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991.
(BO3)3-加入到(La,Ce)PO4:Tb中,一方面使Ce3+吸收峰位置随(BO3)3-加入浓度不同有规律性变化,另一方面可以提高材料的热稳定性。本文用X光电子谱测得了与后者相应的信息,讨论了Ce(3+)、Ce(4+)的共存,价态数比与(BO_3)3 ̄-的关系,从而解释了影响材料热稳定性机制。 相似文献
992.
本文应用模糊数学方法,详细分析了影响综采采区划分及其走向长度的因素,对既定井田内综采采区的合理划分进行综合评判,以确定最优综采采区布置方案,井用此法求出了平顶山一矿三水平最优果区布置方案,表2,参3。 相似文献
993.
Here we describe a new triconodont mammal from the Late Jurassic/Early Cretaceous period of Liaoning, China. This new mammal is represented by the best-preserved skeleton known so far for triconodonts which form one of the earliest Mesozoic mammalian groups with high diversity. The postcranial skeleton of this new triconodont shows a mosaic of characters, including a primitive pelvic girdle and hindlimb but a very derived pectoral girdle that is closely comparable to those of derived therians. Given the basal position of this taxon in mammalian phylogeny, its derived pectoral girdle indicates that homoplasies (similarities resulting from independent evolution among unrelated lineages) are as common in the postcranial skeleton as they are in the skull and dentition in the evolution of Mesozoic mammals. Limb structures of the new triconodont indicate that it was probably a ground-dwelling animal. 相似文献
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996.
Phosphorylation-dependent prolyl isomerization: a novel signaling regulatory mechanism 总被引:7,自引:0,他引:7
Protein phosphorylation on serine or threonine residues preceding proline (Ser/Thr-Pro) plays an essential role for regulating various cellular processes, including cell cycle progression. Although phosphorylation has been proposed to regulate the function of a protein by inducing conformational changes, much less is known about what phosphate additions actually do and how the functions of phosphoproteins are coordinated. Proline is important for determining protein structure because it exists in cis or trans conformation and can put kinks into a polypeptide chain. We have shown that phosphorylation on Ser/Thr-Pro motifs reduces the cis/trans isomerization rate of Ser/Thr-Pro bonds. At the same time, proteins containing phosphorylated Ser/Thr-Pro motifs are substrates for the prolyl isomerase Pin1. The WW domain of Pin1 acts as a phosphoserine/threonine-binding module binding a defined subset of mitosis-specific phosphoproteins, such as Cdc25 and tau. These interactions target the enzymatic activity of Pin1 close to its substrates. In contrast to other prolyl isomerases (peptidyl-prolyl isomerases, PPlases), Pin1 has an extremely high degree of substrate specificity, specifically isomerizing phosphorylated Ser/Thr-Pro bonds. Therefore, Pin1 binds and regulates the function of a defined subset of phosphoproteins. Furthermore, inhibiting Pin1 function is lethal for dividing cells. Interestingly, Pin1, which can restore the biological function of phosphorylated tau, is sequestered in the neurofibrillary tangles in Alzheimer's brains. Thus, we have proposed a novel signaling regulatory mechanism, where protein phosphorylation creates binding sites for Pin1, which can then latch on to and isomerize the phosphorylated Ser/Thr-Pro peptide bond. In turn, this may change the shape of the protein, regulating its activity, dephosphorylation, degradation or location in the cell. This new post-phosphorylation regulatory mechanism appears to play an important role in normal cell function, such as mitotic progression, and in the pathogenesis of some human pathologies, such as Alzheimer's disease. 相似文献
997.
以某X型超高层建筑为工程背景,研究了该超高层建筑顺风向、横风向以及扭转风荷载系数沿高度方向的分布规律.以质量和刚度相同、动力特性相近为原则使用简化的自由度缩聚模型代替结构精确有限元模型,计算结果显示结构位移与加速度响应均以一阶模态响应为主,该模型代替精确有限元模型能够满足工程计算需要.对质量中心和刚度中心重合的结构,扭转加速度响应在合加速度响应中占有的比例较小,结构在3个方向上振动的耦合程度不高.提出的合成位移投影方法计算出的沿坐标轴方向的风振系数能够保证X和Y方向最大位移与合成位移最大值的同步性,并考虑了横风向风振的影响略大于顺风向风振系数. 相似文献
998.
Wang Xia Zhou GuoXin Xiang CaiYu Du MengHao Cheng JiaAn Liu ShuSheng Lou YongGen 《科学通报(英文版)》2008,53(1):53-57
β-Glucosidase has been reported to induce the production of herbivore-induced plant volatiles. However, how it works remains unclear. Here, we investigated the levels of salicylic acid (SA), jasmonic acid (JA), ethylene, and H2O2, all of which are known signaling molecules that play important roles in induced plant defense in rice plants treated with β-glucosidase, and compared these to levels in plants infested by the rice brown planthopper Nilaparvata lugens (Stal). Results showed that wounding and treatment by β-glucosidase increased the levels of SA, ethylene, and H2O2, but not JA, in all plants compared to control plants. The signaling pathways activated by β-glucosidase treatment are similar to those activated by an infestation by N. lugens, although the magnitude and timing of the signals elicited by the two treatments are different. This may explain why both treatments have similar volatile profiles and are equally attractive to the parasitoid Anagrus nilaparvatae Pang et Wang. 相似文献
999.
SLA-Ⅰ/pMAL-p2X为人工构建的原核表达体系.为获取最佳表达的SLA-Ⅰ复合体蛋白及其可溶性表达含量,设计实验对其进行表达优化(pH值、温度、菌体密度、IPTG浓度、诱导时间),SDS-PAGE检查目的蛋白的表达.另外检查目的蛋白的可溶性表达含量.结果显示,SLA-Ⅰ在pMAL-p2X的最佳表达条件为pH=8.0、T(温度)=37 ℃、OD600=1.0、IPTG=0.4 mmol/L和t(诱导时间)=5 h;证明目的蛋白可溶性表达含量占总表达蛋白的70%左右.研究表明pMAL-p2X系统适合于生产可溶性的SLA-Ⅰ复合体蛋白,便于今后进一步研究SLA-Ⅰ类分子结构和功能. 相似文献
1000.
杨东杰;邱学青;庞煜霞;楼宏铭 《华南理工大学学报(自然科学版)》2008,36(3):26-31
研究了改性木质素系外加剂GCL1-M对水泥砂浆物理力学性能和微观结构的影响,结果表明,GCL1-M砂浆减水率达到30%,掺砂浆28天抗压强度比达到了120%。掺GCL1-M砂浆的渗透压力比达到330%,比掺CLS的砂浆提高了1倍多。氮吸附测试和电子扫描显微观测等结果表明,GCL1-M减慢了水泥水化反应放热速度,降低砂浆的总孔容积,阻塞毛细管通道,提高砂浆的抗渗能力。吸附性能、Zeta电位及环境扫描电镜测试结果表明,GCL1-M在水泥颗粒表面形成网状结构吸附,增加了颗粒间的静电斥力位能,增强了对水泥砂浆的分散和保水作用,有利于提高水泥砂浆的抗渗性能和抗压强度。 相似文献