Perhaps you should try some spelling variations:
"du canh trinh he duoc hoc" » "du canh tranh he duoc hoc", "du hanh trinh he duoc hoc", "du canh tinh he duoc hoc", "du canh trinh han duoc hoc", "du canh trinh hoa duoc hoc", "du canh trinh thi duoc hoc", "du canh trinh he quoc hoi", "do canh trinh he duoc hoc", "luc canh trinh he duoc hoc", "du canh trinh che duoc hoc", "du canh trinh te duoc hoc", "du canh trinh ve duoc hoc"
"tu sach re nghe vi hoc" » "thu sach re nghe vi hoc", "su sach re nghe vi hoc", "te sach re nghe vi hoc", "tu sach de nghe vi hoc", "tu sach tren nghe vi hoc", "tu sach kem nghe vi hoc", "tu sach ve nghe vi hoc", "tu sach te nghe vi hoc", "tu sach re nghe va hoc", "tu sach re nghe noi hoc", "tu sach re nghe li hoc"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("tu sach re nghe vi hoc") or ("du canh trinh he duoc hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tu sach re nghe vi hoc") OR ("du canh trinh he duoc hoc")).
• Removing quotes may allow a broader search: (( tu sach re nghe vi hoc ) or ( du canh trinh he duoc hoc )).
• Adding a wildcard symbol may retrieve word variants: (("tu sach re nghe vi hoc") or ("du canh trinh he duoc hoc"))*.