全文获取类型
收费全文 | 826篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
化学 | 580篇 |
晶体学 | 7篇 |
力学 | 9篇 |
数学 | 56篇 |
物理学 | 198篇 |
出版年
2022年 | 12篇 |
2021年 | 10篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 10篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 31篇 |
2012年 | 34篇 |
2011年 | 35篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 38篇 |
2007年 | 26篇 |
2006年 | 50篇 |
2005年 | 38篇 |
2004年 | 38篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 19篇 |
1998年 | 6篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1972年 | 7篇 |
1966年 | 5篇 |
排序方式: 共有850条查询结果,搜索用时 31 毫秒
841.
Variable temperature spectroscopy of as-grown and passivated CdS nanowire optical waveguide cavities
van Vugt LK Piccione B Cho CH Aspetti C Wirshba AD Agarwal R 《The journal of physical chemistry. A》2011,115(16):3827-3833
Semiconductor nanowire waveguide cavities hold promise for nanophotonic applications such as lasers, waveguides, switches, and sensors due to the tight optical confinement in these structures. However, to realize their full potential, high quality nanowires, whose emission at low temperatures is dominated by free exciton emission, need to be synthesized. In addition, a proper understanding of their complex optical properties, including light-matter coupling in these subwavelength structures, is required. We have synthesized very high-quality wurztite CdS nanowires capped with a 5 nm SiO(2) conformal coating with diameters spanning 100-300 nm using physical vapor and atomic layer deposition techniques and characterized their spatially resolved photoluminescence over the 77-298 K temperature range. In addition to the Fabry-Pe?rot resonator modulated emission from the ends of the wires, the low temperature emission from the center of the wire shows clear free excitonic peaks and LO phonon replicas, persisting up to room-temperature in the passivated wires. From laser scanning measurements we determined the absorption in the vicinity of the excitonic resonances. In addition to demonstrating the high optical quality of the nanowire crystals, these results provide the fundamental parameters for strong light-matter coupling studies, potentially leading to low threshold polariton lasers, sensitive sensors and optical switches at the nanoscale. 相似文献
842.
Jean-Luc Pirat Jean Marc Lambert Henri-Jean Cristau 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract A procedure for the preparation of N-protected 1 or unprotected Ca,a-disubstituted (diarylaminomethyl)-phosphonic acids and their esters is reported.1 This method is a generalisation of the Kabachnik-Fields method described in the literature.2 相似文献
843.
This paper describes the synthesis, structural analysis, and investigations of the optical and electrochemical properties of some gold nanoparticles (AuNPs) which consist of a triarylamine ligand shell attached to small gold cores (Au-Tara). The triarylamine chromophores were attached to small 4-bromobenzenethiol covered gold nanoparticles (ca. 2 nm in diameter) by Sonogashira reaction. This procedure yields triarylamine redox centers attached via π-conjugated bridging units of different length to the gold core. The AuNPs were analyzed with (1)H NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), thermogravimetric analysis (TGA), and scanning transmission electron microscopy (STEM). Cyclic voltammetry (CV) technique was used to determine the composition of the redox active particles via the Randles-Sevcik equation. The optical and electrochemical properties of the Au-Tara nanoparticles and of their corresponding unbound ligands (Ref) were investigated with UV/vis/NIR absorption spectroscopy, Osteryoung square wave voltammetry (OSWV), and spectroelectrochemistry (SEC). These data show that the assembling of triarylamines in the vicinity of a gold nanoparticle can change the optical and electrochemical properties of the triarylamine redox chromophores depending on the kind and length of the bridging unit. This is due to gold core-chromophore and chromophore-chromophore interactions. 相似文献
844.
Lambert RF Hinkle RJ Ammann SE Lian Y Liu J Lewis SE Pike RD 《The Journal of organic chemistry》2011,76(22):9269-9277
Catalytic quantities of bismuth(III) triflate efficiently initiate the rearrangement of epoxides to aldehydes, which subsequently react with (Z)-δ-hydroxyalkenylsilanes to afford 2,6-disubstituted 3,6-dihydro-2H-pyrans. Isolated yields of desired products using Bi(OTf)(3) were compared with yields obtained when the reactions were run with TfOH and TMSOTf in the presence and absence of several additives. These studies, as well as NMR spectroscopic analyses, indicate an initial Lewis acid/base interaction between Bi(OTf)(3) and substrates providing TfOH in situ. 相似文献
845.
