$('.sharethis-body .keypress-click').each(function () {
    $(this).keypress(function (e) {
        var key = e.which;
        if (key == 13) // the enter key code
        {
            $(this).click();
            console.log("click");
            return false;
        }
        return true;
    });
});

<div class="sharethis-body">
        <div class="sthoverbuttons-label"><span>Share</span></div>
        <span tabindex="0" class='st_facebook_large keypress-click' displaytext='Facebook' aria-label='Facebook'></span>
        <span tabindex="0" class='st_twitter_large keypress-click' displaytext='Tweet' aria-label='Twitter'></span>
        <span tabindex="0" class='st_googleplus_large keypress-click' displaytext='Google +' aria-label='Google Plus'></span>
        <span tabindex="0" class='st_linkedin_large keypress-click' displaytext='LinkedIn' aria-label='LinkedIn'></span>
        <span tabindex="0" class='st_email_large keypress-click' displaytext='Email' aria-label='Email'></span>
    </div>