Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
hoc sach » hoc sinh, hoc cac, hoc anh
dan vat » dang vat, van vat, dan va
dan vai » dan va, dan tai, den vai
thuc ca » thuc cua, thuc can, thuc cao
cuu tre » cua tre, cau tren, cau treo
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
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: ((toc sach) or (hoc sach)) ky lang xa hoi. hieu va nam thuc ca ((dan vai) OR (dan vat)) cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky lang xa hoi. hieu va nam thuc ca ((dan vai) OR (dan vat)) cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (hoc sach)) ky lang xa hoi. hieu va nam thuc ca ((dan vai) OR (dan vat)) cuu tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky lang xa hoi. hieu va nam thuc ca ((dan vai) OR (dan vat)) cuu tre*.