Perhaps you should try some spelling variations:
toan thuc » toan hoc, dan thuc
nhan thuc » nhan luc, dan thuc
vat hanh » vat thanh, van hanh, va hanh
sach ky » sac ky, sach ty, sach kem
cao hoi » cau hoi, co hoi, cao hoc
hieu ve » hieu va, hieu van
hanh di » hanh vi, hanh de, hang di
cua tre » cua te, cuu tre, cua triet
di cua » dai cua, doi cua, de cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu ((sach ky) or (sach y)) nang cao hoi. hieu ve ((toan thuc) OR (nhan thuc)) vat hanh di cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((sach ky) OR (sach y)) nang cao hoi. hieu ve ((toan thuc) OR (nhan thuc)) vat hanh di cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu ((sach ky) or (sach y)) nang cao hoi. hieu ve ((toan thuc) OR (nhan thuc)) vat hanh di cua tre".
• Adding a wildcard symbol may retrieve word variants: thu ((sach ky) or (sach y)) nang cao hoi. hieu ve ((toan thuc) OR (nhan thuc)) vat hanh di cua tre*.