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1.
The electroclinic effect in the smectic A phase of ferroelectric liquid crystals is a sensitive probe for measuring the soft
mode response near the A-C* transition point. It is possible to evaluate several coefficients of the Landau theory describing
the A-C* transition by simultaneously measuring the frequency dependence of both the optical signal and the current through
the sample. We have made such measurements on a couple of homologous series [2S,3S]-4′-(2-chloro-3-methyl pentanoyloxy) phenyl-trans-4″-n alkoxy cinnamates synthesized in our labortory. The results show that the Landau meanfield theory is adequate to describe
the A-C* phase transition in these compounds.
Presented at the 15th International Liquid Crystal Conference, Budapest, 3–8 July 1994. 相似文献
2.
The thermal degradation of foamed polymethyl methacrylate (PMMA) patterns in the expendable pat-tern casting process has been
studied. Various physical transitions that may occur during the degradation of PMMA have been determined using scanning electron
microscopy, differential scanning calorimetry, and thermogravimetric analysis, and the effects of polymer density on the degradation
characteristics have been investigated. The results indicate that, when exposed to elevated temperatures, the polymer beads
collapse at about 140 to 200 °. The collapsed beads melt at 260 ° and begin to volatilize. Peak volatilization temperatures
are on the order of 370 °. The end temperature for volatilization is between 420 and 430 °. The initial density of the polymer
does not have a significant effect on the transition tem-peratures associated with degradation. 相似文献
3.
Luca Bertelli Shivkumar Chandrasekaran Frédéric Gibou B. S. Manjunath 《International Journal of Computer Vision》2010,90(3):267-282
In this paper we introduce novel regularization techniques for level set segmentation that target specifically the problem
of multiphase segmentation. When the multiphase model is used to obtain a partitioning of the image in more than two regions,
a new set of issues arise with respect to the single phase case in terms of regularization strategies. For example, if smoothing
or shrinking each contour individually could be a good model in the single phase case, this is not necessarily true in the
multiphase scenario. 相似文献
4.
5.
Network protocols coordinate their decision making using information about entities in remote locations. Such information is provided by state entries. To remain valid, the state information needs to be refreshed via control messages. When it refers to a dynamic entity, the state has to be refreshed at a high rate to prevent it from becoming stale. In capacity constrained networks, this may deteriorate the overall performance of the network. The concept of weak state has been proposed as a remedy to this problem in the context of routing in mobile ad-hoc networks. Weak state is characterized by probabilistic semantics and local refreshes as opposed to strong state that is interpreted as absolute truth. A measure of the probability that the state remains valid, i.e. confidence, accompanies the state. The confidence is decayed in time to adapt to dynamism and to capture the uncertainty in the state information. This way, weak state remains valid without explicit state refresh messages. We evaluate the consistency of weak state and strong state using two notions of distortion. Pure distortion measures the average difference between the actual value of the entity and the value that is provided by the remote state. Informed distortion captures both this difference and the effect of confidence value on state consistency. Using a mathematical analysis and simulations, we show that weak state reduces the distortion values when it provides information about highly dynamic entities and/or it is utilized for protocols that is required to incur a low amount of overhead. 相似文献
6.
M. Sankar R. G. Baligidad Shivkumar Khaple V. V. Satya Prasad V. V. Bhanu Prasad 《Transactions of the Indian Institute of Metals》2012,65(5):467-472
Niobium consumable electrodes of 10?mm dia?×?50?mm length were prepared by cold isostaic pressing with compaction pressure of 125?C250?MPa. The compacts were sintered under vacuum at different temperatures in the range of 1000?C1800?oC. The CIPed and sintered electrodes were characterized with respect to chemical analysis, density, microstructure and bend strength. The results showed that there is a marginal improvement in density at a sintering temperature in the range of 1000?C1400?oC, while a significant improvement in density was observed at sintering temperature in the range of 1600?C1800?oC. The bend strength of sintered electrode was found to increase with increasing sintering temperature and that attains a highest value at a sintering temperature in the range of 1600?C1800?oC. Sintering at a temperature higher than 1400?oC leads to decrease in oxygen content of the electrodes. The oxygen content was decreased from 2000 to 500?ppm when electrode was sintered at 1800?oC. 相似文献
7.
