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61.
Milan Randić Damir Vukičević Alexandru T. Balaban Marjan Vračko Dejan Plavšić 《Journal of computational chemistry》2012,33(11):1111-1122
We report on calculated CC bond currents for a dozen derivatives of hexabenzocoroenene in which one or more proximal carbon atoms at the molecular periphery have been bridged. The approach that we use is graph‐theoretical in nature, following our outline of this method in 2003, which is based on finding all conjugated circuits in all Kekulé valence structures of these molecules. To the π‐electrons having 4n + 2 π‐electrons are assigned anticlockwise π‐electron currents and to conjugated circuits having 4n π‐electrons are assigned π‐electron currents. One may summarize the results reported in this work by stating that CC bond currents in the compounds considered decrease on going from peripheral rings to the central ring of the molecule, and also that CC bond currents decrease by insertion of bridges to proximal peripheral benzenoid rings. © 2012 Wiley Periodicals, Inc. 相似文献
62.
Jasminka Kontrec Marko Ukrainczyk Branka Njegi Dakula Damir Kralj 《Crystal Research and Technology》2013,48(9):622-626
A method for preparation of significant amount of hollow rhombohedral calcite nanoparticles, based on carbonation of calcium hydroxide suspension, is described. The mineralogical and morphological analyses of the precipitate confirmed the existence of exclusively stable polymorphic modification, calcite, with the mean particle size of about 100 nm and the diameter of the holes observed at the surfaces that are about 50 nm. The analysis of carbonation kinetics pointed out to a complex mechanism of hollow particles formation at high initial supersaturation, that assumed nucleation of amorphous precursor calcium carbonate phase and its solution mediated transformation into nanosized crystalline calcite. The holes obtained at the calcite surfaces are most probably the imprints remained after the dissolution of amorphous calcium carbonate particles. 相似文献
63.
There is a need for accurate yield stress measurements, especially in the case of low yield stress complex materials such
as biological samples. This task cannot be accomplished with conventional rotational rheometers due to significant wall slip
effects and the necessity to operate the device at very low shear rates, often beyond the limit that such rheometers can achieve.
In this paper, we focused on the slotted plate method proposed recently for low yield stress measurements. Using computational
fluid dynamics, we studied the effects of plate geometry on the measurement accuracy of the slotted plate method. Results
of this study indicate that both wall slip effects and pressure drag force can be substantially reduced by adopting a thin
plate with sharp front and rear edges, high slot area ratio, and large number of slots. If the plate has 30° triangular edges,
a slot area ratio of 80%, and 12 slots, the slotted plate method overpredicts the yield stress of a 0.09 wt.% Carbopol dispersion
(yield stress of 9.17 Pa) by only 8.4% under no-slip conditions and underpredicts the yield stress by 12.3% under free-slip
conditions. Similar results were obtained for human saliva characterized by a very low yield stress (0.073 Pa). 相似文献
64.
We point out at the peculiarity of B→μνμ decay, namely the enhancement of the soft photon events which originate from the structure dependent part of the B→μνμγ amplitude. This may be a dominant source of systematic uncertainty and compromise the projected experimental uncertainty on Γ(B→μνμ). We show that the effect of these soft photons can be controlled if the experimental cut on identification of soft photons is lowered and especially if the better resolution in identifying the momentum of muon emerging from B→μνμ is made. A lattice QCD computation of the relevant form factors would be highly helpful for a better numerical control over the structure dependent soft photon emission. 相似文献
65.
Optimal configurations of functionalized fullerenes C
60
X
n
for n = 2, 4, 6, 8 have been determined by application of three topological stability measures. It has been found that the optimal
configurations with higher n contain optimal configurations with lower values of n. Two stability measures prefer configurations in which functional groups Xs are crowded while the third one points to configurations with isolated pairs of Xs. 相似文献
66.
We study the effective and proof-theoretic content of the polarized Ramsey’s theorem, a variant of Ramsey’s theorem obtained
by relaxing the definition of homogeneous set. Our investigation yields a new characterization of Ramsey’s theorem in all
exponents, and produces several combinatorial principles which, modulo bounding for formulas, lie (possibly not strictly) between Ramsey’s theorem for pairs and the stable Ramsey’s theorem for pairs.
We are grateful to D. Hirschfeldt, A. Montalbán, and R. Soare for making our collaboration possible and for helpful comments
and suggestions. We thank J. Schmerl for first bringing the subject of polarized partitions to our attention and J. Mileti
for his generous insights. We also thank one anonymous referee for valuable observations and corrections. The first author
was partially supported by an NSF Graduate Research Fellowship. 相似文献
67.
Nicola Marchi Qingshan Teng Minh T Nguyen Linda Franic Nirav K Desai Thomas Masaryk Peter Rasmussen Silvia Trasciatti Damir Janigro 《BMC neuroscience》2010,11(1):34
Background
Stem cells or immune cells targeting the central nervous system (CNS) bear significant promises for patients affected by CNS disorders. Brain or spinal cord delivery of therapeutic cells is limited by the blood-brain barrier (BBB) which remains one of the recognized rate-limiting steps. Osmotic BBB disruption (BBBD) has been shown to improve small molecule chemotherapy for brain tumors, but successful delivery of cells in conjunction with BBBD has never been reported. 相似文献68.
L Yan X Chen Q He Y Wang X Wang Q Guo F Bai A Xia D Aumiler S Vdović S Lin 《The journal of physical chemistry. A》2012,116(34):8693-8705
In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (-C═C- or -C≡C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores. 相似文献
69.
Felix D. Sokolov Damir A. Safin Nail G. Zabirov Alexander Yu. Verat Vasiliy V. Brusko Dmitry B. Krivolapov Ekaterina V. Mironova Igor A. Litvinov 《Polyhedron》2006,25(18):3611-3616
The reaction of bis-thiourea o-C6H4[NHC(S)NHP(S)(Oi-Pr)2]2 (1) with iodine, KOH and ClCH2C(O)OCH3 leads to O,O′-diisopropyl-1,3-dihydro-2H-benzimidazol-2-ylideneamidothiophosphate (2) formation. The complex of the potassium salt of compound 2 with 18-crown-6, having the composition [K(18-crown-6)L], has been synthesized. Bis-thiourea [CH2NHC(S)NHP(S)(Oi-Pr)2]2 (6) forms a stable potassium salt, which oxidation by iodine leads to a product of heterocyclization, O,O′-diisopropyl-(1-{[(diisopropoxyphosphorothio)amino]carbonothioyl}imidazolidine-2-ylidene)amidothiophosphate (8), in which one of the thiourea fragments is kept. 相似文献
70.