全文获取类型
收费全文 | 5219篇 |
免费 | 544篇 |
国内免费 | 362篇 |
专业分类
化学 | 1437篇 |
晶体学 | 19篇 |
力学 | 576篇 |
综合类 | 30篇 |
数学 | 270篇 |
物理学 | 2265篇 |
无线电 | 1528篇 |
出版年
2024年 | 16篇 |
2023年 | 74篇 |
2022年 | 178篇 |
2021年 | 196篇 |
2020年 | 244篇 |
2019年 | 197篇 |
2018年 | 177篇 |
2017年 | 236篇 |
2016年 | 321篇 |
2015年 | 273篇 |
2014年 | 339篇 |
2013年 | 288篇 |
2012年 | 313篇 |
2011年 | 344篇 |
2010年 | 265篇 |
2009年 | 263篇 |
2008年 | 289篇 |
2007年 | 296篇 |
2006年 | 275篇 |
2005年 | 236篇 |
2004年 | 238篇 |
2003年 | 216篇 |
2002年 | 180篇 |
2001年 | 139篇 |
2000年 | 97篇 |
1999年 | 67篇 |
1998年 | 75篇 |
1997年 | 60篇 |
1996年 | 32篇 |
1995年 | 40篇 |
1994年 | 27篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有6125条查询结果,搜索用时 12 毫秒
81.
82.
83.
Leslie P Steffe 《The Journal of Mathematical Behavior》2003,22(3):237-295
A case study of two 5th-Grade children, Jason and Laura, is presented who participated in the teaching experiment, Children’s Construction of the Rational Numbers of Arithmetic. The case study begins on the 29th of November of their 5th-Grade in school and ends on the 5th of April of the same school year. Two basic problems were of interest in the case study. The first was to provide an analysis of the concepts and operations that are involved in the construction of three fractional schemes: a commensurate fractional scheme, a fractional composition scheme, and a fractional adding scheme. The second was to provide an analysis of the contribution of interactive mathematical activity in the construction of these schemes. The phrase, “commensurate factional scheme” refers to the concepts and operations that are involved in transforming a given fraction into another fraction that are both measures of an identical quantity. Likewise, “fractional composition scheme” refers to the concepts and operations that are involved in finding how much, say, 1/3 of 1/4 of a quantity is of the whole quantity, and “fractional adding scheme” refers to the concepts and operations involved in finding how much, say, 1/3 of a quantity joined to 1/4 of a quantity is of the whole quantity. Critical protocols were abstracted from the teaching episodes with the two children that illustrate what is meant by the schemes, changes in the children’s concepts and operations, and the interactive mathematical activity that was involved. The body of the case study consists of an on-going analysis of the children’s interactive mathematical activity and changes in that activity. The last section of the case study consists of an analysis of the constitutive aspects of the children’s constructive activity, including the role of social interaction and nonverbal interactions of the children with each other and with the computer software we used in teaching the children. 相似文献
84.
85.
86.
87.
88.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(1):59-82
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem
to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae
enable us to design an additional experiment and to judge its usefulness.
The aim of the paper is to find such formulae for several situations.
Supported by the grant of the Council of Czech Government MSM 6 198 959 214. 相似文献
90.
本文用频响特性与试验研究相结合的方法,对三个微电子产品实例进行模拟,讨论了如何设计补偿元件,防止自激振荡,保证闭环稳定且满足各项性能指标要求的问题。 相似文献