全文获取类型
收费全文 | 141篇 |
免费 | 0篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 35篇 |
金属工艺 | 7篇 |
机械仪表 | 16篇 |
建筑科学 | 10篇 |
能源动力 | 2篇 |
轻工业 | 2篇 |
无线电 | 36篇 |
一般工业技术 | 25篇 |
冶金工业 | 1篇 |
自动化技术 | 6篇 |
出版年
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 22篇 |
2012年 | 11篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 7篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有141条查询结果,搜索用时 15 毫秒
51.
52.
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
53.
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
54.
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
55.
56.
Shirish D. Dhobe B. Doloi B. Bhattacharyya 《The International Journal of Advanced Manufacturing Technology》2011,55(1-4):177-188
Electrochemical machining (ECM) process has great potential on account of the versatility of its applications. ECM is being widely used in the manufacturing industry because hard metals can be machined regardless of the mechanical property of a work piece. Titanium is broadly used in a number of fields such as aerospace, power generation, automotive, chemical including petrochemical, and sporting goods. Apart from these applications, it has tremendous prospective in dental, medical industries, and biomedical engineering. The biological performance of titanium implant depends on their surface topography and form accuracy that includes various surface parameters. ECM is one of the alternative machining processes that can be applied to the machining of titanium implant for biomedical applications. The aim of this paper is to present experimental result of surface characteristics obtained on titanium samples, utilizing developed cross-flow electrolyte supply system in electrochemical machining. It is observed that electrolyte flow velocity and voltage between electrodes are some of the influencing parameters, which affect the surface characteristics. Titanium oxide layer has been generated on the machined surface, which facilitates the improvement of the corrosion and chemical resistance of titanium implant. Effects of electrolyte flow velocity and voltage during electrochemical machining process for generation of various surface characteristics have been successfully studied through experimentation. In the present work, the obtained surface roughness values on the titanium sample machined by ECM were in the range of 2.4 to 2.93???m, which is within acceptable value for the implants. Effects of electrolyte flow velocity and voltage on the material removal rate and machining accuracy in the form of overcut are also presented in the paper. 相似文献
57.
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
58.
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
59.
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
60.
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