全文获取类型
收费全文 | 12370篇 |
免费 | 5209篇 |
国内免费 | 7396篇 |
专业分类
化学 | 10054篇 |
晶体学 | 806篇 |
力学 | 1923篇 |
综合类 | 288篇 |
数学 | 512篇 |
物理学 | 11392篇 |
出版年
2024年 | 167篇 |
2023年 | 564篇 |
2022年 | 686篇 |
2021年 | 693篇 |
2020年 | 502篇 |
2019年 | 610篇 |
2018年 | 460篇 |
2017年 | 546篇 |
2016年 | 597篇 |
2015年 | 698篇 |
2014年 | 1362篇 |
2013年 | 1151篇 |
2012年 | 1075篇 |
2011年 | 1192篇 |
2010年 | 1058篇 |
2009年 | 1049篇 |
2008年 | 1236篇 |
2007年 | 1078篇 |
2006年 | 1004篇 |
2005年 | 969篇 |
2004年 | 1009篇 |
2003年 | 1039篇 |
2002年 | 842篇 |
2001年 | 820篇 |
2000年 | 612篇 |
1999年 | 451篇 |
1998年 | 431篇 |
1997年 | 435篇 |
1996年 | 334篇 |
1995年 | 362篇 |
1994年 | 354篇 |
1993年 | 282篇 |
1992年 | 306篇 |
1991年 | 275篇 |
1990年 | 263篇 |
1989年 | 241篇 |
1988年 | 53篇 |
1987年 | 56篇 |
1986年 | 48篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 7篇 |
1981年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 39 毫秒
81.
82.
Exact Solution of an Extended Hubbard Model with Electron—Lattice Interaction for an Organic Ferromagnetic Polymer 下载免费PDF全文
Using an exact diagonalization method,we study an extended Hubbard model with an electron-lattice interaction for an organic ferromagnetic chain with radical coupling.The result shows that the ferromagnetic ground state originates from the antiferromagnetic correlation between adjoining sites,which is enhanced by the on-site e-e repulsion.The intersite e-e repulsion induces the inhomogeneous distribution of the charge density.The dimerization is decreased by the e-e interaction and the radical coupling.The electron-lattice interaction and the radical coupling can transfer the spin density and charge density between the main chain and the radicals. 相似文献
83.
84.
对Sn-C60薄膜进行紫外可见光吸收,X-射线衍射和扫描电镜的测定结果显示,薄膜样品紫外可见光吸收的两个短波段吸收峰比纯C60薄膜的吸收峰显著下降,说明Sn-C60薄膜的电子光吸收跃迁为间接跃迁,能带中有杂质能级的存在;样品的X射线衍射峰则对应于面心立方结构;扫描电镜结果显示薄膜为纳米级颗粒组成。 相似文献
85.
86.
建立了电子隧穿电导模型,推导了一维无序体系新的直流电导公式.通过计算20000格点无序体系的直流电导率,分析了直流电导率和温度及外场电压的关系,讨论了无序度对直流电导的影响.计算结果表明,无序体系的直流电导率随无序度的增加而减小;外加电场较小时,电导率相对较大,且出现一系列峰值,电压较大时,电导率反而较小;无序体系在低温区出现了负微分电阻特性,电导率随温度的升高而增大,在高温区电导率随温度的升高而减小.计算结果和实验符合很好
关键词:
无序体系
电子隧穿
直流电导率 相似文献
87.
88.
89.
Practical absorption limits of MPP absorber 总被引:1,自引:0,他引:1
MAA Dah-You 《声学学报:英文版》2006,25(4):289-296
The construction and properties of microperforated panel (MPP) absorber are discussed. The absorption limit of the absorber had been shown that low values of the perforate constant k = d(f/10)1/2 and the orifice diameter d (in mm) are essential for MPP to have high absorption in wide frequency band. To find the exact limits, take 1 for k as a start, because both specific resistance and high absorption require k around one. And the orifice diameter d is chosen as 0.1 mm, so that the peak absorption coefficient (resonance absorption) is at 1000 Hz, and high sound frequency may be in the absorption region. Is it possible for a single layer of such an MPP to cover the whole absorption region required in practice? The half-absorption limit is not a good criterion, because low absorption comes in also in some cases. The 0.5 absorption coefficient limit is suggested for practical region, as a standard for comparison. Absorption curves were drawn for different load resistances, of absorption coefficients versus frequency. Ordinary MPP absorber absorbs in slightly over two octaves, and the new absorber with r = 1 (specific resistance equal to the characteristic impedance in air)is slightly better than these, 2.5 octaves. The new absorbers with r > 1, are much better than these, and some satisfies high absorption in broad frequency range. Realization of these will mean great progress of MPP absorbers. 相似文献
90.
We have studied the interracial reactions between amorphous LaAlO3 thin films and Si substrates, using high- resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interracial layer between LaAlO3 film and Si substrate chemical states show that the ratio of La 4d3/2 to Al 2p is SiLaxAlyOz. The depth distributions of La, Si and Al of the interfacial layer remains unchanged with the depth compared to that of the LaAlO3 film. Moreover, the Si content, in the interracial layer gradually decreases with increasing thickness of the interracial layer. These results strongly suggest that the Al element is not deficient in the interracial layer, as previously believed, and the formation of a SiLaxAlyOz interracial layer is mainly due to the diffusion of Si from the substrate during the LaAlO3 film deposition. With the understanding of the interracial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics. 相似文献