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   5099篇
  免费   85篇
  国内免费   173篇
教育   3316篇
科学研究   993篇
各国文化   9篇
体育   378篇
综合类   374篇
文化理论   3篇
信息传播   284篇
  2024年   1篇
  2023年   25篇
  2022年   50篇
  2021年   78篇
  2020年   103篇
  2019年   67篇
  2018年   47篇
  2017年   56篇
  2016年   55篇
  2015年   112篇
  2014年   257篇
  2013年   332篇
  2012年   360篇
  2011年   464篇
  2010年   394篇
  2009年   434篇
  2008年   411篇
  2007年   434篇
  2006年   378篇
  2005年   293篇
  2004年   225篇
  2003年   187篇
  2002年   144篇
  2001年   111篇
  2000年   78篇
  1999年   59篇
  1998年   26篇
  1997年   38篇
  1996年   27篇
  1995年   18篇
  1994年   22篇
  1993年   21篇
  1992年   14篇
  1991年   6篇
  1990年   5篇
  1989年   3篇
  1988年   2篇
  1985年   5篇
  1984年   3篇
  1982年   5篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
  1957年   2篇
排序方式: 共有5357条查询结果,搜索用时 0 毫秒
61.
本文以国内经济管理领域 2003年至2019 年的179篇文献为样本,使用系统性文献回顾法(SLR),探索和总结了新型研发机构的研究现状及其知识结构,分析现有研究的缺失并尝试寻找未来的研究趋势。研究发现: 第一,新型研发机构的知识结构由9个部分构成一个2W1H的主题研究框架。第二,从国家、产业和企业层面分别总结了阻碍新型研发机构发展的因素及其提升对策建议。第三,从研究知识模块、研究切入角度和研究趋势拓展3个方面解剖现有知识断层,并对未来的研究提出具体可行的对策建议  相似文献   
62.
Topic evolution has been described by many approaches from a macro level to a detail level, by extracting topic dynamics from text in literature and other media types. However, why the evolution happens is less studied. In this paper, we focus on whether and how the keyword semantics can invoke or affect the topic evolution. We assume that the semantic relatedness among the keywords can affect topic popularity during literature surveying and citing process, thus invoking evolution. However, the assumption is needed to be confirmed in an approach that fully considers the semantic interactions among topics. Traditional topic evolution analyses in scientometric domains cannot provide such support because of using limited semantic meanings. To address this problem, we apply the Google Word2Vec, a deep learning language model, to enhance the keywords with more complete semantic information. We further develop the semantic space as an urban geographic space. We analyze the topic evolution geographically using the measures of spatial autocorrelation, as if keywords are the changing lands in an evolving city. The keyword citations (keyword citation counts one when the paper containing this keyword obtains a citation) are used as an indicator of keyword popularity. Using the bibliographical datasets of the geographical natural hazard field, experimental results demonstrate that in some local areas, the popularity of keywords is affecting that of the surrounding keywords. However, there are no significant impacts on the evolution of all keywords. The spatial autocorrelation analysis identifies the interaction patterns (including High-High leading, High-Low suppressing) among the keywords in local areas. This approach can be regarded as an analyzing framework borrowed from geospatial modeling. Moreover, the prediction results in local areas are demonstrated to be more accurate if considering the spatial autocorrelations.  相似文献   
63.
本文总结了近年来国内外文献ZrV2O7研究进展,讨论了常用的合成方法以及负热膨胀的机理。并介绍了ZrV2O7复合陶瓷的研制与应用,指出了负热膨胀材料ZrV2O7潜在的应用领域,并对其发展趋势和应用前景进行了预测。  相似文献   
64.
张涛 《情报探索》2010,(1):101-104
以实例介绍了Struts2在数字图书馆中的应用。  相似文献   
65.
