全文获取类型
收费全文 | 1705篇 |
免费 | 237篇 |
国内免费 | 159篇 |
专业分类
化学 | 537篇 |
晶体学 | 8篇 |
力学 | 208篇 |
综合类 | 38篇 |
数学 | 679篇 |
物理学 | 631篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 28篇 |
2021年 | 40篇 |
2020年 | 41篇 |
2019年 | 46篇 |
2018年 | 46篇 |
2017年 | 57篇 |
2016年 | 49篇 |
2015年 | 44篇 |
2014年 | 89篇 |
2013年 | 104篇 |
2012年 | 102篇 |
2011年 | 111篇 |
2010年 | 91篇 |
2009年 | 90篇 |
2008年 | 89篇 |
2007年 | 113篇 |
2006年 | 99篇 |
2005年 | 89篇 |
2004年 | 72篇 |
2003年 | 90篇 |
2002年 | 82篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 62篇 |
1998年 | 50篇 |
1997年 | 45篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2101条查询结果,搜索用时 31 毫秒
1.
2.
自主研制了一套小型脉冲电场屏蔽效能测试系统,该系统由脉冲电场发射设备和脉冲电场测试设备构成。脉冲电场发射设备的天线口面前60 cm处可产生峰值达7.5 kV/m的脉冲电场,测试设备的动态测试范围达97 dB。系统采用光纤测量设备,在测量工作中能有效抑制强电磁场干扰。采用Matlab编写自动测量及数据处理程序,实现了数据采集与处理自动化。实验测量了金属桥架、控制柜、屏蔽帐篷、导电水泥混凝土房的脉冲电场屏蔽效能,其脉冲电场峰值衰减量分别为52,64,66,30 dB。实验表明可用脉冲电场的峰值衰减量来评估屏蔽体的脉冲电场屏蔽效能。 相似文献
3.
4.
5.
R. J. Saykally K. M. Evenson D. A. Jennings L. R. Zink A. Scalabrin 《International Journal of Infrared and Millimeter Waves》1987,8(6):653-662
Twenty new cw FIR laser lines in CD3OH, optically pumped by a CO2 laser, are reported. The frequencies of 39 of the stronger laser lines were measured relative to stabilized CO2 lasers with a fractional uncertainty, as determined by the reproducibility of the FIR frequency itself, of 2 parts in 107.Contribution of the U.S. Government, not subject to copyright. 相似文献
6.
David Morris 《Applied biochemistry and biotechnology》2004,113(1-3):5-12
This article addresses two questions: Has the effectiveness of the US governments federal research and development (R&;D) spending suffered from the post-1980 strategic change from freely shared and publicly owned to privately owned scientific advances? What criteria would a federal R&;D program use to design a strategy that most effectively enhances the well-being of farmers and rural communities? Several studies found that the pre-1980 US Department of Agriculture research strategy was very effective. No comparable studies have analyzed the comparative effectiveness of the post-1980 strategy of restricting access to the results of public research. Recent experience and several analytical studies suggest that to significantly enhance the health of rural economies from an expanded use of plant matter as an industrial material, federal policy should channel scientific and engineering research into small- and medium-sized production and processing technologies and should encourage farmer-owned, value-added enterprises. 相似文献
7.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
8.
We investigate the effects of adding uniformity requirements to concepts in computable structure theory such as computable categoricity (of a structure) and intrinsic computability (of a relation on a computable structure). We consider and compare two different notions of uniformity, previously studied by Kudinov and by Ventsov. We discuss some of their results and establish new ones, while also exploring the connections with the relative computable structure theory of Ash, Knight, Manasse, and Slaman and Chisholm and with previous work of Ash, Knight, and Slaman on uniformity in a general computable structure-theoretical setting. 相似文献
9.
10.