Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, hieu ve
nam thuc » nam thuoc, am thuc, nam thu
cau theo » cau thi, cau tao
thuc va » thuc vat, thuc dan, thuc day
y lang » _ lang, tay lang, yen lang
o lang » hoa lang, hoi lang
va dan » ca dan, va dao, va dau
dan va » doan va, dan ca, ban va
va cau » van cau, va cac, va dau

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