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761.
762.
曲齿锥齿轮的测绘,关键在于精确测定端面模数.背锥坐标法是一种比较精确的测绘方法。本文给背锥公式作了理论证明,并通过实例证实了背锥公式确实大大提高了测绘端面模效的精确性,解决了曲齿锥齿轮难测绘的问题 相似文献
763.
提高水玻璃型壳强度,减薄型壳厚度,对节能降耗有相当大的意义.针对影响硅酸铝质粉料型壳强度的3个主要因素,进行了实验室和生产验证试验,结果表明,粒度分散分布的阳泉三级矾土粉料,在900℃下可获得很高的高温强度.与生产现场用的二级矾土粉料相比,减薄型壳21%以上,节约焙烧时间25% 相似文献
764.
梁海顺 《西安工程科技学院学报》1996,(1)
就绳状绞边装置的设计问题,根据模糊数学的基本理论提出了一种模糊优化设计方法,建立了该问题的模糊优化设计的数学模型,并对实例进行了计算与分析. 相似文献
765.
提出了一种实现协同装配过程VR的方法,以尽可能高的沉浸度复制装配过程为目标,通过对装配过程的分析,设计了一个特定的VR系统架构。该系统的核心特点是装配过程的物理仿真、机器人控制的集成和操作者的触觉反馈。VR技术的应用使工业装配过程更加安全,并减少了人与机器人之间的障碍。 相似文献
766.
Isolation,purification and characterization of a new organphosphorus hydrolase OPHC2 总被引:1,自引:0,他引:1
WUNingfeng DENGMinjie SHIXiuyun LIANGGuoyi YAOBin FANYunliu 《科学通报(英文版)》2004,49(3):268-272
A bacterium with the capability of degrading organphosphorus, identified as Pseudomonas pseudoaicaligenes, is isolated from OP-treated soil. The organphosphorus hydrolase OPHC2 from this bacterium has been purified and characterized. OPHC2 has optimum activity for the reaction at 65℃ and pH 9.0 with methyl parathion as a substrate, it also shows good thermal and pH stability. Most metal ions and chemicals have no effect on the activity of OPHC2. The analyses of nucleotide sequence encoding OPHC2 and amino acid sequence of OPHC2 show that there are lower homologies with those of organphosphorus hydrolase reported in GenBank. 相似文献
767.
Expression of lysine-rich protein gene and analysis of lysine content in transgenic wheat 总被引:2,自引:0,他引:2
MENGChaomin CHENXuqing LIANGRongqi YANGFengping ZHANGLiquan ZHANGXiaodong CHENTianyou S.S.M.Sun 《科学通报(英文版)》2004,49(19):2053-2057
Expression vector pBPC102, which carries winged bean lysine-rich protein (wblrp) gene and dihydropicolinate synthase (DHDPS) gene, was transferred into hexaploid winter wheat cv. Jinghua No.l, Jing411, You899 and Yangnongl5 explants of immature inflorescence and immature embryos by particle bombardment. More than 100 transgenic plants were obtained under the selection of s-(2-aminoethyl)-L-cysteine (AEC). Confirmed transgenic plants of To and TI generation by PCR and PCR-Southern blotting analyses showed successful integration of wblrp gene into wheat genome. Analysis of transgenic plant lines of T2 by Northern dot-blotting showed good expression of wblrp gene in offspring seed. The content of free lysine in leaves, contents of bound lysine and total proteins in seeds of T2 transgenie wheat lines were determined and analyzed. Among 34 tested transgenic lines, levels of free lysine content in leaves of 9 transgenic lines are 2~3times higher than un-trans-formed wild-type cultivars. Among 17 analyzed transgenic lines, bound lysine content of 4 transgenic lines is more than 10% higher than that of wild-type cultivars. Our research suggests that introducing wblrp gene into wheat is an effective way to improve its nutrition quality. 相似文献
768.
769.
770.
VEGF regulates haematopoietic stem cell survival by an internal autocrine loop mechanism 总被引:49,自引:0,他引:49
Gerber HP Malik AK Solar GP Sherman D Liang XH Meng G Hong K Marsters JC Ferrara N 《Nature》2002,417(6892):954-958
Vascular endothelial growth factor (VEGF) is a principal regulator of blood vessel formation and haematopoiesis, but the mechanisms by which VEGF differentially regulates these processes have been elusive. Here we describe a regulatory loop by which VEGF controls survival of haematopoietic stem cells (HSCs). We observed a reduction in survival, colony formation and in vivo repopulation rates of HSCs after ablation of the VEGF gene in mice. Intracellularly acting small-molecule inhibitors of VEGF receptor (VEGFR) tyrosine kinase dramatically reduced colony formation of HSCs, thus mimicking deletion of the VEGF gene. However, blocking VEGF by administering a soluble VEGFR-1, which acts extracellularly, induced only minor effects. These findings support the involvement in HSC survival of a VEGF-dependent internal autocrine loop mechanism (that is, the mechanism is resistant to inhibitors that fail to penetrate the intracellular compartment). Not only ligands selective for VEGF and VEGFR-2 but also VEGFR-1 agonists rescued survival and repopulation of VEGF-deficient HSCs, revealing a function for VEGFR-1 signalling during haematopoiesis. 相似文献