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   1526篇
  免费   144篇
  国内免费   19篇
化学   906篇
力学   17篇
综合类   48篇
数学   538篇
物理学   180篇
  2024年   4篇
  2023年   46篇
  2022年   118篇
  2021年   124篇
  2020年   129篇
  2019年   122篇
  2018年   80篇
  2017年   72篇
  2016年   112篇
  2015年   87篇
  2014年   64篇
  2013年   136篇
  2012年   51篇
  2011年   69篇
  2010年   45篇
  2009年   58篇
  2008年   42篇
  2007年   60篇
  2006年   21篇
  2005年   43篇
  2004年   33篇
  2003年   24篇
  2002年   37篇
  2001年   28篇
  2000年   11篇
  1999年   14篇
  1998年   6篇
  1997年   4篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   6篇
  1992年   5篇
  1991年   1篇
  1989年   1篇
  1988年   2篇
  1986年   23篇
  1985年   2篇
  1979年   3篇
  1972年   1篇
排序方式: 共有1689条查询结果,搜索用时 31 毫秒
131.
中国新疆旅游资源丰富多彩且具特色,但由于特殊的地理位置和当地经济条件,这里的旅游业还不发达,随着西部大开发脚步的加快,新疆的生态环境必将受到冲击和影响,如何保障生态环境免遭破坏,又能在大力开放旅游资源的前提下寻求可持续发展,对上问题,本文在探讨生态旅游的现状利弊基础上,结合西部大开发将面临的平等一系列生态问题及生态旅游资源的可持续利用问题进行了讨论。  相似文献   
132.
分析总结了半个世纪来我国中学物理教学“4个类型实验”的历史、内涵、功能和教法。  相似文献   
133.
灰色动态模型及其在人口预测中的应用   总被引:43,自引:1,他引:42  
一个国家人口的数量直接影响着其经济、社会的发展和资源的利用 ,中国是世界上人口的第一大国 ,人口问题一直是制约中国发展的第一因素 .本文应用灰色系统等维灰数递补动态预测模型 ,对中国未来5 0年的人口数量进行了动态预测 ,通过检验表明 ,该模型合理、方法简便可行、结果符合实际 ,为中国经济和社会发展的决策和研究提供了科学依据  相似文献   
134.
In a research project with one-day teacher education workshops for secondary-school mathematics teachers, our study explores the potential of tool-supported discussions in helping them to notice important and critical aspects of mathematics teaching talk. Mathematical practices of naming and explaining in teaching talk, students’ content learning challenges, and noticing processes of identifying, interpreting and deciding are the components of our framework and the tools that guided the design and implementation of three workshops on linear equations, fractions and plane isometries. The data was collected during the discussions with the seven teachers and the teacher educator throughout these workshops. The coding of the discussions allowed us to see discourse moves that reveal the teachers’ noticing of: (i) challenges in the identification of mathematical naming, (ii) mathematical explaining that voices the students’ learning, (iii) classroom practice in relation to mathematical naming and explaining.  相似文献   
135.
Our study examined ways preservice teachers (PSTs) make connections between teaching practices and use of student resources that support productive struggle and promote equity. Our research questions are: (1) How do PSTs notice and describe the equity-based mathematics teaching practice of leveraging student resources to support student struggles? and (2) In what ways do PSTs make connections to and interpret the role student resources play in the resolution of students’ mathematical struggles? The qualitative study examined 39 PSTs in a mathematics content course for PSTs. Data come from a video analysis assignment where PSTs described their mathematical interpretations of the student struggle(s) and teacher’s use of student resources to support the struggle resolution. Findings show that PSTs noticed teacher moves that leveraged student’s mathematical thinking and linguistic funds of knowledge and based the productive level of the struggle on actions built upon peers, linguistic knowledge and prior mathematical knowledge.  相似文献   
136.
A micromotor‐based strategy for energy generation, utilizing the conversion of liquid‐phase hydrogen to usable hydrogen gas (H2), is described. The new motion‐based H2‐generation concept relies on the movement of Pt‐black/Ti Janus microparticle motors in a solution of sodium borohydride (NaBH4) fuel. This is the first report of using NaBH4 for powering micromotors. The autonomous motion of these catalytic micromotors, as well as their bubble generation, leads to enhanced mixing and transport of NaBH4 towards the Pt‐black catalytic surface (compared to static microparticles or films), and hence to a substantially faster rate of H2 production. The practical utility of these micromotors is illustrated by powering a hydrogen–oxygen fuel cell car by an on‐board motion‐based hydrogen and oxygen generation. The new micromotor approach paves the way for the development of efficient on‐site energy generation for powering external devices or meeting growing demands on the energy grid.  相似文献   
137.
Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single‐crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.  相似文献   
138.
139.
A highly practical and general base‐catalyzed carbonylation of amines to the corresponding N‐formamides has been realized. Cheap inorganic bases, including Group IA and IIA metal hydroxides, alkoxides, carbonates, and phosphates, were effective catalysts for the transformation. In the presence of 10–40 mol % of KOH or K2CO3, various amines were converted into the corresponding N‐formamides in good‐to‐excellent yields using CO as the formylation reagents.  相似文献   
140.
突发公共卫生事件一直是政府组织十分关注的问题。当前,在公共卫生事件出现高频率的发生几率后,健康教育工作已占据着越来越重要的地位。从宏观角度来说,突发公共卫生事件是一个涵盖范围十分广泛的事件内容,其事件包含了多个可预测与不可预测的突发状况,也包含了任何地点、任何社会群体以及任何事件当中,因此在健康教育上,需从宏观范围进行全面计划,以系统式方式对各个突发公共卫生事件做出针对性教育,且对教育内容作出可行性评估,切实保障健康教育对突发公共卫生事件有一定的作用及影响力。对此,为进一步探讨该话题,针对突发公共卫生事件健康教育基本策略展开详细探讨。  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