public ExcelSheetReader GetReader(String sheetName)
{
Sheets sheets = SSDocument.WorkbookPart.Workbook.GetFirstChild<Sheets>();
foreach (Sheet sheet in sheets)
{
if (sheet.Name.Value.ToLower() == sheetName.ToLower())
return new ExcelSheetReader(this, sheet);
}
throw new AegisException("'{0}' is not exists in '{1}'", sheetName, _filename);
}