全文获取类型
收费全文 | 2667篇 |
免费 | 832篇 |
国内免费 | 350篇 |
专业分类
化学 | 874篇 |
晶体学 | 110篇 |
力学 | 162篇 |
综合类 | 21篇 |
数学 | 171篇 |
物理学 | 2511篇 |
出版年
2024年 | 10篇 |
2023年 | 42篇 |
2022年 | 85篇 |
2021年 | 89篇 |
2020年 | 98篇 |
2019年 | 75篇 |
2018年 | 109篇 |
2017年 | 137篇 |
2016年 | 153篇 |
2015年 | 96篇 |
2014年 | 184篇 |
2013年 | 265篇 |
2012年 | 188篇 |
2011年 | 237篇 |
2010年 | 171篇 |
2009年 | 206篇 |
2008年 | 199篇 |
2007年 | 198篇 |
2006年 | 157篇 |
2005年 | 133篇 |
2004年 | 136篇 |
2003年 | 125篇 |
2002年 | 133篇 |
2001年 | 86篇 |
2000年 | 91篇 |
1999年 | 77篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 29篇 |
1994年 | 34篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3849条查询结果,搜索用时 15 毫秒
161.
V. M. Naumenko 《International Journal of Infrared and Millimeter Waves》1981,2(1):149-158
Interaction of host magnons with impurity magnetic excitations in antiferromagnetic crystals CoCO3 and CoF2 containing substitutional impurity amounting to 10–4 and (4±2)×10–3 (by weight) Mn2+ respectively, has been investigated in the wavelength range 0.35–0.8 mm in a magnetic field of up to 20 T. In the CoCO3+10–4 Mn2+ crystal the impurity line was observed to merge with the AFMR line, which is peculiar to incoherent spectrum rearrangement. In the CoF2+4×10–3 Mn2+ crystal the cross splitting of spectrum was revealed as the impurity lower lying Zeeman level approached the AFMR low frequency mode, peculiar to coherent spectrum rearrangement. In both cases the impurity line intensity increases very much as it approaches the spin-wave band of the crystal. The constant of resonance interaction of the impurity excitation with magnons is determined for CoF2+Mn2+ to be m=18 cm–1. 相似文献
162.
163.
D.T. Petkie B.P. Winnewisser R.A.H. Butler F.C. De Lucia 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(2):129-141
The results of millimeter and submillimeter wave rotational spectroscopy are used to simulate the complex structure of the 2ν9-ν9 and ν5-ν9 hot bands. The comparison data were obtained with a high-resolution Bruker FTIR. The combination of the quality of these data and the complexity of the spectra of these interacting states represents a stringent test for the simulation. It is shown that the agreement is very good and that this approach is generally advantageous. From this simulation, the ratios of the transition dipole moments for the 2ν9-ν9 and ν5-ν9 hot bands with respect to the ν9 fundamental band were found to be 1.38(11) and 0.67(20), respectively. Using these results, the calculated integrated band intensities for the hot bands at were determined to be and . These results were used to successfully simulate high-resolution stratospheric spectra obtained from a balloon flight of the FIRS-2 spectrometer. The more general problem of the rotation-vibration database and the optimal use of both microwave and infrared data to define it is discussed. It is concluded that it is best if the combination of data takes place at the level of the original spectra. 相似文献
164.
Bridging the Length Scales: Micromechanics of Granular Media 总被引:1,自引:0,他引:1
Aristotle's statement that the whole is more than the sum of its parts aptly describes the essence of a granular material's rich and complex behaviour, which ultimately arises from internal mechanisms developed on many length scales. Recently, non-invasive experimental studies have given remarkable insight into the evolution of these mechanisms, thereby providing benchmarks and a unique opportunity for the theoretical modelling of these systems. This paper focuses on the challenges of capturing these multiscale mechanisms within the framework of continuum theory. In particular, a new approach toward developing a non-local micropolar constitutive model of granular media using micromechanics and internal variable theory is discussed. To demonstrate the predictive potential of these models, we present their application in the analysis of two fundamental problems to the mechanics of granular media: (i) formation and evolution of shear bands (the precursors of material failure), (ii) the classical Flamant problem. Finally, we briefly discuss the computational challenges in bridging the gap between micromechanical studies of granular media and the applications of continuum theory on the macro-scale via a finite element analysis of the flat punch problem. In practice, this problem is used to assess the load bearing capacity of a material and is fundamental to civil and structural engineering. 相似文献
165.
