首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14266篇
  免费   60篇
教育   11113篇
科学研究   1274篇
各国文化   53篇
体育   447篇
综合类   1篇
文化理论   398篇
信息传播   1040篇
  2023年   17篇
  2022年   23篇
  2021年   40篇
  2020年   86篇
  2019年   107篇
  2018年   2287篇
  2017年   2206篇
  2016年   1691篇
  2015年   188篇
  2014年   230篇
  2013年   748篇
  2012年   292篇
  2011年   757篇
  2010年   888篇
  2009年   499篇
  2008年   707篇
  2007年   1208篇
  2006年   140篇
  2005年   447篇
  2004年   521篇
  2003年   382篇
  2002年   175篇
  2001年   36篇
  2000年   44篇
  1999年   40篇
  1998年   31篇
  1997年   41篇
  1996年   47篇
  1995年   23篇
  1994年   35篇
  1993年   22篇
  1992年   24篇
  1991年   21篇
  1990年   22篇
  1989年   16篇
  1988年   12篇
  1987年   21篇
  1986年   13篇
  1985年   21篇
  1984年   16篇
  1983年   12篇
  1982年   22篇
  1981年   11篇
  1980年   13篇
  1979年   22篇
  1978年   11篇
  1977年   15篇
  1976年   10篇
  1975年   11篇
  1974年   11篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The migration from print books to ebooks is more than a change of format; it is also the first step in an ongoing process, whose final outcome is hard to predict. Ebooks are likely to lead to a restructuring of the industry by enabling cross-border commerce. This in turn is likely to lead to difficult disputes over territorial rights. It appears probable that these disputes will be resolved by an assertion of the dominance of the American market and the publishers that already serve it well, as authors are likely to place their rights with practitioners in the largest markets. This in turn will lead to the acquisition of many smaller “national” publishers, which cannot compete on a world stage with truly global publishers. But rather than simply becoming sources of editorial product for American-based global marketing machines, smaller publishers operating in different regions will respond through innovation, both in product design (attempting to do electronically what cannot be done in print) and in developing new marketing plans that the giant publishers would be indisposed to pursue.  相似文献   
992.
The forces for change in the 600 hundred-year history of book publishing have never been more powerful and fundamental than in 2011. Barely 12 months ago, what publishers viewed as “innovation” was the creation of digitized versions of physical books to be ‘consumed’ on e-reading devices. As 2011 begins, that change is largely regarded as accepted business practice, and the edge of “innovation” is moving in more complex directions. Publishing finds itself in the midst of a ‘phase shift’ from the scarcity model of print to a complex, new world of digital abundance. The dimensions of change, moreover, its speed, and its extent are still unknown. While book publishing begins with the creative work of authors, digital technologies are turning the business models inside out. Among the forces for change acting on book publishing, this article examines several phenomena that are working their way in from the edge to the center of the industry, including complex interwoven considerations around container, context, and customer.  相似文献   
993.
The critical task of predicting clicks on search advertisements is typically addressed by learning from historical click data. When enough history is observed for a given query-ad pair, future clicks can be accurately modeled. However, based on the empirical distribution of queries, sufficient historical information is unavailable for many query-ad pairs. The sparsity of data for new and rare queries makes it difficult to accurately estimate clicks for a significant portion of typical search engine traffic. In this paper we provide analysis to motivate modeling approaches that can reduce the sparsity of the large space of user search queries. We then propose methods to improve click and relevance models for sponsored search by mining click behavior for partial user queries. We aggregate click history for individual query words, as well as for phrases extracted with a CRF model. The new models show significant improvement in clicks and revenue compared to state-of-the-art baselines trained on several months of query logs. Results are reported on live traffic of a commercial search engine, in addition to results from offline evaluation.  相似文献   
994.