Garcia L Maisonneuve S Marcu JO Guillot R Lambert F Xie J Policar C 《Inorganic chemistry》2011,50(22):11353-11362
Glycoligands are a versatile family of ligands centered on a sugar platform and functionalized by Lewis bases. In this article, pentofuranoses were appended with the fluoroionophores 4-(pyridin-2'-yl)-1,2,3-triazol-1-yl and 4-(2',1',3'-benzothiadiazol-4'-yl)-1,2,3-triazol-1-yl using the "click-like" cycloaddition [2 + 3] of Huisgen catalyzed by copper(I). Their fluorescence properties were used to study metal cation complexation. A possible selective functionalization of furanoscaffolds allows the synthesis of "mixed" glycoligands with the successive insertion of these different fluoroionophores. The metal selectivity and the chelating behavior of these six resulting intrinsically fluorescent glycoligands were investigated. The change in the configuration at the carbon C3 of furanose did not influence either the metal selectivity or the binding constants. However, different selectivities and binding constants were found to depend on the nature of the fluoroionophore moieties. Overall, the triazolylbenzothiadiazolyl chelating group was shown to be less efficient than the triazolylpyridyl claw for complexation. Interestingly enough, the triazolylbenzothiadiazolyl claw, which fluoresces in the visible range, did not interfere in the binding and selectivity of the more efficient triazolylpyridyl claw. This study suggests that the triazolylbenzothiadiazolyl moiety could be used as an adequate fluorescent reporter to qualitatively monitor complexation of other moieties. 相似文献
846.
In the present work, an attempt has been made to assess the bioconcentration and distribution of zinc on the selected organs of Labeo rohita and to study the effect of zinc exposure on the biochemical constitutions of gill tissues of L. rohita by using FT-IR Spectroscopy. The concentration pattern in the organs reveals that the liver is the prime site of metal binding and muscle accumulates least metal concentration. The accumulation profile is in the order: liver > gill > kidney > brain > bone > muscle. It has also been observed that the administration of chelating agent d-Penicillamine (DPA) reduces the zinc concentration in all tissues more effectively than the administration of the chelating agent Ethylene Diamine Tetra Acetic acid. The FT-IR spectra reveal that zinc exposure causes significant changes in the biochemical constitutions of the gill tissues. It causes an alteration in the protein secondary structures by decreasing the α-helix and increasing the β-sheet contents. Further, it has been observed that the administration of chelating agent DPA improves the protein and lipid contents in the gill tissues compared to zinc exposed tissues. This result shows that DPA is the effective chelator of zinc in reducing the body burden of L. rohita fingerlings. In conclusion, the findings of the current study suggest that zinc exposure causes significant changes in both lipids and proteins of the gill tissues, and changes the protein profile in favour of β-sheet structure. 相似文献
847.
Dr. Suresh Moorthy Dr. Hugues Lambert Dr. Neetha Mohan Thomas Schwarzlose Prof. Werner M. Nau Dr. Elina Kalenius Dr. Tung-Chun Lee 《Angewandte Chemie (International ed. in English)》2023,62(32):e202303491
In the gas phase, thermal activation of supramolecular assemblies such as host–guest complexes leads commonly to noncovalent dissociation into the individual components. Chemical reactions, for example of encapsulated guest molecules, are only found in exceptional cases. As observed by mass spectrometry, when 1-amino-methyl-2,3-diazabicyclo[2.2.2]oct-2-ene (DBOA) is complexed by the macrocycle β-cyclodextrin, its protonated complex undergoes collision-induced dissociation into its components, the conventional reaction pathway. Inside the macrocyclic cavity of cucurbit[7]uril (CB7), a competitive chemical reaction of monoprotonated DBOA takes place upon thermal activation, namely a stepwise homolytic covalent bond cleavage with the elimination of N2, while the doubly protonated CB7⋅DBOA complex undergoes an inner-phase elimination of ethylene, a concerted, electrocyclic ring-opening reaction. These chemical reaction pathways stand in contrast to the gas-phase chemistry of uncomplexed monoprotonated DBOA, for which an elimination of NH3 predominates upon collision-induced activation, as a heterolytic bond cleavage reaction. The combined results, which can be rationalized in terms of organic-chemical reaction mechanisms and density-function theoretical calculations, demonstrate that chemical reactions in the gas phase can be steered chemoselectively through noncovalent interactions. 相似文献
848.
849.
850.
Camilla Russo Dr. Matthew C. Leech Jamie M. Walsh Dr. Joe I. Higham Lisa Giannessi Emmanuelle Lambert Cyrille Kiaku Dr. Darren L. Poole Dr. Joseph Mason Dr. Charles A. I. Goodall Dr. Perry Devo Dr. Mariateresa Giustiniano Dr. Marco Radi Dr. Kevin Lam 《Angewandte Chemie (International ed. in English)》2023,62(38):e202309563
Hydrogenation reactions are staple transformations commonly used across scientific fields to synthesise pharmaceuticals, natural products, and various functional materials. However, the vast majority of these reactions require the use of a toxic and costly catalyst leading to unpractical, hazardous and often functionally limited conditions. Herein, we report a new, general, practical, efficient, mild and high-yielding hydrogen-free electrochemical method for the reduction of alkene, alkyne, nitro and azido groups. Finally, this method has been applied to deuterium labelling. 相似文献