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排序方式: 共有166条查询结果,搜索用时 15 毫秒
1.
Vicky Mak 《Operations Research Letters》2007,35(1):36-44
This paper, using the Unconstrained Shape Matrix Optimization Problem as a test bed, we investigate various aspects of variable aggregation and disaggregation for a class of integer programs that contains binary expansion. We present theoretical and numerical results, and propose an iterative algorithm for exact solutions. 相似文献
2.
Victor A.?ZammitEmail author Nigel T.?Price Vicky N.?Jackson Byun-Sung?Park 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1299-1309
Summary. Carnitine acyltransferases catalyse equilibria between acyl-CoA esters and the respective acylcarnitines. Therefore, they act not only as pathway enzymes, but also as modulators of acyl-CoA concentrations within individual sub-cellular compartments. Because acyl-CoA esters are potent biologically active metabolites, carnitine acyltransferase activities are potentially able to affect a diverse range of physiological processes, ranging from insulin secretion, to appetite control, and insulin sensitivity of tissues. The distinctive subcellular distributions of the different types of carnitine acyltransferases also enables them to participate in the transfer of acyl moieties across intracellular membranes, and of particular acylcarnitine esters across the plasma membrane and into the plasma. Pharmacological strategies that make use of these properties to improve cell function are discussed. 相似文献
3.
J. M. Gaullier M. Bazin A. Valla M. Giraud R. Santus 《Journal of photochemistry and photobiology. B, Biology》1995,30(2-3)
The pyrrole-amino acid and peptide N-conjugates synthesized from tyrosine, histidine and glutathione very effectively quench the 1270 nm singlet oxygen luminescence, at rates ranging from 108 to 109 M−1 s−1. Nuclear magnetic resonance spectroscopy suggests that the electron-donating properties of the methyl groups after 2,5-dimethyl substitution on the pyrrole ring are probably an important determinant of the reactivity of singlet oxygen with the N-conjugate of glutathione. However, intramolecular interactions between the pyrrole ring and the side chain may also modulate the reactivity of the antioxidant as suggested by absorption and fluorescence spectroscopies carried out on tyrosine derivatives. Efficient fluorescence quenching of the phenol ring by the pyrrole ring occurs in the tyrosine derivatives. The reactivities of these antioxidants with 1O2 are comparable in methanol, ethanol and D2O. 相似文献
4.
Alain Valla Benoist Valla Régis Le Guillou Dominique Cartier Laurent Dufossé Roger Labia 《Helvetica chimica acta》2007,90(3):512-520
Since the C15 β‐end‐group aldehyde 10 ((β‐ionylidene)acetaldehyde), an excellent intermediate in the syntheses of retinoids, can be synthesized in many ways from β‐ionone, and since the corresponding acyclic C15 ψ‐end‐group aldehyde 5 can easily be synthesized from citral ( 1 ) (Scheme 3), we applied the C15+C5 route to the syntheses of γ‐retinal ((all‐E)‐ 8 ) (Scheme 3) and retinal ((all‐E)‐ 13 ) (Scheme 4), and therefore, by coupling (2×C20→C40), to the preparation of lycopene ( 14 ) and β‐carotene ( 15 ) (Scheme 5). Our new syntheses of retinal ((all‐E)‐ 13 ) and γ‐retinal ((all‐E)‐ 8 use an extended aldol reaction with a C6 building block that incorporates a C5 unit after decarboxylation. 相似文献
5.
6.
Manuela F. Frasco Vicky Vamvakaki Nikos Chaniotakis 《Journal of nanoparticle research》2010,12(4):1449-1458
In this study, we report on a novel hybrid structure for the direct sensing of metal ions based on the use of CdSe quantum
dots functionalized with tetrapyridyl-substituted porphyrin, a cation-selective carrier. It is shown that the porphyrin ion
carrier coordinates to Cd atoms of the CdSe quantum dots through the Lewis basic pyridyl groups. The porphyrin-quantum dot
ligation allows for the direct communication between the porphyrin and the underlying CdSe quantum structure. The quantum
yield of CdSe is maintained despite the robust capping generated when the unmetallated porphyrins coordinate onto the quantum
dots. Upon coordination with zinc ions, this porphyrin capping is shown to strongly contribute to the increase in the fluorescence
efficiency of CdSe, via an activating interaction with the quantum dots surface. The results provide the grounds for the development
of highly sensitive and selective nano-optode sensing systems. 相似文献
7.
8.
Easy two‐step synthesis of a series of dithiines was performed from succinic anhydride via cyclization of the corresponding 4‐(alkylamino)‐4‐oxobutanoic acids (succinamic acids). The reaction, carried out in polar aprotic solvents, gave 4,8‐dithiine‐indacene‐1,3,5,7‐tetraones (diimides 3) via 3,7‐bis‐4,8‐dithia‐indacene‐1,5‐diones (diisoimides 2), which could be isolated. Surprisingly, in this reaction, thionyl chloride appeared as an oxidant, and this process seemed to be useful for the syntheses of S‐containing heterocyclic compounds such as 1,4‐dithiins. A mechanistic pathway was considered. 相似文献
9.
Alain Valla Nathalie Méheux Dominique Cartier Benoist Valla Laurent Dufossé 《合成通讯》2013,43(2):184-190
A synthesis of a new C-15 phosphorus ylide from a C-14 enaminone is reported. This reagent, which undergoes selective 1,2- or 1,4-additions with saturated and unsaturated aldehydes, may find some synthetic use for the preparation of β-end-group retinoid derivatives. 相似文献
10.
Colette Lebrun Dr. Matthieu Starck Vicky Gathu Yves Chenavier Dr. Pascale Delangle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16566-16573
Peptides are interesting tools to rationalize uranyl–protein interactions, which are relevant to uranium toxicity in vivo. Structured cyclic peptide scaffolds were chosen as promising candidates to coordinate uranyl thanks to four amino acid side chains pre‐oriented towards the dioxo cation equatorial plane. The binding of uranyl by a series of decapeptides has been investigated with complementary analytical and spectroscopic methods to determine the key parameters for the formation of stable uranyl–peptide complexes. The molar ellipticity of the uranyl complex at 195 nm is directly correlated to its stability, which demonstrates that the β‐sheet structure is optimal for high stability in the peptide series. Cyclodecapeptides with four glutamate residues exhibit the highest affinities for uranyl with log KC=8.0–8.4 and, therefore, appear as good starting points for the design of high‐affinity uranyl‐chelating peptides. 相似文献