Utku Günay Acer Shivkumar Kalyanaraman Alhussein A. Abouzeid 《Wireless Networks》2011,17(5):1305-1321
Routing in communication networks involves the indirection from a persistent name (ID) to a locator. The locator specifies how packets are delivered to a destination with a particular ID. Such a mapping is provided by a routing
table entry, i.e. state. In a DTN, it is hard to maintain routing state because intermittent connectivity prevents protocols from refreshing states
when they become inaccurate. In prior work, per-destination state mostly corresponds to utilities, where a high utility value
about a destination implies that the probability to encounter the destination for the node maintaining the state is high.
This approach depends on a particular mobility pattern in which nodes that met frequently in the past are likely to encounter
in the future. In this paper, we use the concept of weak state that does not rely on external messages to remain valid (Acer et al. in MobiCom ’07: proceedings of the 13th annual ACM international
conference on mobile computing and networking, pp 290–301,
2007). Our weak state realization provides probabilistic yet explicit information about where the destination is located. We build
Weak State Routing protocol for Delay Tolerant Networks (WSR-D) that exploits the direction of node mobility in forwarding.
It provides an osmosis mechanism to disseminate the state information to the network. With osmosis, a node has consistent information about a portion
of the nodes that are located in regions relevant to its direction of mobility. Through simulations, we show that WSR-D achieves
a higher delivery ratio with smaller average delay, and reduces the number of message transfers in comparison to Spray & Wait
(Spyropoulos et al. in Proceedings of ACM SIGCOMM 2005 workshops: conference on computer communications, pp 252–259, 2005) and Spray & Focus (Spyropoulos et al. in IEEE/ACM Trans Netw, 16(1):77–90, 2008), a stateless and a utility based protocol, respectively. 相似文献
8.
The increased usage of directional methods of communications has prompted research into leveraging directionality in every
layer of the network stack. In this paper, we explore the use of directionality in layer 3 to facilitate routing in highly mobile environments. We introduce Mobile Orthogonal Rendezvous Routing Protocol (MORRP) for mobile ad-hoc networks (MANETs). MORRP is a lightweight,
but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space
embedding, node localization, and mobility. This relaxation is done by introducing a novel concept called the directional
routing table (DRT) which maps a set-of-IDs to each interface direction to provide probabilistic routing information based on interface direction. We show that MORRP achieves connectivity with high probability even in
highly mobile environments while maintaining only probabilistic information about destinations. Additionally, we compare MORRP
with various proactive, reactive, and position-based routing protocols using single omni-directional interfaces and multiple
directional interfaces and show that MORRP gains over 10–14 × additional goodput vs. traditional protocols and 15–20% additional
goodput vs. traditional protocols using multiple interfaces. MORRP scales well without imposing DHT-like graph structures
(eg: trees, rings, torus etc). We also show that high connectivity can be achieved without the need to frequently disseminate node position resulting increased scalability even in highly mobile environments. 相似文献
9.
Thapliyal Puneet Sidhartha Li Jiang Kalyanaraman Shivkumar 《Multimedia Tools and Applications》2002,17(2-3):257-294
Congestion control is an important building block of a Quality of Service (QoS) system for multicast-based multimedia services and applications on the World Wide Web. We propose an end-to-end single-rate source-based multicast congestion control scheme (LE-SBCC) for reliable or unreliable multicast transport protocols. It addresses all the pieces of the single-rate multicast congestion control problem including drop-to-zero issues, TCP friendliness and RTT estimation. The scheme design consists of a cascaded set of filters and a rate-based additive-increase multiplicative-decrease (AIMD) module. These filters together transform the multicast tree to appear like a unicast path for the purposes of congestion control. Unlike TCP, the scheme is not self-clocked but acts upon a stream of loss indications (LIs) from receivers. These LIs are filtered to get a stream of loss events (LEs) (S. Floyd et al., in SIGCOMM 2000, Aug. 2000) (at most one per RTT per receiver). This LE stream is further filtered to extract the maximum LEs from any one receiver. Then the scheme effects at most one rate-reduction per round trip time (RTT). A range of results (simulation and experimental) is presented and compared against the mathematical model of the scheme components. Furthermore, we have successfully adapted TFRC (Op. cit) to our scheme, which is important to multimedia services desiring relatively stable rates over short time scales. 相似文献
10.