Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
nam thuc » nam thuoc, am thuc, nam thu
nang xa » nang x, lang xa, nang ma
qua nam » quan nam, cua nam, quang nam
vat dan » va dan, van dan, vat ran
vai cua » hai cua, lai cua, bai 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) OR (doc sach)) ky nang xa hoi. hieu qua nam thuc vat dan ((vai cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) ky nang xa hoi. hieu qua nam thuc vat dan ((vai cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) ky nang xa hoi. hieu qua nam thuc vat dan ((vai cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) ky nang xa hoi. hieu qua nam thuc vat dan ((vai cua) or (dai cua)) tre*.