Django:syncdb无法在数据库中添加任何模型

我是Django的新手，无法将任何模型添加到我的DB中？？好的，这是投资组合模型：

from django.db import models
from core.models import Unit

# Create your models here.
class Portfolio(models.Model):
    """
    Generic class to portfolios
    """
    name = models.CharField(_('Name'), max_length=255)
    youtube_id = models.CharField(_('Youtube_id'), max_length=255)
    url_doc = models.CharField(_('Url_doc'), max_length=255)
    data = models.TextField()
    unit = models.ForeignKey(Unit, verbose_name=_('Unit'), null=True, blank=True,     related_name='portfolios')
    comment = models.TextField(_('Comment'), blank=True)
    class Meta:
        verbose_name = _('Portfolio')
        verbose_name_plural = _('Portfolios')
        ordering = [('id')]
        abstract = True
    def __unicode__(self):
        return u'%s' % (self.name)

这是python manage.py syncdb:的结果

Syncing...
Creating tables ...
Installing custom SQL ...
Installing indexes ...
Installed 0 object(s) from 0 fixture(s)

一切都很好，但表没有创建！！！！

这是setting.py文件：

DATABASES = {
'default': {
    'ENGINE': 'django.db.backends.sqlite3',  # Add 'postgresql_psycopg2', 'mysql', 'sqlite3' or 'oracle'.
    'NAME': 'timtec.sqlite',                # Or path to database file if using sqlite3.
    # The following settings are not used with sqlite3:
    'USER': '',
    'PASSWORD': '',
    'HOST': '',                      
# Empty for localhost through domain sockets or '127.0.0.1' for localhost through TCP.
    'PORT': '',  
             # Set to empty string for default.
  }
 }                                                     
 INSTALLED_APPS = (
'django_extensions',
'south',
'pipeline',
'suit',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.sites',
'django.contrib.messages',
'django.contrib.staticfiles',
'django.contrib.flatpages',
'django.contrib.admin',
# Uncomment the next line to enable admin documentation:
'django.contrib.admindocs',
'rest_framework',
'rosetta',
'autoslug',
'core',
'accounts',
'activities',
'administration',
'forum',
'course_material',
'notes',
'reports',
'portfolio',
'metron',
'allauth',
'allauth.account',
'allauth.socialaccount',
'allauth.socialaccount.providers.facebook',
'django_markdown',
# raven has to be the last one
'raven.contrib.django.raven_compat',
)

谢谢：）