长江河床演变和泥沙观测

由中国水利学会和国际水文计划中国国家委员会联合召开的第二次河流泥沙国际学术讨论会于1983年10月11日～16日在南京召开。会议有20多个国家60多位学者参加,国内有90多位泥沙专业工作者出席。在会上提交的论文有100余篇。主要包括五个方面的内容:1.冲积河流水力学;2.泥沙运动;3.河床演变;4.河道整治;5.河流模型试验及原型观测技术。河流泥沙问题的重要性毋庸置说。它造成水土流失,河流泛滥、改道,水库汙积,对国民经济与人民的生产、生活影响极大。是目前各国关心和研究的大课题。为此,本刊编辑参加了这次会议,现从中摘选5篇以供读者参考。     

Identification of the Credit Guarantee Network of Steel Trade Enterprises in China

The risk points in the credit guarantee network of steel trade enterprises were identified by using the network analysis method in this paper. Firstly, the formation and operation mechanism of steel trade credit guarantee network was analyzed.Secondly,a guarantee network was established to analyze the related network structure indexes based on the mutual guarantee data of 83 enterprises in a steel trade market. These indexes included centrality,honest broker,and structural hole. The results suggest that network analysis method can be used to find out the risk points of the guarantee network. Additionally,some recommendations are brought forth to reduce or prevent future crises.     

数量遗传学与植物选育种

植物遗传性状的变异有两种:一种是具有明确界限,表现为不连续变异的性状,称为质量性状,如桃的黄肉和白肉,豌豆的红花与白花;另一种是需要有重量、长度等计量单位来度量,表现为连续变异的性状,称为数量性状,如产量高低,果实大小,植株高矮等。质量性状是由一对或少数几对基因所控制,在杂种后代分离群体中可明确分组,根据基因作用机制