全文获取类型
收费全文 | 994篇 |
免费 | 6篇 |
国内免费 | 14篇 |
专业分类
教育 | 507篇 |
科学研究 | 415篇 |
各国文化 | 4篇 |
体育 | 27篇 |
综合类 | 45篇 |
信息传播 | 16篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 47篇 |
2018年 | 66篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 18篇 |
2014年 | 63篇 |
2013年 | 43篇 |
2012年 | 79篇 |
2011年 | 91篇 |
2010年 | 64篇 |
2009年 | 89篇 |
2008年 | 80篇 |
2007年 | 67篇 |
2006年 | 67篇 |
2005年 | 51篇 |
2004年 | 31篇 |
2003年 | 34篇 |
2002年 | 26篇 |
2001年 | 15篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有1014条查询结果,搜索用时 15 毫秒
21.
含钒的化合物能够有效地催化H2O2,因此可作为多元Fenton-like催化剂中的有效组份之一,Fe2V4O13中存在Fe(Ⅲ)和V(V)同时和协同活化H2O2的可能性。通过液相合成法制备了Fe2V4O13,并对其对AOⅡ的催化活性进行了研究,研究表明,Fe2V4O13是一种新型高效稳定的多相Fenton-like催化剂。 相似文献
22.
We investigate the relationship between a firm’s compensation structure and the extent to which its innovation is more exploration versus exploitation oriented. Specifically, we assess two aspects of a firm’s compensation design—horizontal dispersion within job levels and vertical tournament incentives between job levels. A six-year panel of compensation records of 671,028 employees working at 81 U.S.-based high technology firms between 1997 and 2002 are used to construct measures that characterize a firm's pay structure, which are linked to these firms’ patents filed in the U.S. We find that firms with higher-powered tournament incentives in vertical compensation structure report higher fraction of innovation directed towards exploration. Horizontal pay dispersion, on the other hand, shows a negative relationship with the exploration in firms where R&D employees’ age variance is low. In firms where R&D employees’ age variance is high, the negative relationship between horizontal pay dispersion and exploration is muted. 相似文献
23.
Vietnam is an important case for studying the impact of foreign firms’ backward linkages on local firms’ productivity. As an emerging economy Vietnam became the second most popular FDI destination after China in Pacific Asia since 2014. Our empirical analysis for Vietnam as a whole demonstrates a significant difference in the productivity growth between domestic suppliers who have a direct linkage with foreign firms and non-suppliers. This is also true for the Southeast Region (SE) with Ho-Chi-Minh City as economic center. However, in the Red River Delta (RRD), that difference is not statistically significant. Based on in-depth interviews with domestic suppliers, we reveal that in the RRD, effects of foreign firms on the productivity upgrading of domestic suppliers are indirect and limited while internal factors like absorptive capacity are more important for the productivity growth. These regional differences can be traced back to different regional specializations which still persist from the pre-reform era. 相似文献
24.
李纪连 《大连教育学院学报》2001,17(4):54-55
介绍了用纳米———ZnFe2 O4/SiO2 半导体材料作光催化剂 ,用分子氧催化氧化环己烷的实验 ,根据目前所建立的半导体粒子光催化反应机理的模式 ,探讨了其反应机理 ,并进一步研究了水分子以及电子或空穴捕获剂对该反应的影响。 相似文献
25.
While the importance of a supportive context for entrepreneurship is widely acknowledged, its antecedents are rarely investigated. We apply the concept of organizational climate to higher education institutions and examine the drivers of students’ perceptions of the entrepreneurial climate in their university. Combining data from two unique datasets and using multilevel techniques, we analyze the relationship between university characteristics and such climate perceptions of 8009 students at public universities in Germany. We find university entrepreneurship measures to have a positive effect on students’ climate perceptions, which also depend on students’ background and gender. In addition, we find evidence for different peer effects, depending on students’ affinity for entrepreneurship. For the general student population, including entrepreneurship content in their normal studies seems to be required to initiate a social process of sensemaking. However, students’ perception of the entrepreneurial climate only depend to a certain degree on intentional entrepreneurship measures. In our study, general university characteristics have the strongest influence on climate perceptions. Overall, our study adds to our understanding of which parameters are important for establishing a more favorable and inspiring climate for becoming an entrepreneur at higher education institutions. 相似文献
26.
