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排序方式: 共有134条查询结果,搜索用时 15 毫秒
1.
Commutation of SR motors 总被引:3,自引:0,他引:3
Commutation schemes for most common types of switched reluctance (SR) motors are presented. Commutation can be achieved using two- or three-positions sensors and a simple commutation logic in a similar fashion to brushless electronically commutated motors. The commutation logic can be easily housed on a programmable logic array (PLA) or similar device. Two-quadrant operation, usually with two position sensors with variable phase shift and dwell angles, can be tuned up to achieve optimum efficiency at low cost. Four-quadrant operation with multimode commutation schemes, such as normal, boost, longdwell, and brake, which cover most of the SR drive applications, can be easily implemented with simple logic control and feedback from low-resolution position sensors. The speed range can be increased beyond the limit reachable with pulse-width modulation (PWM). A 100% increase in the speed range can be easily obtained by switching modes 相似文献
2.
Israel Becerra Rafael Murrieta-Cid Raul Monroy Seth Hutchinson Jean-Paul Laumond 《Autonomous Robots》2016,40(2):395-423
In this paper, we address the problem of determining whether a mobile robot, called the pursuer, is able to maintain strong mutual visibility (a visibility notion between regions over a convex partition of the environment) of an antagonist agent, called the evader. We frame the problem as a non cooperative game. We consider the case in which the pursuer and the evader move at bounded speed, traveling in a known polygonal environment with or without holes, and in which there are no restrictions as to the distance that might separate the agents. Unlike our previous efforts (Murrieta-Cid et al. in Int J Robot Res 26:233–253, 2007), we give special attention to the combinatorial problem that arises when searching for a solution through visiting several locations in an environment with obstacles. In this paper we take a step further, namely, we assume an antagonistic evader who moves continuously and unpredictably, but with a constraint over its set of admissible motion policies, as the evader moves in the shortest-path roadmap, also called the reduced visibility graph (RVG). The pursuer does not know which among the possible paths over the RVG the evader will choose, but the pursuer is free to move within all the environment. We provide a constructive method to solve the decision problem of determining whether or not the pursuer is able to maintain strong mutual visibility of the evader. This method is based on an algorithm that computes the safe areas (areas that keep evader surveillance) at all times. We prove decidability of this problem, and provide a complexity measure to this evader surveillance game; both contributions hold for any general polygonal environment that might or not contain holes. All our algorithms have been implemented and we show simulation results. 相似文献
3.
Mario J. Simirgiotis Mario SilvaJosé Becerra Guillermo Schmeda-Hirschmann 《Food chemistry》2012,131(1):318-327
A simple, fast and direct method was developed for the qualitative analysis of phenolic constituents from infusions of Mapuche medicinal plants. Teas made of Linum chamissonis Schiede, Quinchamalium chilensis Mol., Adesmia emarginata Clos. and Escallonia illinita K. Presl. were analysed by high-performance liquid chromatography with diode array detector (HPLC-DAD) and electrospray mass spectrometry (ESI-MS). This technique allowed for the first time the tentative identification of 16 phenolic compounds in E. illinita, 27 in Q. chilensis, 10 in L. chamissonis and 19 in A. emarginata. The compounds were mainly phenolic acids, flavonoid glycosides, anthocyanins and tannins. The total phenolic and flavonoid content of the infusions was assessed as well as the free radical scavenging capacity measured by the bleaching of a solution of the 2,2-diphenyl-1-picrylhydrazyl (DPPH−) radical. From the four species, Q. chilensis exhibited the strongest antioxidant activity with highest total phenolic and flavonoid content. 相似文献
4.
An efficient parameterization of dynamic neural networks for nonlinear system identification 总被引:1,自引:0,他引:1
Becerra V.M. Garces F.R. Nasuto S.J. Holderbaum W. 《Neural Networks, IEEE Transactions on》2005,16(4):983-988
Dynamic neural networks (DNNs), which are also known as recurrent neural networks, are often used for nonlinear system identification. The main contribution of this letter is the introduction of an efficient parameterization of a class of DNNs. Having to adjust less parameters simplifies the training problem and leads to more parsimonious models. The parameterization is based on approximation theory dealing with the ability of a class of DNNs to approximate finite trajectories of nonautonomous systems. The use of the proposed parameterization is illustrated through a numerical example, using data from a nonlinear model of a magnetic levitation system. 相似文献
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7.