Empirical modeling of the score distributions associated with retrieved documents is an essential task for many retrieval applications. In this work, we propose modeling the relevant documents’ scores by a mixture of Gaussians and the non-relevant scores by a Gamma distribution. Applying Variational Bayes we automatically trade-off the goodness-of-fit with the complexity of the model. We test our model on traditional retrieval functions and actual search engines submitted to TREC. We demonstrate the utility of our model in inferring precision-recall curves. In all experiments our model outperforms the dominant exponential-Gaussian model.  相似文献   
995.
We first present in this paper an analytical view of heuristic retrieval constraints which yields simple tests to determine whether a retrieval function satisfies the constraints or not. We then review empirical findings on word frequency distributions and the central role played by burstiness in this context. This leads us to propose a formal definition of burstiness which can be used to characterize probability distributions with respect to this phenomenon. We then introduce the family of information-based IR models which naturally captures heuristic retrieval constraints when the underlying probability distribution is bursty and propose a new IR model within this family, based on the log-logistic distribution. The experiments we conduct on several collections illustrate the good behavior of the log-logistic IR model: It significantly outperforms the Jelinek-Mercer and Dirichlet prior language models on most collections we have used, with both short and long queries and for both the MAP and the precision at 10 documents. It also compares favorably to BM25 and has similar performance to classical DFR models such as InL2 and PL2.  相似文献   
996.
To evaluate Information Retrieval Systems on their effectiveness, evaluation programs such as TREC offer a rigorous methodology as well as benchmark collections. Whatever the evaluation collection used, effectiveness is generally considered globally, averaging the results over a set of information needs. As a result, the variability of system performance is hidden as the similarities and differences from one system to another are averaged. Moreover, the topics on which a given system succeeds or fails are left unknown. In this paper we propose an approach based on data analysis methods (correspondence analysis and clustering) to discover correlations between systems and to find trends in topic/system correlations. We show that it is possible to cluster topics and systems according to system performance on these topics, some system clusters being better on some topics. Finally, we propose a new method to consider complementary systems as based on their performances which can be applied for example in the case of repeated queries. We consider the system profile based on the similarity of the set of TREC topics on which systems achieve similar levels of performance. We show that this method is effective when using the TREC ad hoc collection.  相似文献   
997.
We study the problem of web search result diversification in the case where intent based relevance scores are available. A diversified search result will hopefully satisfy the information need of user-L.s who may have different intents. In this context, we first analyze the properties of an intent-based metric, ERR-IA, to measure relevance and diversity altogether. We argue that this is a better metric than some previously proposed intent aware metrics and show that it has a better correlation with abandonment rate. We then propose an algorithm to rerank web search results based on optimizing an objective function corresponding to this metric and evaluate it on shopping related queries.  相似文献   
998.
999.
As new media technologies and platforms emerge and take hold in our society, traditional publishers are wondering: What’s in this new content climate for me? The simple answer is: a lot. The digital world, mobile content delivery mechanisms and the public’s increasing comfort—even preference for—a media menu from which they can pick and choose what they want and how they want to receive it, brings exciting and potentially lucrative opportunities. For publishers who understand how to leverage their brand and create authentic, identifiable value in the eyes of the customer, risk can be reduced and new revenue streams built. Here are four best practices to position your publishing company for growth.  相似文献   
1000.
Updated from a presentation given at Biblionext.it in Rome in April 2011, this article will highlight The New York Public Library’s success with e-books and other forms of popular e-content and our efforts to stay one step ahead of the consumer shift from print reading to e-reading. Consumer e-reading is dominated by Amazon.com in the US, followed by one of the largest chain bookstores, BarnesandNoble.com. The availability of digital versions of very popular titles, coupled with the explosion of e-readers, tablets, and smartphones that are priced competitively and fairly easy to use, are helping move a lot of Americans into the e-book world. Last month, Amazon.com announced they sold more e-books than physical books for the first time ever. Print books are not going away, but our experience is that it is clear e-books are no longer just an extra format to offer, they are integral to our future.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号