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排序方式: 共有120条查询结果,搜索用时 15 毫秒
91.
Trzpit M Rigolet S Paillaud JL Marichal C Soulard M Patarin J 《The journal of physical chemistry. B》2008,112(24):7257-7266
Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer. This hydrogen bonding scheme is also supported by X-ray powder diffraction. 相似文献
92.
Fournier F Afonso C Ménand M Hamon L Xie J Tabet JC 《European journal of mass spectrometry (Chichester, England)》2008,14(2):61-69
The affinity of cyclic oligomers of sugar amino acid and sugar-aza-crown ether compounds towards various transition metal cations (Cu(II), Ni(II), Co(II), Fe(II) and Zn(II)) was investigated with positive-ion electrospray mass spectrometry. The binding between the receptors (M) and the different metals (Met) is evidenced mainly by the presence of the [M + Met(II)Cl](+) ion. The experimental results showed that all studied receptors present specificity to Cu(II). An attempt has been made with CuI but no complexation was obtained. The formation of these complexes can be rationalized by considering the presence of two oxygens and two nitrogens on the receptor rim. The lone electron pair can serve as the electron donor to Cu(II). Theoretical calculations were carried out in order to show the structure of the complex and, in particular, to determine if Cu(2+) is situated either on the outer surface, on the rim of the receptor or inside the cavity. Comparison of complex formation was carried out by mixing the four receptors with various amounts of Cu(II) (one equivalent and five equivalents). It appears that the best complexation was obtained with the sugar-aza-crown ethers (amine linker) for both benzylated and methylated compounds. In addition, the stereochemical effects have been investigated. 相似文献
93.
The dynamics of evaporating water droplets deposited on a heated substrate is investigated numerically. Droplets are pinned with a contact line radius of R = 1 mm. Evaporative mass flow and convection occurring inside the droplets are studied for different heating substrate sizes L S and heating temperatures T S. A simplified model neglecting hydrodynamics in air and evaporative cooling and assuming droplets to be spherical caps is simulated with a finite element method. A toruslike convective cell appears inside the droplets as evaporation takes place. For L S/ R > 1, the contact line is warmer than the apex of the droplets, and convection generates a downstream flow in the vicinity of the symmetry axis of the droplets. For L S/ R < 1, it is the apex that is warmer. Convection then generates an upstream flow. The overall evaporation time is described. It slows when L S/ R > 1. 相似文献
94.
Hamon M Ménand M Le Gac S Luhmer M Dalla V Jabin I 《The Journal of organic chemistry》2008,73(18):7067-7071
The straightforward syntheses of C3v symmetrical calix[6]trisureas and -thiourea have been achieved. NMR studies have shown that these flexible compounds possess a major cone conformation. While these neutral hosts can strongly bind anions such as AcO(-) or HSO4(-) through induced fit processes, they can also behave as unique heteroditopic receptors for organic ion pairs with a remarkable positive cooperativity in the complexation process, the anion acting as an allosteric effector. 相似文献
95.
Dr. Pawel Jewula Mickaël Grandmougin Mélanie Choppin Anna Maria Chiara Tivelli Dr. Agnese Amati Dr. Yoann Rousselin Dr. Lydia Karmazin Dr. Jean-Claude Chambron Dr. Michel Meyer 《欧洲无机化学杂志》2023,26(13):e202300038
Six- and seven-membered cyclic hydroxamic acids are found as terminal binding units in different families of siderophores, including exochelins and mycobactins. The simplest models of these preorganized chelating ligands were known, but their coordination chemistry with Fe3+, the target metal ion of siderophores, had never been reported. Four complexes were synthesized and studied: two Fe3+ complexes, one with the six-membered ring hydroxamate PIPO− and one with the seven-membered ring hydroxamate AZEPO−, and the two corresponding Ga3+ complexes. X-ray diffraction studies showed that the interligand repulsion energies were better minimized in the case of the AZEPO− complexes whatever the metal cation considered, and that the Fe−O bond distances were shorter in [Fe(AZEPO)3] by comparison with [Fe(PIPO)3]. 相似文献
96.
97.
