Perhaps you should try some spelling variations:
duc thanh » duc thang, duc tan, de thanh
doc sach » hoc sach, toc sach, nuoc sach
duc hanh » duc anh, du hanh, duc manh
hieu van » hieu va, thien van, lieu va
va trien » va truyen, va thiet, va tuyen
lang xa » lang ha, dang xay, lang van
sach ty » sach y, sach tu, sach thu
van cao » van dao, van bao, van hao
nang xa » nang x, nang ma, mang xa
vi va » vi van, vai va, vu va

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc hanh) OR (duc thanh)) hanh vi va trien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ty ((nang xa) OR (lang xa)) hoi. hieu van cao ((duc hanh) OR (duc thanh)) hanh vi va trien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc hanh) OR (duc thanh)) hanh vi va trien".
• Adding a wildcard symbol may retrieve word variants: doc sach ty ((nang xa) or (lang xa)) hoi. hieu van cao ((duc hanh) OR (duc thanh)) hanh vi va trien*.