Perhaps you should try some spelling variations:
"danh bac trung quoc viet nam" » "danh ba trung quoc viet nam", "danh dac trung quoc viet nam", "danh bao trung quoc viet nam", "danh bac trung nuoc viet nam", "danh bac trung hoc viet nam", "danh bac trung ngoc viet nam", "doanh bac trung quoc viet nam", "danh bat trung quoc viet nam", "dan bac trung quoc viet nam"
"canh tac vung moc viet nam" » "canh tay vung moc viet nam", "canh giac vung moc viet nam", "cong tac vung moc viet nam", "canh tac dung moc viet nam", "canh tac vang moc viet nam", "canh tac dung mo viet nam", "canh tac dung moi viet nam", "canh tac dung mot viet nam", "canh tac vung hoc viet nam", "canh tac vung toc viet nam", "canh tac vung doc viet 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 vung moc viet nam") or ("danh bac trung quoc viet nam"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("canh tac vung moc viet nam") OR ("danh bac trung quoc viet nam")).
• Removing quotes may allow a broader search: (( canh tac vung moc viet nam ) or ( danh bac trung quoc viet nam )).
• Adding a wildcard symbol may retrieve word variants: (("canh tac vung moc viet nam") or ("danh bac trung quoc viet nam"))*.