全文获取类型
收费全文 | 1063篇 |
免费 | 35篇 |
国内免费 | 6篇 |
专业分类
化学 | 758篇 |
晶体学 | 2篇 |
力学 | 19篇 |
数学 | 155篇 |
物理学 | 127篇 |
无线电 | 43篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 7篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 18篇 |
2015年 | 22篇 |
2014年 | 22篇 |
2013年 | 53篇 |
2012年 | 72篇 |
2011年 | 58篇 |
2010年 | 40篇 |
2009年 | 45篇 |
2008年 | 74篇 |
2007年 | 55篇 |
2006年 | 57篇 |
2005年 | 80篇 |
2004年 | 63篇 |
2003年 | 44篇 |
2002年 | 47篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1915年 | 4篇 |
1913年 | 5篇 |
排序方式: 共有1104条查询结果,搜索用时 982 毫秒
81.
Ernesto Estrada 《Journal of mathematical chemistry》2017,55(4):1021-1033
The atom-bond connectivity index—abbreviated ABC—has proven to describe the heat of formation of alkanes with an accuracy comparable to that of high-level ab initio and DFT methods. Its physical interpretation in terms of quantum-theory, its generalization, and many of its mathematical properties have been reported. Here, a probabilistic interpretation of the generalized ABC index is provided. It indicates that the terms defining this index represent the probability of visiting a nearest neighbor edge from one side or the other of a given edge in a graph. This interpretation is general enough as to cover the case of polarizing bonds in a molecular context. We then introduce a matrix representation of these probabilities in the form of generalized ABC matrices. Using this representation we study some indices related to the eigenvalues of the ABC matrices, such as the ABC energy and the ABC Estrada index. We provide some bounds for these parameters in general graphs. 相似文献
82.
Aránzazu Martínez-Gómez Ernesto Pérez Antonio Bello 《Colloid and polymer science》2010,288(8):859-867
The phase transitions and the orientational behavior of liquid crystalline poly(triethylene glycol p,p′-bibenzoate) have been studied. The real-time synchrotron diffraction results indicate that, on cooling from the isotropic
melt, an orthogonal SmA mesophase is formed first, and later it is transformed into a tilted SmC mesophase. However, the SmA
mesophase is stable in a rather wide temperature interval, and the transformation into the SmC phase occurs at temperatures
close to the glass transition, so that not very high tilting angles are attained. The uniaxial deformation of the SmC mesophase
indicates that usual parallel orientation of the molecular axes in relation to the stretching direction is obtained at high
strain rates, while anomalous perpendicular orientation occurs at low deformation rates, with the smectic layers aligned with
the stretching direction and the molecular axes almost perpendicular. A mixture of the two types of orientation is observed
at intermediate rates, with rather interesting features. 相似文献
83.
Cd(SePh)2, CdBr2·4H2O/CdI2 and PCh3 (Ph = phenyl; PCh3 = tricyclohexylphosphine) react to give [(SePh)2Cd2Br2(PCh3)2] (1), [(SePh)2Cd2I2(PCh3)2] (2) and [(SePh)7Cd4Br(PCh3)]n (3). 相似文献
84.
Tagliazucchi M Williams FJ Calvo EJ 《Chemical communications (Cambridge, England)》2010,46(47):9004-9006
We present polyelectrolyte multilayer modified electrodes exhibiting novel chemically responsive redox behaviour due to the combination of both redox and metal-ion-ligand functionalities on the same sites. 相似文献
85.
86.
Ernesto Sánchez‐Mendoza Jesús Hernández‐Trujillo 《Magnetic resonance in chemistry : MRC》2010,48(11):866-872
The indirect vicinal proton–proton coupling constants for pyrrole, furan, thiophene and 15 related heteroaromatic compounds were calculated using the Khon–Sham approximation. An analysis of the four Ramsey contributions to the coupling constants was carried out showing that the Fermi contact term is always positive and dominant, although the remaining contributions have a nonnegligible net negative contribution. The trends observed for the proton–proton coupling constants were rationalized in terms of the properties of the electron density. It was found that electron delocalization between the corresponding hydrogen atoms plays a major role on the observed behavior with the charges of the carbon atoms bonded to them and the accompanying geometric variations being also of importance in the coupling mechanism. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
87.
Miriam Beneito‐Cambra Virginia Bernabé‐Zafón Ernesto F. Simó‐Alfonso Guillermo Ramis‐Ramos 《Rapid communications in mass spectrometry : RCM》2010,24(14):2093-2100
A new derivatization procedure to increase the sensitivity of electrospray ionization mass spectrometry (ESI‐MS) to non‐ethoxylated and ethoxylated alcohols was investigated. The analytes were oxidized with chromium(VI) oxide and the resulting carboxylic and ethoxy‐carboxylic acids were isolated by extraction with ethyl acetate; the extracts were alkalinized and infused into the ESI‐MS system working in the negative‐ion mode. The yields of the combined oxidation‐extraction were ca. 100% for non‐ethoxylated fatty alcohols dissolved in acetone and they decreased moderately in samples containing increasing amounts of water (e.g., a 75% yield was obtained with 50% water). Ethoxylated alcohols with more than two ethylene oxide units resulted in yields of ca. 60%. Low limits of detection (LODs) were obtained when the procedure was applied to the analysis of body‐care products and cosmetics containing fatty alcohols, e.g., in a varicose‐vein cream, the LODs were 25 µg cetyl alcohol and 7.5 µg stearyl alcohol (detected as palmitic acid and stearic acid, respectively) per gram of sample. High molecular mass alcohols were also detected in seawater after pre‐concentration by solid‐phase extraction. Thus, the proposed method is particularly valuable for use in industrial samples having complex matrices and in environmental samples and it is competitive with other methods for the analysis of trace amounts of fatty alcohols. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
88.
89.
90.
Alejandro De Falco Mirta L. Fascio Melisa E. Lamanna Maria A. Corcuera Iaki Mondragon Gerardo H. Rubiolo Norma B. DAccorso Silvia Goyanes 《Physica B: Condensed Matter》2009,404(18):2780-2783
In this work we studied the functionalization of commercially available multiwalled carbon nanotubes (MWCNT) (Nanocyl 3100) with polystyrene by the method so called “grafting from”. The nanotubes were used as received and oxidized in air at 400 °C. The functionalization was started using thionyl chloride under reflux, followed by a reaction with ethylene glycol which allowed the inclusion of hydroxyl groups. The reaction of those with 2-chloropropionyl chloride led to the generation of the polymerization initiator. Last, the radical polymerization of the functionalized nanotubes, using styrene as the monomer, led to new materials which were studied with thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) spectroscopy. 相似文献