function buscar() {
    var form = document.forms['buscador'];
    var resultado = document.getElementById("resultado");
    var contenttype = 'application/x-www-form-urlencoded';

    var req;
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
    } else {
        req = new ActiveXObject("Microsoft.XMLHTTP");
    }
    req.open('POST', 'buscar.php', true);
    req.setRequestHeader('Content-Type', contenttype);
    req.onreadystatechange = 
        function() { 
           if (req.readyState == 4)
               resultado.innerHTML = req.responseText;
        }
    req.send('q=' + escape(form.q.value));
}

function buscar_bytheme() {
    var form = document.forms['bytheme'];
    var resultado = document.getElementById("resultado_bytheme");
    var contenttype = 'application/x-www-form-urlencoded';

    var req;
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
    } else {
        req = new ActiveXObject("Microsoft.XMLHTTP");
    }
    req.open('POST', 'buscar_bytheme.php', true);
    req.setRequestHeader('Content-Type', contenttype);
    req.onreadystatechange = 
        function() { 
           if (req.readyState == 4)
               resultado.innerHTML = req.responseText;
        }
    req.send('subjects=' + escape(form.subjects.value));
}