Lucene.Net.QueryParsers.ParseException: Cannot parse ' Na + ': Encountered "" at line 1, column 6.
Was expecting one of:
    "(" ...
    "*" ...
     ...
     ...
     ...
     ...
    "[" ...
    "{" ...
     ...
     ---> Lucene.Net.QueryParsers.ParseException: Encountered "" at line 1, column 6.
Was expecting one of:
    "(" ...
    "*" ...
     ...
     ...
     ...
     ...
    "[" ...
    "{" ...
     ...
    
   在 Lucene.Net.QueryParsers.QueryParser.Jj_consume_token(Int32 kind)
   在 Lucene.Net.QueryParsers.QueryParser.Clause(String field)
   在 Lucene.Net.QueryParsers.QueryParser.Query(String field)
   在 Lucene.Net.QueryParsers.QueryParser.Parse(String query)
   --- 内部异常堆栈跟踪的结尾 ---
   在 Lucene.Net.QueryParsers.QueryParser.Parse(String query)
   在 SRPCorrecting_UI.journal.Articles.BindSearchPapers(String searchCode, Int32 currentPage, Int32 pageSize, String strFields)
   在 SRPCorrecting_UI.journal.Articles.Page_Load(Object sender, EventArgs e)