首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   35篇
  免费   1篇
化学工业   2篇
轻工业   7篇
水利工程   2篇
石油天然气   3篇
无线电   6篇
一般工业技术   7篇
自动化技术   9篇
  2022年   1篇
  2018年   5篇
  2017年   1篇
  2016年   5篇
  2014年   1篇
  2013年   7篇
  2012年   1篇
  2011年   2篇
  2010年   1篇
  2009年   2篇
  2007年   1篇
  2004年   2篇
  1997年   1篇
  1991年   2篇
  1988年   1篇
  1984年   3篇
排序方式: 共有36条查询结果,搜索用时 31 毫秒
1.
Ultraviolet A (UVA) radiation causes oxidative damage to human skin cells. This damage may be reduced or prevented using plant compounds as photoprotectants. To investigate the relationship between chemical structure and UVA‐protective activity, three structurally related flavonoids, namely luteolin, luteolin‐7‐O‐glucoside (both present in artichoke) and luteolin‐4'‐O‐glucoside (present in wild carrot), were studied. Human skin fibroblasts exposed to UVA (250 and 500 kJ/m2) were treated with each flavonoid (30 µM) for 18 h prior to irradiation. The extent of lipid peroxidation in the cellular extracts was assessed as lipid peroxides and malondialdehyde (MDA). Luteolin and luteolin‐7‐O‐glucoside both prevented a significant increase in lipid peroxides at 250 kJ/m2, but at 500 kJ/m2 their effectiveness was clearly attenuated. Contrastingly, luteolin‐4'‐O‐glucoside was pro‐oxidant at both radiation doses. Measurements of MDA levels highlighted that luteolin was clearly more effective than the two glucosides at both 250 and 500 kJ/m2. Overall, these results show clear differences between the three flavonoids and suggest that the B ring 3',4'‐dihydroxy group, lacking in luteolin‐4'‐O‐glucoside, may be particularly important. Flavonoid: transition metal ion chelation studies confirmed the influence of the 3',4'‐dihydroxy group, which is also relevant to the quenching of singlet oxygen. These features as well as the greater lipophilic nature of luteolin together explain the superior activity of this flavonoid which may be potentially useful as a supplement in photoprotective skin preparations.  相似文献   
2.
In this article, a hybrid technique for user activities outliers detection is introduced. The hybrid technique consists of a two‐stage integration of principal component analysis and fuzzy rule‐based systems. In the first stage, the Hamming distance is used to measure the differences between different activities. Principal component analysis is then applied to the distance measures to find two indices of Hotelling's T2 and squared prediction error. In the second stage of the process, the calculated indices are provided as inputs to the fuzzy rule‐based systems to model them heuristically. The model is used to identify the outliers and classify them. The proposed system is tested in real home environments, equipped with appropriate sensory devices, to identify outliers in the activities of daily living of the user. Three case studies are reported to demonstrate the effectiveness of the proposed system. The proposed system successfully identifies the outliers in activities distinguishing between the normal and abnormal behavioral patterns.  相似文献   
3.
Multimedia Tools and Applications - With the broad development and evolution of digital data exchange, security has become an important issue in data storage and transmission since digital data can...  相似文献   
4.
One of the devices that may help in content development for eLearning services is an Electronic Copyboard (e-board). Once it is available in every classroom, it helps in extracting the lecturer notes in an electronic as-in-class format. This paper introduces an alternative solution to e-boards. The presented solution is much cheaper and much simpler to install if compared to that of the e-boards. It could be implemented using a web camera and a video processing algorithm to extract notes that were added or removed by the lecturer. The notes extracted along with the slides presented and the recorded lecturer voice may compose a complete as-in-class electronic form of the lecture (eLecture). This paper presents first the proposed Notes Extraction Algorithm and runs few experiments when the notes are added on a traditional white board under various scenarios. The algorithm takes into consideration the brightness variations of the video in detecting the notes especially since this is normal to occur due to for instant to the lecturer movements in front of the white board. Second, the paper presents an authoring tool that includes the proposed algorithm to extract notes and combines them along with video and slides, if exist, before generating eLectures that could be viewed using popular players.  相似文献   
5.
Radio-over- fibre (RoF) technology is receiving large attention due to its ability to provide simple antenna front ends, increased capacity and increased wireless access coverage. Coherently detected RoF systems would enable the information to be carried in both the amplitude and phase or in different states of the polarisation of the optical field. Additionally, the selectivity of coherent receiver is very well suited for access networks. We present a 90° optical hybrid built on a silicon-on-insulator planar light-wave circuit, which can be used as the optical front end of the digital coherent receiver in a digitised RoF link and will lead to reduced receiver footprint and cost. The optical hybrid circuit includes 2?×?2 and 4?×?4 multimode interference (MMI) splitters, in a polarisation diversity configuration. The simulation results at vacuum wavelength 1,550 nm show polarisation independence and phase errors between the ports of less than 0.03°. The properties of the prototyped 4?×?4 MMI were measured over a wide range of wavelengths. The 2?×?2 and 4?×?4 MMI showed nearly equal splitting ratios. Measurements of the relative phase relationship between the ports for Transverse Electric mode polarisation are shown to match the simulation results.  相似文献   
6.
