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介绍了δ-函数的定义、性质 ,并且介绍了δ-函数在机械学中的应用 ,特别是线性系统的脉冲响应及频谱分析中的应用 相似文献
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介绍了表面活性剂在建筑业中的应用,主要涉及混凝土添加剂、脱模剂、养护剂、涂料乳化剂和沥青乳化剂,详细介绍了表面活性剂在建筑业中的作用和机理。 相似文献
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Visual C#的Excel编程 总被引:1,自引:0,他引:1
杜秋霞 《青海师范大学学报(自然科学版)》2006,(3):53-55
本文介绍了Excel对象、C#中的受管代码和非受管代码,并介绍了COM组件在.NET环境中的使用. 相似文献
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稀土元素在钢和焊接材料中的应用及研究进展 总被引:3,自引:0,他引:3
介绍了稀土元素在钢中的净化、变质和合金化作用的新进展以及对其使用性能的改善,在此基础上,介绍了稀土元素在焊接材料中的研究进展。 相似文献
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吴磊 《安庆师范学院学报(自然科学版)》2005,11(4):25-27
本文介绍了智能材料与结构的特点,详细介绍了混入光纤维、碳纤维和玻璃纤维的机敏混凝土在土木工程中的应用以及形状记忆合金、电流变体、压电材料等智能材料在土木工程振动控制中的应用。 相似文献
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本文首先从经济、社会、环境等方面分析了顶管施工技术在水利工程建设中的优越性,然后介绍了顶管技术在应用中的准备工作,最后对顶管的几道重要工序做了介绍和说明。 相似文献
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FMRFamide reverses protein phosphorylation produced by 5-HT and cAMP in Aplysia sensory neurons 总被引:3,自引:0,他引:3
Neurotransmitter can modulate neuronal activity through a variety of second messengers that act on ion channels and other substrate proteins. The most commonly described effector mechanism for second messengers in neurons depends on protein phosphorylation mediated by one of three sets of kinases: the cyclic AMP-dependent protein kinases, the Ca2+-calmodulin-dependent protein kinases, and the Ca2+-phospholipid-dependent protein kinases. In addition, some neurotransmitters and second messengers can also inhibit protein phosphorylation by lowering cAMP levels (either by inhibiting adenylyl cyclase or activating phosphodiesterases). This raises the question: can neurotransmitters also modulate neuronal activity by decreasing protein phosphorylation that is independent of cAMP? Various biochemical experiments show that a decrease in protein phosphorylation can arise through activation of a phosphatase or inhibition of kinases. In none of these cases, however, is the physiological role for the decrease in protein phosphorylation known. Here we report that in Aplysia sensory neurons, the presynaptic inhibitory transmitter FMRFamide decreases the resting levels of protein phosphorylation without altering the level of cAMP. Furthermore, FMRFamide overrides the cAMP-mediated enhancement of transmitter release produced by 5-hydroxytryptamine (5-HT), and concomitantly reverses the cAMP-dependent increase in protein phosphorylation produced by 5-HT. These findings indicate that a receptor-mediated decrease in protein phosphorylation may play an important part in the modulation of neurotransmitter release. 相似文献
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Daye Sun 《科学通报(英文版)》2000,45(19):1729-1734
Generally, cell signal molecules are classified into the extracellular signal molecules (the first messengers) and the intracellular
signal ones (the second messengers). Cyclic adenosine monophosphate (CAMP), calcium ions and calmodulin (CaM) are the traditional
intracellular messengers, but they are also present in extracellular matrix (ECM). Some of them have been discovered to act
as the first messengers through cell surface receptors. Other second messengers, such as cyclic guanosine monophosphate (cGMP),
cyclic adenosine diphosphate ribose (cADPR) and annexin, are also found existing outside animal and plant cells. The existence
of these messengers with intracellular-extracellular compatible functions in cells may be a regular biological phenomenon.
