Zotero is unable to detect the articles on this Table of Contents page. There is no folder icon in the location toolbar.
You can download individual citations, though. First, select an article.
Then, choose full text or PDF to open it. Click on the page icon to download the article citation.
If you receive your Table of Contents via email, click on the journal icon to open it in your browser.
To download several citations, click on the folder icon in the browser location bar.
Select the articles you are interested in. They will all be added to your Zotero Library.
To download articles one at a time, open an article and click on the page icon in the toolbar. (This often allows you to also download the article PDF.)
You can see the progress in this box on the lower right side of your screen.
After downloading is complete, open your Zotero library. if you have set your Zotero preferences to get PDFs where possible, the article PDF will be attached to the record.