全文获取类型
收费全文 | 680篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 491篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 67篇 |
物理学 | 132篇 |
出版年
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 56篇 |
2012年 | 48篇 |
2011年 | 53篇 |
2010年 | 32篇 |
2009年 | 30篇 |
2008年 | 40篇 |
2007年 | 33篇 |
2006年 | 39篇 |
2005年 | 34篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有712条查询结果,搜索用时 31 毫秒
681.
K. Salini K. Suseel Rahul Vincent Mathew 《Applied Physics A: Materials Science & Processing》2014,116(3):1371-1377
The electronic and optical properties of a single exciton in a CdSe/CdS/CdSe/CdS quantum dot is studied by using effective mass approximation with parabolic confinement. The Coloumbic interaction between electron and hole is included by Hartree potential. A self-consistent technique is used to calculate the energy eigenvalue and wavefunction of exciton. Based on this approximation we investigate the effect of core size, shell thickness, well width on exciton binding energy, absorption spectra, and oscillator strength. The results provide the tuning possibility of electronic and optical properties of multilayer quantum dot with layer thickness. 相似文献
682.
Srinivas Reddy Dubbaka Shashidhar NizalapurAzmi Reddy Atthunuri Manohar SallaThresen Mathew 《Tetrahedron》2014
Synthesis of trifluoromethylated acetylenes by copper-mediated trifluoromethylation of potassium alkynyltrifluoroborates with CF3 radicals generated from NaSO2CF3 and tert-butyl hydroperoxide (TBHP) is communicated. The trifluoromethylated acetylenes were obtained in good to moderate yields. The presented method tolerates a wide range of aromatic, heteroaromatic, and aliphatic potassium alkynyltrifluoroborates. 相似文献
683.
S. Chithra B. Jasim C. Anisha Jyothis Mathew E. K. Radhakrishnan 《Applied biochemistry and biotechnology》2014,173(1):30-35
Piper nigrum is very remarkable for its medicinal properties due to the presence of metabolites like piperine. Emerging understanding on the biosynthetic potential of endophytic fungi suggests the possibility to have piperine producing fungi in P. nigrum. In the current study, endophytic fungi isolated from P. nigrum were screened for the presence of piperine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This resulted in the identification of a Mycosphaerella sp. with the ability to produce piperine extracellularly. The biosynthesis of piperine (C17H19NO3) by the endophytic fungal isolate was confirmed by the presence of m/z 286.1 (M + H+) in the LC-MS/MS analysis using positive mode ionization. This was further supported by the presence of specific fragment ions with masses 135, 143, 171 and 201 formed due to the fragmentation of piperine present in the fungal extract. 相似文献
684.
Cellulose and chitin nanomaterials for capturing silver ions (Ag+) from water via surface adsorption
Peng Liu Houssine Sehaqui Philippe Tingaut Adrian Wichser Kristiina Oksman Aji P. Mathew 《Cellulose (London, England)》2014,21(1):449-461
The study explores the potential of cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and chitin nanocrystals (ChNC) isolated from bioresidues to remove silver ions from contaminated water. Zeta sizer studies showed negatively charged surfaces for CNC and CNF isolated from cellulose sludge in the acidic and alkaline pHs, whereas ChNC isolated from crab shell residue showed either positive or negative charges depending on pH conditions. Model water containing silver ions showed a decrease in Ag+ ion concentration (measured by inductively coupled plasma-optical emission spectrometer; inductively coupled plasma mass spectrometry), after treatment with CNC, CNF and ChNC suspensions. The highest Ag+ ion removal was measured near neutral pH for CNC, being 34.4 mg/g, corresponding to 64 % removal. ChNC showed 37 % and CNF showed 27 % removal of silver ions. The WDX (wavelength dispersive X-ray analysis) and XPS (X-ray photoelectron spectroscopy) analysis confirmed the presence of silver ions on the surface of the nanocellulose and nanochitin after adsorption. Surface adsorption on the nanoparticles via electrostatic interactions is considered to be the prominent mechanism of heavy metal ion capture from aqueous medium, with CNC with negative surface charge and negatively charged functional groups being most favourable for the adsorption of positively charged Ag+ ions compared to other native bionanomaterials. 相似文献
685.
The surface plasmon resonance (SPR) properties of Au/AuxAg1?x core/alloy nanoparticles (NPs) have been investigated by means of the discrete dipole approximation. The core/alloy microstructure was varied by changing the shell alloy composition x, its thickness tS, and the shell thickness to core radius ratio (tS/rC) in the range of 0.05–1.0. These changes resulted in a novel tuning of SPR shape, frequency, and extinction. These models were compared with experimental results for Au/AuxAg1?x NPs prepared by a microwave‐mediated hydrothermal processing method, which produces core/alloy NPs with SPR signatures closely resembling those of the models. 相似文献
686.
