全文获取类型
收费全文 | 296篇 |
免费 | 47篇 |
国内免费 | 57篇 |
专业分类
化学 | 251篇 |
晶体学 | 2篇 |
力学 | 9篇 |
综合类 | 1篇 |
数学 | 17篇 |
物理学 | 120篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 25篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 24篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 3篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
1.
利用六面顶高压设备制备了高密度、低脆性、纳米级的ZnO块体材料,用MDI/JADE5 X射线衍射仪(Cu靶)和XL30S-FEG场发射扫描电子显微镜对高压样品的相组成、晶粒尺寸及微观形貌进行了表征.利用E55+FRA106/5傅里叶变换激光拉曼光谱仪通过ZnO块体样品位于50—500cm-1之内的拉曼光谱, 研究了极性半导体纳米材料的拉曼光谱学特征.发现在极性半导体ZnO纳米块体材料中,没有出现明显的尺寸限制效应.
关键词:
ZnO纳米块体
拉曼光谱
尺寸限制效应 相似文献
2.
Principles and recent developments in ultrasound contrast agents 总被引:6,自引:1,他引:5
The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications. 相似文献
3.
4.
用循环计时电量法、循环伏安法、电化学现场(in-situ)紫外可见反射光谱技术和光电流谱技术研究了溶剂和阳离子(H~+,Li~+)对阳极氧化膜WO_3电显色稳定性和过程的影响。从循环计时电量图可以测定表征膜稳定性的氢或锂的累积量和暂态周期数。实验发现W/WO_3/LiCLO_4乙腈溶液体系具有高的电显色稳定性。引起WO_3膜可逆电显色的H~+和Li~+离子的嵌-脱过程的界面电化学机理不同。着色态WO_3膜的色心是自由电子,其密度超过10~(21)/cm~3,生色机理是等离子体振荡。 相似文献
5.
6.
Richard W.M. Ten Hoedt Gerard van Koten Jan G. Noltes 《Journal of organometallic chemistry》1980,201(1):327-342
Thermal decomposition of configurationally pure 1,2-diarylpropenylcopper compounds Z-Vi2CU4Br2 and Z-Vi2Cu4R2 [Vi (2-Me2NC6H4)CC(Me)-(C6H4Me-4), R 2-Me2NC6H4 or 4-MeC6H4CC] predominantly results in the formation of ViH. In contrast, only dimers (ViVi) were formed on thermolysis of (Z-ViCu2OTf)η which is a further illustration of the influence of the counter anion on the reactivity of organocopper cluster compounds. However, in both cases partial inversion of configuration, giving mixtures of isomers, was observed. The thermolysis of (Z-ViCu2OTf)η is discussed in terms of OTf-enhanced intraaggregate electron-transfer processes. The formation of incipient vinyl cations which are η2-coordinated to the copper cluster can explain the observed isomerization.Also in the hydrolysis reaction of Z-Vi2Cu4Br2 mixtures of isomeric ViH compounds were obtained, the E/Z ratio being dependent on the type of reagent used. Mixtures of isomeric ViX compounds (X Br, Cl, I) were formed in the reaction of Z-Vi2Cu4Br2 with I2 and CuCl2. An explanation for the occurrence of isomerization is presented.Dimers (ViVi) were almost absent in the product mixture resulting from the reaction of Z-Vi2Cu4Br2 with CuCl2. In contrast, ViVi is obtained in about 50% yield from the reaction of ViLi with CuCl2 which is in accord with earlier observations for the reaction of aryllithium compounds with cupric halides.Highly selective E-ViBr formation was observed in the reaction of E-ViLi with AgBr. This reaction probably proceeds via a thermally unstable Z-ViAg2Br intermediate. 相似文献
7.
The exchange of the PPh3 ligand in the complex [1,3-bis(2,6-dimethylphenyl)4,5-dihydroimidazol-2-ylidene](PPh3)(Cl)2Ru=CHPh (7) for a pyridine ligand at ambient temperature leads to the formation of the stable phosphine-free carbene ruthenium complex [1,3-bis(2,6-dimethylphenyl)4,5-dihydroimidazol-2-ylidene](C5H5N)2(Cl)2 Ru=CHPh (8). The resulted ruthenium complex exhibits highly catalytic activity for the cross metathesis of acrylonitrile with various functionalized olefins under mild conditions, and its activity can be further improved by the addition of a Lewis acid such as Ti(OiPr)4. In the mixture products, the Z-isomer predominates. 相似文献
8.
The force fields, in-plane vibrations, and relative intensities of Raman spectra have been calculated and analyzed for the N1H and N3H tautomers of imidazole, imidazolium cation, and their model structures. The results obtained for the isolated state of imidazole correspond to the intramolecular mechanism of proton transfer. 相似文献
9.
G. N. Ten V. V. Nechaev V. I. Berezin V. I. Baranov 《Journal of Structural Chemistry》1997,38(2):262-267
The vibrational spectra of adenine and its deuterium-substituted analogs are calculated in the valence force field approximation.
The frequencies and forms of normal vibrations of the molecule at 1700–300 cm-1 are interpreted.
Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 324–333, March–April, 1997. 相似文献
10.
将线性三原子分子离子CS2+的对称伸缩振动简化为SC和S之间的简谐振动, 用谐振子的势能曲线和波函数对CS2+分子离子 C2Σg+和 B2Σu+电子态(对称伸缩)振动能级间跃迁的Franck-Condon因子进行了计算, 得到的结果与 C2Σg+←B2Σu+跃迁的光解离谱实验强度进行了比较, 对前人给出的分子数据(转动常数、分子平衡核间距)进行了验证和分析, 讨论了经由 C2Σg+←B2Σu+电子态振动能级间跃迁的光解离机理. 相似文献