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71.
This article addresses the problem of hybrid flexible flow line where some constraints are considered to alleviate the chasm between the real-world industries scheduling and the production scheduling theories. Sequence-dependent setup times, machine release date and time lags are three constraints deemed to project the circumstances commonly found in real-world industries. To tackle the complexity of the problem at hand, we propose an approach base on genetic algorithm (GA). However, the performance of most evolutionary algorithms is significantly impressed by the values determined for the miscellaneous parameters which these algorithms possess. Hence, response surface methodology is applied to set the parameters of GA and to estimate the proper values of GA parameters in continually intervals. Finally, problems of various sizes are utilized to test the performance of the proposed algorithm and to compare it with some existing heuristic in the literature such as SPT, LPT and NEH.  相似文献   
72.
The flow field inside a cylindrical mixing vessel was visualized by electrical resistance tomography (ERT), a non‐intrusive measurement technique. Six tomography planes, each containing 16 sensing electrodes, measured the mixing time in the agitation of pseudoplastic fluid exhibiting yield stress. The effects of various parameters such as impeller types, impeller speed, fluid rheology, power consumption, Reynolds number, and absence of baffles on the mixing time were investigated. The Maxblend impeller was able to improve the mixing performance of non‐Newtonian fluids in a batch reactor. The mixing quality could be further enhanced by decreasing the xanthan gum concentration and using baffles in the mixing vessel.  相似文献   
73.
BACKGROUND: Airlift bioreactors have been used extensively in biotechnology industries in recent years in a variety of arrangements and applications. The insertion of packing inside the bioreactors has the potential to provide high productivity within a compact size through utilizing immobilized species. RESULTS: A novel recirculating external loop airlift bioreactor that has two rolls of fiberglass packing and a gas distributor in between was designed and built. Electrical resistance tomography (ERT) images showed that the gas holdup increased after installing the packing and the gas distributor. Gas holdup in the riser increased with decreasing static liquid height in the bioreactor. This decreased the liquid superficial velocity, which contributed to a higher gas holdup in the bioreactor. Results also showed that riser gas holdup varied slightly with different sparger configurations. Higher gas holdup increases the oxygen mass transfer rate by increasing the residence time and interfacial mass transfer area. CONCLUSION: ERT results showed that fiberglass packing with an installed gas distributor in bioreactors can achieve higher gas holdup at higher superficial gas velocity. This can contribute to improved conversion in bioreactors with packing through utilizing higher biomass concentrations and higher oxygen concentration. © 2012 Society of Chemical Industry  相似文献   
74.
The emulsion polymerization of methyl methacrylate (MMA) was carried out in a lab‐scale reactor, which was equipped with a top‐entry agitator, four wall baffles, a U‐shaped cooling coil, and a temperature controller. Potassium per sulfate and sodium dodecyl sulfate as were used as the initiator and the surfactant, respectively. The experimental investigation demonstrated the impact of the impeller type (45° six pitched‐blade turbine and Rushton impeller), number of impellers (single and double impellers), and impeller speed (100–350 rpm) on the monomer conversion, polymer particles size, molecular weight, and glass transition temperature. The results revealed that the effect of the impeller speed on the characteristics of the polymer attained using the pitched‐blade turbine was more prominent than that for the Rushton turbine. It was also found that the impact of the impeller speed on the polymer characteristics was much more pronounced for the double pitched‐blade turbines rather than for the double Rushton turbines. However, more uniform size distribution was achieved with the Rushton turbine. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40496.  相似文献   
75.
Electrical resistance tomography (ERT), which is a non‐invasive and robust measurement technique, was employed to visualize, in three dimensions, the concentration field inside a cylindrical mixing vessel equipped with a radial‐flow Scaba 6SRGT impeller. The ability of ERT to work in opaque fluids makes this technique very attractive from an industrial perspective. An ERT system with a 4‐plane assembly of peripheral sensing rings, each containing 16 electrodes, was used to measure the mixing time in agitation of xanthan gum solution which is a pseudoplastic fluid with yield stress. An image reconstruction algorithm was used to generate images of the tracer distribution within the sensing zone. In this study, the effect of impeller speed, fluid rheology, power consumption, and Reynolds number on the mixing time was investigated.  相似文献   
76.
