MarcRoot record = new MarcRoot(this.MarcRecord);
record.ChildNodes.Add(new MarcField("200", " ",SUBFLD + "aAAAA"));
record.ChildNodes.Add(new MarcField("300", " ", SUBFLD + "bBBBB"));
MarcNodeList nodes = record.SelectNodes("200");
nodes.First().Name = "999"; // 修改了第一个200字段的字段名
this.MarcRecord = record.Content;
this.Changed = true;