Perhaps you should try some spelling variations:
thanh vi » thanh va, thanh ve, nhanh vi
thuc dan » thuc hanh, hoc dan, thuc vat
su sach » so sach, vu sach
sach ty » sach y, sach tu, sach thu
su viet » so viet
thuc va » thuc vat, thuc day
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
xang o » lang o, tang o, dang o
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ty xang o hoi. hieu ve cac ((thuc va) OR (thuc dan)) ((thanh vi) or (hanh vi)) su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty xang o hoi. hieu ve cac ((thuc va) OR (thuc dan)) ((thanh vi) OR (hanh vi)) su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty xang o hoi. hieu ve cac ((thuc va) OR (thuc dan)) ((thanh vi) or (hanh vi)) su viet".
• Adding a wildcard symbol may retrieve word variants: su sach ty xang o hoi. hieu ve cac ((thuc va) OR (thuc dan)) ((thanh vi) or (hanh vi)) su viet*.