全文获取类型
收费全文 | 2837篇 |
免费 | 207篇 |
国内免费 | 76篇 |
专业分类
化学 | 1119篇 |
晶体学 | 3篇 |
力学 | 52篇 |
综合类 | 21篇 |
数学 | 1299篇 |
物理学 | 626篇 |
出版年
2023年 | 33篇 |
2022年 | 40篇 |
2021年 | 69篇 |
2020年 | 107篇 |
2019年 | 89篇 |
2018年 | 54篇 |
2017年 | 58篇 |
2016年 | 86篇 |
2015年 | 90篇 |
2014年 | 87篇 |
2013年 | 137篇 |
2012年 | 116篇 |
2011年 | 304篇 |
2010年 | 254篇 |
2009年 | 370篇 |
2008年 | 300篇 |
2007年 | 248篇 |
2006年 | 208篇 |
2005年 | 101篇 |
2004年 | 73篇 |
2003年 | 76篇 |
2002年 | 37篇 |
2001年 | 29篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有3120条查询结果,搜索用时 31 毫秒
101.
School STEM Culture—an aspect of culture within a school community—is defined as the beliefs, values, practices, and resources in STEM fields as perceived by students, parents, teachers, and administrators and counselors within a school. This study validates the STEM Culture Assessment Tool (STEM‐CAT), an instrument intended to advance the use of the School STEM Culture construct within the research community. Internal consistency was determined through the use of Cronbach's alpha and factor analyses, and the instrument was found to be a reliable measure of School STEM Culture. The instrument can be used in future research to quantify School STEM Culture to determine if interventions change the culture of a school to further STEM education. 相似文献
102.
Findings from physics education research strongly point to the critical need for teachers’ use of multiple representations in their instructional practices such as pictures, diagrams, written explanations, and mathematical expressions to enhance students' problem‐solving ability. In this study, we explored use of problem‐solving tasks for generating multiple representations as a scaffolding strategy in a high school modeling physics class. Through problem‐solving cognitive interviews with students, we investigated how a group of students responded to the tasks and how their use of such strategies affected their problem‐solving performance and use of representations as compared to students who did not receive explicit, scaffolded guidance to generate representations in solving similar problems. Aggregated data on students' problem‐solving performance and use of representations were collected from a set of 14 mechanics problems and triangulated with cognitive interviews. A higher percentage of students from the scaffolding group constructed visual representations in their problem‐solving solutions, while their use of other representations and problem‐solving performance did not differ with that of the comparison group. In addition, interviews revealed that students did not think that writing down physics concepts was necessary despite being encouraged to do so as a support strategy. 相似文献
103.
本文在分析福建省历年R&D强度及特征的基础上.构建了R&D强度的灰色预测模型和增长型曲线外推模型,并利用它们构建了组合预测模型,同时以全国平均水平为依据构建了预警系统,得到2008—2010年的R&D强度预测值分别为1.0321%、1.1186%、1.2115%,预警结果3年都是巨警。结果表明,福建省的R&D强度在2010年达不到1.7%的水平,这与福建省“十一五”R&D投入强度的既定目标相去甚远。随后,文章提出了福建省实现“十一五”科技投入强度目标的条件要求,为政府制订和调整科技投入政策提供参考。 相似文献
104.
Thomas Nagel Margarethe Rammerstorfer 《Central European Journal of Operations Research》2009,17(2):111-129
Motivated by the frequently observed criticism of the regulatory practice arising from companies in the industries concerned,
we investigate the impact of regulation on investment behavior. Therefore, we model the investment timing and volume of a
firm acting in a regulated market. When capping prices, the regulatory authority imposes a price ceiling on market prices.
Accordingly, we use a real option approach where the price cap that limits possible future firm values enters the firm’s portfolio
in form of a short call option position. By comparing this framework to a competitive benchmark model, we derive an optimal
price setting rule for regulators. Moreover, it can be shown how deviations from this optimum affect the investment behavior
of firms.
相似文献
105.
《Helvetica chimica acta》2017,100(12)
A collection of excerpts from letters written by R. B. Woodward to his friends, colleagues, young students and others is presented. These excerpts are representative of Woodward 's lengthy correspondence and illustrate many aspects of his personality and philosophies of life. 相似文献
106.
107.
《中国化学会会志》2017,64(6):574-588
This review is aimed at the current research progression of a unique class of Pt(II ) metal complexes bearing at least one azolate‐containing bidentate chelate. The azole fragment can link to a neutral heteroaromatic entity or another azole and form bidentate chelates, such as monoanionic 3‐pyridyl‐1H ‐pyrazole and derivatives, dianionic 3,3′‐bi‐1H ‐pyrazole, 3,3′‐(1‐methylethylidene)‐bis‐1H ‐pyrazole, and their analogs. These azole‐containing chelates readily react with a variety of Pt(II) reagents to afford the corresponding bis‐bidentate Pt(II) complexes. Most of them were highly emissive in solution, doped polymer matrix, thin film, and even as crystal or powder, due to the high ligand field strength exerted by these chelates and their high propensity in forming the singular square‐planar architecture and intermolecular aggregates with substantially strengthened Pt⋯Pt interaction, according to their structural design. Therefore, they hold bright prospects in academic research and future optoelectronic applications such as organic light‐emitting diodes. 相似文献
108.
109.
Prof. Hans‐Joachim Freund Dr. Niklas Nilius Dr. Thomas Risse Dr. Swetlana Schauermann Dr. Thomas Schmidt 《Chemphyschem》2011,12(1):79-87
We describe four new experimental techniques advanced during the last decade in the authors’ laboratory. The techniques include photon scanning tunneling microscopy; aberration‐corrected low‐energy electron microscopy in combination with photoelectron emission microscopy, microcalorimetry, and electron‐spin resonance spectroscopy. It is demonstrated how those techniques may be applied to solve fundamental problems in surface science with growing demands to tackle complex nanoscopic systems, and, in particular in catalysis science, which, without the availability of those techniques, would be difficult if not impossible to address. 相似文献
110.