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1.
Vinyl ketones are prepared by reaction of an aldehyde with a vinyl Grignard reagent followed by a Swern oxidation. β-Phthalimido ketones are then obtained by 1,4-addition of phthalimide. 相似文献
2.
The first general approach to enantioselective catalysis of the Diels-Alder reaction with simple ketone dienophiles has been accomplished. The use of iminium catalysis has enabled enantioselective access to a fundamental Diels-Alder reaction variant that has previously been unavailable using chiral Lewis acid catalysis. A new chiral amine catalyst has been developed that allows a variety of monodentate cyclic and acyclic ketones to successfully participate in enantioselective [4 + 2] cycloadditions. A wide spectrum of cyclic and acyclic diene substrates can also be accommodated in this new organocatalytic transformation. A computational model is provided that is in accord with the sense of enantioinduction observed for all reactions conducted during the course of this study. 相似文献
3.
Conrad T. Pfeiffer Justin D. Northrup Jae Eun Cheong Melody A. Pham Matthew F.L. Parker Christian E. Schafmeister 《Tetrahedron letters》2018,59(30):2884-2888
Spiroligomers are a class of peptidomimetics that connect interchangeable, stereochemically pure, cyclic monomers through pairs of amide bonds to form diketopiperazines between the monomers. This enables them to adopt predictable and programmable structure due to the rigidity of the final molecule. We present a new method for the solid phase synthesis of highly functionalized spiroligomers that incorporates the use of the p-nitrobenzyloxycarbonyl (pNZ) as a temporary amine protecting group and the pentafluorophenyl ester for monomer activation. This new method allows for the synthesis of spiroligomers with higher purity and increased yields when compared to previous methods. This improved method of synthesis of functionalized spiroligomers will facilitate the development of applications as catalysts, therapeutics and membrane channels. 相似文献
4.
Two different adatom models for monolayer Ge coverage of the Si(111)?2 × 1 surface were studied with the Pseudopotential method. Total energy calculations indicate that the T4 model (adatom above the second layer) is preferable to the H3 model (adatom above the hollow site) 相似文献
5.
A formulation for diffusion-influenced reactions in solution is given in which reactive and translational contributions are separated, steady state rate-limiting step formulations are generalized to the dynamical case and the influence of different experimental initial conditions is isolated. 相似文献
6.
Voyles PM Chadi DJ Citrin PH Muller DA Grazul JL Northrup PA Gossmann HJ 《Physical review letters》2003,91(12):125505
Electron channeling experiments performed on individually scanned, single columns of atoms show that in highly n-type Si grown at low temperatures the primary electrically deactivating defect cannot belong to either the widely accepted class of donor-vacancy clusters or a recently proposed class of donor pairs. First-principles calculations suggest a new class of defects consisting of two dopant donor atoms near a displaced Si atom, which forms a vacancy-interstitial pair. These complexes are consistent with the present experimental results, the measured open volume of the defects, the observed electrical activity as a function of dopant concentration, and the enhanced diffusion of impurities in the presence of deactivated dopants. 相似文献
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