Basically, the standard is HowNet, and several other systems have their own advantages and disadvantages:
Wanfang: Never used it. It is said that the resources are not complete, and the test results are quite different from HowNet.
Paperpass: After several years of operation, it has a certain brand awareness and the effect is OK. Much stricter than HowNet and much higher.
Paperyy: The price is cheap, the speed is fast, and the database is powerful, which is not bad.
Pen: At present, I personally think that the duplicate checking system closest to HowNet has cooperated with many schools and is worth recommending. Our school library can be used.