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排序方式: 共有80条查询结果,搜索用时 15 毫秒
1.
Sadagopan Raghavan A. RajenderM.Abdul Rasheed S.Ramakrishna Reddy 《Tetrahedron letters》2003,44(45):8253-8256
A novel, unprecedented transformation of δ-hydroxysulfoxides into substituted tetrahydrofurans by a silicon promoted Pummerer type reaction is disclosed. The transformation is shown to be general and is brought about under very mild reaction conditions. The products with the sulfide group at the anomeric carbon provide a suitable handle to carry out further transformations. 相似文献
2.
A convergent, flexible and stereoselective formal synthesis of MeBmt, the nonproteinogenic amino acid constituent of cyclosporin A is disclosed. The sulfinyl moiety has been exploited as the internal nucleophile to stereo- and regioselectively functionalize an allylic carbamate. 相似文献
3.
A highly efficient and stereoselective synthesis of (2R,3R,4R)-HMP is disclosed employing the sulfinyl group as an internal nucleophile to functionalize an olefin in the key step of the reaction sequence. The proline ring is elaborated by a (4C+N) cyclization. 相似文献
4.
A stereoselective synthesis of (−)-allosedamine is disclosed. β-Aminosulfoxide 4 was generated stereoselectively by condensation of the sulfinyl anion 2 with N-Ts imine 3. The bromohydrin 5 was obtained by intramolecular sulfinyl group participation and the piperidine ring of allosedamine was elaborated using the ring-closing metathesis (RCM) reaction. 相似文献
5.
A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products. 相似文献
6.
A straightforward and stereospecific synthesis of (+)-polyoxamic acid is disclosed. The key step of the synthesis involves the regio- and stereospecific bromohydration of an olefin via intramolecular participation by the sulfinyl group. 相似文献
7.
The key steps in the enantioselective synthesis of Tamiflu include an asymmetric Diels-Alder reaction, Mitsunobu inversion using Fukuyama modified Weinreb reagent, carbamate directed epoxidation. Epoxide opening with trimethylsilyl azide furnished a 3:1 mixture of regioisomers that converged to afford the same aziridine. Attempted preparation of the unsaturated ester regioselectively using 2-iodoxybenzoic acid (IBX) following Nicolaou’s protocol failed. The unsaturated ester was prepared by phenylselenylation followed by selenoxide elimination. 相似文献
8.
The kinetics of oxidation of ethyl S-phenylmercapto acetate and several para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B have been studied in 50% (V/V) aqueous ethanol medium containing phosphate buffer. This oxidation is of first order with respect to substrate and zero order with respect to oxidant. A catalytic effect of mercury is observed and the order with respect to mercury is fractional (0.74). The increase in pH decreases the rate of oxidation and the order with respect to H+ is 0.05. In general electron-releasing substituents accelerate the rate while electron-attracting groups retard the rate. A good correlation is found to exist between log k 1 and Hammett constants. Susceptibility of the reaction to the steric effect of ortho-substituents has been analyzed in the light of application of Taft's steric energy parameters. © John Wiley & Sons, Inc. 相似文献
9.
10.
Sadagopan Sathiyanarayanan Mario Sahre W. Kautek 《Fresenius' Journal of Analytical Chemistry》1999,363(2):197-201
The successful application of in-situ grazing incidence x-ray diffractometry (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12
electrolytes is demonstrated. A penetration/escape depth of about 1 μm could be detected for a smooth polycrystalline copper
foil and an x-ray incidence angle of 1.7°. Oxide layers generated at overpotentials less than about 0.5 V in respect to the
equilibrium formation potentials of Cu2O or CuO, respectively, showed a dependence of the crystalline oxide formation on the defect density of the copper substrate.
Highly disordered ground or polished specimens exhibited an order of magnitude higher GIXD reflexes from crystalline Cu2O than electrodeposited copper. Beyond overpotentials of 0.5 V, this epitaxial information for the Cu2O crystal growth became irrelevant. Further, GIXD turned out to be an appropriate tool to monitor atmospheric corrosion processes
under thin humidity films with oxygen access. When oxygen diffusion through the polymer window membrane is allowed, oxygen
reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)2 and Cu2O, though the potential was kept in the region of Cu2O.
Received: 30 July 1997 / Revised: 28 May 1998 / Accepted: 13 July 1998 相似文献