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1.
Journal of Thermal Analysis and Calorimetry - The paper presents the results of investigation on the development of frits for single fast-firing glazes with variable BaO content based on the... 相似文献
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Monika Szulc Justyna Samaszko-Fiertek Rafał Ślusarz Kornelia Kowalska Artur Sikorski 《Journal of carbohydrate chemistry》2016,35(3):161-171
Solid phase peptide synthesis (SPPS) of two selected muramyl pentapeptide derivatives is described. The simplicity of removing the protecting groups via one-step deprotection and cleavage from the resin is the biggest advantage of SPPS. Using this method, two muramyl pentapeptide derivatives, D-MurN3-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ser (5) and D-MurN3-L-Ala-D-iGlu-L-Lys-D-Ala-D-Ala (6), were obtained. Their chemical structures were confirmed by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy. To determine the absolute configuration of the carbon atom in the side chain of the muramic acid derivative, single-crystal X-ray diffraction measurements were recorded. 相似文献
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Bis(N‐Confused Porphyrin) as a Semirigid Receptor with a Chirality Memory: A Two‐Way Host Enantiomerization through Point‐to‐Axial Chirality Transfer 下载免费PDF全文
Prof. Piotr J. Chmielewski Dr. Marta Siczek Prof. Marcin Stępień 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2547-2559
The adduct formation of protonated bis(N‐confused porphyrin) (BNCP, 3,3′‐bis(meso‐tetratolyl‐2‐aza‐21‐carbaporphyrin) with chiral anions, carboxylic acids, and alcohols was studied in solution by means of 1H NMR and circular dichroism (CD) spectroscopic analysis and DFT methods. The addition of enantiopure guests to the acidified BNCP resulted in optical activity that vanished after neutralization. Pairs of the 1H NMR‐distinguishable diastereomers were formed when enantiopure guests were applied, although a single form was observed upon the addition of the racemic mixtures in each case. Unidirectional configuration change that led to diastereomeric excess was observed in several instances. Such an excess was memorized by metalation of the adducts with AgBF4, thus resulting in optically active silver(III) complexes of BNCP with some enantiomeric excess. Absolute configurations of BNCP cations and bis(zinc) and bis(silver(III)) complexes were determined on the basis of time‐dependent (TD)‐DFT calculations of their CD spectra. It was shown that some of the chiral carboxylates induced opposite directions of enantiomerization of di‐ and tetracations or di‐/tetracation and bis(zinc) complexes. The source of the optical activity of the equimolar diastereomeric mixture of adducts is discussed. 相似文献
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Nonlinear Dynamics - The modeling of a ferromagnetic core coil magnetic hysteresis has been considered. The measurement basis consisted of waveforms that have been recorded for various levels of... 相似文献
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Marcin Kujawa 《Continuum Mechanics and Thermodynamics》2020,32(3):647-664
The paper addresses the issue of local buckling of compressed flanges of cold-formed thin-walled channel columns and beams with nonstandard flanges composed of aluminium alloys. The material behaviour follows the Ramberg–Osgood law. It should be noted that the proposed solution may be also applied for other materials, for example: stainless steel, carbon steel. The paper is motivated by an increasing interest in nonstandard cold-formed section shaping in local buckling analysis problems. Furthermore, attention is paid to the impact of material characteristics on buckling stresses in a nonlinear domain. The objective of the paper is to propose a finite element method (FEM) model and a relevant numerical procedure in ABAQUS, complemented by an analytical one. It should be noted that the proposed FEM energetic technique makes it possible to compute accurately the critical buckling stresses. The suggested numerical method is intended to accurately follow the entire structural equilibrium path under an active load in elastic and inelastic ranges. The paper is also focused on correct modelling of interactions between sheets of cross section of a possible contact during buckling analysis. Furthermore, the FEM results are compared with the analytical solution. Numerical examples confirm the validity of the proposed FEM procedures and the closed-form analytical solutions. Finally, a brief research summary is presented and the results are discussed further on. 相似文献
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Karol Kraszewski Ireneusz Tomczyk Dr. Aneta Drabinska Dr. Krzysztof Bienkowski Dr. Renata Solarska Dr. Marcin Kalek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11584-11592
The oxidative dearomatization of phenols with the addition of nucleophiles to the aromatic ring induced by hypervalent iodine(III) reagents and catalysts has emerged as a highly useful synthetic approach. However, experimental mechanistic studies of this important process have been extremely scarce. In this report, we describe systematic investigations of the dearomatizing hydroxylation of phenols using an array of experimental techniques. Kinetics, EPR spectroscopy, and reactions with radical probes demonstrate that the transformation proceeds by a radical-chain mechanism, with a phenoxyl radical being the key chain-carrying intermediate. Moreover, UV and NMR spectroscopy, high-resolution mass spectrometry, and cyclic voltammetry show that before reacting with the phenoxyl radical, the water molecule becomes activated by the interaction with the iodine(III) center, causing the Umpolung of this formally nucleophilic substrate. The radical-chain mechanism allows the rationalization of all existing observations regarding the iodine(III)-promoted oxidative dearomatization of phenols. 相似文献