A study has been carried out to investigate the dissolution rate profiles of twelve batches of sugar-coated phenylbutazone tablets belonging to four commercial brands. Using the rotating basket method, significant inter-brand and inter-batch variations in dissolution rates were found. Only two batches of one brand passed the B.P. dissolution limit whilst other batches had percentages dissolution between 0.3 and 58 after 45 min. Batches with poor dissolution characteristics exhibited significant tablet-to-tablet variations in dissolution rates; a finding which was not observed in the relatively fast-dissolving batches. When the paddle method was substituted for the B.P. basket method, the dissolution rates were relatively faster but similar dissolution failure was found. However, the tablet-to-tablet dissolution variability was decreased in some of the batches. The observed differences in dissolution rates of the batches examined were unrelated to their disintegration times. Inspite of the poor dissolution characteristics of most of the batches studied, no apparent chemical degradation was found. It is recommended that when evaluating the dissolution rates of brands of phenylbutazone tablets, a number of batches from each brand should be tested.  相似文献   
7.
Creating desirable layouts of building interiors is a complex task as designers have to manually adhere to various local and global considerations arising from competing practical and design considerations. In this work, we present an interactive design tool to create desirable floorplans by computationally conforming to such design constraints. Specifically, we support three types of constraints: (i) functional constraints such as number of rooms, connectivity among the rooms, target room areas, etc., (ii) design considerations such as user modifications and preferences, and (iii) fabrication constraints such as cost and convenience of manufacturing. Based on user specifications, our system automatically generates multiple floor layouts with associated 3D geometry that all satisfy the design specifications and constraints, thus exposing only the desirable family of interior layouts to the user. In this work, we focus on pre-cast concrete-based constructions, which lead to interesting discrete and continuous optimization possibilities. We test our framework on a range of complex real-world specifications and demonstrate the control and expressiveness of the exposed design space relieving the users of the task of manually adhering to non-local functional and fabrication constraints.  相似文献   
8.
A three‐dimensional flow and transport model was used to simulate the flow of water and assumed conservative substance in a large number of hypothetical, sea‐connected lagoons and harbours experiencing tidal effects. The dimensions of the lagoons and harbours were selected to cover a wide range of widths, lengths, depths and entrance channel widths. The tidal flow in and out of each lagoon and harbour was simulated for durnal and semidurnal conditions for different tidal ranges. The water exchange for each lagoon and harbour was assessed on the basis of the exchange coefficient. The results of model runs and non‐linear multiple regression techniques were used to develop equations for calculating the average exchange, in terms of lagoon dimensions, depth and tidal range for durnal and semidurnal conditions. These equations can be used for a quick assessment of water exchange conditions in lagoons and harbours, upon which their water quality depends. In designing an artificial, sea‐connected lagoon and harbour, the developed equations can be used in the preliminary stages for testing options regarding the number and widths of entrances and the physical layout of the lagoon and harbour. This approach also allows for identification of unsuitable options, with the acceptable options being subjected to detailed mathematical modelling to assess their expected water exchange and water quality. The same approach can be applied to existing lagoons (natural or artificial) and harbours in designing layout modifications for improving water exchange and water quality conditions, as well as lakes directly connected to coastal waters and subject to tidal effects. The use of the equations presented in this report also can provide knowledge regarding the preferred water flushing conditions and/or improvements needed to enhance the water exchange in order to preserve the ecosystems in such water systems.  相似文献   
9.
In order to increase the safety of intelligent road vehicles of the future and to automate their driving, priority is being given to help systems for drivers. One critical need is the determination of real-time information about the instantaneous motion of the vehicles. Small-sized, low-cost, low-time constant, low-power consumption, contactless microwave sensors are well suited to these applications and give reliable measures in the real-time domain. A K-band Doppler sensor has been developed both in hybrid and monolithic technology. For both the X-band and K-band sensors, printed microstrip flat patch antennas were used. Some experimental results obtained both in the laboratory and on vehicles with some different experimental integrated Doppler radar are provided. The performance are compared at 10 and 24 GHz  相似文献   
10.
A total of 110 prawn individuals were collected from different markets at Cairo and Giza Governorates. The average counts of Aerobes, Psychrophiles, Enterobacteriaceae, Coliforms and Staphylococci were 5 × 103, 3 × 102, < 2 × 102, < 3 and 2 × 102 organisms per gram newly caught prawn sample, respectively. Such counts were significantly increased in samples collected from markets including raw prawn in shell, raw peeled samples and frozen samples either peeled or in shell. Arizona group, Escherichia coli, Enterobacter group, Proteus group, Providencia group A & B, Shigella group and Staphylococcus aureus could be isolated from examined samples with variable percentages. The public health significance of isolated organisms is discussed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号