The Jin-Neelin model for the El Ni$\wt{\rm n}$o--Southern
Oscillation (ENSO for short) is considered for which the authors
establish existence and uniqueness of global solutions in time over
an unbounded channel domain. The result is proved for initial data
and forcing that are sufficiently small. The smallness conditions
involve in particular key physical parameters of the model such as
those that control the travel time of the equatorial waves and the
strength of feedback due to vertical-shear currents and upwelling;
central mechanisms in ENSO dynamics.
From the mathematical view point, the system appears as the coupling
of a linear shallow water system and a nonlinear heat equation.
Because of the very different nature of the two components of the
system, the authors find it convenient to prove the existence of
solution by semi-discretization in time and utilization of a
fractional step scheme. The main idea consists of handling the
coupling between the oceanic and temperature components by dividing
the time interval into small sub-intervals of length $k$ and on each
sub-interval to solve successively the oceanic component, using the
temperature $T$ calculated on the previous sub-interval, to then
solve the sea-surface temperature (SST for short) equation on the
current sub-interval. The passage to the limit as $k$ tends to zero
is ensured via a priori estimates derived under the aforementioned
smallness conditions. 相似文献
98.
99.
Sadakane M Tsukuma D Dickman MH Bassil BS Kortz U Capron M Ueda W 《Dalton transactions (Cambridge, England : 2003)》2007,(26):2833-2838
We report the dimerization of a mono-ruthenium(III) substituted alpha-Keggin-type tungstosilicate [alpha-SiW(11)O(39)Ru(III)(H2O)](5-) to a micro-oxo-bridged dimer [{alpha-SiW(11)O(39)Ru(m)}2O](n-) (m = III, n = 12; m = IV/III, n = 11; m = IV, n = 10). Single crystal X-ray structure analysis of Rb(10)[{alpha-SiW(11)O(39)Ru(IV)}2O].9.5H2O (triclinic, P1, with a = 12.7650(6) A, b = 18.9399(10) A, c = 20.2290(10) A, alpha = 72.876(3) degrees, beta = 88.447(3) degrees, gamma = 80.926(3) degrees, V = 4614.5(4) A(3), Z = 2) reveals that two mono-ruthenium substituted tungstosilicate alpha-Keggin units are connected through micro-oxo-bridging Ru-O-Ru bonds. Solution (183)W-NMR of [{SiW(11)O(39)Ru(IV)}2O](10-) resulted in six peaks (-63, -92, -110, -128, -132, and -143 ppm, intensities 2 : 2 : 1 : 2 : 2 : 2) confirming that the micro-oxo bridged dimer structure is maintained in aqueous solution. The dimerization mechanism is presumably initiated by deprotonation of the aqua-ruthenium complex [alpha-SiW(11)O(39)Ru(III)(H2O)](5-) leading to a hydroxy-ruthenium complex [alpha-SiW(11)O(39)Ru(III)(OH)](6-). Dimerization of two hydroxy-ruthenium complexes produces the micro-oxo bridged dimer [{alpha-SiW(11)O(39)Ru(III)}2O](12-) and a water molecule. The Ru(III) containing dimer is oxidized by molecular oxygen to produce a mixed valence species [{alpha-SiW(11)O(39)Ru(IV-III)}2O](11-), and further oxidation results in the Ru(IV) containing [{alpha-SiW(11)O(39)Ru(IV)}2O](10-). 相似文献
100.
Mendes M Hamadi S Le Naour C Roques J Jeanson A Den Auwer C Moisy P Topin S Aupiais J Hennig C Di Giandomenico MV 《Inorganic chemistry》2010,49(21):9962-9971
The complexation of protactinium(V) by oxalate was studied by X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) and solvent extraction. XAS measurements showed unambiguously the presence of a short single oxo-bond, and the deduced structure agrees with theoretical calculations. CE-ICP-MS results indicated the formation of a highly charged anionic complex. The formation constants of PaO(C(2)O(4))(+), PaO(C(2)O(4))(2)(-), and PaO(C(2)O(4))(3)(3-) were determined from solvent extraction data by using protactinium at tracer scale (C(Pa) < 10(-10) M). Complexation reactions of Pa(V) with oxalate were found to be exothermic with relatively high positive entropic variation. 相似文献