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41.
Massimo Tornatore Diego Lucerna Biswanath Mukherjee Achille Pattavina 《Journal of Network and Systems Management》2012,20(1):34-55
Survivability is a key concern in modern network design. This paper investigates the problem of survivable dynamic connection
provisioning in general telecom backbone networks, that are mesh structured. We assume differentiated services where connections
may have different availability requirements, so they may be provisioned differently with protection (if needed) based on
their availability requirements and current network state. The problem of effectively provisioning differentiated-service
requests, that has been widely investigated for connections routed at the physical layer, assumes peculiar features if we
consider sub-wavelength requests at the logical layer that have to be protected (or more generically, whose availability target has to be guaranteed), but also have to be groomed
for an efficient use of network resources. An integrated multilayer approach is necessary that considers requirements and
grooming of connections at the logical layer as well as their routing and availability at the physical layer. Joint availability-guaranteed
routing and traffic grooming may lead to a negative interaction, since the objective of the first problem (guaranteeing a
given level of availability to the connections) clashes with the objective of the other problem (minimizing resource consumption).
For a multilayer WDM mesh network, we propose new multilayer routing strategies that perform effective availability-guaranteed
grooming of sub-wavelength connections. These strategies jointly considers connection availability satisfaction and resource
optimization and are developed under two different practical hypotheses: guaranteed target, i.e., a connection is routed only if its availability target is satisfied, and best-effort target, a connection is always routed and, when the availability target cannot be guaranteed, the path with the best possible
availability is provisioned. Numerical results are reported and discussed for the two approaches mentioned above. In both
cases, the results show high effectiveness of our provisioning strategy. 相似文献
42.
Wireless networking technology is evolving as an inexpensive alternative for building federated and community networks (relative to the traditional wired networking approach). Besides its cost-effectiveness, a wireless network brings operational efficiencies, namely mobility and untethered convenience to the end user. A wireless network can operate in both the “Ad-Hoc” mode, where users are self-managed, and the “Infrastructure” mode, where an authority manages the network with some Infrastructure such as fixed wireless routers, base stations, access points, etc. An Ad-Hoc network generally supports multi-hopping, where a data packet may travel over multiple hops to reach its destination. Among the Infrastructure-based networks, a Wireless Mesh Network (with a set of wireless routers located at strategic points to provide overall network connectivity) also provides the flexibility of multi-hopping. Therefore, how to route packets efficiently in wireless networks is a very important problem.A variety of wireless routing solutions have been proposed in the literature. This paper presents a survey of the routing algorithms proposed for wireless networks. Unlike routing in a wired network, wireless routing introduces new paradigms and challenges such as interference from other transmissions, varying channel characteristics, etc. In a wireless network, routing algorithms are classified into various categories such as Geographical, Geo-casting, Hierarchical, Multi-path, Power-aware, and Hybrid routing algorithms. Due to the large number of surveys that study different routing-algorithm categories, we select a limited but representative number of these surveys to be reviewed in our work. This survey offers a comprehensive review of these categories of routing algorithms.In the early stages of development of wireless networks, basic routing algorithms, such as Dynamic Source Routing (DSR) and Ad-Hoc On-demand Distance Vector (AODV) routing, were designed to control traffic on the network. However, it was found that applying these basic routing algorithms directly on wireless networks could lead to some issues such as large area of flooding, Greedy Forwarding empty set of neighbors, flat addressing, widely-distributed information, large power consumption, interference, and load-balancing problems. Therefore, a number of routing algorithms have been proposed as extensions to these basic routing algorithms to enhance their performance in wireless networks. Hence, we study the features of routing algorithms, which are compatible with the wireless environment and which can overcome these problems. 相似文献
43.
44.
The formation of two structurally different cokes during thermal hydrocracking of Athabasca bitumen is attributed to differences in coking properties of the asphaltenes and the deasphalted heavy oils. The grain-mosaic coke structure formed from the asphaltenes may be ascribed to the presence of crosslinkage groups derived from the phenolic character of this fraction of the bitumen. Carbonization of the deasphalted heavy oils of the bitumen results in a flow-type coke structure. These two cokes appear to form independently of each other and can therefore be readily identified in samples collected from the reactor. 相似文献
45.
