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51.
52.
Gravimetry experiments in a well-controlled environment have been performed to investigate aging for a glassy PMMA/toluene
film. The temperature is constant and the control parameter is the solvent vapor pressure above the film (i.e. the activity). Several experimental protocols have been used, starting from a high activity where the film is swollen and
rubbery and then aging the film at different activities below the glass transition. Desorption and resorption curves have
been compared for the different protocols, in particular in terms of the softening time, i.e. the time needed by the sample
to recover an equilibrium state at high activity. Non-trivial behaviors have been observed, especially at small activities
(deep quench). A model is proposed, extending the Leibler-Sekimoto approach to take into account the structural relaxation
in the glassy state, using the Tool formalism. This model well captures some of the observed phenomena, but fails in describing
the specific kinetics observed when aging is followed by a short but deep quench. 相似文献
53.
Vertically aligned monodomain nematic liquid-crystal elastomers contract when heated. If a temperature gradient is applied
across the width of such a cantilever, inhomogeneous strain distribution leads to bending motion. We modelled the kinetics
of thermally induced bending in the limit of a long thin strip and the predicted time variation of curvature agreed quantitatively
with experimental data from samples with a range of critical indices and nematic-isotropic transition temperatures. We also
deduced a value for the thermal diffusion coefficient of the elastomer. 相似文献
54.
《先进技术聚合物》2018,29(6):1861-1869
π‐Plasmon absorbance films of carboxylic functionalized multiwall carbon nanotubes (CNTs) coupled with renewable and recycled polycaprolactone grafted pectin (PGP) platforms as successful alternative for ordinary nondegradable platforms were investigated. Characterization of the synthesized carboxylic functionalized CNTs was performed using 1H NMR and attenuated total reflectance Fourier transform infrared for structural identification, thermogravimetric analysis and derivative thermogravimetric analysis for thermal stability, and X‐ray powder diffraction for crystal structure, whereas the characterization of prepared PGP was done by means of attenuated total reflectance Fourier transform infrared for chemical structure, differential scanning calorimetry for melting endotherms of polycaprolactone and high crystalline structure of PGP, and thermogravimetric analysis and derivative thermogravimetric analysis for thermal stability of PGP. Fabrication of water‐dispersed carboxylic functionalized CNTs coupled with PGP films was performed by casting technique in the presence of Ca2+ as cross‐linker. The thin films were tested for π‐plasmon absorbance using UV‐Vis spectrometry. Different fractions of carboxylic functionalized CNTs and PGP films demonstrated π‐plasmon absorbance broad peaks at λmax = 232 nm, which corresponded to 5.36 eV. The fabrication of novel films from renewable recycled PGP platform and advanced carboxylic functionalized CNTs properties will be the key features for many of next forthcoming technologies. The PGP considered as environment‐friendly and easily degradable platforms will be a successful alternative for conventional nondegradable electronic platforms, and water‐dispersed carboxylic functionalized CNTs with advanced properties will be finding accelerating executive applications. 相似文献
55.
《先进技术聚合物》2018,29(2):716-725
Foaming of trans‐1,4‐polyisoprene (TPI) polymer was carried out through a batch process using nitrogen (N2) as the blowing agent. TPI vulcanizates having varying crosslink densities were prepared by varying crosslinking agent content and curing time. The vulcanizates were then saturated with N2 inside a pressure vessel at a pressure of 14 MPa and varying temperatures for 5 hours before effecting the foaming by rapidly quenching the pressure. The effects of varying the crosslinking agent content, silica filler content, and precuring time of the vulcanizates and the effects of varying the gas saturation temperature of foaming on the cell characteristics and physical properties of the foam prepared were investigated. The cells of the TPI foams had a spherical, closed structure. The density, expansion ratio, cell size, cell density, and tensile properties of the foams varied with varying crosslink density of the TPI vulcanizates as well as the saturation temperature of foaming. The important effects of crosslink density and saturation temperature on the N2 solubility in the TPI matrix and thus on the foam expansion were discussed. The silica filler was found to be acting as a cell nucleating agent and reinforcing filler for the TPI foams. 相似文献
56.
《Arabian Journal of Chemistry》2023,16(4):104584
Due to the high cost of bioplastic production, sesame wastewater, generated from the sesame seed hulling process, was investigated to be used as inexpensive and renewable carbon source for the production of biodegradable polyhydroxyalkanoate (PHA) by extreme Haloferax mediterranei. The sesame wastewater (SWW) was hydrolyzed using different concentrations of hydrochloric acid (0.4. 1.00 and 2.00 M) at different period of times (15, 60 and 90 min). The concentration of salt (NaCl) and nitrogen source (NH4Cl and yeast) required for H. mediterranei cells growth and the accumulation of PHA biopolymer was optimized. A maximum 0.53 g/L concentration of PHA was achieved when the SWW extract media was supplemented with 100 g/L NaCl and 6.0 g/L yeast extract. The cultivation was scaled-up using sequencing batch reactor (SBR) fermentation under non-sterile conditions. The SBR results showed that SWW needs an auxiliary carbon source to obtain high PHA production. Consequently, the system fed with SWW and glucose produced higher PHA (20.9 g/L) than the system fed with SWW. 相似文献
57.
G. Reiter G. Castelein P. Hoerner G. Riess J.-U. Sommer G. Floudas 《The European physical journal. E, Soft matter》2000,2(4):319-334
Spin-coated thin films of about 100nm of low-molecular-weight hydrogenated poly(butadiene-b- ethyleneoxide) (PBh-PEO) diblock copolymers have been crystallized at various constant temperatures. Crystallization has been observed in real
time by light microscopy. Detailed structural information was obtained by atomic force microscopy, mainly enabled by the large
viscoelastic contrast between amorphous and crystalline regions. The behavior in thin films is compared to the bulk properties
of the polymer. Crystallization started from an annealed microphase separated melt where optical microscopy indicated a lamellar
orientation parallel to the substrate. A small difference in the length of the crystallizable block produced significantly
different crystallization behavior, both in the bulk and in thin films. For thin films of the shortest diblock copolymer (45%
PEO content) and for an undercooling larger than about 10 degrees, crystallization created vertically oriented lamellae. These
vertical lamellae could be preferentially aligned over several micrometers when crystallization occurred close to a three-phase
contact line. Annealing at temperatures closer to the melting point or keeping the sample at room temperature for several
months allowed the formation of a lamellar structure parallel to the substrate. A tentative interpretation based on kinetically
caused chain folding and relaxation within the crystalline state, with implications on general aspects of polymer crystallization,
is presented.
Received 19 March 1999 and Received in final form 14 December 1999 相似文献
58.
We propose a simple friction model for isolated polymer chains on a solid substrate. The chains are pulled at constant velocity
by one end, the other end can be trapped on the solid substrate on localised sites. We focus on the energy dissipation due
to the traps. This simple model leads to nontrivial friction laws, depending on the velocity and the distance between traps.
Some refinements of the model such as the effect of thermal fluctuations are also reported.
Received 20 March 2000 相似文献
59.
A.N. Semenov 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):497-507
Secondary domain superstructures in correlated random block copolymers are considered theoretically using the concept of the
second order parameter related to fluctuations of the local mean block length. It is shown that the size of secondary domains,
, is much larger than the primary domain size, L: , while , where is a small parameter defining the composition asymmetry. Different secondary morphologies are characterized. It is also shown
that separation of the system in two macroscopic phases with different primary morphologies predicted earlier using the free
energy expansion up to ( is the usual order parameter related to local composition) is an artifact of this widely accepted theoretical model.
Received 15 July 1998 and Received in final form 18
January 1999 相似文献
60.