Perhaps you should try some spelling variations:
su triet » su viet, su tien, ve triet
lang mai » lang dai, lang man, sang mai
lang hai » lang chai, lang thai, lang ha
hanh ki » hanh vi, hanh ky, hanh kien
duc van » duc va, duc tan, duc manh
duc ban » duc tan, dua ban, duc man
tu sach » thu sach, su sach, te sach
sach vu » sach va, sach tu, sach uu
hieu va » lieu va, hieu qua
ki su » ky su

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 vu ((lang mai) or (lang hai)) hoi. hieu va cac ((duc ban) OR (duc van)) hanh ki su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach vu ((lang mai) OR (lang hai)) hoi. hieu va cac ((duc ban) OR (duc van)) hanh ki su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach vu ((lang mai) or (lang hai)) hoi. hieu va cac ((duc ban) OR (duc van)) hanh ki su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach vu ((lang mai) or (lang hai)) hoi. hieu va cac ((duc ban) OR (duc van)) hanh ki su triet*.