用字符串方式导出到excel的数据类型被识别成科学计数

public void ExportToExcel(string FilterName, DataTable dt,string[] headtxt)
        {
            HttpResponse resp;        
            resp = System.Web.HttpContext.Current.Response;
            //resp.ContentType=
            resp.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312"); 
            resp.AppendHeader("Content-Disposition", "attachment;filename=oursjia."+FilterName);
            resp.AppendHeader("Content-Type", "application/ms-excel");
            string colHeaders = "", 
            ls_item = "";  
            DataRow[] myRow=dt.Select(); 
            int i=0; 
            int cl=dt.Columns.Count;  
             
                for(i=0;i<headtxt.Length;i++)
                {
                    if (i == (headtxt.Length-1)) 
                        { 
                                colHeaders += headtxt[i] + "\n";                             
                        } 
                else 
                    {
                        if (FilterName == "csv")
                        {
                            colHeaders += headtxt[i] + ",";
                        }
                        else
                        {
                            colHeaders += headtxt[i] + "\t";
                        }
                    }
                }
                 
                resp.Write(colHeaders);  
                foreach(DataRow row in myRow) 
                { 
                    for(i=0;i<cl;i++)
                    { 
                        if(i== (cl-1)) 
                        {
                            ls_item += row[i].ToString() + "\n"; 
                        }
                    else
                        {
                            if (FilterName == "csv")
                            {
                                ls_item += row[i].ToString() + ",";
                            }
                            else
                            {
                                ls_item += "\'"+row[i].ToString() + "\t";
                            }
                        }
                    }               
                    resp.Write(ls_item);
                    ls_item=""; 
                } 
                resp.End();
         }这是个导出的方法，导出的文件是excel的。
导出来变成:
1.0302E+19
1.0302E+19
1.0302E+19
1.0302E+19
1.0302E+19
而实际数据是:
10302001900009504391
10302001900009309641
10302001900009309664
10302001900009309598
10302001900009309753
这个字符串导出，能不能把导出全部成字符串显示呢,我这里是asp.net（C#）的，希望大家指教下。