This study uses household survey data to estimate determinants of schooling in Uganda, with a model that includes the price of school. Uganda's universal education policy offered free tuition, fees, and supplies to up to four children per family, including two daughters. The empirical method includes an estimation of a child-specific price of schooling. Despite widespread subsidies, the cost of primary school remained an obstacle under this policy, but the effects of price were similar for boys and girls. Regressions by wealth quintile estimate nonlinear effects of wealth and price, suggesting that there are opportunities to expand education through targeted cash transfer and subsidy policies. 相似文献
27.
Annalisa Caloffi Marco Mariani Federica Rossi Margherita Russo 《Research Policy》2018,47(8):1437-1447
We analyse whether public subsidies supporting collaborative research and development (R&D) projects in small and medium-sized enterprises (SMEs) are able to encourage persistent R&D investment and interorganisational networking more than subsidies supporting individual R&D projects. Adopting a counterfactual approach to policy evaluation, we compare subsidies for collaborative R&D and for individual R&D implemented in the same Italian region in the same period. Our findings suggest that, once public support is no longer available, the two subsidies have different effects on different types of SMEs. If the policymakers’ objective is to increase the number of R&D-performing SMEs over time, they should provide subsidies for collaborative R&D to firms with modest R&D experience. If their objective is to increase the amount of spontaneous R&D investment over time, they should target SMEs with some prior R&D experience, using either subsidy. Finally, if their objective is to induce SMEs to network with external organisations, subsidies for collaborative R&D projects should be preferred to subsidies for individual R&D projects. 相似文献
28.
采用湿化学/高温煅烧法制备ZrV2O7粉末,并以其和金属Al粉为原料,利用粉末冶金法的堆层技术制备ZrV2O7/Al复合梯度材料。通过XRD、SEM抗热震性实验分析,研究了材料的组织及强度。结果表明:湿化学/高温煅烧法制备的ZrV2O7粉末纯度高;在ZrV2O7/Al复合梯度材料中沿梯度材料纵截面方向的成分梯度过渡明显,各层之间结合紧密。热震性实验表明,ZrV2O7/Al梯度材料的耐高温强度高,各层之间粘结性好。 相似文献
29.
利用Windows的DLL(动态连接库)和全局共享内存技术来建立系统实时数据库的设计思想,采取传统数据库系统、文件系统和内存数据库系统兼用,利用多种存储介质来构造系统的实时数据库系统,并通过给用户提供一套接口标准——实时数据库系统接口,来实现I/O驱动程序与用户程序和实时数据库系统间的高速数据传递。 相似文献
30.
This article develops a general framework to describe the changes in university IPR regulations in Europe and their effects on the patenting activities of universities and on knowledge transfer processes. Understanding the effects of changes in IPR regulations on academic patenting is a complex issue, and parallels with the US case can be misleading. First, despite the general trend towards institutional ownership, university IPR regulations in Europe remain extremely differentiated and there is no one-to-one mapping to the US system. Second, it is difficult to disentangle the quantitative and qualitative effects of changes in IPR ownership regulations on academic patenting activities from the effects of concurrent transformations in the institutional, cultural and organizational landscape surrounding academic knowledge transfer. The article proposes a review and typological classification of national university IPR ownership systems on the basis of their development since 2000, and uses it to analyze the aggregate dynamics of academic patent ownership in several European countries. The analysis of patterns of ownership of academic patents shows that there has been a general increase in university patenting since 1990, with a significant slowdown (and even reduction in some countries) after early 2000s accompanied by a switch in academic patents ownership in favor of university ownership though preserving the European specificity of high company ownership of academic invented patents. 相似文献