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   125篇
  免费   6篇
  国内免费   2篇
化学   64篇
力学   3篇
综合类   1篇
数学   50篇
物理学   15篇
  2024年   1篇
  2023年   2篇
  2022年   1篇
  2021年   5篇
  2020年   3篇
  2019年   19篇
  2018年   4篇
  2017年   10篇
  2016年   3篇
  2015年   3篇
  2014年   6篇
  2013年   9篇
  2012年   6篇
  2011年   1篇
  2010年   4篇
  2009年   11篇
  2008年   6篇
  2007年   6篇
  2006年   3篇
  2005年   3篇
  2004年   1篇
  2003年   5篇
  2002年   3篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1990年   1篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1976年   1篇
  1975年   1篇
排序方式: 共有133条查询结果,搜索用时 15 毫秒
91.
In this paper we develop a Malmquist productivity index for public sector production characterized by the influence of environmental variables. We extend Johnson and Ruggiero (2011) to the more general case of variable returns to scale to further decompose the Malmquist productivity index into technical, efficiency, scale and environmental change. We apply our model to analyze productivity of Dutch schools using 2002–2007 data. The results indicate that the environment influences the productivity index as well as the technical, efficiency, scale and environmental change components. We see that schools with a moderate classification of environment have the highest productivity numbers. In line with expectations, schools with the worst environment also perform worse and would perform better with an improved environment.  相似文献   
92.
基于教育基金保险的期权定价   总被引:1,自引:0,他引:1  
本文基于文献[1]引入一种基于教育年金保险的欧式看涨期权,它赋予合约持有人在约定时间以约定价格购买一份连续支付一定年限的教育年金的权利,本文运用保险精算和期权定价的二叉树方法对其进行的定价,并说明这种合约方便于一些低收入家庭进行教育投资.  相似文献   
93.
以 2009—2018 年《化学教育》期刊“问题讨论与思考”栏目的载文为研究对象,采用系统查阅年度总目录与阅读原始文献相结合的方法,从载文的数量、内容、作者、引文等 4 个方面进行统计分析。发现近 10 年《化学教育》“问题讨论与思考”栏目的年均载文量为33篇;研究内容涉及化学知识讨论、教学讨论、实验探究、教材讨论、习题讨论等;载文作者所属地区、机构分布不均衡;研究方法以思辨和化学实验为主;作者之间的合作研究成为一种趋势;引文数量呈现逐渐增多的趋势。  相似文献   
94.
This paper presents a method that creates instructionally sound learning experiences by means of learning objects. The method uses a mathematical model, distinguishes two kinds of Learning Objects Properties and proceeds in two major steps: first, the Course Creation is transformed into Set Covering under specific requirements derived from Learning Theories and practice; second, the Alternative Learning Sources are selected by using a similarity measure specially defined for this purpose.  相似文献   
95.
The solid state complex between ammonium iodide and 1,4-dioxane has been found by TGA studies to be a (11) adduct rather than a (12) adduct as previously formulated. The laser Raman spectra of NH4I· dioxane and ND4I· dioxane in the N-H and N-D stretching regions show decreases in frequency compared to NH4I and ND4I which are consistent with hydrogen bonding of the N-H · O variety as a means of incorporation of the dioxane into the salt crystal lattice.  相似文献   
96.
当前理工科院校有机化学教师教学、学生学习以及课程考试三者之间的矛盾日益突出,而课程考试作为高校考查学生是否达到教学要求的一种基本评价方式,其必要性和重要性不容置疑。为了保证教学质量,提高学生的学习能力,本文针对有机化学课程考试中所存在的问题从多方面进行了改革和完善。  相似文献   
97.
Text editing directs students’ attention to the problem structure as they classify whether the texts of word problems contain sufficient, missing or irrelevant information for working out a solution. Equation worked examples emphasize the formation of a coherent problem structure to generate a solution. Its focus is on the construction of three equation steps each of which comprises essential units of relevant information. In an experiment, students were randomly assigned to either text editing or equation worked examples condition in a regular classroom setting to learn how to solve algebra word problems in a chemistry context. The equation worked examples group outperformed the text editing group for molarity problems, which were more difficult than dilution problems. Empirical evidence supports the theoretical rationale in using equation worked examples to facilitate students’ construction of a coherent problem structure so as to develop problem skills and expertise to solve molarity problems.  相似文献   
98.
Our research centered on developing the Conservation Science and Technology Identity (CSTI) instruments as an empirical way to measure STEM identities and the intersection of identity constructs such as competence, performance, recognition, and ways of seeing and being. The surveys were used in a large funded multi-year project for teens and adults learning geospatial technologies and conservation science to use in intergenerational community conservation projects. We investigated whether an informal STEM learning program was developing new STEM identities or advancing well-developed identities. The instruments’ content validity was determined through a vetting process from national STEM identity research experts. Reliability was estimated with Cronbach coefficient alpha. Mann-Whitney and Wilcoxon Signed Rank tests were used to determine participants’ STEM identities and the workshop’s effect on specific identity constructs. We found teens and adults had historically similar STEM identities, with stronger conservation science than technology. Both science and technology competences, as well as technology ways of seeing and being, significantly increased, suggesting CSTI can be a valuable instrument in empirically assessing STEM identities.  相似文献   
99.
Photodynamic therapy (PDT) has shown promise as an effective treatment modality for cancer and other localized diseases due to its noninvasive properties and spatiotemporal selectivity. Near-infrared (NIR) fluorescent dyes based on organic small molecules are characterized with low cytotoxicity, good biocompatibility and excellent phototoxicity, which are widely used in PDT. In this review, we attempt to summarize the development of imaging-induced PDT based on organic small molecules and classify it according to the structures of dyes including cyanines, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) analogues, phthalocyanine and other agents such as rhodamine analogues.  相似文献   
100.
Vocal education programs for teachers may prevent the emergence of vocal disorders; however, only a few studies have tried to evaluate the effectiveness of these preventive programs, particularly in the long term. Two hundred and sixty-four subjects, mostly kindergarten and primary school female teachers, participated in a course on voice care, including a theoretical seminar (120 minutes) and a short voice group therapy (180 minutes, small groups of 20 subjects). For 3 months, they had to either attend the vocal ergonomics norms and, as psychological reinforcement, they had to make out a daily report of vocal abuse, or to follow the given exercises for a more efficient vocal technique, reporting on whether the time scheduled was respected or not. The effectiveness of the course was assessed in a group of 21 female teachers through a randomized controlled study. Evaluation comprehended stroboscopy, perceptual and electro-acoustical voice analysis, Voice Handicap Index, and a course benefit questionnaire. A group of 20 teachers matched for age, working years, hoarseness grade, and vocal demand served as a control group. At 3 months evaluation, participants demonstrated amelioration in the global dysphonia rates (P=0.0003), jitter (P=0.0001), shimmer (P=0.0001), MPT (P=0.0001), and VHI (P=0.0001). Twelve months after the course, the positive effects remained, although they were slightly reduced. In conclusion, a course inclusive of two lectures, a short group voice therapy, home-controlled voice exercises, and hygiene, represents a feasible and cost-effective primary prevention of voice disorders in a homogeneous and well-motivated population of teachers.  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