排序方式: 共有70条查询结果,搜索用时 328 毫秒
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层次模型的关系表示法 总被引:1,自引:1,他引:0
层次模型是DBMS所支持的三大数据模型之一.论述了利用关系模型表达层次模型的方法,用关系代数表示层次模型的DL/1语言;描述了增加和删除的算法,比较其检索效率,给出了一个具体设计实例 相似文献
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一种新型手性配体交换色谱键合固定相 总被引:6,自引:0,他引:6
采用气相或液相色谱法拆分氨基酸对映体通常一化过程,费时而麻烦,而且有可能发生消旋,影响分析结果,手性配体交换色谱法是拆分氨基酸和羟基酸对映体的一种有效方法,其选择性高,不需柱前衍生。Davankov等对此方法进行了评述。此法大都采用刚性环状结构的光活性脯氨酸或羟基脯氨酸键合相作为柱填料,Jeanneret-Gris等曾采用1,2,3,4-四氢-3-异喹啉羧酸接枝的聚丙烯酰胺相拆分氨基酸对映体。 相似文献
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提出一种求解大型稀疏对称矩阵几个最大(最小)特征值和相应特征向量的迭代块DL(即Davidson-Lanczos)算法并且讨论了迭代块DL算法的收敛率 相似文献
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Carina de Souza Gondim Otávio Augusto Mazzoni CoelhoRonália Leite Alvarenga Roberto Gonçalves JunqueiraScheilla Vitorino Carvalho de Souza 《Analytica chimica acta》2014
The lack of well-established references for the validation of qualitative analyses and the increasing demand for reliable binary responses were the main motivating factors for this study. A detailed procedure for single-laboratory validation of qualitative methods is proposed. The experimental design and the tools for data analysis were based on the theoretical background, as well as the aspects of efficiency, convenience and simplicity. Four experimental steps were defined, as follows: (i) preliminary tests for the determination of the concentration range, (ii) a study of the rates, unreliability region, detection limit, and the accordance and concordance values, (iii) a study of the selectivity in the presence of known interferences, and (iv) a study of robustness. The applicability of the procedure was demonstrated by the validation of a qualitative commercial kit for detecting sulfonamide residues in raw milk using both the visual and instrumental reading techniques. Reliability rates of 100% were obtained for the blank samples. For the samples spiked with sulfamethazine at 10.8 and 108 μg L−1 and with sulfadimethoxine or sulfathiazole at 10 and 100 μg L−1, the reliability rates ranged from 93.3 to 100%. Selectivity was demonstrated using trimethoprim as a potential interferent. The method was considered robust for the factors of the temperature (54 and 58 °C) and time (6 and 10 min) for incubating the test strips. The estimated detection limits and unreliability regions confirmed the suitability of the kit for this purpose, based on the legislated residue limits. 相似文献
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针对小流域污染源分散,污染类别繁杂,传统净化工艺水质处理效果不明显等存在的问题,采用微生物复合菌剂分解污水中有机物的方法,以沈阳满堂河作示范流域,通过对DL微生物菌剂室内模拟研究并将研究结果应用于河水治理。研究结果表明,DL生物复合菌剂能有效净化污水。水温在15~20℃时,COD平均去除率64.2%。但菌剂的活化受温度影响很大,水温在13℃以下COD平均去除率仅为25%。水温环境偏低抑制菌种的繁殖和生命代谢过程即影响DL菌种对污水中有机物的去除效率。 相似文献
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Effect of gamma‐irradiation sterilization on the physical and mechanical properties of a hybrid wound dressing 下载免费PDF全文
A wound dressing should ideally provide an optimal healing environment which enables rapid healing. It should maintain a moist environment at the wound surface, allow gas exchange, act as a barrier to microorganisms, remove excess exudates and afford mechanical protection to the wound. A new bioresorbable hybrid wound dressing which combines a poly(DL‐lactic‐co‐glycolic acid) porous top layer with a spongy collagen sublayer was developed and studied. The top layer contained the antibiotic drug gentamicin for controlled release to the wound site. It is of very high importance to use an appropriate sterilization process for this special new wound dressing, which will not have a deleterious effect on its function. Our investigation therefore focused on the effects of gamma‐irradiation sterilization (10, 25, 35 and 50 kGy) on the structure properties of this wound dressing. The physical and mechanical properties were of the wound dressings were affected by the gamma irradiation because of a combination of chain scission and crosslinking of the collagen layer mainly. The weight loss and water vapor transmission rate were increased, while the water uptake was decreased with the increase in the irradiation dose. The changes were small when doses of 10 or 25 kGy were applied at room temperature. The gamma‐irradiation resulted in stronger but more brittle wound dressings. These trends were smaller when the sterilization process was carried out in liquid nitrogen. Our research shows that gamma‐sterilization process is feasible for our new concept of hybrid wound dressings and optimal conditions can be chosen. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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柳馨 《重庆工商大学学报(自然科学版)》2017,34(5):13-18
基于带有割线条件的DL方法,提出了两个满足改进的割线条件的修正共轭梯度方法——MDDL1方法与WMDDL1方法.在步长满足Wolfe线搜索的条件下,证明了MDDL1方法具有充分下降性;进一步地证明了WMDDL1方法不依赖任何线搜索具有充分下降性;最后分析和证明了两个方法在步长满足强Wolfe线搜索的条件下对一般函数均具有全局收敛性. 相似文献
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郭瑞伟 《甘肃教育学院学报(自然科学版)》2013,(5):122-125
以"学生为本"的教育理念已经成为高校育人工作的核心,探索依托学科教学有效途径是高校进一步落实科学发展观的必然趋势.基于我校物流管理专业人才培养模式改革的实践,对"工学交替,教学伴随"人才培养模式进行了探讨,阐述了"DL"工学结合模式的内涵、课程改革方案的内容和运作方式,并总结了通过改革实践后的效果. 相似文献
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