全文获取类型
收费全文 | 876篇 |
免费 | 28篇 |
国内免费 | 47篇 |
专业分类
教育 | 409篇 |
科学研究 | 406篇 |
各国文化 | 16篇 |
体育 | 45篇 |
综合类 | 20篇 |
文化理论 | 2篇 |
信息传播 | 53篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 40篇 |
2018年 | 53篇 |
2017年 | 29篇 |
2016年 | 14篇 |
2015年 | 38篇 |
2014年 | 56篇 |
2013年 | 82篇 |
2012年 | 63篇 |
2011年 | 76篇 |
2010年 | 52篇 |
2009年 | 47篇 |
2008年 | 47篇 |
2007年 | 44篇 |
2006年 | 44篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 6篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
排序方式: 共有951条查询结果,搜索用时 15 毫秒
861.
862.
863.
Chang-Yang Lee 《Research Policy》2009,38(5):861-870
This paper aims to contribute to the literature on the long-debated relationship between market competition and firm research and development (R&D) by investigating the effect of competitive market pressure on firms’ incentives to invest in R&D. The paper shows that a firm's R&D response to competitive market pressure depends primarily on its level of technological competence or R&D productivity: firms with high levels of technological competence tend to respond aggressively (i.e., exhibit a higher level of R&D efforts) to intensifying competitive market pressure, while firms with low levels of technological competence tend to respond submissively (i.e., exhibit a lower level of R&D efforts). The differential effect of competitive market pressure on firm R&D, conditioned primarily by the level of firms’ technological competence, is empirically supported by unique firm-level data from the World Bank. Furthermore, the role of firm-specific technological competence in conditioning the R&D-competition relationship is more evident and statistically more significant for firms facing consumers whose utility is relatively more elastic to product quality than to price. 相似文献
864.
Determinants of environmental innovation—New evidence from German panel data sources 总被引:1,自引:0,他引:1
Jens Horbach 《Research Policy》2008,37(1):163-173
In most cases, empirical analyses of environmental innovations based on firm-level data relied on surveys for one point in time. These surveys allow for the inclusion of many explanatory variables such as different policy instruments or the influence of pressure groups but it is not possible to address the dynamic character of environmental innovations. This paper uses two German panel databases, the establishment panel of the Institute for Employment Research (IAB) and the Mannheim innovation panel (MIP) of the Centre for European Economic Research (ZEW), to explore the determinants of environmental innovations. The econometric estimations show that the improvement of the technological capabilities (“knowledge capital”) by R&D triggers environmental innovations. Environmental regulation, environmental management tools and general organizational changes also encourage environmental innovation, a result that has also been postulated by the famous Porter-hypothesis. 相似文献
865.
本文在DEA中的C2R模型的基础上,针对决策单元输入与输出为区间上的连续函数,建立了在一个时间区间[0,1]内评价决策单元间的相对有效性的连续模型以及与之等价的模型,同时给出了决策单元的效率定义和弱DEA有效、DEA有效的定义。为经济管理中相关问题的研究与解决提供了一种新的方法。 相似文献
866.
新型研发机构能有效发挥自身技术优势,组建创投基金实现金融资本的持续性增值。本文从股权分配、控制度和开放性角度,将创投基金发展模式分为独立控制、控股组建和合资管理三种类型,新型研发机构应根据发展阶段、资本规模、技术成熟度选择合适的发展模式。基于双方存在的委托代理关系,提出创投基金在运营上采用了二元决策机制、增值服务管理机制、利益分配机制、投资监管机制、信息传递机制,有效实现了新型研发机构对创投基金决策行为的激励和约束。最后,提出政府应深化管理机制创新,强化培育和监管,积极引进社会资本,提高创投基金的管理能力和运作效率。 相似文献
867.
基于文献含油制冷剂R600a两相流动摩擦压降实验数据,采用文献中6种关联式模型对含油制冷剂R600a两相摩擦压降的实验数据进行预测判断。结果表明:油影响因子模型Schlager关联式和Eckel关联式的预测值与实验值平均绝对偏差分别为27.3%和24.4%;混合物性的两相增强因子模型Zurcher关联式和Hu关联式的预测值与实验值的平均绝对偏差分别为33.8%和34.0%,上述关联式预测值普遍低于实验值。 相似文献
868.
We investigate the effect of Europe's largest multilateral subsidy program for R&D-performing small and medium-sized enterprises. The program applied a specific budget allocation rule, referred to as Virtual Common Pot (VCP), which is designed to avoid cross-subsidization between participating countries. This rule creates exogenous variation in funding status and allows us to identify the causal effect of public R&D grants on firm growth. In addition, we compare the program's effect under the VCP rule with the standard situation of a Real Common Pot (RCP), in which program authorities allocate a single budget according to uniform project evaluation criteria. Our estimates suggest that R&D grants had no average effect on job creation and sales growth, but treatment effects were heterogeneous and positive for high-quality projects. Under an RCP the program would have created 53% more jobs and 48% higher sales. 相似文献
869.
The paper focuses on cluster policies with particular attention to the role of R&D collaborative incentives in the structuring of knowledge networks in clusters. We disentangle the main network failures in regional innovation systems, and discuss the selection procedures designed by policy makers to foster knowledge collaborations. We draw evidence from the French Aerospace Valley cluster from 2006 to 2015. The case study is based on a dataset of 248 granted research consortia, from which we build 4-cohort knowledge networks that enable us evidencing the evolving structural properties of the cluster over time. We suggest avoiding the bias and limitations of 1 and 2-mode network analysis by developing an original place-based network methodology that emphasizes on structural equivalence and groups’ behaviors. We discuss the results focusing on the convergence degree between the structural properties of the cluster selected by the Program and the policy makers’ objectives. Finally, the methodology allows us to identify the agents of the structural and technological changes observed throughout the period. 相似文献
870.
一种电能收集充电器模型的设计 总被引:1,自引:0,他引:1
陆春妹 《苏州市职业大学学报》2010,21(3):23-25
设计了一种电能收集充电器模型,该充电器的核心为直流电源变换器,将从直流电源中吸收的电能转移到可充电电池充电中.系统根据输入电压不同采用HT7712和HT7750来构建充电控制电路,通过HT46E47单片机进行功率最大点的监测.直流电源输入电压为20V时候,实现以最大144.95mA的电流向可充电池充电;直流电源电压下降到0.13V时,系统依然实现对可充电池充电;同时系统具有实现自动启动充电等功能. 相似文献