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71.
72.
E E Leutzinger W A Bowles R K Robins L B Townsend 《Journal of the American Chemical Society》1968,90(1):127-136
73.
Myong K. Ahn Thomas C. Stringfellow Matthew Fasano Kenneth J. Bowles Michael A. Meador 《Journal of Polymer Science.Polymer Physics》1993,31(7):831-841
PMR-15 is a high-performance thermoset polyimide resin that is used in many high-temperature applications. Postcured PMR-15 produces room-temperature electron paramagnetic resonance (EPR) spectra from stable freeradical species that are formed during the postcuring stages. The variable-temperature EPR spectral intensities show a minimum at Tmin in the range ?60 to ?40°C, and a maximum at Tmax in the range 80–120°C. The EPR intensities follow the inverse temperature dependence of Curie's law below Tmin and are due to a stable free radical. The intensities then increase with increasing temperature between Tmin and Tmax. The free radical with such temperature dependence is not present below Tmin and is undetectable by EPR at temperatures above Tmax. These free radicals are generated during the postcuring process at elevated temperature above 310°C. The thermo-oxidative degradation involves free radicals generated during the postcuring process in the presence of oxygen gas. © 1993 John Wiley & Sons, Inc. 相似文献
74.
A high-precision, Fizeau-type laser-interferometric dilatometer system has been developed for low-expansion composite materials.
The strain resolution is about one microstrain. The system is automated to operate over a large temperature range and record
data during the test. A technique has been developed to reduce the data in real time. The dilatometer system is described
and thermal-expansion measurements for several fiber-reinforced and particle-filled composites are presented.
Paper was presented at V International Congress on Experimental Mechanics held in Montreal, Quebec, Canada on June 10–15,
1984. 相似文献
75.
Morris CL Anaya JM Bowles TJ Filippone BW Geltenbort P Hill RE Hino M Hoedl S Hogan GE Ito TM Kawai T Kirch K Lamoreaux SK Liu CY Makela M Marek LJ Martin JW Mortensen RN Pichlmaier A Saunders A Seestrom SJ Smith D Teasdale W Tipton B Utsuro M Young AR Yuan J 《Physical review letters》2002,89(27):272501
We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time. 相似文献
76.
77.
Soto-Campos Gerardo Bowles Richard Itkin Andrey Reiss Howard 《Journal of statistical physics》1999,96(5-6):1111-1123
Statistical geometry furnishes the tool that allows the transfer of results from a lattice with finite lattice parameter to the continuum. Since lattice simulations are simpler than continuum ones, this suggests that larger scale simulations for the continuum might be more effectively carried out on a lattice with finite lattice parameter followed by the indicated transfer. We also show that a statistical geometry, peculiar to hard particles on a lattice, can be developed. Among other things, this opens the possibility that a scaled particle theory on a lattice might be derived. 相似文献
78.
Cut-on cut-off transition of acoustic modes in hard-walled ducts with irrotational mean flow is well understood for Helmholtz numbers of order unity. Previous finite-element simulations of this phenomenon, however, appear to indicate the possibility of energy scattering into neighbouring modes at moderately large Helmholtz numbers. In this paper, such scattering phenomena are explained and predicted in slowly varying aeroengine ducts using a multiple-scales approach. It is found that, for sufficiently high frequencies, two mechanisms exist whereby energy can be scattered into neighbouring modes by an incident propagating mode. One mechanism occurs only when there is a mean flow inside the duct and induces scattering at significantly lower frequencies than the other mechanism which remains present without mean flow. A coupled system of ordinary differential equations is derived and then solved numerically for a number of example cases to obtain the corresponding transmitted and reflected amplitudes of the scattered modes as well as the overall acoustic pressure field. The theory appears to demonstrate that some exchange of energy between the acoustic and mean flow fields occurs during scattering. 相似文献
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