A hybrid mathematical modeling/optimization approach based on the response surface methodology (RSM) and desirability function (DF) capabilities was applied here to imitate and optimize the mechanical properties of thermoplastic starch-based biocomposites. In order to prepare the biodegradable and renewable biocomposites, rice straw (RS) was chemically modified to obtain more effective sustainable reinforcing fillers for starch, having semi-thermoset and core-shell structures. A combination of different RS products was used in the biocomposites and the composition of RS-based fillers was chosen as control variable. A series of experiments, by using RSM, were designed to assess the effects of filler loading and composition on the Young modulus, tensile strength, ultimate strain, and absorbed energy of the biocomposites. The best-fitting regression functions were identified via RSM statistical analysis and transformed into DF to optimize the desired responses concurrently. The findings demonstrate that the starch/RS product biocomposites with optimum elastic modulus (339.3 MPa), tensile strength (9.8 MPa), elongation at break (13.8%), and absorbed energy (1831.2 kJ/m2) were obtained by incorporating RS-based fillers with both semi-thermoset and core-shell structures in combination with each other at loadings of 13.5 and 6.5 phr, respectively.  相似文献   
77.
The effects of spherical nanosilica particles on the lower critical solution temperature (LCST) phase diagram of poly(ε-caprolactone) (PCL)/poly(styrene-co-acrylonitrile) (SAN) blends are investigated by using isochronal dynamic temperature sweep tests at different cooling rates. A stronger dependency of the rheologically determined phase-transition points on the cooling rate is observed in the presence of nanoparticles, which results from the large contribution of entropic surface tension of chains in the Gibbs free energy of mixing and much slower rate of PCL/SAN phase dissolution. By alleviating the effects of kinetic factors, it is found that the drop in the LCST-type phase boundary of PCL/SAN blends by adding nanofiller is more apparent than real. However, the closest LCST phase diagram to the real steady-state thermodynamic diagram shows an unexpected shift to lower temperatures by adding nanosilica. The migration of nanosilica particles to the SAN domains especially at lower cooling rates in the dynamic measurements is the most likely explanation of these observations. The findings that prove the profound impact of kinetic factors in dynamic temperature measurements are reached in a hybrid system, wherein the SAN chains are preferentially absorbed on the surface of a nanofiller having very small primary particle size. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48679.  相似文献   
78.
In this study, the correlations between the mechanical performance and structural properties of injected-molded polyethylene (PE)/ethylene-vinyl acetate copolymer (EVA)/nanoclay (NC) nanocomposites are investigated by revisiting the interfacial phenomena and miscibility state of the component pairs. The effects of different parameters including the injection molding temperature, mixing sequence in melt-compounding process, blend composition, and nanoclay loading are studied. A great complexity arises in the filling and cooling process of the injected-molded parts owing to the phase behavior of the polyolefin blend, crystallization, and morphological changes. The injection molding temperature positively influences the elastic modulus, tensile strength and impact strength of PE/EVA/NC systems through the improvements in the PE/EVA partial miscibility, mutual solubility, and interfacial interactions of PE/clay and PE/EVA pairs. By applying a two-step mixing process before the injection molding, more nanoclay stacks with smaller thicknesses and larger clay interlayer spacing are formed. The stronger pinning effect of nanoparticles in the second mixing sequence retards the phase separation phenomenon of PE/EVA blend during the cooling stage. As a result of improved mutual PE/EVA solubility, the elastic modulus and tensile strength decrease and the impact resistance increases in the PE-rich systems. On the other hand, an opposite trend for these properties is found for the EVA-rich systems.  相似文献   
79.
Selected mapping (SLM) is a technique for reducing the high peak-to-average power ratio (PAPR) in which a suitable signal is selected among a set of alternative signals which all indicate alike information. The chief drawback existing in this method is that transmitter is compelled to send several additional bits called side information (SI) for each data block in order that recovering at the receiver side can be possible. In this paper, we present a novel SLM scheme by using the linear feedback shift register circuit and m-sequence named MSLM technique by which any side information bit is not explicitly sent. In MSLM, The basic idea is to fit the side information into transmitted symbols based upon which some special locations in the transmitted data block are expanded, i.e. some transmitted symbols are extended. In the receiver side, by using some properties of m-sequence the SI bits can be detected. We present the example of our method for an OFDM system through the use of 16-QAM modulation and different m-sequences and finally, concerned results are illustrated from the view point of bit error rate, probability of detection failure and PAPR reduction.  相似文献   
80.
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