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排序方式: 共有45条查询结果,搜索用时 46 毫秒
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Friis Helmer André Pedersen Janne Jettestuen Espen Helland Johan Olav Prodanović Maša 《Transport in Porous Media》2019,128(1):123-151
Transport in Porous Media - Multiphase flow simulations on imaged porous rock structures require numerical methods that are accurate and robust when applied on complex geometries. A key element in... 相似文献
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Christian Fabiansen Charles W. Yaméogo Sarita Devi Henrik Friis Anura Kurpad Jonathan C. Wells 《Isotopes in environmental and health studies》2017,53(4):344-355
Childhood malnutrition is highly prevalent and associated with high mortality risk. In observational and interventional studies among malnourished children, body composition is increasingly recognised as a key outcome. The deuterium dilution technique has generated high-quality data on body composition in studies of infants and young children in several settings, but its feasibility and accuracy in children suffering from moderate acute malnutrition requires further study. Prior to a large nutritional intervention trial among children with moderate acute malnutrition, we conducted pilot work to develop and adapt the deuterium dilution technique. We refined procedures for administration of isotope doses and collection of saliva. Furthermore, we established that equilibration time in local context is 3?h. These findings and the resulting standard operating procedures are important to improve data quality when using the deuterium dilution technique in malnutrition studies in field conditions, and may encourage a wider use of isotope techniques. 相似文献
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A metal-free acetate shift of 3-acetoxy ynamides to access α-iodo, bromo, and chloro acrylamides/acrylimides under very mild conditions is demonstrated. The inherent alkyne activation of ynamides is sufficient to ensure the α-halo acrylamides/acrylimides in high yields without the addition of a catalyst. In all cases high Z-stereoselectivity is observed. 相似文献
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Svend-Holger Friis Ulrich Rieder Jürgen Weishaupt 《Mathematical Methods of Operations Research》1993,37(2):187-205
A general single-server queueing network model is considered. It is well-known that an optimal policy is determined by the largest-index policy. There is an index for each given queue and one allocates the server to a queue with largest current index. Using discounted dynamic programming we give a new and short proof of this result and derive some characterizations and bounds of the indices. Moreover, it is shown that an approximate largest-index policy yields an approximately optimal policy. These results lead to efficient methods for computing the indices. In particular, we present a general largest-remaining-index method. 相似文献
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In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed. 相似文献
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J. E. T. Andersen J. -D. Zhang Q. Chi A. G. Hansen J. U. Nielsen E. P. Friis J. Ulstrup 《Trends in analytical chemistry : TRAC》1999,18(11):1020-674
The resolution of scanning tunnelling microscopy (STM) and other scanning probe microscopies is unprecedented but the techniques are fraught with limitations as analytical tools. These limitations and their relationship to the physical mechanisms of image contrast are first discussed. Some new options based on in situ STM, which hold prospects for molecular- and mesoscopic-scale analytical chemistry, are then reviewed. They are illustrated by metallic electro-crystallisation and -dissolution, and in situ STM spectroscopy of large redox molecules. The biophysically oriented analytical options of in situ atomic force microscopy, and analytical chemical perspectives for the new microcantilever sensor techniques are also discussed. 相似文献
8.
V. Srinivasan M. Friis A. Vaidya T. Streibl S. Sampath 《Plasma Chemistry and Plasma Processing》2007,27(5):609-623
External injection of high-melting point low thermal conductivity ceramics orthogonal to a typical direct current thermal
plasma jet plays a vital role in determining the in-flight state of the particles and the process downstream. The interactions
between low density ceramic particles and high temperature plasma jet is quite complex, which influences the spray process
and associated deposition. Detailed in-flight particle diagnostics as well as spray stream visualization have significantly
enhanced our capability to diagnose and control the process. In this paper we present some salient observations on the role
of key variables on particle injection. A number of experiments were conducted using a 7MB torch (Sulzer Metco, Westbury,
NY) with both Ar–H2 and N2–H2 plasma gases, where the carrier gas flow to inject Yttria Stabilized Zirconia (YSZ) was varied systematically and the resulting
in-flight particle state was captured using an array of particle and spray stream sensors arranged in a 3D set-up. A notable
observation is the existence of a “sweet-spot” in the plasma jet where the particle temperatures and velocities achieved a
maximum. This sweet-spot can be characterized by the plume position (location of centroid of the spray stream) rather than
carrier gas flow rate and is independent of primary gas flows and other process/material conditions. This result suggests
a possible approach to optimize particle injection independent of plasma-forming-torch-parameters. Controlling particle injection
at this sweet-spot has shown to benefit the overall process efficiency (in terms of melting) and process reliability (both
in-flight measurement and coating build-up) with concomitant application benefits. 相似文献
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