全文获取类型
收费全文 | 27146篇 |
免费 | 4551篇 |
国内免费 | 4121篇 |
专业分类
化学 | 16851篇 |
晶体学 | 366篇 |
力学 | 1999篇 |
综合类 | 236篇 |
数学 | 1584篇 |
物理学 | 8824篇 |
无线电 | 5958篇 |
出版年
2024年 | 102篇 |
2023年 | 493篇 |
2022年 | 940篇 |
2021年 | 1013篇 |
2020年 | 1137篇 |
2019年 | 929篇 |
2018年 | 903篇 |
2017年 | 1126篇 |
2016年 | 1322篇 |
2015年 | 1216篇 |
2014年 | 1585篇 |
2013年 | 2373篇 |
2012年 | 1831篇 |
2011年 | 1941篇 |
2010年 | 1557篇 |
2009年 | 1660篇 |
2008年 | 1737篇 |
2007年 | 1828篇 |
2006年 | 1651篇 |
2005年 | 1448篇 |
2004年 | 1200篇 |
2003年 | 1126篇 |
2002年 | 932篇 |
2001年 | 824篇 |
2000年 | 780篇 |
1999年 | 617篇 |
1998年 | 580篇 |
1997年 | 460篇 |
1996年 | 416篇 |
1995年 | 341篇 |
1994年 | 363篇 |
1993年 | 262篇 |
1992年 | 239篇 |
1991年 | 158篇 |
1990年 | 123篇 |
1989年 | 105篇 |
1988年 | 99篇 |
1987年 | 59篇 |
1986年 | 58篇 |
1985年 | 44篇 |
1984年 | 48篇 |
1983年 | 15篇 |
1982年 | 39篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 22篇 |
1977年 | 10篇 |
1973年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
H. Okumura T. Takahagi N. Nagai S. Shingubara 《Journal of Polymer Science.Polymer Physics》2003,41(17):2071-2078
The structural change in the depth direction of a polyimide (UPILEX‐S) film treated in alkaline solution, which was a representative surface treatment used to form a seed layer for plating and to improve the adhesive strength, was analyzed by means of micro Fourier transform infrared attenuated total reflection (FTIR‐ATR) line analysis with gradient shaving preparation. The polyimide film was treated with KOH. The imide ring opened through the alkaline treatment, and the amide structure and carboxylic acid salt were formed. The attainment depth of this structural change was almost proportional to the treatment time, and it reached about 8 μm after a 30‐min treatment. The degree of structural change through the alkaline treatment was almost constant after it reached a considerably degraded stage, and the chemically changed region penetrated into the inner part of the film from the surface. An intermediate layer before the final degraded stage appeared in the treated layer, and its thickness increased with the treatment time. The region that was changed chemically by the alkaline treatment progressed to the inner part simultaneously and continuously as the treatment time increased. The combined use of gradient shaving preparation and micro FTIR‐ATR line analysis was found to be extremely effective for the depth profiling of organic materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2071–2078, 2003 相似文献
72.
A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials. 相似文献
73.
An m‐covering of a graph G is a spanning subgraph of G with maximum degree at most m. In this paper, we shall show that every 3‐connected graph on a surface with Euler genus k ≥ 2 with sufficiently large representativity has a 2‐connected 7‐covering with at most 6k ? 12 vertices of degree 7. We also construct, for every surface F2 with Euler genus k ≥ 2, a 3‐connected graph G on F2 with arbitrarily large representativity each of whose 2‐connected 7‐coverings contains at least 6k ? 12 vertices of degree 7. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 26–36, 2003 相似文献
74.
Andrzej Dabrowski Erich Robens Peter Klobes Klaus Meyer Przemyslaw Podkocielny 《Particle & Particle Systems Characterization》2003,20(5):311-322
Since a comprehensive survey published in 1999 [1] much work was done in standardizing measuring methods to characterize the surface geometry of dispersed and/or porous solids and to certify reference materials. The present paper is an extension of a short communication [2]. It gives a survey on existing standards and reports on new drafts and proposals. 相似文献
75.
76.
The modifying action of chloroform on photochemical reactions induced in the eye lenses of rats by UVB radiation is revealed. In anesthetic concentrations, halogenmethane increases the quantum yield of photodisintegration of protein tryptophanyls with formation of a new photochemical product that absorbs radiation in the UVA range and possesses the photosensitizing activity. 相似文献
77.
通过解析推导和数值计算的方法,得到了平衡态指向矢满足的微分方程和边界条件.研究了表面弹性能K13项对磁场作用下的弱锚定向列液晶盒Fréedericksz转变性质的影响.结果表明,表面弹性能K13项的存在对液晶系统的自由能有很大的影响,从而改变转变的性质,诱导液晶盒在阈值点发生一级Fréedericksz转变.给出了发生一级转变的物理条件,它除了与液晶的结构和材料有关外,还依赖于液晶表面弹性能K13项,同时给出了由此判断K13项是否存在的检验方法.
关键词:
表面弹性能K13项
弱锚定
Fréedericksz转变 相似文献
78.
概述污水处理厂的一般工艺,简单介绍了风机、水泵等的节能特点,介绍了变频调速装置在污水处理厂各处理工段的应用。 相似文献
79.
硅表面上的纳米量子点的自组织生长 总被引:1,自引:1,他引:0
纳米半导体量子点以其所具有的新颖光电性质与输运特性正在受到人们普遍重视。作为制备高质量纳米量子点的工艺技术 ,自组织生长方法倍受材料物理学家的青睐。而如何制备尺寸大小与密度分布可控的纳米量子点更为人们所注目。因为这是关系到纳米量子点最终能否器件实用化的关键。文中以此为主线 ,着重介绍了各种 Si表面 ,如常规表面、氧化表面、台阶表面以及吸附表面上 ,不同纳米量子点的自组织生长及其形成机理 ,并展望了其未来发展前景 相似文献
80.
本文利用矩量法和广义散射矩阵理论分析了多层频率选择表面的散射特性。通过引入广义波导概念,可以统一分析单元形状为任意的多层频率选择表面。作为示例,计算了几种不同结构频率选择表面的散射特性,结果与文献中给出的数据相符。 相似文献