Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
toc sach » hoc sach, doc sach, nuoc sach
thuc dan » thuc hanh, hoc dan, thuc vat
ky lang » ky dang, ky tang, tay lang
hieu va » lieu va, hieu qua
dan dan » dang dan, ban dan, dao dan
cuu tre » cua tre, cau tren, cau treo
dan va » doan va, dan ca, ban va
va cuu » va cau, va chu, va huu
va am » va lam, va cam

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 (thuoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va am thuc dan dan va cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (thuoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va am thuc dan dan va cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (thuoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va am thuc dan dan va cuu tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (thuoc sach)) ((ky lang) OR (ky nang)) xa hoi. hieu va am thuc dan dan va cuu tre*.