Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
hieu van » hieu va, thien van, lieu va
cau phuc » cau truc, chau phu, huu phuc
hanh de » hanh ve, hanh kem
hanh di » hanh vi, hang di, danh di
sach ky » sac ky, sach y, sach ty
van cau » van dau, van hau, van chat
nang ma » tang ma, nang cao, mang may
sang ma » tang ma, sang tao, mang may
cua tre » cua te, cuu tre, cua triet

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

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