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131.
Woravimol Krittaphol Arlene McDowell Christine D. Thomson Ian G. Tucker J. Paul Fawcett Momir Mikov 《Biomedical chromatography : BMC》2009,23(11):1169-1174
Selenomethionine (SeMet) is a widely used nutritional supplement that has potential benefit for people living in selenium‐deficient areas. Previous research has shown that selenium administered as SeMet undergoes significant enterohepatic recycling which may involve the gut microflora. In order to investigate this we have developed a simple method for the quantitation of l ‐SeMet in rat gut content suspensions prepared from jejunum, ileum, caecum and colon. After incubation of l ‐SeMet with gut content suspensions, samples were deproteinized with sulfosalicylic acid and derivatized with o‐phthaldialdehyde (OPA) and N‐acetyl‐l ‐cysteine (NAC). Mass spectrometry confirmed the formation of a 1:1:1 derivative of l ‐SeMet with OPA and NAC. Samples were analysed by reversed‐phase high‐performance liquid chromatography with fluorescence detection. The assay was linear in the concentration range 0.5–100 µg/mL (r2 = 0.9992) with a limit of detection of 0.025 µg/mL (signal‐to‐noise ratio of 5). Intra‐day and inter‐day accuracies were 91.1–92.8 and 91.7–95.5%, respectively with corresponding precisions as relative standard deviation of <5%. Incubation of l ‐SeMet with gut content suspensions from different parts of the rat intestine showed that l ‐SeMet metabolism occurs mainly in the caecum. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
132.
We develop a Eulerian model for a particle suspension in fully developed turbulent liquid in a horizontal pipe. Virtual mass effects and hydrodynamic interactions are accounted for by an extension of the kinetic theory of Reeks and Swailes. 相似文献
133.
Birefringence effects in the two typical installation techniques of fibre Bragg grating(FBG) sensor are investigated: surface-mounting and embedding configurations. When the FBG is bonded on a host material, the sensitivity loss in ultrasonic measurement caused by glue-induced low-birefringence is first reported. Next, the transverse stress-induced high birefringence when the FBG is embedded into a fabric composite laminate is measured as 3.6×10−4. Such induced-birefringence effects are experimentally analysed in mechanical applications. Simple and effective solutions with respect to the respective installation configurations for removing the birefringence effect are proposed and the obtained zero-birefringence cases are compared with the birefringent cases. 相似文献
134.
The electrostatic potential of a highly charged disc (clay platelet) in an electrolyte is investigated in detail. The corresponding non-linear Poisson-Boltzmann (PB) equation is solved numerically, and we show that the far-field behaviour (relevant for colloidal interactions in dilute suspensions) is exactly that obtained within linearized PB theory, with the surface boundary condition of a uniform potential. The latter linear problem is solved by a new semi-analytical procedure and both the potential amplitude (quantified by an effective charge) and potential anisotropy coincide closely within PB and linearized PB, provided the disc bare charge is high enough. This anisotropy remains at all scales; it is encoded in a function that may vary over several orders of magnitude depending on the azimuthal angle under which the disc is seen. The results allow to construct a pair potential for discs interaction, that is strongly orientation dependent. 相似文献
135.
The undissolved fibre and gel residuals that had not completely reacted to form fully dissolved carboxymethyl cellulose (CMC) ID the production of CMC were studied to clarify the reactivity of wood components ID the pulp. The undissolved residuals, the pulp and the CMC were therefore analysed on the fibre level, the cell-wall level and the chemical composition level. The results may be interpreted as indicating that the presence of undissolved residuals ID the CMC was not due to any chemical difference. The undissolved residuals were shown to consist mainly of swollen cell wall parts and some whole wood cells, mainly thick-walled compression wood and summerwood cells. They react more slowly ID the mercerisation and etherification, probably because of a greater diffusion resistance due to their larger dimensions or to a more dense structure. These cells are assumed to be less accessible for chemical penetration, but they may also contain supramolecular structures that slow down the CMC reaction. 相似文献
136.
C.?L.?de?Vasconcelos T.?N.?C.?Dantas M.?R.?Pereira J.?L.?C.?FonsecaEmail author 《Colloid and polymer science》2004,282(6):596-601
Rheological properties of concentrated alumina suspensions using a charged copolymer as the dispersant have been studied. The non-Newtonian behavior of these fluids was characterized and correlated to potential measurements and sedimentation column data, obtained with these dispersions. As a result, a clear relationship between dispersion stability and pseudoplastic/dilatant rheological behavior was established. 相似文献
137.
