Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
dang hai » dang khai, hang hai, dung hai
cam thuc » nam thuc, cam thu, can thuc
hieu van » hieu va, thien van, lieu va
nang ma » tang ma, sang ma, nang cao
sach ty » sach y, sach tu, sach thu
sach ha » sach nha, sach han, sach xa
va dang » van dang, va nang, va lang
hai cau » hai chau, hai chu, hai hau
ma hoi » mai hoi, xa hoi, ma hoa

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 ha) or (sach ty)) nang ma hoi. hieu van ((cam thuc) or (am thuc)) va dang hai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ha) OR (sach ty)) nang ma hoi. hieu van ((cam thuc) OR (am thuc)) va dang hai cau tren.
• Adding a wildcard symbol may retrieve word variants: su ((sach ha) or (sach ty)) nang ma hoi. hieu van ((cam thuc) or (am thuc)) va dang hai cau tren*.