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71.
Molecular Engineering of Fracture Energy Dissipating Sacrificial Bonds Into Cellulose Nanocrystal Nanocomposites
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Jason R. McKee Johannes Huokuna Lahja Martikainen Mikko Karesoja Dr. Antti Nykänen Dr. Eero Kontturi Prof. Heikki Tenhu Prof. Janne Ruokolainen Prof. Olli Ikkala 《Angewandte Chemie (International ed. in English)》2014,53(20):5049-5053
Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one‐component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2‐ureido‐4[1H]‐pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites. 相似文献
72.
In this article we investigate when a complete ideal in a two-dimensional regular local ring is a multiplier ideal of some ideal with an integral multiplying parameter. In particular, we show that this question is closely connected to the Gorenstein property of the blowup along the ideal.Dedicated to Prof. Kei-ichi Watanabe on the occasion of his 60th birthday. 相似文献
73.
Kiviniemi T Hulkko E Kiljunen T Pettersson M 《The journal of physical chemistry. A》2008,112(23):5025-5027
The structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature have been studied with infrared and resonance Raman spectroscopy and with MP2 calculations. The structure of the ground-state complex is found to be unsymmetric, and the I-I vibrational frequency is found to be red-shifted by 3.94 cm(-1) upon complexation. The experimental data agree well with computational results, leading to the conclusion that the I2-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes. 相似文献
74.
Ruuska H Arola E Kortelainen T Rantala TT Kannus K Valkealahti S 《The Journal of chemical physics》2011,134(13):134904
Influence of acrylic acid grafting of isotactic polypropylene on the dielectric properties of the polymer is investigated using density functional theory (DFT) calculations, both in the molecular modeling and three-dimensional (3D) bulk periodic system frameworks. In our molecular modeling calculations, polarizability volume, and polarizability volume per mass which reflects the permittivity of the polymer, as well as the HOMO-LUMO gap, one of the important measures indicating the electrical breakdown voltage strength, were examined for oligomers with various chain lengths and carboxyl mixture ratios. When a polypropylene oligomer is grafted with carboxyl groups (cf. acrylic acid), our calculations show that the increase of the polarizability volume α' of the oligomer is proportional to the increase of its mass m, while the ratio α'/m decreases from the value of a pure polymer when increasing the mixture ratio. The decreasing ratio of α'/m under carboxyl grafting indicates that the material permittivity might also decrease if the mass density of the material remains constant. Furthermore, our calculations show that the HOMO-LUMO gap energy decreases by only about 15% in grafting, but this decrease seems to be independent on the mixture ratio of carboxyl. This indicates that by doping polymers with additives better dielectric properties can be tailored. Finally, using the first-principles molecular DFT results for polarizability volume per mass in connection with the classical Clausius-Mossotti relation, we have estimated static permittivity for acrylic acid grafted polypropylene, assuming the structural density keeping constant under grafting. The computed permittivity values are in a qualitative agreement with the recent experiments, showing increasing tendency of the permittivity as a function of the grafting composition. In order to validate our molecular DFT based approach, we have also carried out extensive three-dimensional bulk periodic first-principles total-energy calculations in the frameworks of the density functional theory and density functional perturbation theory (DFPT) for crystalline acrylic acid grafted polypropylene. Interestingly, the computed electronic and dielectric properties behave very similarly between the simplified molecular DFT modeling and the more realistic 3D bulk periodic DFPT method. In particular, the static permittivity values [ε(r)(0)] from the molecular DFT-Clausius-Mossotti modeling are in excellent agreement with the high-frequency dielectric constant values (ε(∞)) from the DFPT method. This obviously implies that the chain-to-chain interaction to dielectric and electronic properties of acrylic acid polypropylene, to a first approximation, can be neglected, therefore justifying the usage of molecular DFT modeling in our calculations. 相似文献
75.
76.
Pekka J. Nieminen Eero Saksman 《Journal of Mathematical Analysis and Applications》2004,298(2):501-522
Let φ and ψ be analytic self-maps of the unit disc, and denote by Cφ and Cψ the induced composition operators. The compactness and weak compactness of the difference T=Cφ−Cψ are studied on Hp spaces of the unit disc and Lp spaces of the unit circle. It is shown that the compactness of T on Hp is independent of p∈[1,∞). The compactness of T on L1 and M (the space of complex measures) is characterized, and examples of φ and ψ are constructed such that T is compact on H1 but non-compact on L1. Other given results deal with L∞, weakly compact counterparts of the previous results, and a conjecture of J.E. Shapiro. 相似文献
77.
Every complete doubling metric space carries a doubling measure 总被引:4,自引:0,他引:4
We prove that a complete metric space carries a doubling measure if and only if is doubling and that more precisely the infima of the homogeneity exponents of the doubling measures on and of the homogeneity exponents of are equal. We also show that a closed subset of carries a measure of homogeneity exponent . These results are based on the case of compact due to Volberg and Konyagin.
78.
Hannele Juvaste Eero I. Iiskola Tuula T. Pakkanen 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):1-9
Novel modified catalyst carriers have been prepared. First, aminopropyltriethoxysilane (APTES) was immobilized on the silica surface by using the saturated gas–solid reactions. Secondly, two different (tetramethylcyclopentadienyl)chlorosilanes, (Me2Si(C5Me4H)Cl and MeHSi(C5Me4H)Cl), were synthesized and anchored on the amine surface using liquid-phase reactions. Characterization of these stepwise prepared surfaces was carried out by 1H, 13C and 29Si solid state NMR and FTIR spectroscopy. 相似文献
79.
80.
Pekka J. Nieminen Eero Saksman 《Transactions of the American Mathematical Society》2004,356(8):3167-3187
Let be a holomorphic self-map of the unit disc . For every , there is a measure on (sometimes called Aleksandrov measure) defined by the Poisson representation . Its singular part measures in a natural way the ``affinity' of for the boundary value . The affinity for values inside is provided by the Nevanlinna counting function of . We introduce a natural measure-valued refinement of and establish that the measures are obtained as boundary values of the refined Nevanlinna counting function . More precisely, we prove that is the weak limit of whenever converges to non-tangentially outside a small exceptional set . We obtain a sharp estimate for the size of in the sense of capacity.