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71.
The separation process in reversed-phase high-performance liquid chromatography employing C18 phases is mainly due to hydrophobic interactions. The separation of tocopherol isomers, exhibited by the C30 phases, however, is additionally driven by shape selectivity. This phenomenon is investigated by suspended-state nuclear magnetic resonance spectroscopy using the saturation transfer difference technique, which was originally introduced to study protein-ligand interactions. The interaction strength between beta-/gamma-tocopherol and three different stationary phases was estimated qualitatively. The nuclear magnetic resonance data are compared to chromatographic data, and a similar mode of interaction between the analytes and the stationary phases is elucidated. 相似文献
72.
Patrick Trouillas Philippe Marsal Didier Siri Roberto Lazzaroni Jean-Luc Duroux 《Food chemistry》2006
Over the past decade, the chemical behaviour of flavonoids as antioxidants has become the subject of intense experimental research. In this paper, we use a quantum-chemical approach to shed light on the reactivity of two flavonoids, quercetin and taxifolin. We particularly focus on the 3-OH site and the role played by the 2,3-double bond in the reactivity of that site. In order to establish the most efficient theoretical methodology, different methods, either Hartree–Fock-based or derived from density functional theory, and different basis sets (from 6-311G(d) to 6-311++G(2d,p)) were tested on phenol and catechol, for which experimental bond dissociation enthalpy (BDE) values are available. It appears that (U)B3P86/6-311+G(d,p) is the most relevant method for BDE prediction of these phenolic compounds and it has, therefore, been used for an extensive study of the two flavonoids. 相似文献
73.
Onshore wind turbine technology is moving offshore, and the offshore wind industry tends to use larger turbines than those used over land. This calls for an improved understanding of the marine boundary layer. The standards used in the design of offshore wind turbines, particularly the rotor–nacelle assembly, are similar to those used for onshore wind turbines. As a result, simplifications regarding the marine boundary layer are made. Atmospheric stability considerations and wave effects, including the dynamic sea surface roughness, are two major factors affecting flow over sea versus land. Neutral stratification and a flat, smooth sea surface are routinely used as assumptions in wind energy calculations. Newly published literature in the field reveals that the assumption of a neutral stratification is not necessarily a conservative approach. Design tests based on neutral stratification give the lowest fatigue damage on the rotors. Turbulence, heat exchange and momentum transfer depend on the sea state, but this is usually ignored, and the sea surface is thought of as level and smooth. Field experiments and numerical simulations show that during swell conditions, the wind profile will no longer exhibit a logarithmic shape, and the surface drag relies on the sea state. Stratification and sea state are parameters that can be accounted for, and they should therefore be considered in design calculations, energy assessments and power output predictions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
74.
Davide Giglio Riccardo Minciardi Simona Sacone Silvia Siri 《Discrete Event Dynamic Systems》2009,19(3):423-448
The paper deals with the optimal control of production processes characterized by the possibility of performing operations
(relevant to the processing of a set of jobs) with variable execution times. A production process relevant to a single machine
is addressed first. An optimization problem with a quite general cost function is considered, and some properties of optimal
solutions are derived. Then, a particular version of the problem is analyzed, in which the cost function is the weighted sum
of the quadratic earliness and tardiness of jobs and of quadratic deviations between pre-defined nominal unitary processing
times and the actual ones. The decision variables of the problem are the possible idle times inserted before job executions
and the processing times of jobs. This single machine problem is stated as an optimal control problem and a closed-loop solution
is derived. Then, a second production process is considered, in which multiple machines serve jobs in parallel, again with
variable processing times and with different processing costs. With reference to this second production scheme, a significant
decision problem refers to the splitting of jobs over the different machines. Then, on the basis of a sensitivity analysis
of the single machine problem solution, some conditions to verify the optimality of a pre-defined splitting are derived. An
on-line splitting scheme using such conditions is finally presented.
相似文献
Silvia Siri (Corresponding author)Email: |