4937-4946
The metal-support interactions on a series of catalysts of different acidities, including platinum-modified zeolites and H-MCM-41, are investigated by means of XPS, CO and pyridine adsorption, and a model reaction (ring opening of decalin). The electronic properties of Pt are influenced by the acidity of the support, and the alteration of Pt properties increases with increasing acidity of the support, as can be seen from the changes in the Pt binding energy and stretching frequency of adsorbed CO. At the same time, the presence of platinum affects the acidic properties of the supports by reducing the strength of the acid sites. This is observed directly as the changes in desorption of pyridine from the acid sites and indirectly as the suppression of cracking reactions during the ring opening of decalin on the Pt-modified catalysts. The observed results are discussed in terms of the interatomic potential model. 相似文献
106.
Antonio Doménech Igor O. Koshevoy Noemí Montoya Tapani A. Pakkanen 《Electrochemistry communications》2010,12(2):206-209
The heterotrimetallic Au(I)–Cu(I) aggregate [{Au3Cu2(C2C6H4Fc)6}Au3(PPh2C6H4PPh2)3](PF6)2 exhibits a well-defined solid state electrochemistry in contact with aqueous media, based on ferrocenyl-centred oxidation processes involving anion insertion. Upon attachment of microparticulate deposits of the cluster to graphite electrodes, distinctive electrochemical responses can be obtained for fluoride and chloride ions in aqueous media. 相似文献
107.
108.
Tapani Hyttinen 《Mathematical Logic Quarterly》1997,43(1):134-142
In the first part of this paper we let M be a stable homogeneous model and we prove a nonstructure theorem for the class of all elementary submodels of M, assuming that M is ‘unsuperstable’ and has Skolem functions. In the second part we assume that M is an unstable homogeneous model of large cardinality and we prove a nonstructure theorem for the class of all elementary submodels of M. 相似文献
109.
Tapani Hyttinen 《Mathematical Logic Quarterly》2005,51(3):291-298
We show that if M is a strongly minimal large homogeneous structure in a countable similarity type and the pregeometry of M is locally modular but not modular, then the pregeometry is affine over a division ring. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
110.
Jarmo Ropponen Tero Tuuttila Manu Lahtinen Sami Nummelin Kari Rissanen 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5574-5586
The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004 相似文献