Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
van hanh » van thanh, ban hanh, van anh
nhan luc » nang luc
hanh de » hanh ve, hanh kem
hau luc » hau loc, cau luc, hieu luc
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
cua tre » cua te, cuu tre, cua triet
de cua » le cua, te cua, dieu cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ky ((nang ma) OR (tang ma)) hoi. hieu van ((hau luc) or (nhan luc)) van hanh de cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((nang ma) OR (tang ma)) hoi. hieu van ((hau luc) OR (nhan luc)) van hanh de cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((nang ma) OR (tang ma)) hoi. hieu van ((hau luc) or (nhan luc)) van hanh de cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((nang ma) OR (tang ma)) hoi. hieu van ((hau luc) or (nhan luc)) van hanh de cua tre*.