这位学者花了二十年时间构建自己的理论体系。

Zhè wèi xuézhě huā le èrshí nián shíjiān gòujiàn zìjǐ de lǐlùn tǐxì.

This scholar spent twenty years building his own theoretical system.

如果没有一套科学的管理体系，公司很难长期发展。

Rúguǒ méiyǒu yí tào kēxué de guǎnlǐ tǐxì, gōngsī hěn nán chángqī fāzhǎn.

Without a scientific management system, it is hard for a company to develop in the long term.

这个国家已经建立起比较完善的法律体系。

Zhège guójiā yǐjīng jiànlì qǐ bǐjiào wánshàn de fǎlǜ tǐxì.

This country has already established a relatively complete legal system.