Avoid the quotes and go straight to the value.
{section name=articles loop=$list_article}
{assign var="article" value=$list_article[articles]}
// now use many properties of the object $article...
<h2>{$article->title}</h2>
{$article->text}
...
{/section}
However, in this case, you can also use foreach.
{foreach from=$list_article item=article}
// now use many properties of the object $article...
<h2>{$article->title}</h2>
{$article->text}
...
{/section}