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131.
Nikolay O. Mchedlov‐Petrossyan Natalya A. Vodolazkaya Anna G. Yakubovskaya Aleksey V. Grigorovich Vera I. Alekseeva Lyubov P. Savvina 《Journal of Physical Organic Chemistry》2007,20(5):332-344
The peculiarities of the structure of the fluorescent dye N,N'‐di‐n‐octadecylrhodamine advantage its using as an interfacial acid–base probe in aqueous micellar solution of colloidal surfactants. Two long hydrocarbon tails of the dye provide similar orientation of both cation and zwitterion on the micelle/water interface, with the ionizing group COOH exposed to the Stern region in all the systems studied. Further, the charge type of the acid–base couple, A+B±, ensures similar values of the ‘intrinsic’ contribution, pK, to the ‘apparent’ pK value in micelles of different surfactants. This makes the indicator suitable for determination of electrical surface potentials, Ψ. The pKs have been obtained in cationic, anionic, zwitterionic, and nonionic surfactant systems, at various salt background. In total 17 systems were studied. At bulk counterion concentration of ca. 0.05 M, the pK values vary from 2.14 ± 0.07 in n–C18H37N(CH3)Cl– micelles to 5.48 ± 0.06 in n–C16H33OSONa+ micelles. The Ψ values, corresponding to the Stern region of micelles, have been evaluated as Ψ = 59.16 pK–pK for T = 298.15 K. The pK parameter was equated to the average value of 4.23 in nonionic surfactants (4.12–4.32, depending on the surfactant type). For cetyltrimethylammonium bromide and sodium n‐dodecylsulfate micelles, the Ψ values (±(7–11) mV) appeared to be +118 mV and at bulk Br? concentration 0.019 M and ?76 mV at bulk Na+ concentration 0.020 M, respectively. This satisfactorily agrees with the theoretical values +111 and ?84 mV, estimated using the Oshima, Healy, and White equation for these well‐defined colloidal systems. Finally, not only absorption, but also fluorescence spectra display the same response to changes in bulk pH. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
132.
Maiko Kateryna O. Dmitruk Igor M. Obernikhina Nataliya V. Kachkovsky Aleksey D. 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):559-566
Monatshefte für Chemie - Chemical Monthly - A quantum-chemical study of the atomic charges and bond orders in the cations of the linear conjugated systems was performed. It is shown that total... 相似文献
133.
Vasilisa V. Krasitskaya Natalia S. Goncharova Vladislav V. Biriukov Eugenia E. Bashmakova Marsel R. Kabilov Ivan K. Baykov Aleksey E. Sokolov Ludmila A. Frank 《Photochemistry and photobiology》2020,96(5):1041-1046
Bioluminescent solid-phase analysis was proposed to monitor the selection process and to determine binding characteristics of the aptamer–target complexes during design and development of the specific aptamers. The assay involves Ca2+-regulated photoprotein obelin as a simple, sensitive and fast reporter. Applicability and the prospects of the approach were exemplified by identification of DNA aptamers to cardiac troponin I, a highly specific early biomarker for acute myocardial infarction. Two structurally different aptamers specific to various epitopes of troponin I were obtained and then tested in a model bioluminescent assay. 相似文献
134.
An enantioselective and diastereoselective aza-[3+3] annulation of pyrrolidine-based exo-cyclic vinylogous amides and urethanes with chiral vinyl iminium salts is described. This asymmetric annulation manifold is possible because of an unexpected regiochemical reversal whereby head-to-tail annulations dominated over the predicted head-to-head. It should find prevalent synthetic applications in the enantioselective synthesis of indolizidines. 相似文献
135.
Aleksey E. Kuznetsov Yurii V. Geletii Craig L. Hill Keiji Morokuma Djamaladdin G. Musaev 《Theoretical chemistry accounts》2011,130(2-3):197-207
The mechanism of reaction of the di-Ru-substituted polyoxometalate, {??-[(H2O)RuIII(??-OH)2RuIII(H2O)][X n+W10O36]}(8?n)?, I_X, with O2, i.e. I_X?+?O2????{??-[(·O)RuIV(??-OH)2RuIV(O·)][X n+W10O36]}(8?n)??+?2H2O, (1), was studied at the B3LYP density functional and self-consistent reaction field IEF-PCM (in aqueous solution) levels of theory. The effect of the nature of heteroatom X (where X?=?Si, P and, S) on the calculated energies and mechanism of the reaction (1) was elucidated. It was shown that the nature of X only slightly affects the reactivity of I_X with O2, which is a 4-electron oxidation process. The overall reaction (1): (a) proceeds with moderate energy barriers for all studied X??s [the calculated rate-determining barriers are X?=?Si (18.7?kcal/mol)?<?S (20.6?kcal/mol)?<?P (27.2?kcal/mol) in water, and X?=?S (18.7?kcal/mol)?<?P (21.4?kcal/mol)?<?Si (23.1?kcal/mol) in the gas phase] and (b) is exothermic [by X?=?Si [28.7 (22.1) kcal/mol]?>?P [21.4 (9.8) kcal/mol]?>?S [12.3 (5.0) kcal/mol]. The resulting $ \left\{ {\gamma - \left[ {\left( {^{ \cdot } {\text{O}}} \right) {\text{Ru}}^{\text{IV}} \left( {\mu - {\text{OH}}} \right)_{2} {\text{Ru}}^{\text{IV}} \left( {{\text{O}}^{ \cdot } } \right)} \right]\left[ {{\text{X}}^{{{\text{n}} + }} {\text{W}}_{10} {\text{O}}_{36} } \right]} \right\}^{{\left( {8 - {\text{n}}} \right) - }} $ , VI_X, complex was found to have two RuIV?=?O· units, rather than RuV?=?O units. The ??reverse?? reaction, i.e., water oxidation by VI_X is an endothermic process and unlikely to occur for X?=?Si and P, while it could occur for X?=?S under specific conditions. The lack of reactivity of VI_X biradical toward the water molecule leads to the formation of the stable [{Ru 4 IV O4(OH)2(H2O)4}[(??-XW10O36]2}m? dimer. This conclusion is consistent with our experimental findings; previously we prepared the $ \left[ {\left\{ {{\text{Ru}}_{4}^{\text{IV}} {\text{O}}_{4} ({\text{OH}})_{2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{4} } \right\}} \right[\left( {\gamma - {\text{XW}}_{10} {\text{O}}_{36} } \right]_{2} \}^{{{\text{m}} - }} $ dimers for X?=?Si (m?=?10) [Geletii et al. in Angew Chem Int Ed 47:3896?C3899, 2008 and J Am Chem Soc 131:17360?C17370, 2009] and P (m?=?8) [Besson et al. in Chem Comm 46:2784?C2786, 2010] and showed them to be very stable and efficient catalysts for the oxidation of water to O2. 相似文献
136.
