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911.
Roussel F Saidi S Guittard F Geribaldi S 《The European physical journal. E, Soft matter》2002,8(3):283-288
The thermophysical properties of fluorinated acrylate homopolymers are investigated by differential scanning calorimetry (DSC)
and optical microscopy and discussed in terms of relative lengths of the fluorinated chain and the hydrocarbon spacer between
the acrylate moiety and the fluorinated chain. These compounds exhibit an intrinsic microphase-separation (Isotropic+Isotropic
morphology) occurring between the fluorinated chains and the acrylate polymer backbone. It is shown that the enthalpy of mixing
is a function of the length of the lateral fluorocarbon chains. The thermophysical behaviour of these materials may be regarded
as demixed systems exhibiting an Upper Critical Solution Temperature. The photopolymerization process of one of the monomer
is studied by isothermal photocalorimetry. High acrylate double-bond conversion and fast curing rates were obtained thus demonstrating
the promising use of these materials for coating and film processing applications using UV-curing techniques.
Received 30 January 2002 相似文献
912.
Hutchings LR Richards RW Thompson RL Bucknall DG 《The European physical journal. E, Soft matter》2002,8(2):121-128
High-molecular-weight heterotelechelic deuteriopolystyrene, NDPSF, possessing an amine functional group at one end of the
chain and a fluorocarbon group at the other was tethered to a silicon substrate by its amine functional group. These layers
were coated with an unfunctionalised polystyrene matrix, HPS, such that the total film thickness covered a range from 2.2
to 9 times the radius of gyration of NDPSF. The detailed distribution of the polymers after annealing for times much greater
than the reptation period of either of the components, was obtained using neutron reflectometry. No evidence for bridging
of the two interfaces was found for the thicker films, but the finite concentration of the NDPSF polymer observed for the
thinnest films may be due to bridging since the energy gain of the fluorocarbon end is just greater than the loss due to configurational
entropy losses. A linear increase in the ellipsometric thickness of the excess of NDPSF at the substrate was discovered and
we attribute this to the NDPSF slowly being leached out of the layer initially at the substrate followed by diffusion into
the bulk of the film. The concentration profiles obtained are consistent with hindered relaxation of the large NDPSF molecules,
when they are tethered at the substrate or at the vacuum surface.
Received 21 August 2001 and Received in final form 7 January 2002 相似文献
913.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献
914.
Segmental order in end-linked monomodal and bimodal polymer networks is investigated by means of bond-fluctuation Monte Carlo
simulations. The tensor order parameter, which is a central observable in NMR experiments, is not uniquely related to simple
vectorial order. The relaxation of NMR-detected tensorial interactions towards their finite long-time limit is best described
by a power law and occurs over much longer time scales than the relaxation of vectorial order. The well-known prediction for
the segmental order of Gaussian chains as a simple function of the segment number between constraints is not straightforwardly
obeyed, neither in dry nor in swollen networks. Excluded-volume interactions tend to significantly reduce the tensorial order,
as is clearly observed in single-chain simulations. A distribution extends along the chain, where order is increased in a
region of 30-40 bonds around the cross-links in networks. The dominating contribution to the order parameter distribution
arises from the frozen-in distribution of end-to-end separations. We find strong deviations from the Gamma distribution, which
has so far been implicitly used in most NMR works, as it is a straightforward consequence of a Gaussian distribution of end
separations. Specifically, we find narrower distributions, as small values of the tensor order parameter are strongly suppressed,
most probably as a result of trapped entanglements. The markedly subaffine behavior of the average order parameter and the
changes in its distribution on swelling are assigned to orientation processes of strands which compensate for the non-affine
local deformation. Our central observations and interpretations are well supported by our previous experimental and theoretical
work. 相似文献
915.
Neutron scattering from equilibrium-swollen networks 总被引:1,自引:0,他引:1
Sukumaran SK Beaucage G Mark JE Viers B 《The European physical journal. E, Soft matter》2005,18(1):29-36
Small-angle neutron scattering measurements were performed on end-linked poly (dimethylsiloxane) (PDMS) networks swollen to
equilibrium with d-benzene. Comparison was made with equivalent concentration PDMS solutions. Equilibrium-swollen networks
consistently displayed a linear scattering regime at low q followed by a good-solvent-like scaling regime at high q in agreement with the predictions of the Gel Tensile Blob (GTB) model. Data are fit using the unified function modified for
the GTB model (3-parameter fit). Equilibrium-swollen networks display a base structural size, the gel tensile-blob size, ξ,
that was found to be independent of the molecular weight between crosslinks for the series of molecular weights studied, consistent
with the predictions of the model. The length of the extended tensile structure, L, can be larger than the length of the fully extended network strand. The predicted scaling relationship for L, L ∼ Q1/2Navg, where Navg = (1/fNc2+1/4Ne2
, Q is the equilibrium swelling ratio, Nc is the molecular weight between crosslinks, Ne is the entanglement molecular weight and f is the crosslink functionality is in agreement with experimental results for the networks studied. 相似文献
916.
