From Crystal growing

All site pages are published under PublicDomain license.

It means that you can use any information published on the website for any purpose without attribution and without notice to users or the site administration. Science is free for everyone, copyright must die.

However, it is still recommended to leave links to your website or specified articles to avoid the situation, when placed on an external resource information is incorrect, while the it has already been fixed on the original page, but end users do not know about it.