These compatible messengers might be the communication factors between intracellular and extracellular regions or among the
cell populations, and are also important in regulating cell development procedure. 相似文献
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水分胁迫下植物体内的信号传递 总被引:2,自引:0,他引:2
本文综述了水分胁迫下植物体内的干旱信号传递,包括水分胁迫下信号的识别、信号通过第二信使、蛋白磷酸化/去磷酸化参与的胞内传递,水分胁迫下木质部汁液中蛋白质、pH值的变化及化学物质脱落酸(ABA)、茉莉酸(JA)等参与的化学信号传递等。 相似文献
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Phosphatidylinositol 4,5-bisphosphate (PIP2), which comprises only about 1% of the phospholipids in the cytoplasmic leaflet of the plasma membrane, is the source of three second messengers, activates many ion channels and enzymes, is involved in both endocytosis and exocytosis, anchors proteins to the membrane through several structured domains and has other roles. How can a single lipid in a fluid bilayer regulate so many distinct physiological processes? Spatial organization might be the key to this. Recent studies suggest that membrane proteins concentrate PIP2 and, in response to local increases in intracellular calcium concentration, release it to interact with other biologically important molecules. 相似文献
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Tyrosine phosphatase CD45 is essential for coupling T-cell antigen receptor to the phosphatidyl inositol pathway 总被引:48,自引:0,他引:48
Stimulation of T lymphocytes through their antigen receptor (T-cell receptor; TCR) results in the activation of a tyrosine kinase and the generation of phosphatidyl inositol (PtdIns)-derived second messengers. Several reports have indicated that CD45, a haematopoietic cell-specific surface glycoprotein with tyrosine phosphatase activity in its cytoplasmic domain, is important in lymphocyte activation. To examine the possibility that CD45 might influence proximal signal transduction events through the TCR, we have isolated a variant of the human T-cell leukaemic line, HPB-ALL, which fails to express this phosphatase. Unlike cells expressing CD45, stimulation of the TCR in the CD45-negative cell does not result in PtdIns-derived second messengers. Reconstitution of CD45 expression restored early signalling events through the TCR. To localize the site of CD45 action, the human muscarinic type 1 receptor, which also activates the PtdIns second messenger pathway, was transfected into the CD45-negative cell. Although stimulation of the TCR failed to generate PtdIns-derived second messengers, there was normal activity of the PtdIns pathway when human muscarinic receptor type 1 was stimulated, despite the absence of CD45. These data indicate that CD45 influences a cellular component that is essential for effective coupling of the TCR to the PtdIns second messenger pathway. 相似文献
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Lipoxygenase metabolites of arachidonic acid as second messengers for presynaptic inhibition of Aplysia sensory cells 总被引:20,自引:0,他引:20
D Piomelli A Volterra N Dale S A Siegelbaum E R Kandel J H Schwartz F Belardetti 《Nature》1987,328(6125):38-43
Biochemical and biophysical studies on Aplysia sensory neurons indicate that inhibitory responses to the molluscan peptide FMRFamide are mediated by lipoxygenase metabolites of arachidonic acid. These compounds are a new class of second messengers in neurons. 相似文献
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环二鸟苷酸(c-di-GMP)是在细菌中广泛存在的第二信使分子,它介导的信号转导途径涉及调控细菌的运动、致病性、生物膜形成、细胞周期进程和有机溶剂耐受性等多种重要功能.该文主要从c-di-GMP的合成与降解、c-di-GMP的效应子及c-di-GMP的生理作用3方面对c-di-GMP介导的信号转导途径进行总结,并对该信号转导途径的研究前景进行了展望. 相似文献
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近来的许多研究表明有两类分子可作为胰岛素信号传递的第二信使而将激素所携带的信号传递进入靶细胞内 .一类是磷酸寡聚糖或肌醇磷酸多糖 ,另一类是二酰基甘油 (dicylglycerol DAG) .胰岛素对代谢的调节作用是通过磷酸寡聚糖控制代谢关键酶的磷酸化状态而实现的 .二酰基甘油可介导胰岛素刺激葡萄糖的跨膜转运过程 .许多证据表明位于细胞穴样内陷在胰岛素信号传递过程中具有聚集信号传递分子的作用 . 相似文献
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Nishiyama M Hoshino A Tsai L Henley JR Goshima Y Tessier-Lavigne M Poo MM Hong K 《Nature》2003,423(6943):990-995
Signalling by intracellular second messengers such as cyclic nucleotides and Ca2+ is known to regulate attractive and repulsive guidance of axons by extracellular factors. However, the mechanism of interaction among these second messengers in determining the polarity of the guidance response is largely unknown. Here, we report that the ratio of cyclic AMP to cyclic GMP activities sets the polarity of netrin-1-induced axon guidance: high ratios favour attraction, whereas low ratios favour repulsion. Whole-cell recordings of Ca2+ currents at Xenopus spinal neuron growth cones indicate that cyclic nucleotide signalling directly modulates the activity of L-type Ca2+ channels (LCCs) in axonal growth cones. Furthermore, cGMP signalling activated by an arachidonate 12-lipoxygenase metabolite suppresses LCC activity triggered by netrin-1, and is required for growth-cone repulsion mediated by the DCC-UNC5 receptor complex. By linking cAMP and cGMP signalling and modulation of Ca2+ channel activity in growth cones, these findings delineate an early membrane-associated event responsible for signal transduction during bi-directional axon guidance. 相似文献