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排序方式: 共有55条查询结果,搜索用时 15 毫秒
1.
A new approach for link modelling in wireless multi-hop networks is described for portable devices, based on Kernel Regression Statistics. A non-parametric estimation of errors in the wireless medium provides an efficient and accurate model of link errors between any two nodes. This estimation results from the analysis of the inter-arrival time between any periodically sent packets. The obtained results prove that it is possible to infer on link quality without having unrealistic assumptions or additional overhead, by using Kernel Methods. Moreover, similar performances were achieved for different scenarios, without requiring model recalculations. The presented results show that the proposed link quality estimation can be used in order to improve wireless connectivity and ubiquity in future networks. 相似文献
2.
Vitor G. Rolla Marilia Curado 《Engineering Applications of Artificial Intelligence》2013,26(10):2243-2250
Delay Tolerant Reinforcement-Based (DTRB) is a delay tolerant routing solution for IEEE 802.11 wireless networks which enables device to device data exchange without the support of any pre-existing network infrastructure. The solution utilizes Multi-Agent Reinforcement Learning techniques to learn about routes in the network and forward/replicate the messages that produce the best reward. The rewarding process is executed by a learning algorithm based on the distances between the nodes, which are calculated as a function of time from the last meetings. DTRB is a flooding-based delay tolerant routing solution. The simulation results show that DTRB can deliver more messages than a traditional delay tolerant routing solution does in densely populated areas, with similar end-to-end delay and lower network overhead. 相似文献
3.
Marilia Panayiotou 《Polymer》2005,46(3):615-621
Stimuli-responsive poly(N,N′-diethylacrylamide) gels were prepared by free radical polymerisation in aqueous solution, using N,N-methylenebisacrylamide as crosslinking agent. The gels were compared with the corresponding poly(N-isopropylacrylamide)-based gels. In particular, the swelling ratio of both gel types including the effect of the crosslinker content, their swelling and deswelling kinetics, their permeability and finally their drug (insulin) storage and controlled release ability were compared. In spite of the similarity in the monomer/crosslinker ratio, the deswelling kinetics and the critical temperatures (ca. 30-32 °C in pure water), some differences could be observed. Compared to poly(N-isopropylacrylamide)-based gels, poly(N,N′-diethylacrylamide)-based gels show a broader phase transition temperature interval, a more pronounced dependency of the swelling ratio on the crosslinker content, slower reswelling kinetics, a higher ingress percentage for dextran standards ranging from 5 to 70 kD, but lower ingress percentages for proteins (BSA, insulin) and much faster drug (insulin) release kinetics. While a non-linear release kinetic was observed in the case of the poly(N-isopropylacraylamide)-based gels both in water and in PBS (phosphate buffered saline), this was not the case for the poly(N,N′-diethylacrylamide)-based gels. 相似文献
4.
Desirrê Morais Dias Neuza Maria Brunoro Costa Marilia Regini Nutti Elad Tako Hércia Stampini Duarte Martino 《Critical reviews in food science and nutrition》2018,58(13):2136-2146
ABSTRACTBiofortification aims to improve the micronutrient concentration of staple food crops through the best practices of breeding and modern biotechnology. However, increased zinc and iron concentrations in food crops may not always translate into proportional increases in absorbed zinc (Zn) and iron (Fe). Therefore, assessing iron and zinc bioavailability in biofortified crops is imperative to evaluate the efficacy of breeding programs. This review aimed to investigate the advantages and limitations of in vitro and in vivo methods of iron and zinc bioavailability evaluation in the assessment of biofortification program effectiveness. In vitro, animal and isotopic human studies have shown high iron and zinc bioavailability in biofortified staple food crops. Human studies provide direct knowledge regarding the effectiveness of biofortification, however, human studies are time consuming and are more expensive than in vitro and animal studies. Moreover, in vitro studies may be a useful preliminary screening method to identify promising plant cultivars, however, these studies cannot provide data that are directly applicable to humans. None of these methods provides complete information regarding mineral bioavailability, thus, a combination of these methods should be the most appropriate strategy to investigate the effectiveness of zinc and iron biofortification programs. 相似文献
5.