Nicola J. van Leeuwen Henrik G. Kjaergaard Andrew C. Wilson 《Journal of Molecular Spectroscopy》2004,228(1):83-91
A highly sensitive cavity-enhanced frequency modulation spectroscopy technique has been used to measure ultraweak transitions in molecular oxygen that had not previously been characterized. The self-broadened half-width and line intensity of the measured transitions are reported. We include 12 high J transitions in the band of 16O2 (the so-called A band), 59 transitions in the hot band of 16O2, and 17 high J transitions in the band of 16O18O. Our measurements of line positions of the 16O18O transitions are used to determine improved molecular constants for the excited state of 16O18O. 相似文献
166.
突破间接带局限创新Si基激光器 总被引:2,自引:0,他引:2
Si基高效发光与受激光发射是Si基光子学突破性发展的关键课题,它的实现对Si基微电子学的发展有深远的重大意义.由于受到天然Si材料间接带能带结构的限制,Si材料的发光效率极低,更谈不上可实现受激光发射,人工改性就成为当代研究、开拓的主要途径.新的Si基直接带体材料(如β-FeSi2等)的探索,Ge/Si量子阱、超晶格、量子点的能带工程介观改性,子带发光跃迁的探索,异类元素插入短周期超晶格中的化学键改性,以及SiO2高浓度nc-Si的生成和高激活度稀土离子的掺入发光等已开展了多途径的研究,不同程度上取得了重要的进展,一种MIS结构电子隧道注入高效发光器件已在SiO2:RE MOS结构中实现.运用激光器件物理的深入设计和新的器件技术的引入,可以预计本世纪初叶,对实现Si基激光器的奢望将会成为现实,无疑它对Si基光子学、Si基集成光电子学乃至信息高科技的发展将作出历史性的巨大贡献. 相似文献
167.
运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法,计算研究了闪锌矿结构的ZnS晶体在不同的外界压强下的电子结构. 通过分析发现,随着外界压强的增大,晶格常数和键长在不断缩小,从S原子向Zn原子转移的电荷越来越少,Zn—S键的共价性逐渐增强,Zn原子和S原子的态密度都有不同程度的变化,而且还有向低能量移动的趋势. 当外界压强达到24GPA时,ZnS从直接带隙半导体变成间接带隙半导体,而且随着压强的增大,间接带隙逐渐变小,直接带隙逐渐增大.
关键词:
闪锌矿结构
态密度
能带结构
密度泛函理论 相似文献
168.
169.
用金属离子注入方法在锐钛矿TiO2薄膜中掺杂了V+,采用全势线性缀加平面波方法计算了锐钛矿TiO2及V+掺杂TiO2超原胞的电子结构,通过紫外-可见吸收光谱测试方法检测了注入不同剂量的V+对TiO2薄膜吸收光谱的影响.理论计算和实验结果表明,锐钛矿TiO2薄注入V+后,带隙宽度变小,吸收光谱发生红移,并且TiO
关键词:
+注入')" href="#">V+注入
2')" href="#">TiO2
全势线性缀加平面波方法
能带结构 相似文献
170.
采用分子束外延的方法在BaF2(111)衬底上制备出了高质量的Pb1-xMnxSe(0≤x≤0.0681)薄膜.X射线衍射结果表明,Pb1-xMnxSe薄膜为立方相NaCl型结构,没有观察到MnSe相分离现象,薄膜的取向为平行于衬底(111)晶面.晶格常数随着Mn含量的增加逐渐减小,Mn含量由Vegard公式得到.通
关键词:
1-xMnxSe外延薄膜')" href="#">Pb1-xMnxSe外延薄膜
透射光谱
带隙
折射率 相似文献