The [3 + 2] cycloaddition of azides and acetylenes followed by nitrogen quaternization was applied for the generation of novel and highly modular triazolium salts. The selective substitution of the 1,3,4-substitution pattern presets such salts as precursors for a new class of abnormal carbene ligands, thus expanding the family of these high-impact ligands. Metalation of the triazolium salts is highly versatile and is illustrated by direct C-H bond activation as well as by applying a transmetalation protocol, thus providing access to Pd(II), Ru(II), Rh(I), and Ir(I) abnormal carbene complexes. The donor properties of these carbenes were analyzed by using Tolman electronic parameters and were found to be slightly stronger than those the most basic normal carbenes. 相似文献
687.
A palladium-catalyzed reductive N-heteroannulation of enamines derived from 2-nitrobenzenamines forming mixtures of 1,2-dihydroquinoxalines and 3,4-dihydroquinoxalin-2-ones is described. The reactions are performed using bis(dibenzylideneacetone)palladium(0), 1,3-bis(diphenylphosphino)propane, and 1,10-phenanthroline in DMF under 6 atm of carbon monoxide at 70 °C. 相似文献
688.
Dr. Fabio de Moliner Zuzanna Konieczna Dr. Lorena Mendive-Tapia Dr. Rebecca S. Saleeb Katie Morris Dr. Juan Antonio Gonzalez-Vera Dr. Takeshi Kaizuka Prof. Dr. Seth G. N. Grant Dr. Mathew H. Horrocks Dr. Marc Vendrell 《Angewandte Chemie (International ed. in English)》2023,62(4):e202216231
The multiple applications of super-resolution microscopy have prompted the need for minimally invasive labeling strategies for peptide-guided fluorescence imaging. Many fluorescent reporters display limitations (e.g., large and charged scaffolds, non-specific binding) as building blocks for the construction of fluorogenic peptides. Herein we have built a library of benzodiazole amino acids and systematically examined them as reporters for background-free fluorescence microscopy. We have identified amine-derivatized benzoselenadiazoles as scalable and photostable amino acids for the straightforward solid-phase synthesis of fluorescent peptides. Benzodiazole amino acids retain the binding capabilities of bioactive peptides and display excellent signal-to-background ratios. Furthermore, we have demonstrated their application in peptide-PAINT imaging of postsynaptic density protein-95 nanoclusters in the synaptosomes from mouse brain tissues. 相似文献
689.
Mathew M. Simpson Ching Ching Lam Prof. Jonathan M. Goodman Prof. Shankar Balasubramanian 《Angewandte Chemie (International ed. in English)》2023,62(26):e202304756
The epigenetic modification 5-methylcytosine plays a vital role in development, cell specific gene expression and disease states. The selective chemical modification of the 5-methylcytosine methyl group is challenging. Currently, no such chemistry exists. Direct functionalisation of 5-methylcytosine would improve the detection and study of this epigenetic feature. We report a xanthone-photosensitised process that introduces a 4-pyridine modification at a C(sp3)−H bond in the methyl group of 5-methylcytosine. We propose a reaction mechanism for this type of reaction based on density functional calculations and apply transition state analysis to rationalise differences in observed reaction efficiencies between cyanopyridine derivatives. The reaction is initiated by single electron oxidation of 5-methylcytosine followed by deprotonation to generate the methyl group radical. Cross coupling of the methyl radical with 4-cyanopyridine installs a 4-pyridine label at 5-methylcytosine. We demonstrate use of the pyridination reaction to enrich 5-methylcytosine-containing ribonucleic acid. 相似文献
690.
Dr. Christoph Helling Lars J. C. van der Zee Jelle Hofman Felix J. de Zwart Dr. Simon Mathew Dr. Martin Nieger Assoc. Prof. Dr. J. Chris Slootweg 《Angewandte Chemie (International ed. in English)》2023,62(48):e202313397
Herein, we present the formation of transient radical ion pairs (RIPs) by single-electron transfer (SET) in phosphine−quinone systems and explore their potential for the activation of C−H bonds. PMes3 (Mes=2,4,6-Me3C6H2) reacts with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) with formation of the P−O bonded zwitterionic adduct Mes3P−DDQ ( 1 ), while the reaction with the sterically more crowded PTip3 (Tip=2,4,6-iPr3C6H2) afforded C−H bond activation product Tip2P(H)(2-[CMe2(DDQ)]-4,6-iPr2-C6H2) ( 2 ). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip3]⋅+[DDQ]⋅−, and subsequent homolytic C−H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip2P(H)(2-[CMe2{TCQ−B(C6F5)3}]-4,6-iPr2-C6H2) ( 4 , TCQ=tetrachloro-1,4-benzoquinone) and Tip2P(H)(2-[CMe2{oQtBu−B(C6F5)3}]-4,6-iPr2-C6H2) ( 8 , oQtBu=3,5-di-tert-butyl-1,2-benzoquinone), from reactions of PTip3 with Lewis-acid activated quinones, TCQ−B(C6F5)3 and oQtBu−B(C6F5)3, respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C−H bond activation by the synergistic action of radical ion pairs. 相似文献