排序方式: 共有13条查询结果,搜索用时 531 毫秒
1.
以半胱氨酸为配体合成一种新型亚金配合物NH4Au(Cys)2,对该配合物进行元素分析、红外光谱、紫外光谱、热失重分析和导电性测量等理化性质研究;以该亚金配合物为金源开展相关的电镀金工艺探索,并通过四因素三水平的正交试验获得其最佳条件参数;采用扫描电子显微镜(SEM)和X线衍射(XRD)对镀金层的表面质量进行探讨。研究结果表明:该目标产物的分子式为NH4Au(Cys)2·2H2O,该配合物中以半胱氨酸的巯基和金配位为成健特征,在170℃以下热稳定性较好,该亚金配合物是一个典型的离子化合物。在电流密度为200~300 A/m2,p H为10.5~12.0,温度为35~45℃,金质量浓度为15~25 g/L的电镀工艺条件下,得到粒度为0.5~1.0μm的单质金,且主要沿着(111)面进行生长。 相似文献
2.
随机纳米碳管网络及其渗流性质 总被引:1,自引:0,他引:1
数值模拟了实验上构造纳米碳管网络的溶液沉积方法.与一般的随机网络模型不同,将碳管的长度计算在内,而且考虑了不同的空间相交位形.数值模拟发现网络的度分布为高斯分布,平均集聚系数约为0.11.当网络中碳管平均面密度取值在σ0=179 200根/cm2附近时,网络系综达到渗流.在临界点附近,网络的连通概率p、两极之间电导G、... 相似文献
3.
本文在分析CCT-88/51/98教学实验系统监控程序的基础上,对该教学实验系统监控程序中存在的问题作出了一些改进。 相似文献
4.
用脸谱图对太子河本溪市区段河流沉积物中重金属污染进行评价的研究 总被引:9,自引:0,他引:9
本文将沉积学原理及国际上新发展的两种重金属污染评价方法与多变量的图表示法——脸谱图相结合,对太子河本溪市区段河道沉积物中重金属的污染状况及潜在生态危害进行了综合性的评价研究。从脸谱图上可以直观地看出各采样点重金属的污染情况和潜在生态危害程度。从研究结果可以看出,太子河本溪市区段河道沉积物中重金属的污染是很严重的。 相似文献
5.
6.
Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADP-ribose) polymerase 总被引:2,自引:0,他引:2
Bryant HE Schultz N Thomas HD Parker KM Flower D Lopez E Kyle S Meuth M Curtin NJ Helleday T 《Nature》2005,434(7035):913-917
Poly(ADP-ribose) polymerase (PARP1) facilitates DNA repair by binding to DNA breaks and attracting DNA repair proteins to the site of damage. Nevertheless, PARP1-/- mice are viable, fertile and do not develop early onset tumours. Here, we show that PARP inhibitors trigger gamma-H2AX and RAD51 foci formation. We propose that, in the absence of PARP1, spontaneous single-strand breaks collapse replication forks and trigger homologous recombination for repair. Furthermore, we show that BRCA2-deficient cells, as a result of their deficiency in homologous recombination, are acutely sensitive to PARP inhibitors, presumably because resultant collapsed replication forks are no longer repaired. Thus, PARP1 activity is essential in homologous recombination-deficient BRCA2 mutant cells. We exploit this requirement in order to kill BRCA2-deficient tumours by PARP inhibition alone. Treatment with PARP inhibitors is likely to be highly tumour specific, because only the tumours (which are BRCA2-/-) in BRCA2+/- patients are defective in homologous recombination. The use of an inhibitor of a DNA repair enzyme alone to selectively kill a tumour, in the absence of an exogenous DNA-damaging agent, represents a new concept in cancer treatment. 相似文献
7.
贾巍巍 《山西师范大学学报:自然科学版》2004,18(3):6-11
本文讨论F4上n维线性空间的k维子空间W,这些子空间都有特定的自同构群(实际上是典型群GLn(F4)的一个子群),根据群中元素形式的不同可将子空间W分为两类,并对寻找n维空间中形如这两类的n/2维自对偶子空间提供了一种采用降低维数寻找的方法。 相似文献
8.
多梯度复杂图像的分割 总被引:1,自引:1,他引:0
图像分割是一种重要的图像分析技术,它不仅得到人们广泛的重视和研究,也在实际中得到大量的应用。本文针对一些经典分割算法对多梯度复杂图像分割边缘定位不准确,易受噪声干扰的特点,提出了一种利用图像边缘区域对多梯度复杂图像进行自适应阈值分割的算法。通过对各种算法的比较,本算法抗干扰能力较强,稳定性好,而且完全自动,不需预先设定任何参数。对多种图像的实验表明本文方法十分有效。 相似文献
9.
10.
DNA double strand breaks (DSBs) in repetitive sequences are a potent source of genomic instability, owing to the possibility of non-allelic homologous recombination (NAHR). Repetitive sequences are especially at risk during meiosis, when numerous programmed DSBs are introduced into the genome to initiate meiotic recombination. In the repetitive ribosomal DNA (rDNA) array of the budding yeast Saccharomyces cerevisiae, meiotic DSB formation is prevented in part through Sir2-dependent heterochromatin formation. Here we show that the edges of the rDNA array are exceptionally susceptible to meiotic DSBs, revealing an inherent heterogeneity in the rDNA array. We find that this localized DSB susceptibility necessitates a border-specific protection system consisting of the meiotic ATPase Pch2 and the origin recognition complex subunit Orc1. Upon disruption of these factors, DSB formation and recombination increased specifically in the outermost rDNA repeats, leading to NAHR and rDNA instability. Notably, the Sir2-dependent heterochromatin of the rDNA itself was responsible for the induction of DSBs at the rDNA borders in pch2Δ cells. Thus, although the activity of Sir2 globally prevents meiotic DSBs in the rDNA, it creates a highly permissive environment for DSB formation at the junctions between heterochromatin and euchromatin. Heterochromatinized repetitive DNA arrays are abundant in most eukaryotic genomes. Our data define the borders of such chromatin domains as distinct high-risk regions for meiotic NAHR, the protection of which may be a universal requirement to prevent meiotic genome rearrangements that are associated with genomic diseases and birth defects. 相似文献