Co-solutes and co-solvents influence the thermoprecipitation of stimulus-responsive polymers from aqueous solution. Taking the behavior of oligomeric poly-(N-isopropylacrylamide) prepared by chain transfer polymerization as reference, the influence of organic solvents (concentration <2 M) on the thermoprecipitation of polyacrylamides with critical solution temperatures (CST) in pure water between 30 and 75 °C is investigated using turbidity and differential scanning calorimetry. Depending on the system, both increase and decrease but also the disappearance of the CST is observed. The strength of the observed effect is related not only to the size but also the structure of the hydrophobic domain of the solvent molecule. Contrary to the effects observed upon the addition of simple salts as additives, the chemistry of the investigated polyacrylamide is of direct consequence for the effect of a given solvent. Certain parallels can hence be drawn to the behavior previously observed for additives such as anionic surfactants and alkylamines. 相似文献
6.
G.C.Pedersen J.E.Eldridge 《硫酸工业》2009,(4):21-26
介绍Kimre公司的SXF^TM半错流洗涤器的结构、优点和应用。该洗涤器采用卧式并流气液接触方式,可根据需要分隔成不同操作段,在由交织单丝构成的纤维介质上完成气体的冷却、净化和除沫。与传统立式逆流填料塔相比,该洗涤器的优点为:高度低,泵、阀门、控制器等可在地面安装,容易操作和维修;液气比范围宽;可进行多级操作,包括在一台设备内完成多个化学过程。如用于冶炼烟气净化,所有步骤可在一台设备内完成。列举了化肥厂造粒塔气体净化、磷酸厂气体除氟和硫酸厂干燥塔除沫等应用实例。 相似文献
7.
Vasconcellos LA Blando E Souto AA Oliveira MG Woitchunas GF Hübler R 《Journal of materials science. Materials in medicine》2007,18(8):1659-1663
The use of multi-component femoral implants to replace the femur head and re-establish bone motion has been widespread since
the 70s. Frequently these implants have spherical metallic heads made of, for example, 316-L stainless steel or Cr–Co alloys,
which allow rotational motion towards a polymeric component (UHMWPE). One of the major causes of implant rejection is the
generation of UHMWPE debris on the surface between the implant head and the polymeric component. The gamma ray sterilization
of implants and the periodical X-ray medical control could contribute to premature degradation of the polymeric surface, resulting
in increased wear and shortened lifetime of the implant. In this work we study the degradation degree of the polymeric UHMWPE
component as function of the X-ray dose. The elasto-plastic deformation and recovery were carried out by means of a nanohardness
tester equipment and the polymer degradation was measured using a fast Fourier transform infra-red (FT-IR) equipment. The
results show the compromise among the irradiation doses, the surface oxidation and the mechanical properties of the samples. 相似文献
8.
Marilia M. Horn Virginia C. A. Martins Yasmin O. M. Fernandes Valcinir A. S. Vulcani Ana Maria G. Plepis 《应用聚合物科学杂志》2018,135(33)
Natural compounds, such as pequi oil, could be added to collagen/gelatin mixtures to improve its properties. Gels characterized by rheological analysis indicated modifications in entanglement network of the mixtures after pequi oil addition. Films processed by casting were analyzed by mechanical and thermal properties, contact angle, and scanning electron microscopy (SEM). The pequi oil addition reduced the contact angle values due to the addition of carboxyl groups found in the palmitic and oleic acid chains of pequi oil. The rough characteristic observed by SEM images was a result of a good homogenization process after oil incorporation. In addition, pequi oil addition decreased the tensile forces and elongation of the films and increased the thermal stability possibly due to lower inter‐ and intra‐molecules interactions. The results suggested a good compatibility between pequi oil and biopolymers and the potential application of this natural compound to increase the wound healing process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46627. 相似文献
9.
10.
Despite efforts to improve the current IEEE 802.11 standard to fully optimize the physical layer, the performance of wireless mesh networks still depends on the routing process for a correct selection of routes. With regard to this question, several cross-layer routing metrics have been developed to improve wireless multi-hop mesh routing. This paper sets out a new taxonomy that can be used to help understand, classify and compare the state-of-the-art situation with regard to cross-layer routing metrics for wireless mesh networks. A simulation study has been carried out to evaluate the capability of the most recent and promising cross-layer routing metrics to support multimedia applications, such as Voice over IP. The evaluation of the routing metrics has been undertaken from three main perspectives: user perception, network performance, and routing stability. The simulation results show that the impact of routing metrics is more noticeable on the network and routing stability evaluation parameters than on the user-perception parameters. Furthermore, the results show that the routing metrics, the level of stability attained, and the application performance are interdependent. Finally, there is a discussion of the direction that future research might take with regard to some open issues in the design of routing metrics for wireless mesh networks. 相似文献