Perhaps you should try some spelling variations:
su triet » su viet, su tien, ve triet
thanh vi » hanh vi, thanh va, thanh ve
va thanh » gia thanh, ban thanh, va tinh
truc va » thuc va, thuc vat, trung va
sach ty » sach y, sach thu, xach tay
sach tu » sach thu, cach tu, sach uu
xang o » lang o, tang o, dang o
ve cac » va cac, vien cac
ve cau » ke cau, va cau, le cau
o hoi » co hoi, o hoc, o hai
vi su » va su, ve su, ki su

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 ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (ve cac)) truc va thanh vi su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((sach ty) OR (sach tu)) xang o hoi. hieu ((ve cau) OR (ve cac)) truc va thanh vi su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((sach ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (ve cac)) truc va thanh vi su triet".
• Adding a wildcard symbol may retrieve word variants: so ((sach ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (ve cac)) truc va thanh vi su triet*.