How to make search engine traffic to view one question page like on quora?

Question

Now there is an option to show question pages only to registered members.

How can I make people coming from search engine directly to a question page to view the answers? But whenever they click on another question page, then the page should prompt for a login. That's the success of Quora.

Comments

No need of a login prompt. The message 'log in to view' we already have is more than enough

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Oh ok. Then I would advice you to implement a custom plugin to make it work that way, which would exceed the complexity of an answer

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Actually we can make it by adding a modal pop-up on window click. Inside the modal a login form should be there. But the problem is a JavaScript disabled browser can access all pages.

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Another best option is enabling a modal pop-up with login form, only on the question pages with a timer function. Open login form can be used inside a modal window.