To fully utilize the capabilities of a SONET/ADM network, traffic grooming is needed to multiplex a number of lower-rate traffic streams into a higher-rate stream, and vice versa. Although the capacity of a SONET ring network can be upgraded by operating it over multiple wavelengths, the corresponding network design may be costly if it employs a large number of ADMs. A cost-effective design attempts to minimize the total number of ADMs used in the network while carrying the offered traffic. We introduce and evaluate the performance characteristics of two new traffic-grooming approaches for WDM ring networks, called single-hop and multihop. Our single-hop implementation uses the simulated-annealing heuristic. After placing all the traffic on virtual circles, we group the circles in order to reduce the number of ADMs in the network. Our multihop implementation places an ADM at each node based on the requested traffic in the traffic-demand matrix; then, it tries to groom the wavelengths which can be groomed. We select one of the nodes to be the hub node which has an ADM for each wavelength. The hub node, therefore, can bridge traffic between all of the wavelengths. Each algorithm is specified and illustrated by a simple example. Our results demonstrate that it is beneficial to use a single-hop approach based on simulated annealing for a small grooming ratio, but for a large grooming ratio and node number, we advocate the use of the multihop approach. 相似文献
46.
Ethernet PON (ePON): Design and Analysis of an Optical Access Network 总被引:29,自引:0,他引:29
With the expansion of services offered over the Internet, the last mile bottleneck problems continue to exacerbate. A passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we propose the design and analysis of a PON architecture which has an excellent performance-to-cost ratio. This architecture uses the time-division multiplexing (TDM) approach to deliver data encapsulated in Ethernet packets from a collection of optical network units (ONUs) to a central optical line terminal (OLT) over the PON access network. The OLT, in turn, is connected to the rest of the Internet. A simulation model is used to analyze the systems performance such as bounds on packets delay and queue occupancy. Then, we discuss the possibility of improving the bandwidth utilization by means of timeslot size adjustment, and by packet scheduling. 相似文献
47.
Xiaoling Qiu Haiping Liu Dipak Ghosal Biswanath Mukherjee John Benko Wei Li Rashmi Bajaj 《Wireless Personal Communications》2011,56(3):535-557
Multihop wireless mesh networks (WMNs) provide ubiquitous wireless access in a large area with less dependence on wired networks.
However, some emerging applications with high bandwidth requirement and delay and loss constraints, such as video streaming,
suffer poor performance in WMNs, since high compression rates and/or high packet loss rates deteriorate the video quality.
In this paper, we propose a novel mechanism composed of (1) a network route selection scheme which provides paths for multiple
video streams with the least interference, called Minimum Interference Route Selection (MIROSE) and (2) an optimization algorithm
that determines the compression rates depending on the network condition, called Network State Dependent Video Compression
Rate (NSDVCR) algorithm. Simulation results of the proposed mechanisms show the significant improvement of the video quality
measured with a popular metric, Peak-Signal-to-Noise Ratio (PSNR), compared with standard routing and default compression
rates. 相似文献
48.
Ammonium-12-molybdophosphate, a heterogeneous catalyst, has been utilized for the first time for rapid (within 15–20 min) regioselective ring-opening of aziridines with KSCN at room temperature to form the corresponding β-aminothiocyanates in high yields. 相似文献
49.
Kapil M S Bajaj Biswanath Sarkar S T Lakshmikumar Ravi Mehrotra 《Bulletin of Materials Science》1991,14(3):763-766
V-I characteristics of sintered superconducting pellets of YBa2Cu3O7−δ
was measured with a resolution one order of magnitude better than the usual dc techniques employing nanovoltmeters. For this
purpose software-based lock-in-amplifier technique was developed and used. A square-wave excitation current was used. The
voltage signal was digitized into a time series and Fourier-analysed on a computer in this technique. Our results show a very
small frequency-dependent resistance in some samples which are nominally superconducting. These results help in checking the
material quality and defining the critical current densities better. 相似文献
50.
Biswanath Sa 《Drug development and industrial pharmacy》1991,17(6):893-900
Polyvinylacetate microspheres containing theophylline were prepared by emulsification and solvent removal method. The release pattern of theophylline from the microspheres was found to be best explained by diffusion controlled process. The rates of release were found to be influenced by drug-polymer ratios, size of microspheres, concentration of surfactant used for the preparation of microspheres, and pH of the dissolution media. 相似文献