Perhaps you should try some spelling variations:
duoc tren » nuoc tren, thuoc tren, dung tren
tai duoc » tao duoc, tan duoc, mai duoc
hang tai » hang va, dung tai
van hang » van khang, van hoang, van thang
de nhan » do nhan, tue nhan, de thanh
luc van » luoc van, luu van, duc van
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
dai hai » dai han, dai hoi, dai tai
mai hoi » mai khoi, dai hoi, lai hoi
ve nhan » ve nha, va nhan, ve phan

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ky nang ((mai hoi) or (dai hai)). hieu ((ve nhan) OR (de nhan)) luc van hang tai duoc tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky nang ((mai hoi) OR (dai hai)). hieu ((ve nhan) OR (de nhan)) luc van hang tai duoc tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ky nang ((mai hoi) or (dai hai)). hieu ((ve nhan) OR (de nhan)) luc van hang tai duoc tren".
• Adding a wildcard symbol may retrieve word variants: so sach ky nang ((mai hoi) or (dai hai)). hieu ((ve nhan) OR (de nhan)) luc van hang tai duoc tren*.