Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
khoa thon » khoa than, khoa thuoc, khoa hoc
thuc cac » thuc cach, tuc cac, phuc cac
cac toan » cac khoan, hach toan, cac thanh
hoa thon » hoa trong, khoa than, hoa khong
te sach » toc sach
su sach » so sach, vu sach

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) or (su sach)) tham thuc cac toan ((khoa thon) or (hoa thon))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (su sach)) tham thuc cac toan ((khoa thon) OR (hoa thon)).
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (su sach)) tham thuc cac toan ((khoa thon) or (hoa thon))*.