全文获取类型
收费全文 | 125篇 |
免费 | 1篇 |
专业分类
化学 | 120篇 |
力学 | 3篇 |
数学 | 1篇 |
物理学 | 2篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2014年 | 1篇 |
2013年 | 3篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 1篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有126条查询结果,搜索用时 15 毫秒
21.
22.
The cycloadduct (5) , which is conveniently prepared by irradiation of (4), is converted a 4-step sequence, into the tricyclic ketone (2) and its epimer (2); the sequence formally completes a new total synthesis of (±)-zizaene (1) and its Me-epimer. 相似文献
23.
Matthew J. Palframan Krishna K. Bandi James G.C. Hamilton Gerald Pattenden 《Tetrahedron letters》2018,59(20):1921-1923
A new sex-aggregation pheromone, sobralene, produced by the sand fly Lutzomyia longipalpis from Sobral (Ceará State, Brazil) is shown to have the novel 6,12-membered ring-fused diterpene structure 3. It is proposed that sobralene is a likely shunt metabolite of the taxadiene synthase-catalysed cyclisation of geranygeranyl diphosphate. 相似文献
24.
Pattenden G Ashweek NJ Baker-Glenn CA Kempson J Walker GM Yee JG 《Organic & biomolecular chemistry》2008,6(8):1478-1497
A new, second generation, total synthesis of ulapualide A (1), whose stereochemistry was recently determined from X-ray analysis of its complex with the protein actin, is described. The synthesis is designed and based on some speculation of the biosynthetic origin of the contiguous tris-oxazole unit in ulapualide A, alongside that of the related co-metabolites that contain only two oxazole rings, e.g. 6 and 7. The mono-oxazole carboxylic acid 67b and the mono-oxazole secondary 55b alcohol which, together, contain all of the 10 asymmetric centres in the natural metabolite, were first elaborated using a combination of contemporary asymmetric synthesis protocols. Esterification of 67b with 55b under Yamaguchi conditions gave the ester 77 which was then converted into the omega-amino acid 18a following simultaneous deprotection of the t-butyl ester and the N-Boc protecting groups. Macrolactamisation of 18a, using HATU, now gave the key intermediate macrolactam 17, containing two of the three oxazole rings in ulapualide A (1). A number of procedures were used to introduce the third oxazole ring in ulapualide A from 17, including: a) cyclodehydration to the oxazoline 78a followed by oxidation using nickel peroxide leading to 76; b) dehydration to the enamide 79, followed by conversion into the methoxyoxazoline 78b, via 80, and elimination of methanol from 78b using camphorsulfonic acid. The tris-oxazole macrolide 76 was next converted into the aldehyde 82b in four straightforward steps, which was then reacted with N-methylformamide, leading to the E-alkenylformamide 83. Removal of the TBDPS protection at C3 in 83 finally gave (-)-ulapualide A, whose 1H and 13C NMR spectroscopic data were indistinguishable from those obtained for naturally derived material. It is likely that the tris-oxazole unit in ulapualide A (1) is derived in nature from a cascade of cyclodehydrations from an acylated tris-serine precursor, e.g.9, followed by oxidation of the resulting tris-oxazoline intermediate, i.e.10. It is also plausible to speculate that the biosynthesis of metabolites related to ulapualide A, e.g. the bis-oxazole 6 and the imide 7, involve cyclisations of just two of the serine units in 9. These speculations were given some credence by carrying out pertinent interconversions involving the bis-oxazole amide 24, the enamide 25, the imide 26, the oxazoline 27 and the tris-oxazole 30 as model compounds. An alternative strategy to the tris-oxazole macrolide intermediate 76 was also examined, involving preliminary synthesis of the aldehyde 73, containing a shortened (C25-C34) side chain from 67b and 47b. A Wadsworth-Emmons olefination reaction between 73 and the phosphonate ester 74 led smoothly to the E-alkene 75, but we were not able to reduce selectively the conjugated enone group in 75 to 76 without simultaneous reduction of the oxazole alkene bond, using a variety of reagents and reaction conditions. 相似文献
25.
Bertram A Maulucci N New OM Mohd Nor SM Pattenden G 《Organic & biomolecular chemistry》2007,5(10):1541-1553
Treatment of a 1 : 1 mixture of the thiazole-based amino acids 8a and 8b with FDPP-i-Pr(2)NEt in CH(3)CN gave a mixture of the cyclic trimers 14, 15, 16 and 17 and the cyclic tetramers 19 and 23 in the ratio 2 : 7 : 5 : 8 : 1 : 1 and in a combined yield of 70%. Separate coupling reactions between the bisimidazole amino acid 45 and the thiazole/oxazole amino acids 43a and 42a in the presence of FDPP-i-Pr(2)NEt led to the bisimidazole based cyclic trimers 55 and 57 respectively (54-57%) and to the cyclic tetramer 56 (8-11%). Similar coupling reactions involving the bisthiazole and bisoxazole amino acids 49 and 47 with the imidazole/oxazole/thiazole amino acids 41a, 42a and 43a gave rise to the library of oxazole, thiazole and imidazole-based cyclic peptides 58, 59, 60, 61, 62, 63, 64 and 65. A coupling reaction between the bisthiazole amino acid 49 and the oxazole amino acid 73 led to an efficient (36% overall) synthesis of bistratamide H (67) found in the ascidian Lissoclinum bistratum. Coupling reactions involving oxazolines with thiazole amino acids were less successful. Thus, a coupling reaction between the phenylalanine-based oxazoline amino acid 71a and either the thiazole amino acid 8a or the bisthiazole amino acid 74 gave only a 2% yield of the cyclic hexapeptide didmolamide A (4) found in the ascidian Didemnum molle. Didmolamide B (68) was obtained in 9% yield from a coupling reaction between 74 and the phenylalanine threonine amino acid 72, using either FDPP or DPPA. 相似文献
26.
F.L. Pratt S.J. Blundell P.A. Pattenden W. Hayes K.H. Chow A.P. Monkman T. Ishiguro K. Ishida K. Nagamine 《Hyperfine Interactions》1997,106(1-4):33-38
We report studies of spin dynamics in the conducting polymers polyaniline and polypyrrole using both μ+SR and μ-SR techniques. These measurements reveal characteristic field dependences and cutoff frequencies for the muon spin relaxation
which can be related to the spin diffusion process. Clear evidence is seen for increased spin localisation at low temperatures
where a crossover occurs from two or three dimensional spin diffusion to a one dimensional diffusion regime.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
27.
A total synthesis of the 5-ylidenepyrrole-2-one pukeleimide A (3), a constituent of the marine blue-green alga , is described. 相似文献
28.
A total synthesis of (±)-pentalenene (1), based on transannulation of the bicyclo[6.3.0] undecadiene (15) in the presence of boron trifluoride etherate, is described. 相似文献
29.
30.
The total synthesis of (±)-citreoviral(2) and also of -citreoviral(21), using two conceptually distinct approaches starting from methyl tiglate, are described. 相似文献