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581.
A stereoselective synthesis of the C-glycoside analogue of beta-D-galactosyl-(5R,2S)-hydroxylysine (1) has been achieved starting from tetra-O-benzyl-D-galactopyranosyl lactone. The synthesis involved establishment of three stereogenic centers in an unambiguous manner. A facially selective Grignard reaction followed by a silane reduction was used for the anomeric position of the C-galactose residue. An Evans allylation established the configuration of the delta-aminomethylene group of the hydroxylysine moiety, whereas an asymmetric hydrogenation utilizing Burk's catalyst was used for the alpha-amino acid moiety itself. The synthesis was completed in 17 steps with an overall yield of 18%, resulting in the most complex and functionalized C-glycoside analogue of a naturally occurring glycosylated amino acid prepared to date. In addition, amino acid 1 was incorporated in a glycopeptide from type II collagen known to be crucial for the response of autoimmune T cells obtained in models of rheumatoid arthritis. A preliminary immunological study revealed that four out of five members in a panel of T cell hybridomas were able to recognize this C-linked glycopeptide when presented by A(q) class II MHC molecules. 相似文献
582.
Lei Tao David B. Dahl Lisa M. Pérez David H. Russell 《Journal of the American Society for Mass Spectrometry》2009,20(9):1593-1602
Molecular dynamics (MD) is an essential tool for correlating collision cross-section data determined by ion mobility spectrometry
(IMS) with candidate (calculated) structures. Conventional methods used for ion structure determination rely on comparing
the measured cross-sections with the calculated collision cross-section for the lowest energy structure(s) taken from a large
pool of candidate structures generated through multiple tiers of simulated annealing. We are developing methods to evaluate
candidate structures from an ensemble of many conformations rather than the lowest energy structure. Here, we describe computational
simulations and clustering methods to assign backbone conformations for singly-protonated ions of the model peptide (NH2-Met-Ile-Phe-Ala-Gly-Ile-Lys-COOH) formed by both MALDI and ESI, and compare the structures of MIFAGIK derivatives to test
the ‘sensitivity’ of the cluster analysis method. Cluster analysis suggests that [MIFAGIK + H]+ ions formed by MALDI have a predominantly turn structure even though the low-energy ions prefer partial helical conformers.
Although the ions formed by ESI have collision cross-sections that are different from those formed by MALDI, the results of
cluster analysis indicate that the ions backbone structures are similar. Chemical modifications (N-acetyl, methylester as
well as addition of Boc or Fmoc groups) to MIFAGIK alter the distribution of various conformers; the most dramatic changes
are observed for the [M + Na]+ ion, which show a strong preference for random coil conformers owing to the strong solvation by the backbone amide groups. 相似文献
583.
J.J.K. Lång P. Laukkanen M.P.J. Punkkinen M. Ahola-Tuomi M. Kuzmin V. Tuominen J. Dahl M. Tuominen R.E. Perälä K. Schulte J. Adell J. Sadowski J. Kanski M. Guina M. Pessa K. Kokko B. Johansson L. Vitos I.J. Väyrynen 《Surface science》2011,605(9-10):883-888
Tin (Sn) induced (1 × 2) reconstructions on GaAs(100) and InAs(100) substrates have been studied by low energy electron diffraction (LEED), photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS) and ab initio calculations. The comparison of measured and calculated STM images and surface core-level shifts shows that these surfaces can be well described with the energetically stable building blocks that consist of Sn–III dimers. Furthermore, a new Sn-induced (1 × 4) reconstruction was found. In this reconstruction the occupied dangling bonds are closer to each other than in the more symmetric (1 × 2) reconstruction, and it is shown that the (1 × 4) reconstruction is stabilized as the adatom size increases. 相似文献
584.
585.
Yu. M. Dahl 《Doklady Physics》2016,61(6):293-296
An exact analytical solution of the problem in elasticity theory about stretching of a plane with an infinite lattice of rectilinear cuts has been obtained. The analysis is based on G.V. Kolosov’s formulas associating the stress components with two regular functions of a complex variable. The obtained solution revealed the original effects of stretching stress screening and localization of compressive stresses between cuts. 相似文献
586.
587.
Mattias Appel Gerald Fleischer Dieter Geschke Jrg Krger Mario Winkler Amadou C. Dieng Grard Riess 《Macromolecular rapid communications》1996,17(2):81-85
The decrease of the droplet radii of silicone oil dispersed in a polystyrene matrix at a temperature of 140°C with increasing time was measured by NMR dynamic imaging. From this time dependence the diffusion coefficient of the silicone oil into the matrix was calculated to be 7 · 10−18 m2 · s−1. The uptake of the silicone oil in the polystyrene matrix was confirmed by broad line NMR measurements. 相似文献