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1.
Active flow-separation control is an effective and efficient mean for drag reduction and unsteady load alleviation resulting
from locally or massively separated flow. Such a situation occurs in configurations where the aerodynamic performance is of
secondary importance to functionality. The performance of heavy transport helicopters and aeroplanes, having a large, and
almost flat, aft loading ramp suffer from the poor aerodynamics of the aft body. Hence, a combined experimental and numerical
investigation was undertaken on a generic transport aeroplane/helicopter configuration. The experimental study provided surface
pressures, direct drag measurements, surface and smoke flow visualization. The baseline flow was numerically analyzed, using
finite volume solutions of the RANS equations. The baseline flow around the model was insensitive to the Reynolds number in
the range it was tested. The flow separating from the aft body was characterized by two main sources of drag and unsteadiness.
The first is a separation bubble residing at the lower ramp corner and the second is a pair of vortex systems developing and
separating from the sides of the ramp. As the model incidence is decreased, the pair of vortex systems also penetrates deeper
towards the centerline of the ramp, decreasing the pressure and increasing the drag. As expected, the ramp lower corner bubble
was highly receptive to periodic excitation introduced from four addressable piezo-fluidic actuators situated at the ramp
lower corner. Total drag was reduced by 3–11%, depending on the model incidence. There are indications that the flow in the
wake of the model is also significantly steadier when the bubble at the lower ramp corner is eliminated. The vortex system
is tighter and steadier when the ramp-corner bubble is eliminated. 相似文献
2.
Using molecular dynamics simulations, we have determined that the nature of dynamical heterogeneity in jammed liquids is very sensitive to short-ranged attractions. Weakly attractive systems differ little from dense hard-sphere and Lennard-Jones fluids. Particle motion is punctuated and tends to proceed in steps of roughly a single particle diameter. Both of these basic features change in the presence of appreciable short-ranged attractions. Transient periods of particle mobility and immobility cannot be discerned at intermediate attraction strength, for which structural relaxation is greatly enhanced. Strong attractions, known to dramatically inhibit relaxation, restore bimodality of particle motion. But in this regime, transiently mobile particles move in steps that are significantly more biased toward large displacements than those in the case of weak attractions. This modified feature of dynamical heterogeneity, which cannot be captured by conventional mode coupling theory, verifies recent predictions from a model of spatially correlated facilitating defects. 相似文献
3.
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5.
Adva Mechaly Noam Cohen Shay Weiss Eran Zahavy 《Analytical and bioanalytical chemistry》2013,405(12):3965-3972
Amplified Luminescent Proximity Homogeneous Assay (AlphaLISA) technology is an energy-transfer-based assay, utilizing singlet oxygen as an energy donor to a fluorescent acceptor. The long singlet oxygen migration distance allows the energy transfer mechanism to go up to ~200 nm, facilitating flexible and sensitive homogeneous immunoassays. While soluble protein detection using AlphaLISA was previously described, the detection of particles such as bacteria and viruses was not reported. In this work, we show for the first time the implementation of the AlphaLISA technology for the detection of a particulate antigen, i.e., Bacillus anthracis spores. Here, we show that an efficient particle immunoassay requires a high acceptor-to-donor ratio (>4:1). The results suggested that the high acceptor/donor ratio is required to avoid donor aggregation (“islands”) on the spore surface, hence facilitating donor/acceptor interaction. The developed assay enabled the detection of 106 spores/mL spiked in PBS. We also demonstrate the development of a highly sensitive AlphaLISA assay for the detection of the main toxin component of anthrax, protective antigen (PA). The assay enabled the detection of 10 and 100 pg/mL PA in buffer and spiked naïve rabbit sera, respectively, and was successfully implemented in sera of anthrax-infected rabbits. To summarize, this study demonstrates that AlphaLISA enables detection of anthrax spores and toxin, utilizing short homogeneous assays. Moreover, it is shown for the first time that this technology facilitates the detection of particulate entities and might be suitable for the detection of other bacteria or viruses. 相似文献
6.
Eran Briman 《电子设计应用》2009,(5)
本文涵盖了关于DSP的各种问题,包括DSP如何定义、为何需要DSP、如何实现DSP功能等,并介绍了一些认知上的陷阱。 相似文献
7.
We demonstrate experimentally a novel technique for characterizing transverse spatial coherence by using the Wigner distribution function. The method is based on the measurement of interference between a pair of rotated and displaced replicas of the input beam with an area-integrating detector, and it provides an optimal signal-to-noise ratio in regimes when array detectors are not available. We analyze the quantum-optical picture of the presented measurement for single-photon signals and discuss possible applications in quantum information processing. 相似文献
8.
We report the use of nanotube field-effect transistor devices for chemical sensing in a conducting liquid environment. Detection of ammonia occurs through the shift of the gate voltage dependence of the source-drain current. We attribute this shift to charge transfer from adsorbed ammonia molecules, with the amount of charge estimated to be as small as 40 electrons for the smallest shift detected. Using the concentration dependence of the response as an adsorption isotherm, we are able to measure the amount of charge transfer to be 0.04 electron per ammonia molecule. 相似文献
9.
The well known g-conjecture for homology spheres follows from the stronger conjecture that the face ring over the reals of a homology sphere,
modulo a linear system of parameters, admits the strong-Lefschetz property. We prove that the strong-Lefschetz property is
preserved under the following constructions on homology spheres: join, connected sum, and stellar subdivisions. The last construction
is a step towards proving the g-conjecture for piecewise-linear spheres. 相似文献
10.
Mireille Bousquet-Mélou Svante Linusson Eran Nevo 《Journal of Algebraic Combinatorics》2008,27(4):423-450
The enumeration of independent sets of regular graphs is of interest in statistical mechanics, as it corresponds to the solution
of hard-particle models. In 2004, it was conjectured by Fendley et al., that for some rectangular grids, with toric boundary conditions, the alternating number of independent sets is extremely simple. More precisely, under a coprimality condition on the sides of the rectangle,
the number of independent sets of even and odd cardinality always differ by 1. In physics terms, this means looking at the
hard-particle model on these grids at activity −1. This conjecture was recently proved by Jonsson.
Here we produce other families of grid graphs, with open or cylindric boundary conditions, for which similar properties hold
without any size restriction: the number of independent sets of even and odd cardinality always differ by 0, ±1, or, in the
cylindric case, by some power of 2.
We show that these results reflect a stronger property of the independence complexes of our graphs. We determine the homotopy
type of these complexes using Forman’s discrete Morse theory. We find that these complexes are either contractible, or homotopic
to a sphere, or, in the cylindric case, to a wedge of spheres.
Finally, we use our enumerative results to determine the spectra of certain transfer matrices describing the hard-particle
model on our graphs at activity −1. These results parallel certain conjectures of Fendley et al., proved by Jonsson in the toric case. 相似文献