各位老师！！！请问如何筛选观测值为中文的数据呢，像Excel一样平行数据也一并筛选？我想只保留出口的数据，将进口的筛选掉。数据如下：
* Example generated by -dataex-. To install: ssc install dataex
clear
input str6 export str8 tax
"出口" "49019900"
"出口" "49019900"
"出口" "49019900"
"出口" "49019900"
"进口" "39261000"
"进口" "48192000"
"进口" "49030000"
"出口" "49019900"
"进口" "39261000"
"进口" "39269090"
end