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81.
Anatoly A. Darinskii Igor M. Neelov Anna Zarembo Nikolai K. Balabaev Franciska Sundholm Kurt Binder 《Macromolecular Symposia》2003,191(1):191-200
Molecular dynamic simulations are reported for system of semi-flexible linear rod-like molecules. The molecules are composed of Nc tangent soft spheres, connected by elastic springs. Rigidity is introduced by additional springs between all pairs of spheres along the molecule. The formation of only a nematic LC phase is shown for all systems with Nc = 8 and different flexibility. The effect of flexibility on the order parameter and the volume fraction at the LC phase transition is compared with theoretical predictions by Khokhlov-Semenov and with available simulation data. The dependence of the anisotropy of diffusion on chain flexibility in LC phase was studied. The polymer brushes consisting of flexible and semi-flexible (composed of linear rod-like segments) chains were simulated at different grafting densities. Height of brush, order parameter, distribution of density and chain ends in brush were obtained in both cases and compared with theoretical predictions. 相似文献
82.
B. Mattsson H. Ericson L. M. Torell F. Sundholm 《Journal of polymer science. Part A, Polymer chemistry》1999,37(16):3317-3327
Proton-conducting membranes of poly(vinylidene fluoride), PVDF, grafted with styrene and thereafter sulfonated, were investigated by Raman spectroscopy. The depth and surface distribution of polystyrene grafts and crosslinker, as well as the sulfonation efficiency, were determined by using confocal micro-Raman spectroscopy. Highly grafted samples show homogeneous distribution of grafted material and homogeneous sulfonation. Depth profiles reveal uneven graft distribution for samples with low and intermediate degrees of grafting. In crosslinked samples, the crosslinker concentration in the interior of the film is found to be roughly 50% of the surface concentration. In contrast to what has previously been reported, the sulfonation efficiency is poor at low graft levels and is further inhibited by the presence of divinyl benzene, DVB, as crosslinker. At degrees of grafting above ∼ 60%, the crosslinker does not affect the sulfonation efficiency and a level of 70–90% sulfonation is reached. The matrix polymer structure is found to be largely retained after irradiation, grafting, and sulfonation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3317–3327, 1999 相似文献
83.
Ch. Porcher R. Dage L. W. Ferris Sirot Joret J. T. Keister G. Ambühl H. Weiss H. Kreis J. Pritzker und F. Reiss 《Fresenius' Journal of Analytical Chemistry》1920,59(8-9):382-385
Ohne Zusammenfassung 相似文献
84.
Sami Hietala Mikael Paronen Svante Holmberg Jan Nsman Jyrki Juhanoja Milja Karjalainen Ritva Serimaa Minna Toivola Tero Lehtinen Katri Parovuori Gran Sundholm Hanna Ericson Britta Mattsson Lena Torell Franciska Sundholm 《Journal of polymer science. Part A, Polymer chemistry》1999,37(12):1741-1753
A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF‐g‐PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1741–1753, 1999 相似文献
85.
Marina Saphiannikova Igor Neelov Victor Pryamitsyn Anatoly A. Darinskii Franciska Sundholm 《Rheologica Acta》2000,39(5):469-475
Recently two different methods were used to simulate the stationary properties of polymer brushes under strong shear: stochastic
dynamics of a multi-chain brush model, and self-consistent Brownian dynamics of a one-chain model. The former explicitly describes
volume interactions (VI) between polymer segments but does not take into account hydrodynamic interactions (HI) inside the
brush. In the latter the self-consistent molecular field method has been chosen to calculate VI, and HI were accounted for
using the Brinkman equation. Despite a significant difference between models a collapse of the brush under shear was observed
in both studies. In particular, the density profile changes from parabolic to step-like and the free ends of the chains become
concentrated in a narrow region at the periphery of the brush. However, when HI are taken into account much higher shear rates
are necessary to attain the same brush deformation because the shear flow only slightly penetrates into the brush in contrast
to the free-draining case. The inner brush structure is also found to be different for the two models. In the first model
all chains are inclined approximately at the same angle when shear is applied. In the second model chains with the free ends
found in the inner sublayer of the brush do not feel the flow at all whereas those in the upper sublayer are stretched and
inclined by the flow.
Received: 24 June 1999 Accepted: 8 February 2000 相似文献
86.
E.G. Sundholm 《Tetrahedron》1978,34(5):577-586
The preparations of several chlorinated derivatives of norlichexanthone 6a by unambiguous methods are described. The 1H NMR spectra of these compounds are discussed and several structures previously assigned for lichen xanthones are questioned. The suggested revisions are summarized in Table 3. 相似文献
87.
E.G. Sundholm 《Tetrahedron》1977,33(9):991-994
Acylation of methyl and benzylethers of orcinol with the same ethers of phloroglucinol carboxylic acid using trifluoroacetic anhydride (TFAA) in chloroform or dichloro methane afforded both unsymmetrical and symmetrical benzophenones. Magnetic resonance measurements were performed on the reactions between various deuterium labelled methylethers of phloroglucinol and phloroglucinol carboxylic acid. The reaction was found to proceed via several equilibria resulting in a total scrambling of the aromatic rings around the carbonyl function. The occurrence of an intermediate in the reaction was observed and is thought to consist of an ion pair between a protonated benzophenone and trifluoroacetate ion which rapidly catalyses an exchange between TFAA and TFA. 相似文献
88.
89.
Sundholm D 《The Journal of chemical physics》2005,122(19):194107
A computational approach to determine electrostatic interaction and gravitational potentials by performing direct numerical integration is presented. The potential is expanded using finite-element functions of arbitrary order. The method does not involve any solutions of systems of linear equations. The potential is instead obtained as a sum of differential contributions. Thus, no boundary conditions for the potential are needed. It is computationally efficient and well suited for parallel computers, since the innermost loops constitute matrix multiplications and the outer ones can be used as parallel indices. Without using prescreening or other computational tricks to speed up the calculation, the algorithm scales as N4/3 where N denotes the grid size. 相似文献
90.
Magnetically induced current densities in the four-membered rings of Al4(2-) and Al4(4-) species have been calculated at the coupled-cluster singles and doubles (CCSD) level by applying the recently developed gauge-including magnetically induced current (GIMIC) method. The strength of the ring-current susceptibilities were obtained by numerical integration of the current densities passing through a cross section perpendicular to the Al4 ring. The GIMIC calculations support the earlier notion that Al4 (2-) with formally two pi electrons sustains a net diatropic ring current. The diatropic contribution to the ring-current susceptibility is carried by the electrons in both the sigma (16.7 nAT) and the pi (11.3 nAT) orbitals. The induced ring current in the Al4 (4-) compounds, with four pi electrons, consists of about equally strong diatropic sigma and paratropic pi currents of about 14 and -17 nAT, respectively. The net current susceptibilities obtained for Al4Li-, Al4Li2, Al4Li3(-), and Al4Li4 at the CCSD level using a triple-zeta basis set augmented with polarization functions are 28.1, 28.1, -5.9, and -3.1 nAT, respectively. The corresponding diatropic (paratropic) contributions to the ring-current susceptibilities are 32.4 (0.0), 36.7 (0.0), 18.9 (-19.9), and 18.6 (-16.8) nAT, respectively. For the Al4(2-) and Al4(4-) species, the net currents circling each Li+ cation is estimated to 4.3 and 2.4 nAT, respectively. 相似文献