这样就把上面的隐藏起来了

.navbar .dropdown-menu:before {
   display:none;
}
.navbar .dropdown-menu:after {
   display:none;
}

使用jQuery会更好:

jQuery('ul.nav li.dropdown').hover(function() {
  jQuery(this).find('.dropdown-menu').stop(true, true).show();
  jQuery(this).addClass('open');
}, function() {
  jQuery(this).find('.dropdown-menu').stop(true, true).hide();
  jQuery(this).removeClass('open');
});

在我看来，最好的办法是这样的:

;(function($, window, undefined) {
    // Outside the scope of the jQuery plugin to
    // keep track of all dropdowns
    var $allDropdowns = $();

    // If instantlyCloseOthers is true, then it will instantly
    // shut other nav items when a new one is hovered over
    $.fn.dropdownHover = function(options) {

        // The element we really care about
        // is the dropdown-toggle's parent
        $allDropdowns = $allDropdowns.add(this.parent());

        return this.each(function() {
            var $this = $(this),
                $parent = $this.parent(),
                defaults = {
                    delay: 500,
                    instantlyCloseOthers: true
                },
                data = {
                    delay: $(this).data('delay'),
                    instantlyCloseOthers: $(this).data('close-others')
                },
                settings = $.extend(true, {}, defaults, options, data),
                timeout;

            $parent.hover(function(event) {

                // So a neighbor can't open the dropdown
                if(!$parent.hasClass('open') && !$this.is(event.target)) {
                    return true;
                }

                if(settings.instantlyCloseOthers === true)
                    $allDropdowns.removeClass('open');

                window.clearTimeout(timeout);
                $parent.addClass('open');
            }, function() {
                timeout = window.setTimeout(function() {
                    $parent.removeClass('open');
                }, settings.delay);
            });

            // This helps with button groups!
            $this.hover(function() {
                if(settings.instantlyCloseOthers === true)
                    $allDropdowns.removeClass('open');

                window.clearTimeout(timeout);
                $parent.addClass('open');
            });

            // Handle submenus
            $parent.find('.dropdown-submenu').each(function(){
                var $this = $(this);
                var subTimeout;
                $this.hover(function() {
                    window.clearTimeout(subTimeout);
                    $this.children('.dropdown-menu').show();

                    // Always close submenu siblings instantly
                    $this.siblings().children('.dropdown-menu').hide();
                }, function() {
                    var $submenu = $this.children('.dropdown-menu');
                    subTimeout = window.setTimeout(function() {
                        $submenu.hide();
                    }, settings.delay);
                });
            });
        });
    };

    $(document).ready(function() {
        // apply dropdownHover to all elements with the data-hover="dropdown" attribute
        $('[data-hover="dropdown"]').dropdownHover();
    });
})(jQuery, this);

样本的标记:

<li class="dropdown">
    <a href="#" class="dropdown-toggle" data-toggle="dropdown" data-hover="dropdown" data-delay="1000" data-close-others="false">
        Account <b class="caret"></b>
    </a>
    <ul class="dropdown-menu">
        <li><a tabindex="-1" href="#">My Account</a></li>
        <li class="divider"></li>
        <li><a tabindex="-1" href="#">Change Email</a></li>
        <li><a tabindex="-1" href="#">Change Password</a></li>
        <li class="divider"></li>
        <li><a tabindex="-1" href="#">Logout</a></li>
    </ul>
</li>

这样就把上面的隐藏起来了

.navbar .dropdown-menu:before {
   display:none;
}
.navbar .dropdown-menu:after {
   display:none;
}

jQuery的解决方案是好的，但它将需要处理点击事件(移动或平板电脑)悬停将无法正常工作…也许可以做一些窗口重新大小检测?

安德烈斯·伊里奇的回答似乎很有效，但它应该被包装在一个媒体问题中:

@media (min-width: 980px) {

    .dropdown-menu .sub-menu {
        left: 100%;
        position: absolute;
        top: 0;
        visibility: hidden;
        margin-top: -1px;
    }

    .dropdown-menu li:hover .sub-menu {
        visibility: visible;
    }

    .dropdown:hover .dropdown-menu {
        display: block;
    }

    .nav-tabs .dropdown-menu, .nav-pills .dropdown-menu, .navbar .dropdown-menu {
        margin-top: 0;
    }

    .navbar .sub-menu:before {
        border-bottom: 7px solid transparent;
        border-left: none;
        border-right: 7px solid rgba(0, 0, 0, 0.2);
        border-top: 7px solid transparent;
        left: -7px;
        top: 10px;
    }
    .navbar .sub-menu:after {
        border-top: 6px solid transparent;
        border-left: none;
        border-right: 6px solid #fff;
        border-bottom: 6px solid transparent;
        left: 10px;
        top: 11px;
        left: -6px;
    }
}

你可以使用默认的$().dropdown('toggle')方法来切换悬停时的下拉菜单:

$(".nav .dropdown").hover(function() {
  $(this).find(".dropdown-toggle").dropdown("toggle");
});