全文获取类型
收费全文 | 313篇 |
免费 | 41篇 |
国内免费 | 14篇 |
专业分类
化学 | 141篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 26篇 |
数学 | 174篇 |
物理学 | 17篇 |
出版年
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 39篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 19篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 28篇 |
2012年 | 19篇 |
2011年 | 12篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有368条查询结果,搜索用时 171 毫秒
61.
Adults’ Perceptions of Children's Science Abilities and Interest After Participating in a Family Science Night 下载免费PDF全文
The goal of this research was to examine adults’ and children's perceptions of participating in a family science night event, especially in the context of parental belief about children's science abilities. Family science nights are becoming increasingly popular and are used in a wide range of settings. During family science nights, adults and students jointly engaged in a variety of science activities. Results revealed that adults, 90% of whom were parents of attending students, reported learning more about children's interests and abilities in science. Students also agreed that that the adults had learned more about their abilities and interests. Personal characteristics of adults and children, such as gender and ethnicity, were not found to have any relationship to ratings. 相似文献
62.
James A. Kitts Michael W. Macy Andreas Flache 《Computational & Mathematical Organization Theory》1999,5(2):129-145
This study extends previous research that showed how informal social sanctions can backfire when members prefer friendship over enforcement of group norms. We use a type of neural network to model the coordination of informal social control in a small group of adaptive agents confronted with a social dilemma. This model incorporates two mechanisms of social influence, informal sanctions and imitation. Both mechanisms vary with the strength of the social tie between source and target. Previous research focused on the effects of social sanctions. Here, we demonstrate a curvilinear effect of imitation on compliance with prosocial norms. Moderate doses of imitation reduce the coordination complexity of self-organized collective action and help the network achieve satisfactory levels of cooperation. High doses, however, undermine the agent-based learning required to find cooperative solutions. Increasing group size also diminishes compliance due to increased complexity, with larger groups requiring more imitation to overcome the coordination problem. 相似文献
63.
Spatial Correlation Network and Regional Differences for the Development of Digital Economy in China
The rapid development of the digital economy is a powerful driving force to promote high-quality economic growth all over the world. Although a number of studies have been conducted to investigate the development of the digital economy in China, these studies pay little attention to the spatial linkages between the 30 provinces in China and the developmental differences between northern and southern China. Using Chinese digital economic data from 2004 to 2019, we propose an index system to measure the developmental levels of the digital economy and obtain the annual developmental levels of these provinces by using the factor analysis method. We analyze the regional differences of developmental levels by using the Theil index and kernel density estimation method. More importantly, the network method is used to analyze the correlations between the developmental levels of the digital economy in all provinces of China. By decomposing regional differences, our study shows that polarized and uncoordinated development is prominent. The development level of the digital economy in the southern region is higher than that in the northern region. In terms of regional correlations, the network study suggests that there are beneficial and spillover effects of the digital economy development between provinces. Based on the analysis results, we propose policies for improving the development of the digital economy in China. 相似文献
64.
65.
Noah Z. Burns Phil S. Baran Prof. Dr. Reinhard W. Hoffmann Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(16):2854-2867
Stimulus package for organic synthesis : The economy of step and atom usage has been widely reviewed and acknowledged as being useful frameworks to evaluate the efficiency of synthesis. This Review brings to attention another form of economy which should be considered in the planning and evaluation of a multistep synthesis: redox economy. Several guidelines and examples are included to illustrate the logic of this approach and to stimulate the design of syntheses.
66.
考虑资本闲置的多年时滞人力资本投入占用产出模型 总被引:1,自引:1,他引:0
人力资本理论强调的是由教育所新增的人力资本对经济增长的决定作用.为了规划与中国经济持续增长相适应的人力资本需求,建立了一个新颖的考虑资本闲置的多年时滞投入占用产出模型.为了考虑人力资本时滞长的特点以及人力资本占用的损耗补偿,在斯通人口投入产出模型和Leontief动态投入产出模型基础上,提出了多年时滞人力资本投入占用产出模型.将LDS模型推广为考虑资本闲置的多年时滞人力资本投入占用产出模型,以便考虑影响教育产出的外生因素,并推导出既适于产出增加也适于产出减少的正解.应用上,预测至2015年的各种教育水平人力资本的总量和部门需求,发现高级人力资本短缺和人才行业结构不合理是经济发展需要解决的重要问题. 相似文献
67.
68.
基于灰色关联度的中国海洋产业结构分析 总被引:1,自引:0,他引:1
简要分析了中国海洋经济的发展现状与趋势, 着重对我国主要海洋产业进行了关联度分析, 得出我国海洋经济的支柱产业和主导产业以及海洋产业结构存在的问题, 并据此提出了中国海洋产业结构优化升级对策等方面的建议. 相似文献
69.
70.
本文讨论多期有限理性条件下可再生资源开发的寡头博弈模型。在每个经济时期以实现多个相邻时期的总贴现利润最大化为目的而得到双寡头决策者资源开发的最优策略组合,并以各期最优策略组合构建资源开发决策的动力系统。通过对系统的动力学分析,讨论了系统中各参数对系统的稳定性与稳定状态的作用与影响,并给出了相应的经济解释。分析了反馈控制系统的稳定性。最后通过对系统的数值模拟,分析了各参数的取值变化与系统稳定速度之间的关系。本文通过系统的稳定性分析获得的主要结论是,资源市场竞争的稳定与可持续发展与决策者注重后期经济利益的决策理性密切相关。 相似文献