共查询到20条相似文献，搜索用时 609 毫秒
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在测量微弱信号被掩盖在强噪声中的信号时,锁相放大器(Lock-in Amplifier,LIA)表现出了良好的性能.但是由于其本生存在中心频率不稳定、带宽不能太窄及对信号缺乏跟踪能力等缺点,造成对测量微弱信号的限制.对锁相放大器进行一些分析的基础上,设计出一个双相位锁相放大器(Dual Phrase Lock-in Amplifier),并用Pspice/OrCAD进行了实验性的论证.结果表明该放大器可以实现微伏(μV)级别的信号识别,噪声信号的均方根值约为1mV,幅值识别准确率在0.5％以内. 相似文献
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嗜酸乳杆菌高密度发酵条件的研究 总被引：2，自引：0，他引：2
主要研究了嗜酸乳杆菌生长繁殖的环境条件(温度、接种量、起始pH等)和培养基组成对其影响.优化后确定了嗜酸乳杆菌的高密度培养条件为:起始pH值为5.8,培养温度为37℃,培养条件为亨-盖特厌氧培养,接种量为4%,培养时间为22 h.并且筛选了碳源,氮源及氮源的浓度.基配比为:2%乳清粉(w/v),1.5%牛肉膏(w/v),1.5%蛋白胨(w/v),0.058%硫酸镁(w/v),0.025%硫酸锰(w/v),0.22%乙酸钠(w/v),0.2%磷酸氢二钾(w/v).将该菌在此增菌培养基上培养,在37℃下培养22 h,菌数可达到1.17×1011cfu/mL. 相似文献
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随着科学的日益进步,电子产品被广泛应用到社会各个领域,线性集成运算放大器(以下简称集成运放)的应用也就越来越广泛,如何方便的分析所用的集成运算放大器线路,也就成为每一个集成运放线路应用工作者所关心的问题。本方法是利用集成运算放大器的理想特性及一般电工定律,方便而迅速地分析集成运放的各种应用线路。 相似文献
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配网生产工作作为电网企业主要生产工作之一,其信息化管理系统必须在构建一体化的思想指导下,面向"标准、开放、集成",在电力企业整体信息化的大框架下进行规划、设计和开发。配网生产管理信息系统应与相关业务管理系统实现流程集成和信息共享。需要对应用集成相关的内容进行充分考虑,兼顾开放性、可扩展性和效率,遵循通用的数据模型标准(如基于IEC61970/61968CIM模型),以便为相关业务系统提供通用的服务。 相似文献
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针对目前我国中小型模具企业在CAD/CAPP/CAM系统集成中存在的主要问题,本文提出了一种种一体化解决方案.对模具CAD/CAPP/CAM集成系统进行了结构设计,并叙述了该系统工作的实现过程. 相似文献
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随着数字信号处理器（DSP）技术的迅速发展,相应其硬件结构和指令系统也更加复杂.为提高数字信号处理器系统的开发速度,需采用更加简便的系统开发模式和方法.Matlab/Simulink作为功能强大的数值计算和分析工具,已将DSP系统所有开发工具集成在其中.通过TI公司与MathWorks公司推出的Matlab-DSP系统集成开发环境,可在Matlab/Simulink环境下完成从系统设计、模拟/仿真,到目标代码生成、运行与调试的整个过程.本文通过AD转换并输出PWM信号,通过输入电压的变化调整PWM输出信号占空比,分析了利用Matlab/Simulink生产DSP TMS320F2812的代码开发设计方法. 相似文献
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系统由程控放大器、程控滤波器、A/D转换器和D/A转换器、单片机控制及显示电路组成,以AT89C51和FPGA器件为控制中心,实现滤波器工作模式选择,增益控制、调节截止频率等功能,并通过LCD显示滤波器的截止频率和放大器的放大倍数。整个系统具有良好的人机交互界面,精度高,实用性很强。 相似文献
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《科技风》2017,(18)
恒温槽可以为计量器具的检定或校准提供温度基准环境,但传统恒温槽的不便携带和低集成化已不能满足一些计量器具的现场自动检定或校准。针对这一问题,设计了一种集成了多功能电测仪器和温度控制模块、可实现现场自动检定或校准的高精度便携式恒温槽。首次在便携恒温槽中采用侧面搅拌技术设计,保证了温场的高质量,并使恒温工作区域的有效工作深度提高至200 mm,克服了被检计量器具因插入深度不足对计量结果造成的影响。采用局部控温散热设计,减少了高温环境时对仪器仪表的影响,提高了检定或校准的精度。实验结果表明,恒温槽工作温场范围为50℃~300℃,水平最大温差优于0.005℃,均匀性优于0.01℃,波动性优于0.03℃/10 min.。利用该集成化恒温槽实现了一体化温度变送器的现场自动校准,其扩展不确定度优于0.08℃(k=2)。此外,该集成化恒温槽在中温热电偶和热电阻的现场自动校准和检定中也极具应用前景。 相似文献
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A research group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol-a chemical found in the skins of red grapes in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said. 相似文献
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Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors. 相似文献
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Active biological molecules functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery disease diagnosis therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction. 相似文献
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A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007. 相似文献
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《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
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Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction. 相似文献
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《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
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Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies. 相似文献
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Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 相似文献
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Puay Tang 《The Information Society》1998,14(1):19-31
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means. 相似文献