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   12120篇
  免费   20篇
教育   9417篇
科学研究   1227篇
各国文化   8篇
体育   379篇
文化理论   384篇
信息传播   725篇
  2023年   5篇
  2022年   6篇
  2021年   8篇
  2020年   14篇
  2019年   23篇
  2018年   2196篇
  2017年   2103篇
  2016年   1595篇
  2015年   129篇
  2014年   135篇
  2013年   212篇
  2012年   234篇
  2011年   710篇
  2010年   851篇
  2009年   450篇
  2008年   653篇
  2007年   1167篇
  2006年   88篇
  2005年   408篇
  2004年   458篇
  2003年   376篇
  2002年   136篇
  2001年   13篇
  2000年   29篇
  1999年   12篇
  1997年   22篇
  1996年   8篇
  1995年   7篇
  1994年   2篇
  1993年   6篇
  1992年   3篇
  1991年   14篇
  1990年   2篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   2篇
  1985年   2篇
  1983年   2篇
  1982年   5篇
  1981年   2篇
  1979年   4篇
  1977年   4篇
  1976年   4篇
  1975年   3篇
  1971年   3篇
  1969年   2篇
  1859年   2篇
  1835年   4篇
  1828年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
In this study, an electro-mechanical valve (EMV) system for the intake valve ofa fottr stroke, single cylinder, overhead valve and spark ignition (SI) engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption (BSFC). A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons (HC) and NOx emissions increased by 12% and 13% respectively.  相似文献   
942.
Temporal variation of dynamical modal properties of a base-isolated building is investigated using earthquake records in the building. A batch processing least-squares estimation method is applied to segment-wise time-series data. To construct an input-output system, an auto-regressive model with exogenous input (ARX) of second-order including a forgetting coefficient as a weighting coefficient is used for the estimation of modal parameters. The fundamental and second natural frequencies and the damping ratios of the fundamental and second natural modes of the base-isolated building are identified in the time domain. The identified results are consistent with the results obtained from the micro-tremor vibration data, forced-vibration test data and earthquake records in the present base-isolated building in the case of taking into account the amplitude-dependency of the iso- lators and viscous dampers. It is finally pointed out that several factors, e.g., amplitude dependency of the isolator and damper system and special characteristics of the series-type viscous damper system, may be related complicatedly with the temporal variation in modal properties of the above-mentioned system.  相似文献   
943.
The aim of this study was to design and construct an improved response surface method (RSM) based on weighted regression for the anti-slide reliability analysis of concrete gravity dam. The limitation and lacuna of the traditional RSM were briefly analyzed. Firstly, based on small experimental points, research was devoted to an improved RSM with singular value decomposition techniques. Then, the method was used on the basis of weighted regression and deviation coefficient correction to reduce iteration times and experimental points and improve the calculation method of checking point. Finally, a test example was given to verify this method. Compared with other conventional algorithms, this method has some strong advantages: this algorithm not only saves the arithmetic operations but also greatly enhances the calculation efficiency and the storage efficiency.  相似文献   
944.
Niels C. Taubert 《Minerva》2012,50(3):261-275
This article analyzes the transformation of Minerva from an intellectual towards a scholarly journal by making use of bibliometric methods. The aim is to provide some empirical insights that help to understand what properties of the journal changed in the course of this transformation process. Minerva was one of the first journals that reflected on science and its role in society and science policy in particular. Analyzing the development of the journal sheds light on the emergence of science (policy) studies and on Minerva’s role as a forerunner in this field. In a first step, the methods will be described. The second section provides some empirical results of the publication output of Minerva and its relations to other journals in the field. The empirical findings are put into a broader perspective in the concluding third section.  相似文献   
945.
Elena Aronova 《Minerva》2012,50(3):307-337
The Congress for Cultural Freedom is remembered as a paramount example of the “cultural cold wars.” In this paper, I discuss the ways in which this powerful transnational organization sought to promote “science studies” as a distinct – and politically relevant – area of expertise, and part of the CCF broader agenda to offer a renewed framework for liberalism. By means of its Study Groups, international conferences and its periodicals, such as Minerva, the Congress developed into an influential forum for examining the ways Big Science impacted the relations between science, society, and politics, thus constituting a semi-institutional niche for Science Studies before its professionalization within academia during the 1970s. I argue that the Congress contributed to the construction of public space in which the relations between science, society and politics were debated, and science was reconceptualized as a social activity. The vision of “science studies” the CCF-associated intellectuals promulgated was different from the science studies we know today. Yet, this alternative vision, in which the issues of science politics appeared inseparable from those of science policy, science organization, and science governance, constituted the “pre-history” of science studies today.  相似文献   
946.
947.
Differences in racial socialization practices and their effects were examined in a sample of 241 African American 1st graders (average age 6.59 years) living in an urban area. Child outcomes included cognitive development, receptive language skills, and child problem behavior. The cultural environment of the home was associated with higher cognitive scores for boys living in high negative social climate and low social capital neighborhoods and for girls living in high social capital neighborhoods. The positive association of promotion of mistrust and child behavior problems was magnified in neighborhoods that had low levels of social capital. A high negative social climate in the neighborhood attenuated the positive association between preparation for bias/promotion of mistrust and externalizing problems.  相似文献   
948.
A concise review is presented of the essential elements of the book publishing and bookselling business in a complex and diverse market. Demographics create the diversity while Arabic is the one language spoken across a multitude of different countries. Three features are common to all of these countries and they are: the dominance of English as the second language, education has and will remain to be a priority, and economic pressures cause price sensitivity to be a major challenge especially in the educational market segments. It is the price sensitivity as a key factor for the lack of respect for intellectual property and copyright regulations. A review of distribution and retail stores is a very important topic in relation to this complex collection of countries. The emergence of e-books is discussed especially in the educational, professional and reference market segments. Finally, there is a review of the Arabic language publishers and local book fairs to bring this article to closure.  相似文献   
949.
950.
We explore the feasibility of automatically identifying sentences in different MEDLINE abstracts that are related in meaning. We compared traditional vector space models with machine learning methods for detecting relatedness, and found that machine learning was superior. The Huber method, a variant of Support Vector Machines which minimizes the modified Huber loss function, achieves 73% precision when the score cutoff is set high enough to identify about one related sentence per abstract on average. We illustrate how an abstract viewed in PubMed might be modified to present the related sentences found in other abstracts by this automatic procedure.  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