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81.
82.
This article describes the Diels–Alder reaction between methyl thiocinnamates, substituted at the para position by electron-donating and electron-withdrawing groups, with cyclopentadiene in the presence of catechol boron bromide (CBB) as a Lewis acid catalyst. The adduct configuration was confirmed by 1H NMR coupling constants and single-crystal x-ray diffraction. Total endo stereoselectivity was observed in all reactions and was attributed to the effective secondary interaction between the boron atom and the incipient double bond in the norbonene resulting from the planar geometry of the catalyst. 13C NMR chemical shifts of the coordinated dienophile carbonyl carbons with CBB compared to those of the non coordinated thiocinammates suggest a strong complexation with the catalyst. 相似文献
83.
Dr. Shokoufeh Rastgar Dr. Keyla Teixeira Santos Prof. Dr. Camilo Andrea Angelucci Prof. Dr. Gunther Wittstock 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10882-10890
Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2O2, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase. 相似文献
84.
Luis Sanhueza Diego Cortés-Arriagada Ramiro Díaz Paulina Dreyse Camilo García Iván A. Gonzalez Bárbara Loeb 《International journal of quantum chemistry》2020,120(24):e26412
Density functional theory calculations of polypyridyl ruthenium complexes with polyaromatic ligands have been performed to understand the metal fragment effect on the modulation of their electronic properties and the influence on the aromatic character. The change of positions of the nitrogen atoms in the ligand structure, as well as the metal moiety, seems to influence the electronic behavior of the π-extended structure and the aromatic character of the complexes at both the ground and excited states. In this framework, structural, electronic, and magnetic-based aromaticity indices were used to understand the aromaticity of the free and coordinated ligands. The aromaticity character of the ligands is highly influenced by the metal fragment, and the aromaticity/antiaromaticity is achieved according to both the electron-withdrawing capability of the ligand and the metal fragment. The electronic distribution observed on the aromatic ligand determines their π-stacking ability; thus, it is proposed that the control of the π-stacking ability is modulated according to the electronic nature of the ruthenium moiety. 相似文献
85.
Marcus Vinícius Nora de Souza Maria Cristina Silva Lourenço Mônica Amado Peralta Raoni Schroeder Borges Gonçalves Thais Cristina Mendonça Nogueira Camilo Henrique da Silva Lima 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2990-2997
The series of new N,N′-di(thiopheneacetyl)diamines derivatives, 8–17, were synthesized and evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis(TB), and the activity expressed as the minimum inhibitory concentration (MIC) in μ g/mL. Compound 13 was the only one determined to be active and exhibited a MIC 50 μg/mL, indicating that the alkyl chain-length of the diamines is critical for biological activity. This class of compound has not been evaluated before, and it could be a good starting point to find new lead compounds in the fight against multi-drug resistant TB. 相似文献
86.
We propose a new 13C DEPTQ+ NMR experiment, based on the improved DEPTQ experiment, which is designed to unequivocally identify all carbon multiplicities (Cq, CH, CH2, and CH3) in two experiments. Compared to this improved DEPTQ experiment, the DEPTQ+ is shorter and the different evolution delays are designed as spin echoes, which can be tuned to different 1JCH values; this is especially valuable when a large range of 1JCH coupling constants is to be expected. These modifications allow (i) a mutual leveling of the DEPT signal intensities, (ii) a reduction in J cross-talk in the Cq/CH spectrum, and (iii) more consistent and cleaner CH2/CH3 edited spectra. The new DEPTQ+ is expected to be attractive for fast 13C analysis of small-to medium sized molecules, especially in high-throughput laboratories. With concentrated samples and/or by exploiting the high sensitivity of cryogenically cooled 13C NMR probeheads, the efficacy of such investigations may be improved, as it is possible to unequivocally identify all carbon multiplicities, with only one scan, for each of the two independent DEPTQ+ experiments and without loss of quality. 相似文献
87.
We examine the role of the condensing agent in the formation of polyelectrolyte bundles, via grand-canonical Monte Carlo simulations. Following recent experiments we use linear, rigid divalent cations of various lengths to induce condensation. Our results clarify and explain the experimental results for short cations. For longer cations we observe novel condensation behavior owing to the alignment of the cations. We also study the role of the polyelectrolyte surface-charge density, and find a nonmonotonic variation in bundle stability. This nonmonotonicity captures two trends that have been observed in separate experiments. 相似文献
88.
?eljka Ljuji? Camilo Sanabria 《Topology and its Applications》2011,158(8):1012-1018
Let K⊆R2 be a compact set such that K+Z2=R2 and let K−K={a−b|a,b∈K}. We prove, via Algebraic Topology, that the integer points of the difference set of K, (K−K)∩Z2, is not contained on the coordinate axes, Z×{0}∪{0}×Z. This result implies the negative answer to the inverse problem posed by M.B. Nathanson (2010) [5]. 相似文献
89.
Cardoso CR de Aguiar I Camilo MR Lima MV Ito AS Baptista MS Pavani C Venâncio T Carlos RM 《Dalton transactions (Cambridge, England : 2003)》2012,41(22):6726-6734
The monodentate cis-[Ru(phen)(2)(hist)(2)](2+)1R and the bidentate cis-[Ru(phen)(2)(hist)](2+)2A complexes were prepared and characterized using spectroscopic ((1)H, ((1)H-(1)H)COSY and ((1)H-(13)C)HSQC NMR, UV-vis, luminescence) techniques. The complexes presented absorption and emission in the visible region, as well as a tri-exponential emission decay. The complexes are soluble in aqueous and non-aqueous solution with solubility in a buffer solution of pH 7.4 of 1.14 × 10(-3) mol L(-1) for (1R + 2A) and 6.43 × 10(-4) mol L(-1) for 2A and lipophilicity measured in an aqueous-octanol solution of -1.14 and -0.96, respectively. Photolysis in the visible region in CH(3)CN converted the starting complexes into cis-[Ru(phen)(2)(CH(3)CN)(2)](2+). Histamine photorelease was also observed in pure water and in the presence of BSA (1.0 × 10(-6) mol L(-1)). The bidentate coordination of the histamine to the ruthenium center in relation to the monodentate coordination increased the photosubstitution quantum yield by a factor of 3. Pharmacological studies showed that the complexes present a moderate inhibition of AChE with an IC(50) of 21 μmol L(-1) (referred to risvagtini, IC(50) 181 μmol L(-1) and galantamine IC(50) 0.006 μmol L(-1)) with no appreciable cytotoxicity toward to the HeLa cells (50% cell viability at 925 μmol L(-1)). Cell uptake of the complexes into HeLa cells was detected by fluorescence confocal microscopy. Overall, the observation of a luminescent complex that penetrates the cell wall and has low cytotoxicity, but is reactive photochemically, releasing histamine when irradiated with visible light, are interesting features for application of these complexes as phototherapeutic agents. 相似文献
90.
Camilo Enrique Argoty Pulido 《Mathematical Logic Quarterly》2014,60(6):403-424
We study a closed unbounded self‐adjoint operator Q acting on a Hilbert space H in the framework of Metric Abstract Elementary Classes (MAECs). We build a suitable MAEC for such a structure, prove it is ?0‐categorical and ?0‐stable up to a system of perturbations. We give an explicit continuous axiomatization for the class. We also characterize non‐splitting and show it has the same properties as non‐forking in superstable first order theories. Finally, we characterize equality, orthogonality and domination of (Galois) types in that MAEC. 相似文献