Perhaps you should try some spelling variations:
thong trong » thuong trong, thong thong, thong thuong
hieu quag » hieu quang, hieu quan, thieu quang
hanh hang » thanh hang, hang hang, hanh han
trong san » trong cac, cong san, dong san
va thong » va thuong, va phuong, he thong
san van » tan van, luan van, tran van

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

• Performing a fuzzy search may retrieve terms with similar spellings: nho ((hieu quag) or (hieu qua)) - hanh hang va thong trong san van ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: nho ((hieu quag) OR (hieu qua)) - hanh hang va thong trong san van ban*.