I cannot download any packages through the packages manager. does anyone know where can I download these packages through browsers? thanks.
Why can’t you download them through the package manager?
there is a firewall in our country’s network, which blocks many IP outside our country.
Use a VPN. If Unity’s package manager is anything like the Asset Store there are no directly links to the packages.
I have a VPN, but it is just working for browser. 
So use a VPN that works at a lower level. Most VPN services offer this.