137.
Naumov AV Gorshelev AA Vainer YG Kador L Köhler J 《Physical chemistry chemical physics : PCCP》2011,13(5):1734-1742
We present a technique for the measurement of the low-temperature fluorescence excitation spectra and imaging of a substantial fraction of all single chromophore molecules (hundreds of thousands and even more) embedded in solid bulk samples as nanometre-sized probes. An important feature of our experimental studies is that the full information about the lateral coordinates and spectral parameters of all individual molecules is stored for detailed analysis. This method enables us to study a bulk sample in a broad spectral region with ultimate sensitivity, combining excellent statistical accuracy and the capability of detecting rare events. From the raw data we determined the distributions of several parameters of the chromophore spectra and their variations across the inhomogeneous absorption band, including the frequencies of the electronic zero-phonon lines, their spectral linewidths, and fluorescence count rates. Relationships between these distributions and the disorder of the matrix were established for the examples of two polycrystalline solids with very different properties, n-hexadecane and o-dichlorobenzene, and the amorphous polymer polyisobutylene. We also found spatially inhomogeneous distributions of some parameters. 相似文献
138.
We developed and employed the incremental gauge cell method to calculate the chemical potential (and thus free energies) of
long, flexible homopolymer chains of Lennard-Jones beads with harmonic bonds. The free energy of these chains was calculated
with respect to three external conditions: in the zero-density bulk limit, confined in a spherical pore with hard walls, and
confined in a spherical pore with attractive pores, the latter case being an analog of adsorption. Using the incremental gauge
cell method, we calculated the incremental chemical potential of free polymer chains before and after the globual-random coil
transitions. We also found that chains confined in attractive pores exhibit behaviors typical of low temperature physisorption
isotherms, such as layering followed by capillary condensation. 相似文献
139.
Zavyalova EG Protopopova AD Kopylov AM Yaminsky IV 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4922-4927
Interactions between fibrinogen molecules proteolytically cleaved with thrombin were investigated using atomic force microscopy (AFM) and dynamic light scattering (DLS). Gradually decreased fibrinogen concentrations were used to study the fibrin network, large separated fibrils, small fibrils in the initial association stages, and protofibrils. In addition, a new type of structure was found in AFM experiments at a low fibrinogen concentration (20 nM): the molecules in these single-stranded associates are arranged in a row, one after the other. The height, diameter, and distance between domains in these single-stranded associates were the same as those in the original fibrinogen molecules. DLS data assumed formation of extended associates in bulk solution at fibrinogen concentration as low as 20 nM. 相似文献
140.
Koltunov KY Chernov AN Surya Prakash GK Olah GA 《Chemical & pharmaceutical bulletin》2012,60(6):722-727
It is known that 1-naphthol, as a result of superelectrophilic (dicationic) activation in superacid media, is able to react with such deactivated aromatic compound as o-dichlorobenzene to give 4-(3,4-dichlorophenyl)-1-tetralone (2), which is a highly valuable intermediate in the synthesis of the antidepressant, sertraline (1) and other useful derivatives. However, the analogous reactivity of 2-naphthol and a variety of naphthalenediols towards o-dichlorobenzene has not been investigated thus far, although the corresponding tetralones, bearing dichlorophenyl moiety, could be of great pharmacochemical interest. In present work, we disclose that 1,5-, 1,6-, and 1,7- naphthalenediols (6a-c) react smoothly with o-dichlorobenzene in the presence of an excess of aluminum chloride or aluminum bromide to give the pairs of isomeric 4-(3,4-dichlorophenyl)- and 4-(2,3-dichlorophenyl)- 5-, 6-, and 7-hydroxy-1-tetralones (10a-c and 11a-c) in high overall yields. 2-Naphthol and 2,7-naphthalenediol (6d) exhibited comparatively lower reactivity, which however was sufficient to obtain the corresponding dichlorophenyl-2-tetralones in moderate yields. The mechanism of these reactions involving superelectrophilic dicationic or even tricationic intermediates, is discussed. 相似文献