Tamm MV Nechaev SK Erukhimovich IY 《The European physical journal. E, Soft matter》2005,17(2):209-219
We investigate the statistical properties of a randomly branched 3-functional N-link polymer chain without excluded volume, whose one point is fixed at the distance d from the impenetrable surface in a 3-dimensional space. Exactly solving the Dyson-type equation for the partition function Z(N, d )= N-θeγN in 3D, we find the “surface” critical exponent θ =
, as well as the density profiles of 3-functional units and of dead ends. Our approach enables to compute also the pairwise correlation function of a randomly branched polymer in a 3D semi-space. 相似文献
917.
Glass transition for atactic poly(methyl methacrylate)
(a-PMMA) prepared in
nano-cells by microemulsion polymerization was measured at a
faster heating rate after slow cooling of the sample from a
temperature above Tg. An
additional enthalpy relaxation and glass transition were
observed at higher temperatures for the a-PMMA sample due to the partial
organization of the chain segments which occurred during
microemulsion polymerization. The re-precipitated
a-PMMA did not show any
self-organization under the same thermal conditions, although
there are no changes in molecular weight or tacticity of the
polymer chains. A depletion-interaction phenomenon was
understood to provide entropic force for the self-organization
of polymer chains inside the walls of the microemulsion cells. 相似文献
918.
Kowalewski T McCullough RD Matyjaszewski K 《The European physical journal. E, Soft matter》2003,10(1):5-16
The development of new controlled/living radical polymerization processes, such as Atom Transfer Radical Polymerization (ATRP)
and other techniques such as nitroxide mediated polymerization and degenerative transfer processes, including RAFT, opened
the way to the use of radical polymerization for the synthesis of well-defined, complex functional nanostructures. The development
of such nanostructures is primarily dependent on self-assembly of well-defined segmented copolymers. This article describes
the fundamentals of ATRP, relevant to the synthesis of such systems. The self-assembly of block copolymers prepared by ATRP
is illustrated by three examples. In the first, block copolymers of poly(butyl acrylate) with polyacrylonitrile phase separate,
leading to spherical, cylindrical or lamellar morphologies, depending on the block copolymer composition. At a higher temperature,
polyacrylonitrile block converts to nanostructured carbon clusters, whereas poly(butyl acrylate) block serves as a sacrificial
block, aiding the development of designed nanostructures. In the second example, conductive nanoribbons of poly(n-hexylthiophene)
surrounded by a matrix of organic polymers are formed from block copolymers prepared by ATRP. The third example describes
an inorganic-organic hybrid system consisting of hard nanocolloidal silica particles (20 nm) grafted by ATRP with well-defined
polystyrene-poly(benzyl acrylate) block copolymer chains (1000 chains per particle). Silica cores in this system are surrounded
by a rigid polystyrene inner shell and softer polyacrylate outer shell.
Received 9 July 2002 Published online: 11 March 2003 相似文献
919.
D. Vignolles A. Audouard L. Brossard S. Pesotskii R. Lyubovskii M. Nardone E. Haanappel R. Lyubovskaya 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):53-61
Interlayer magnetoresistance and magnetisation of the quasi-two dimensional organic metal (BEDT-TTF)8Hg4Cl12(C6H5Br)2 have been investigated in pulsed magnetic fields extending up to 60 T and 33 T, respectively. About fifteen fundamental frequencies,
composed of linear combinations of only three basic frequencies, are observed in the oscillatory spectra of the magnetoresistance.
The dependencies of the oscillation amplitude on the temperature and on the magnitude and orientation of the magnetic field
are analyzed in the framework of the conventional two-dimensional Lifshitz-Kosevitch (LK) model. This model is implemented
by damping factors which accounts for the magnetic breakthrough occurring between electron and hole orbits yielding conventional
Shubnikov-de Haas closed orbits (model of Falicov and Stachowiak) and quantum interferometers. In particular, a quantum interferometer
enclosing an area equal to the first Brillouin zone area is evidenced. The LK model consistently accounts for the temperature
and magnetic field dependence of the oscillation amplitude of this interferometer. On the contrary, although this model formally
accounts for almost all of the observed oscillatory components, it fails to give consistent quantitative data in most other
cases.
Received 4 September 2002 / Received in final form 14 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: audouard@insa-tlse.fr
RID="b"
ID="b"UMR 5830: Unité Mixte de Recherche CNRS - Université Paul Sabatier - INSA de Toulouse
RID="c"
ID="c"UMS 5642: Unité Mixte de Service CNRS - Université Paul Sabatier - INSA de Toulouse 相似文献
920.
Summary Melt-crystallized samples of polyethylene show a reversible change of the line-width in X-ray wide angle scattering. The width increases with decreasing temperature, the largest changes occur in the temperature ranges of the- and-relaxation processes. Fourier analyses of the line profiles using the method of Warren and Averbach are indicative of strain variances which can be attributed to stress variances over larger domains in the semi-crystalline superstructure. An explanation for this effect is found in the stress parallel to the planes of the lamellae produced by the differences of the thermal expansion coefficients of the crystalline and amorphous domains in the lamellar two-phase systems. The magnitude of the stress is determined by the difference of the thermal expansion coefficients as well as the Young's moduli of the domains whereas the stress variances are related to the statistics of the lamellar thicknesses.With 23 figures and 3 tables 相似文献