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1.
2.
Three fixtures for conducting laboratory fretting fatigue tests are described and their respective testing methods and the
results of the analysis are compared. Each of these fixtures has been used to investigate the effects of various parameters
of interest in fretting fatigue. These fixtures include a unique apparatus in which all load applied to the specimen is transferred
to the fretting pads, an apparatus similar to many found in the literature where partial load transfer occurs across the pads,
and a simplified dovetail fixture in which the clamping load, P, and the shear load, Q, are varied in phase. Select test conditions from prior experiments performed on identical material and resulting in similar
lives ranging from one to ten million cycles from these fixtures are identified. The various testing conditions were used
to compute the unique stress field for each case. The resulting contact stresses were used to calculate crack initiation based
criteria, and to calculate stress intensity factors. The three fixtures were shown to be able to accommodate a range of loads,
fretting pad contours, and specimen geometries that produced a variety of stress fields. A crack-initiation-based criterion
was shown to predict the failure lives of thinner specimens accurately. The stress intensity factor calculations showed the
possibility of a crack arresting for a stress field that decays rapidly and the possibility of a local minimum for K as a function of depth. The fixtures are shown to be complementary in generating data for development of robust fretting
fatigue models that use these criteria. 相似文献
3.
Timothy B. Hutson Ming J. W. Chang Joseph T. Keller David J. Long 《Mikrochimica acta》1988,94(1-6):339-341
Fourier transform infrared techniques were used to monitor mammalian cell growth plated on attenuated total reflection (ATR) crystals. Consistently, the growth kinetics plots generated from the obtained spectra demonstrated a sigmoidal curve representing a sequence of slow, rapid, then tapering cell growth which correlated well with non-spectral cell growth determinations. Significant advantages over traditional methods of measuring cell growth kinetics are demonstrated. The technique has promising potential to be used to study events in areas such as toxicology and cell biology. 相似文献
4.
C. Boekema A. B. Denison D. W. Cooke R. H. Heffner R. L. Hutson M. Leon M. E. Schillaci 《Hyperfine Interactions》1983,15(1-4):529-532
Muon Spin Rotation (SR) results for magnetite (Fe3O4) are analyzed and discussed. At room temperature, a SR signal is observed due to the presence of an internal magnetic field (Bint) at the muon site. External transverse field measurements show that Bint is parallel to the magnetic spin direction, the <111> direction in zero applied field. Calculations of the hyperfine field to pinpoint muon stopping sites in magnetite show that the local field contains supertransfer (covalent) and dipolar field contributions. The implanted muons appear to stop at sites structurally similar to those reported for hematite (-Fe3O4), where muon-oxygen bond formation was strongly indicated.Research partially supported by US Department of Energy 相似文献
5.
R. H. Heffner J. A. Brown R. L. Hutson M. Leon D. M. Parkin M. E. Schillaci W. B. Gauster O. N. Carlson D. K. Rehbein A. T. Fiory 《Hyperfine Interactions》1979,6(1-4):237-240
We present the first results of a study of the effects of varying impurity concentration on the temperature dependence of the depolarization rate of positive muons implanted into vanadium. Data are reported for the most highly purified polycrystalline sample yet measured, and the same sample subsequently doped with about 500 ppm oxygen by weight. The data for the pure sample shows a low depolarization rate (<.15 sec–1) at all temperatures measured, showing a broad minimum centered at 35 K, followed by a sharp peak near 90 K and a rapid drop to negligible values at 200 K. The data is contrasted with previously published data [2] on less pure samples, and calls into question previous interpretations of the behavior of the + at low temperatures in impure vanadium [1] as one-phonon-assisted tunneling.This work was supported by the U. S. Department of Energy 相似文献
6.
One of the principal techniques for treating sustems of reaction–diffusion equations is based on a comparison method using sub and super–solutions. In practice this method is much more effective if non–smooth subsolutions are allowed. In this note we extend the analysis in [2,3] for cooperative systems and prove a comparison principle for a natural and rather general class of weak subsolutions satisfying a Phragmen–Lindelöf condition. An application is then given to a biological model in involving a pair of mutualists. 相似文献
7.
We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo)--specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo--especially at 355 nm--due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water. 相似文献
8.
Let be a Sturm-Liouville operator acting on functions defined on R. The authors have recently shown how to construct commutative associative algebras of distributions of compact support for which L is a centralizer (in the sense that for distributions f, g of compact support) when q is locally bounded. Here, it is assumed either that q is bounded and is integrable, or that q is of bounded variation. A function ψ is then found such that ψ={μ : μ is a measure on R and | μ |(ψ) < & infin;} becomes a Banach algebra containing the algebra of measures of compact support. The representation theory of ψ is discussed and conditions for its semisimplicity are obtained. 相似文献
9.
Alisdair O. G. Wallis Edward J. J. Longdon Piotr S. Żuchowski Jeremy M. Hutson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(1-2):151-160
We calculate the quartet potential energy surface for Li+NH and use it to calculate elastic and spin-relaxation cross sections for collisions in magnetically trappable spin-stretched states. The potential is strongly anisotropic but spin-relaxation collisions are still suppressed by centrifugal barriers when both species are in spin-stretched states. In the ultracold regime, both the elastic and inelastic cross sections fluctuate dramatically as the potential is varied because of Feshbach resonances. The potential-dependence is considerably reduced at higher energies. The major effect of using an unconverged basis set in the scattering calculations is to shift the resonances without changing their general behaviour. We have calculated the ratio of elastic and spin-relaxation cross sections, as a function of collision energy and magnetic field, for a variety of potential energy surfaces. Most of the surfaces produce ratios that are favorable for sympathetic cooling, at temperatures below about 20 mK. 相似文献
10.
C. Boekema V. A. M. Brabers R. L. Lichti A. B. Denison D. W. Cooke R. H. Heffner R. L. Hutson M. E. Schillaci D. E. Maclaughlin S. A. Dodds 《Hyperfine Interactions》1986,31(1-4):369-374
Zero-field longitudinal muon-spin-relaxation (μSR) experiments have been performed on single crystals of pseudo-brookite (Fe2−xTil+x
O
5; x=0.25), an anisotropic spin-glass system. The spinglass temperature (Tg) is determined to be 44.0±0.5K. Above Tg, a distinct
exponential muon-spin-relaxation rate (λ) is observed, while below Tg a square-root exponential decay is seen, indicating
fast spin fluctuations in the ‘frozen’ state. Near 8K, a maximum in λ is observed, which is due to transverse spin ordering
at these low temperatures. Even near Tg, λ is very low (<1 μs−1), likely due to a well-defined muon-oxygen state in the single crystals. The sharp λ-increase (with decreasing temperatures)
above Tg allows a comparison between spinfreezing models like the Vogel-Fulcher law and a power law. The results of these
initial measurements indicate that dynamic (and static) magnetism in oxide spin glasses can be directly monitored through
μSR. 相似文献