Gorce JP Bovey D McDonald PJ Palasz P Taylor D Keddie JL 《The European physical journal. E, Soft matter》2002,8(4):421-429
We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films,
testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile
in the vertical direction (i.e. normal to the substrate). When Pe < 1, the water concentration in films cast from an alkyd emulsion is found via magnetic-resonance profiling to be uniform with depth, which is consistent with expectations. When Pe > 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal
that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface
layer develops, but particles are not coalesced in this layer to form a continuous “skin”, but rather the structure is likely
to be that of a biliquid foam.
Received 20 March 2002 and Received in final form 12 June 2002 相似文献
138.
Tasinkevych M Silvestre NM Patrício P Telo da Gama MM 《The European physical journal. E, Soft matter》2002,9(4):341-347
The interaction between two disks immersed in a 2D nematic is investigated i) analytically using the tensor order parameter
formalism for the nematic configuration around isolated disks and ii) numerically using finite-element methods with adaptive
meshing to minimize the corresponding Landau-de Gennes free energy. For strong homeotropic anchoring, each disk generates
a pair of defects with one-half topological charge responsible for the 2D quadrupolar interaction between the disks at large
distances. At short distance, the position of the defects may change, leading to unexpected complex interactions with the
quadrupolar repulsive interactions becoming attractive. This short-range attraction in all directions is still anisotropic.
As the distance between the disks decreases, their preferred relative orientation with respect to the far-field nematic director
changes from oblique to perpendicular.
Received 1 October 2002 and Received in final form 12 November 2002
RID="a"
ID="a"e-mail: miko@cii.fc.ul.pt 相似文献
139.
In this paper, fiber motion near a planar wall was investigated using a planar shear flow apparatus. Fibers were placed (one
at a time) perpendicular to the flow direction at various locations throughout the flow field. The location and orientation
of each fiber versus time was measured, using an image processing system, until the fiber aligned with the flow direction.
When the centroid of the fiber was located at distances greater than a fiber length from the wall, Jeffery's equations governing
particle motion were verified. For distances less than a fiber length and greater than a fiber diameter from the wall, the
fiber experienced an increased rate of rotation. In this regime, the motion of the fiber could be described by Jeffery's equations
if an increased effective shear rate was used. The effective shear rate was found to increase logarithmically with decreasing
separation distance. The wall effect was higher for longer aspect ratio fibers and was also a function of orientation; fibers
oriented perpendicular to the wall rotated faster than those oriented parallel to the wall at the same separation distance.
Once the fiber aligned with the flow direction, it ceased to rotate within the field of view. In this orientation, the wall
had a stabilizing effect on the fiber. In efforts to relate the increase in shear rate to the aspect ratio of the fiber and
the separation distance between the fiber and a solid wall, a translation model based on the work of De Mestre and Russel
was explored. This model allows one to quantify the increase in shear rate experienced by the fiber due to the presence of
a wall or obstruction in the flow field. However, the model has its limitations and care should be taken when applying this
model outside its realm of validity. When compared to experimental data, the translation model provides a very good estimate
of the increased shear rate experienced by the fiber when it is located less than 2/3 of a fiber length from a planar wall.
Received: 20 April 2000 Accepted: 28 September 2000 相似文献
140.
The motion of fibres in turbulent flow, stochastic simulation of isotropic homogeneous turbulence 总被引:6,自引:0,他引:6
James A. Olson 《International Journal of Multiphase Flow》2001,27(12):2083-2103
The state of fibres suspended in a turbulent fluid is described in terms of a probability distribution function of fibre orientation and position throughout the suspending fluid. The evolution of the fibre's probability distribution function is governed by a convection–dispersion equation, where the randomizing effect of the turbulence is modelled by rotational and translational dispersion coefficients. To estimate these coefficients a numerical simulation of fibres moving in a turbulent fluid was developed. The trajectory of an ensemble of inertialess, rigid, thin, free-draining fibres was calculated through a stochastic model of homogeneous, isotropic turbulence. The results of the simulation were compared with analytical estimates and were found to provide reasonable agreement over a wide range of fibre length. However, the simulation showed that the Lagrangian integral time scale for rotation was significantly smaller than for translation and the ratio of rotational to translational Lagrangian time scales was smaller than the ratio of Eulerian time scales. The simulation also showed that the Lagrangian velocity correlation increased as fibre length increased and that the temporal correlations approached the analytical estimates of the Eulerian correlations in the limit of long fibres. 相似文献