Perhaps you should try some spelling variations:
thanh hai » thanh phan, thanh hoa, thanh san
thanh lai » thanh lap, thanh loi, thanh tai
duc manh » suc manh, duc anh, duc minh
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
nam duc » nam duoc, pham duc, nam thuc
lang xa » dang xay, lang van
lang ha » long ha
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach y ((lang xa) or (lang ha)) hoi. hieu van nam duc manh ((thanh lai) OR (thanh hai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((lang xa) OR (lang ha)) hoi. hieu van nam duc manh ((thanh lai) OR (thanh hai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((lang xa) or (lang ha)) hoi. hieu van nam duc manh ((thanh lai) OR (thanh hai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((lang xa) or (lang ha)) hoi. hieu van nam duc manh ((thanh lai) OR (thanh hai)) cua tre*.