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实验利用传统的电子陶瓷制备工艺,制备了纯CaCu3Ti4O12（CCTO）陶瓷,并且研究了结构及介电性。实验结果表明：CCTO陶瓷样品生成具有单一相的钙钛矿结构。纯CCTO陶瓷具有稳定的介电性能、相对高的介电常数和相对低的介电损耗。在室温条件下,介电常数基本上能够达到104,并观察到CCTO陶瓷具有介电现象。 相似文献
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采用化学共沉淀法和溶胶凝胶法制备BaTiO3-CoFe2O4两相复合陶瓷粉体,并通过成型1200℃烧结制备BaTiO3-CoFe2O4两相复合陶瓷,测试XRD和TEM,并对其介电,漏电,铁电进行了研究。XRD分析制备的BTO陶瓷为四方结构,铁电性较好,具有较大的介电常数和较低的介电损耗,CFO陶瓷为尖晶石结构,复合陶瓷具有两相结构,同时具有铁电性和磁性。 相似文献
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新型功能陶瓷是以电、磁、光、声、热、力学、化学和生物等信息的检测、转换、耦合、传输、处理和存储等功能为其特征的新型材料,在国民经济和国防建设中具有重要而广泛的应用。随着现代高新技术的发展,功能陶瓷及其应用正向精细化、多功能、智能化、集成化、高性能、高可靠和复合结构发展。因此,通过解决功能陶瓷材料在制备中的各种基础性科学 相似文献
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本文研究了熔盐法合成的PMN-PT粉末的烧结特性,以及合成工艺对PMN-PT陶瓷致密度,显微结构和介电性能的影响.结果显示,熔盐合成的粉料具有较小的颗粒尺寸和良好的分散性,能够降低陶瓷的烧结温度,在1150～1180℃范围烧结可得到致密度≥96%的PMN-PT陶瓷.在1100～1200℃烧结温度范围,硫酸盐熔盐体系制备的陶瓷呈沿晶断裂,而氯化物熔盐体系制备的陶瓷均呈穿晶断裂.在相同的烧结温度下,氯化物熔盐制备的陶瓷的晶粒尺寸明显大干硫酸盐熔盐体系的陶瓷的晶粒尺寸.用熔盐法制备的组分为0.67PMN-0.33PT陶瓷具有优良的压电和介电性能.在1175℃/2h烧结条件下,制备的0.67PMN-0.33PT陶瓷的最大介电常数为29385,d33 ≈ 660pC/N. 相似文献
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在众多的陶瓷材料中氧化锆材料是一颗引人注目的新星,它以一些与众不同的性能引起了世人的极大兴趣,例如氧化锆陶瓷是目前陶瓷材料中韧性最高的陶瓷,有人称之为“摔不碎的陶瓷”;氧化锆陶瓷是优良的高温固体电解质,在高温下氧离子可以顺利通过,有人称之为“对氧开绿灯的陶瓷”。氧化锆陶瓷用途很广, 相似文献
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研究了中温烧结的BaO—TiO2～Nd2O3系陶瓷的介电性能。实验结果表明,在这一系统中分别或联合掺入适量的PbO、Bi2O3、CuO、V2O5、2Bi203·3TiO2和Bi2O3·2TiO2可以降低系统的烧结温度,拓宽烧成温度范围,并有助于改善介电性能,增大介电常数,从而得到了介电性能优良的高频陶瓷材料。 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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《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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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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《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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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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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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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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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