Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
tay lang » tai lang, tay tang, tay quang
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
thuc va » thuc vat, thuc dan, thuc day
va danh » va dinh, va dan, va hanh
danh va » doanh va, hanh va, anh va
cua tre » cuu tre, cua triet, dua tren
y lang » o lang, _ lang, yen lang
cua te » cua tu

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