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131.
Joel S. Reis Robert C. Simon Wolfgang Kroutil Leandro H. Andrade 《Tetrahedron: Asymmetry》2013,24(23):1495-1501
The asymmetric reductive amination of aryl-ketones bearing various boron-functionalities (acid, ester or potassium trifluoroborates) was investigated employing enantiocomplementary ω-transaminases as catalysts. Under the optimized conditions, high conversions (up to 94%) and excellent ee’s (up to >99%) were obtained providing access to both (R)- and (S)-configured amino-aryl boronates under mild reaction conditions. 相似文献
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João Pedro A. Souza Dr. Leociley R. A. Menezes Dr. Francielle P. Garcia Dr. Débora B. Scariot Dr. Pamela T. Bandeira Mateus B. Bespalhok Dr. Siddhartha O. K. Giese Dr. David L. Hughes Prof. Dr. Celso V. Nakamura Prof. Dr. Andersson Barison Prof. Dr. Alfredo R. M. Oliveira Prof. Dr. Renan B. Campos Prof. Dr. Leandro Piovan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(58):14427-14437
Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te−O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te−O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center–containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4-oxatellurane LQ50 (IC50=4.1±1.0; SI=12), 1,2λ4-oxatellurolane LQ04 (IC50=7.0±1.3; SI=7) and 1,2λ4-benzoxatellurole LQ56 (IC50=5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C. 相似文献
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Eduardo S. G. Leandro 《Archive for Rational Mechanics and Analysis》2003,167(2):147-177
We consider here the classical question of finiteness (see Smale [13] and Wintner [15]) – given n point masses, is the corresponding number of central configurations finite? We prove finiteness for a particular family of
d-dimensional symmetrical configurations of d+2 point masses. Also, we study the bifurcations of these configurations and provide the exact number of central configurations
when d=2, 3. All our results stem from the application of a new method for studying symmetrical classes of central configurations,
which is presented in this work.
(Accepted September 23, 2002) Published online February 14, 2003
Communicated by P. Rabinowitz 相似文献
139.
Leandro M. Del Pezzo Carolina A. Mosquera Julio D. Rossi 《Bulletin of the Brazilian Mathematical Society》2014,45(3):405-432
In this paper we give some estimates for nonlinear harmonic measures on trees. In particular, we estimate in terms of the size of a set D the value at the origin of the solution to u(x) = F((x, 0),...,(x,m ? 1)) for every x ∈ \(\mathbb{T}_m \) , a directed tree with m branches with initial datum f + χD. Here F is an averaging operator on ? m , x is a vertex of a directed tree \(\mathbb{T}_m \) with regular m-branching and (x, i) denotes a successor of that vertex for 0 ≤ i ≤ m ? 1. 相似文献
140.
The use of multivariate curve resolution (MCR) to build multivariate quantitative models using data obtained from comprehensive two-dimensional gas chromatography with flame ionization detection (GC × GC-FID) is presented and evaluated. The MCR algorithm presents some important features, such as second order advantage and the recovery of the instrumental response for each pure component after optimization by an alternating least squares (ALS) procedure. A model to quantify the essential oil of rosemary was built using a calibration set containing only known concentrations of the essential oil and cereal alcohol as solvent. A calibration curve correlating the concentration of the essential oil of rosemary and the instrumental response obtained from the MCR-ALS algorithm was obtained, and this calibration model was applied to predict the concentration of the oil in complex samples (mixtures of the essential oil, pineapple essence and commercial perfume). The values of the root mean square error of prediction (RMSEP) and of the root mean square error of the percentage deviation (RMSPD) obtained were 0.4% (v/v) and 7.2%, respectively. Additionally, a second model was built and used to evaluate the accuracy of the method. A model to quantify the essential oil of lemon grass was built and its concentration was predicted in the validation set and real perfume samples. The RMSEP and RMSPD obtained were 0.5% (v/v) and 6.9%, respectively, and the concentration of the essential oil of lemon grass in perfume agreed to the value informed by the manufacturer. The result indicates that the MCR algorithm is adequate to resolve the target chromatogram from the complex sample and to build multivariate models of GC × GC-FID data. 相似文献