全文获取类型
收费全文 | 214篇 |
免费 | 4篇 |
专业分类
化学 | 196篇 |
力学 | 2篇 |
数学 | 8篇 |
物理学 | 12篇 |
出版年
2022年 | 1篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 8篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 13篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1967年 | 3篇 |
1963年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有218条查询结果,搜索用时 15 毫秒
41.
Diverted total synthesis and biological evaluation of gambierol analogues: elucidation of crucial structural elements for potent toxicity 总被引:2,自引:0,他引:2
Fuwa H Kainuma N Tachibana K Tsukano C Satake M Sasaki M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(19):4894-4909
Gambierol is a polycyclic ether toxin, which has been isolated from the marine dinoflagellate Gambierdiscus toxicus. A series of gambierol analogues have been prepared from an advanced intermediate of our total synthesis of gambierol and investigated for their toxicity against mice, thus providing the first systematic structure-activity relationships (SAR) of this polycyclic ether class of marine toxin. The SAR studies described herein clearly indicate that 1) the C28=C29 double bond within the H ring and the unsaturated side chain are the crucial structural elements required for exerting potent biological activity and 2) the C1 and C6 hydroxy groups, the C30 methyl group, and the C37=C38 double bond have little influence on the degree of neurotoxicity against mice. 相似文献
42.
Kadota I Takamura H Sato K Ohno A Matsuda K Satake M Yamamoto Y 《Journal of the American Chemical Society》2003,125(39):11893-11899
The convergent total syntheses of gambierol (1) and 16-epi-gambierol (2) have been achieved. The ABC and FGH ring segments 4 and 5 were prepared from known compounds 6 and 13, respectively, by linear manners. The fragments prepared were connected by our own synthetic strategy including the intramolecular allylation of alpha-acetoxy ether followed by ring-closing metathesis to furnish the octacyclic ether 3. The diiodoalkene 45, prepared from 3, was converted to the Z-iodoalkene 50 via a novel and stereoselective hydrogenolysis followed by deprotection. Construction of the triene side chain was performed by the modified Stille coupling of 50 with the Z-vinylic stannane 41 to afford 1. The similar transformations were carried out on the epimeric octacycle 34 to give 2, which showed no toxicity against mice at the concentration of 14 mg/kg. 相似文献
43.
44.
Tomohiro Shirai Jeffrey L.C. Wright Masayuki Satake Kazuo Tachibana 《Tetrahedron letters》2010,51(10):1394-3639
A monocyclic ether alkaloid, brevisamide (1) was isolated from the dinoflagellate Karenia brevis that produces a variety of ladder-frame polyethers. Its proposed biosynthetic intermediate (2) comprising a linear backbone with an E-olefin functionality was synthesized for biosynthetic studies on the marine ladder-frame polyethers. 相似文献
45.
Hirashita T Kamei T Satake M Horie T Shimizu H Araki S 《Organic & biomolecular chemistry》2003,1(21):3799-3803
Diastereoselective couplings of salicylaldehyde, anisaldehyde and 2-pyridylaldehyde with crotyl- and cinnamylindium reagents were studied. The syl/anti selectivity was found to depend largely on the ligands on the indium atom of the allylic indium reagents. A syn-selective cinnamylation of salicylaldehyde was realized by the combination of cinnamyl acetate and indium(I) iodide, whereas an anti-selective coupling with salicylaldehyde was achieved by the indium trichloride/aluminium-mediated cinnamylation. 相似文献
46.
Ukena T Satake M Usami M Oshima Y Fujita T Naoki H Yasumoto T 《Rapid communications in mass spectrometry : RCM》2002,16(24):2387-2393
Negative-ion fast-atom bombardment collision-induced dissociation tandem mass spectrometric (FAB-CID-MS/MS) methodology was successfully applied to verify the highly complex structure of ostreocin-D (MW 2633), a new palytoxin analog isolated from the marine dinoflagellate Ostreopsis siamensis and proposed to be 42-hydroxy-3,26-didemethyl-19,44-dideoxypalytoxin based on NMR data. The charge-remote fragmentations were facilitated by a negative charge introduced to a terminal amino group or to a hydroxyl group at the other terminus by a reaction with 2-sulfobenzoic acid cyclic anhydride. Product ions generated from the [M - H](-) ions provided information on the structural details of ostreocin-D. Comparisons between the spectral data for ostreocin-D and palytoxin also provided a rational basis for the assignments of product ions. 相似文献
47.
Naphthalene powder doped with 1-(2-thiazolylazo)-2-naphthol is used as collector for traces of metals, which are then determined by X-ray fluorescence analysis of the naphthalene. The method is used for traces of nickel. 相似文献
48.
The purpose of our research is to obtain an understanding of the binding mechanism and its correlations in terms of chemical structure and the potentiactive drug activity. The interaction of 5-fluorouracil (5-fluorouracil is used as an anticancer drug) with sodium poly-,L-glutamate in aqueous solution was studied with a spectral method and viscosity measurement. From the binding data, the molar change in enthalpy, entropy and the number of binding sites on the polymer were calculated. It is very interesting that the value ofH0 of the binding of 5-fluorouracil with sodium poly-,L-glutamate is smaller than that of 5-trifluoromethyluracil (although 5-trifluoromethyluracil is not used as an anticancer drug, the compound has a similar structure to 5-fluorouracil). 相似文献
49.
[reaction: see text] Although the reactivity of tropylium ion with aromatic substrates is low, the reaction of azepinium ion with aromatic substrates such as benzene, phenol, furan, and thiophene resulted in the formation of 2-aryl-2H-azepine as a major product. An exceptional result in the formation of ring-contracted product was observed in the reaction with pyrrole. 相似文献
50.
Ferrocene-bridged trisporphyrin (2) was synthesized by two-steps condensation of corresponding aldehydes and dipyrromethanes, and its self-assembling behavior based on the complementary coordination motif of imidazolylporphyrinatozinc(II) was investigated in conjunction with hinge-like flexibility given by freely rotating cyclopentadienyl rings of ferrocene connector. Ferrocene-bridged trisporphyrin (2) spontaneously and exclusively generated the dimeric ring (7) upon simple zinc(II) insertion, indicating that the freely rotating hinge connector favored the smallest ring formation. Taking advantage of the unique hinge-like flexibility of ferrocene, we attempted to transform the dimer ring into a mixture of porphyrin macrocycles by reorganizing the structure cleaved once by pyridine. A series of porphyrin macrocycles from trimer to decamer can be separated into its components by preparative gel permeation chromatograms. Macrocycles obtained are kept stable in the absence of coordinating solvents. On the other hand, they were easily transformed to the dimer ring in the presence of coordinating solvents such as methanol, showing that the transformation is completely reversible and can be controlled by the choice of the solvent system. A series of porphyrin macrocycles was confirmed via covalent linking of each complementary coordination dimer pair by metathesis reaction in the presence of Grubbs's catalyst. The coordination behavior of the bidentate ligands with different spacer lengths toward the dimer ring revealed that only the bidentate ligand (15) with a spacer length that matched the facing central porphyrins was selectively accommodated inside the ring. Coordination assembled flexible rings with tunable cavities and multiple coordination sites will be used as versatile hosts for a wide variety of guest molecules. 相似文献