Flor Yunuén García Becerra D. Grant Allen Edgar J. Acosta 《Journal of surfactants and detergents》2010,13(3):261-271
In order to assess the potential for utilizing wastewater biosolids as a source of useful substances, the surface activity
of materials extracted from wastewater biosolids (activated sludge) by simple incubation with sodium hydroxide solutions at
room temperature was assessed. The surface activity, measured by surface and interfacial tension methods, of the extracts
was shown to be dependent on the extraction pH and the concentration of the organic matter solubilized in the alkaline solution.
Increasing the extraction pH increased the surface activity of the extract (lower surface tensions), which is linked to the
presence of more hydrophobic species in the extract. After adjusting the pH to more acidic values (e.g., pH = 4), the extracts
retained their surface activity. The apparent CMC (critical micelle concentration) of pH 12.6 extracts was approximately 1,000 mg/L
(based on total organic carbon or TOC), and the surface tension after CMC approximately 35 mN/m. While the CMC of the extract
is significantly higher, when compared to a conventional surfactant, sodium dodecyl benzene sulfonate (SDBS, CMC ~ 25 mg/L),
its surface tension at CMC was comparable. Above its CMC, the pH 12.6 extract had similar interfacial tensions than SDBS against
toluene, heptane and hexadecane. Furthermore, the extract and SDBS had similar detergency performance for the removal of hexadecane
from cotton. Skin corrosivity tests of the neutralized extracts show that they have comparable toxicity to conventional anionic
surfactants such as sodium dodecyl sulfate. The potential use of these extracts in commercial products is discussed. 相似文献
8.
9.
M. Luz Pizarro Mercedes Becerra Ana Sayago María Beltrán Rafael Beltrán 《Food Analytical Methods》2013,6(1):123-132
A comparison between different extraction methods has been performed in order to assess their effectiveness for the analysis of total phenols (liquid–liquid extraction (LLE), liquid–liquid micro extraction (LLME), and ultrasound liquid–liquid extraction (USE)) and individual phenols (LLME, USE, and solid-phase extraction (SPE)) from virgin olive oil (VOO). Statistical analysis of the analytical data obtained for the total phenol content of a VOO, showed that LLME and USE can represent a reliable alternative to the traditional procedure based on LLE that needs more amount of sample, generates more wastes, and is more time consuming. When an olive oil spiked with phenols was used to test the efficiency of LLME, USE, and SPE methods, the statistical analysis of the data obtained for each individual phenol, again proved LLME and USE methods to be the most suitable, in terms of precision and recoveries, for this purpose. The analysis of real samples (Arbequina and Picual cultivars) confirmed the results obtained for the spiked oil. 相似文献
10.
Silvia Claros Gustavo A. Rico-Llanos José Becerra José A. Andrades 《International journal of molecular sciences》2014,15(7):11255-11274
Transforming growth factor-beta (TGF-β) is involved in processes related to the differentiation and maturation of osteoprogenitor cells into osteoblasts. Rat bone marrow (BM) cells were cultured in a collagen-gel containing 0.5% fetal bovine serum (FBS) for 10 days in the presence of rhTGF (recombinant human TGF)-β1-F2, a fusion protein engineered to include a high-affinity collagen-binding decapeptide derived from von Willebrand factor. Subsequently, cells were moderately expanded in medium with 10% FBS for 4 days and treated with a short pulse of rhBMP (recombinant human bone morphogenetic protein)-2 for 4 h. During the last 2 days, dexamethasone and β-glycerophosphate were added to potentiate osteoinduction. Concomitant with an up-regulation of cell proliferation, DNA synthesis levels were determined. Polymerase chain reaction was performed to reveal the possible stemness of these cells. Osteogenic differentiation was evaluated in terms of alkaline phosphatase activity and mineralized matrix formation as well as by mRNA expression of osteogenic marker genes. Moreover, cells were placed inside diffusion chambers and implanted subcutaneously into the backs of adult rats for 4 weeks. Histological study provided evidence of cartilage and bone-like tissue formation. This experimental procedure is capable of selecting cell populations from BM that, in the presence of rhTGF-β1-F2 and rhBMP-2, achieve skeletogenic potential in vitro and in vivo. 相似文献