Perhaps you should try some spelling variations:
hoc viet » hoc hien
may thoi » gay thoi, may thi, tay thoi
tuc van » thuc van, truc van, tuc va
sach ky » sach y, sach ty, sach kem
hieu ve » hieu va, hieu van
ve cam » ve cham, ve cac, va cam
sac ky » cac ky, sai ky
anh vi » hanh vi, anh va, anh ve
vi hoc » li hoc, va hoc

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 ky) OR (sac ky)) mang may thoi. hieu ve cam ((tuc van) or (thuc vat)) anh vi hoc viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sac ky)) mang may thoi. hieu ve cam ((tuc van) OR (thuc vat)) anh vi hoc viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) OR (sac ky)) mang may thoi. hieu ve cam ((tuc van) or (thuc vat)) anh vi hoc viet".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) OR (sac ky)) mang may thoi. hieu ve cam ((tuc van) or (thuc vat)) anh vi hoc viet*.