Perhaps you should try some spelling variations:
quang quang » quan quang, dang quang, dung quang
tinh khong » tinh khang, tinh huong, benh khong
khong luan » thong luan, khong quan, khung luan
hieu suat » hieu luat, hieu qua
quang va » quang van, quan va, quang ma
van tien » toan tien, van tuan
van hieu » cao hieu
va hieu » va dieu, va hien, cao hieu

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( tinh quang quang va hieu suat ) or ( tinh khong luan ((van tien) or (van hieu)) soat ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tinh quang quang va hieu suat ) OR ( tinh khong luan ((van tien) OR (van hieu)) soat )).
• Adding a wildcard symbol may retrieve word variants: (( tinh quang quang va hieu suat ) or ( tinh khong luan ((van tien) or (van hieu)) soat ))*.