Perhaps you should try some spelling variations:
"danh thuc dan khoan viet nam" » "danh thuc dan hoa viet nam", "danh thuc dan thon viet nam", "danh thuc dan han viet nam", "dan thuc dan khoan viet nam", "anh thuc dan khoan viet nam", "dinh thuc dan khoan viet nam", "danh thuc dan khoa viet nam", "danh thuc dai khoang viet nam", "danh thuc toan khoan viet nam", "danh thuc hanh khoan viet nam", "danh hoc dan khoan viet nam", "danh thuc vat khoan viet nam"
"canh tac dung hoc viet nam" » "canh tay dung hoc viet nam", "canh giac dung hoc viet nam", "cong tac dung hoc viet nam", "canh sach dung hoc viet nam", "canh xay dung hoc viet nam", "canh tin dung hoc viet nam", "canh tac dong hoc viet nam", "canh tac dung thuoc viet nam", "canh tac trung hoc viet nam", "canh tac dung hoc hien nam"

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: (("canh tac dung hoc viet nam") or ("danh thuc dan khoan viet nam"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("canh tac dung hoc viet nam") OR ("danh thuc dan khoan viet nam")).
• Removing quotes may allow a broader search: (( canh tac dung hoc viet nam ) or ( danh thuc dan khoan viet nam )).
• Adding a wildcard symbol may retrieve word variants: (("canh tac dung hoc viet nam") or ("danh thuc dan khoan viet nam"))*.