This paper deals with the stability and dissipative problem of a class of stochastic hybrid system. The system under study involves Markovian jump, impulsive effects and time delay, which are often encountered in practice and are the sources of instability. Our attention is focused on analysis of whether the stochastic hybrid system with time-delay is stochastically asymptotically stable and strictly (Q, S, R) dissipative. By introducing an extra artificial time instance, the equivalent system is obtained and the sufficient conditions are derived by using linear matrix inequality (LMI) techniques. The main results of this paper unify the existing results on H control.  相似文献   
66.
当前化学防火材料耐火极限较低,且成本较高。设计一种新型的有机防火材料,结合传统的有机植物纤维防火材料和酚醛FRP型防火材料的优点,采用酚醛植物纤维素粘附CO2技术得到一种新型防火材料。以活化的天然酚醛聚合材料为聚阴离子性正极材料,并把有机植物纤维素溶解到超临界溶剂中,研究其化学平衡和极相平衡,通过化学反应产生一种惰性液相介质,采用固相辅助回流法合成新型的酚醛植物纤维素。材料在受到高温燃烧过程中形成活性电子极性传导性差,能有效吸附CO2,阻止燃烧。通过实验和性能测试验证了该防火材料的良好性能,防火能力和抵抗时间增强。  相似文献   
67.
S. Negassi 《Research Policy》2004,33(3):365-384
The scope of this paper is to report new empirical evidence on the determinants of R&D co-operation. Indeed, the literature on the capabilities of firms emphasises the role of knowledge in the performance and evolution of firms who use knowledge developed in others to build their own knowledge capital. R&D co-operation between firms is one of the many strategies by which this knowledge may be transmitted. Several theoretical models have stressed that R&D co-operation is more likely when the level of spillovers is high. While this supposition is used in many theoretical models, it has rarely been tested before. Our results do not lend strong support to this intuition. Indeed, our spillover variables (national pure spillovers, national rent spillovers and imports of machine tools), which were supposed to match the theoretical notion of spillovers used in these theoretical models have a positive but not a significant role when explaining R&D co-operation. The R&D co-operation increases with size and with R&D intensity, but not with market share. It also increases with the budget spent on paying license fees and on acquiring patents and labour from foreign firms. In this study, we also analyse the determinants of innovation. In more precise terms, we compare the effects of R&D co-operation to those played by traditional internal factors and those exerted by external, pure and rent spillovers on the innovation capacity of the firms. Our results show that the commercial success of innovations of French firms depends mainly on size, market share, R&D intensity and human capital. Inward FDI from industrialised countries exerts a positive and significant effect. The finding highlights the important role of the absorptive capacity of firms. Spillover measurements, such as the acquisition of machine tools, foreign patents, licenses, and technological opportunities have a positive impact on innovation.  相似文献   
68.
人体有氧能力的研究   总被引:3,自引:1,他引:3  
本文概述了国内外有关儿童少年最大吸氧量的自然增长规律及其性别差异;并着重阐述了人体有氧能力与耐力运动项目成绩的关系。并根据研究数据和国内外学者的同类研究的数据,进行非线性回归模型的最小二乘拟合,建立了予测13~岁男性最大摄氧量的公式。本文还首次提出了最大摄氧量平台(VO2maxPD)的概念,进而深入的讨论了VO2max、VO2maxPD和VO2AT三者的关系。  相似文献   
69.
9——18岁学生最大吸氧量的纵向研究   总被引:5,自引:0,他引:5  
本文采用复盖式纵向研究法,对9—18岁男女学生的最大吸氧量进行连续4年的直接测定,分析研究了其自然发展规律及年龄、性别特征。  相似文献   
70.
This article develops and tests a model examining the relationship between firm globalization, scope of e-commerce use, and firm performance, using data from a large-scale cross-country survey of firms from three industries. We find that globalization leads to both greater scope of e-commerce use and improved performance, measured as efficiency, coordination, and market impacts. Scope of e-commerce use also leads to greater firm performance of all three types. Globalization has differential effects on B2B and B2C e-commerce, however, such that highly global firms are more likely to do B2B but less likely to do B2C. Our findings provide support for Porter's (1986) thesis that upstream business activities (namely, B2B) are more global while downstream business activities (B2C) are more local or multidomestic.  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