Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
thuc day » thuc dan
sach ky » sac ky, sach y, sach ty
tai cuu » tai cuc, tai buu, tai cua
han tai » hang tai, nhan tai, van tai
cuu tre » cua tre, cau tren, cau treo
hieu va » lieu va, hieu qua
ky hang » ky nang, ly hang, ky dang
va hoc » van hoc
va hoe » van hoe, va hoa, va hoi
va nam » van nam, ha nam, va nay

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky hang ((va hoe) OR (va hoc)). hieu va nam ((thuc vat) or (thuc day)) han tai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky hang ((va hoe) OR (va hoc)). hieu va nam ((thuc vat) OR (thuc day)) han tai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky hang ((va hoe) OR (va hoc)). hieu va nam ((thuc vat) or (thuc day)) han tai cuu tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky hang ((va hoe) OR (va hoc)). hieu va nam ((thuc vat) or (thuc day)) han tai cuu tre*.