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41.
Correa A Tellitu I Domínguez E Moreno I Sanmartin R 《The Journal of organic chemistry》2005,70(6):2256-2264
[reaction: see text] The synthesis of a series of optically pure benzo-, naphtho-, and heterocycle-fused pyrrolo[2,1-c][1,4]-diazepin-5,11-dione derivatives starting from l-proline methyl ester is presented. The synthetic plan includes an aroylation step at the proline nitrogen followed by transformation of the ester residue into a N-methoxyamide group. The subsequent key cyclization step embraces the PIFA mediated formation of a N-acylnitrenium intermediate and its succeeding intramolecular trapping by the aromatic ring. The presented general approach solves the need of starting from not very accessible amino (or a related functionality) aromatic starting materials, and its effectiveness is demonstrated in the synthesis of the antitumor antibiotic DC-81. 相似文献
42.
Zingaretti L Mariano Correa N Boscatto L Chiacchiera SM Durantini EN Bertolotti SG Rivarola CR Silber JJ 《Journal of colloid and interface science》2005,286(1):245-252
The distribution of different aliphatic and aromatic amines: n-butylamine (n-BA), isobutylamine (i-BA), tert-butylamine (t-BA), piperidine (PIP), N,N-dimethylaniline (DMA) and N-methylaniline (MA) in water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate(AOT)/n-hexane reverse micelles was investigated by steady-state fluorescence measurements. The partition constants were measured by an indirect method based on the effect that amine partitioning exert on the bimolecular rate of the reaction between a microphase incorporated fluorophore (Ru(bpy)2+(3)) and the quencher, (Fe(CN)3-(6)). For MA, that can act as a quencher of the fluorophore a direct method was used. The results show that primary amines have larger partition constants than the secondary ones. For tertiary amines the distribution constants were practically negligible. Laser flash photolysis experiments confirmed that tertiary amines, both aliphatic and aromatic, are not incorporated to the micellar pseudophase. The effect of the amine structure on the partition constant was analyzed through linear solvation free energy relationships (LSER) using solute parameters and compared with those obtained for alcohols. Hydrogen bond interactions with the AOT polar heads appear to be the main driving force for the distribution of amines between the organic and micellar pseudophases, whereas the size of the alkyl or aromatic group tends to hinder it. 相似文献
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José R. Correa Cristina G. Fernandes Yoshiko Wakabayashi 《Mathematical Programming》2010,124(1-2):255-269
In the late seventies, Megiddo proposed a way to use an algorithm for the problem of minimizing a linear function a 0 + a 1 x 1 + . . . + a n x n subject to certain constraints to solve the problem of minimizing a rational function of the form (a 0 + a 1 x 1 + . . . + a n x n )/(b 0 + b 1 x 1 + . . . + b n x n ) subject to the same set of constraints, assuming that the denominator is always positive. Using a rather strong assumption, Hashizume et al. extended Megiddo’s result to include approximation algorithms. Their assumption essentially asks for the existence of good approximation algorithms for optimization problems with possibly negative coefficients in the (linear) objective function, which is rather unusual for most combinatorial problems. In this paper, we present an alternative extension of Megiddo’s result for approximations that avoids this issue and applies to a large class of optimization problems. Specifically, we show that, if there is an α-approximation for the problem of minimizing a nonnegative linear function subject to constraints satisfying a certain increasing property then there is an α-approximation (1/α-approximation) for the problem of minimizing (maximizing) a nonnegative rational function subject to the same constraints. Our framework applies to covering problems and network design problems, among others. 相似文献
45.
Diego Paolo F. Correa José Roberto C. Piqueira 《Communications in Nonlinear Science & Numerical Simulation》2013,18(8):2142-2152
There are several works showing that nonzero time delay between nodes in an oscillator network can be responsible for several kinds of behavior as synchronization and chaos. Here, by using the Lyapunov linearizing method, in a system of two coupled oscillators derived as a particular case of the full connected network, it is shown that the time delay parameter has two sets of values: one that destabilizes the whole system and other that implies stability. Besides, there is a set of time delay values responsible for chaotic behaviors, even in a simple coupled oscillators system. 相似文献
46.
In this article we study nonassociative rings satisfying the polynomial identity x(yz) = y(zx), which we call “cyclic rings.” We prove that every semiprime cyclic ring is associative and commutative and that every cyclic right-nilring is solvable. Moreover, we find sufficient conditions for the nilpotency of cyclic right-nilrings and apply these results to obtain sufficient conditions for the nilpotency of cyclic right-nilalgebras. 相似文献
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For any positive integer D, we construct a minimal dynamical system with mean dimension equal to D/2 that cannot be embedded into (([0, 1] D )?, shift). 相似文献
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Mathematical Programming - We study the worst-case performance guarantee of locally optimal solutions for the problem of minimizing the total weighted and unweighted completion time on parallel... 相似文献
50.