992 resultados para 209-1270


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云市野生鲤鱼种娄为全国之冠。过去在渔业生产中,它们的产量曾占一定比重j现在种 群数量普遍减少,亟待保护 文中讨论了种质资源保存的意义和应采取的描箍。

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Three causes involved in the instability of the ISFET are proposed in this study. First, it is ascertained that hydroxyl group resident at the surface of the Si3N4 film or in the electrolyte solution is most active and subject to gain or loss of electrons. This is one of the main causes for ISFET structural instability. Secondly, the stability of the pH-sensitive FET varies with deposition conditions in the fabrication process of the ISFET. This proves to be another cause of ISFET instability. Thirdly, the pH of the measured solution varies with the measuring process and time, contributing to the instability, but is not a cause of the instability of the pH-ISFET itself. We utilized the technique of readjusting and controlling the ratio of hydroxyl groups to amine groups to enhance the stability of the ISFET. Our techniques to improve stability characteristics proved to be effective in practice.

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The damage removal and strain relaxation in the As+-implanted Si0.57Ge0.43 epilayers were studied by double-crystal x-ray diffractometry and transmission electron microscopy. The results presented in this paper indicate that rapid thermal annealing at temperatures higher than 950 degrees C results in complete removal of irradiation damage accompained by the formation of GeAs precipitates which enhance the removal process of dislocations.

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Three different types of GaAs metal-semiconductor field effect transistors (MESFET) by employing ion implantation, molecular beam epitaxy (MBE) and low-temperature MBE (LT MBE) techniques respectively were fabricated and studied in detail. The backgating (sidegating) measurement in the dark and in the light were carried out. For the LT MBE-GaAs buffered MESFETs, the output resistance R(d) and the peak transconductance g(m) were measured to be above 50 k Omega and 140 mS/mm, respectively, and the backgating and light sensitivity were eliminated. A theoretical model describing the light sensitivity in these kinds of devices is given. and good agreement with experimental data is reached.

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采用射频磁控反应溅射法制备了氮化硅薄膜。利用X射线衍射谱(XRD)、红外光谱(IR)、能谱(EDS)和光致发光谱(PL),通过与氮气中和空气中退火薄膜比较,对原沉积薄膜进行了成分与结构和发光特性研究。研究发现原沉积薄膜是部分晶化的富硅氮化硅薄膜,薄膜中晶态氮化硅颗粒的平均粒径为33nm;在氮气中退火后,纳米颗粒增大;在空气中退火后,薄膜被氧化,晶态颗粒消失。在4.67eV的光激发下,原沉积薄膜中观测到7个强的PL峰,其峰位分别为3.39,3.24,3.05,2.82,2.61,2.37和2.11eV。在氮气和空气中退火后,PL峰位和强度有变化。对其光致发光机制进行了探讨,认为硅悬挂键≡Si,氮悬挂键=N,硅错键≡Si-Si≡以及与氧有关的缺陷在富硅氮化硅薄膜高强度荧光发射中起主导作用。

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基于耦合模理论,通过对耦合波方程进行相位共轭变换,将反向耦合波方程变换为Riccati微分方程,利用数值解法对耦合系数和高斯型耦合系统线性啁啾光栅的反射特性、色散特性和时延特性进行了详细分析,为设计具有理想效果的色散补偿器件提供了有效的理论方法。

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于2010-11-23批量导入

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辽宁省是以石油化工、煤炭化工和钢铁工业为主的重工业基地。辽河流域近年来经济发展迅速,城市化水平不断提高,但由于产业结构的不合理和污染治理水平的相对滞后,致使辽河流域水体污染严重。对辽河流域水体污染状况、污染物化学与生物学的相互作用、微生物群落结构与功能的关系开展调查研究,对开展污染水体的生物生态修复具有重要的指导意义。 本论文选取辽河流域干流8个水文监测站点的不同时期(丰水期和平水期)底质为研究对象,调查了有机污染物(总油TPHs)和有毒污染物(多环芳烃PAHs)污染程度以及主要来源;采用变性梯度凝胶电泳(DGGE)和磷脂脂肪酸(PLFA)两种分析方法,对其微生物群落结构及多样性进行了分析;并以13C标记的菲和芘为代谢底物,以PLFA为生物标记物,采用气相色谱-稳定同位素比率质谱(GC-c-IRMS)分析技术,鉴定了底质样品中参与菲和芘代谢的主要微生物类群;并利用不同的吸附性载体进行了芘降解菌的富集和筛选。 研究结果表明: 1)平水期总石油烃污染比丰水期严重,TPH 含量分别在276.1~560.6mg/kg(平水期)和157.9~462.2mg/kg(丰水期)之间,辽河入海口TPH污染最重;PAHs含量分别在124.1~270.4ug/kg(平水期)和93.5~209.1ug/kg(丰水期)之间;主要来源于石油类污染物和化石燃料的热解,汽车尾气的污染等。 2) 采用DGGE和PLFA两种方法分析微生物群落结构得到基本一致的结果。微生物多样性与总石油烃含量、总多环芳烃含量无显著相关性,多样性指数是多种污染物和环境因子综合影响的结果。 3) 稳定同位素代谢示踪实验表明,底质中存在菲和芘的降解菌群;参与菲和芘降解的微生物均以G-细菌为主,真菌次之;G+细菌和放线菌也参与代谢;参与菲和芘代谢的菌群有一定的相似性。 4) 利用不同吸附性载体从污染底质样品中筛选到6株降解菌。