全文获取类型
收费全文 | 131篇 |
免费 | 4篇 |
专业分类
化学 | 92篇 |
力学 | 3篇 |
数学 | 20篇 |
物理学 | 20篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 9篇 |
2012年 | 3篇 |
2011年 | 12篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1926年 | 2篇 |
排序方式: 共有135条查询结果,搜索用时 15 毫秒
101.
D. Acel A. Hahn M. Richter-Quittner J. K. Parnas R. Wagner R. Wodon O. Folin H. Bierry L. Moquet C. M. Wilhelmj E. Ponder W. Autenrieth H. Taege P. Cristol F. Utz G. E. Youngburg J. Munich L. Michaelis M. Maeda F. Fonseca Pincussen A. T. Merril H. Lucke J. C. Bock M. Gilbert 《Analytical and bioanalytical chemistry》1926,69(7-8):314-320
102.
Room temperature solution synthesis of alkyl-capped tetrahedral shaped silicon nanocrystals 总被引:2,自引:0,他引:2
Baldwin RK Pettigrew KA Garno JC Power PP Liu GY Kauzlarich SM 《Journal of the American Chemical Society》2002,124(7):1150-1151
We report the room temperature solution synthesis of alkyl protected silicon nanocrystals. The nanocrystals are of unusually uniform tetrahedral morphology and of a limited size distribution. The nanocrystals were characterized by transmission and scanning electron microscopy as well as atomic force microscopy. 相似文献
103.
Hurley CA Wong JB Ho J Writer M Irvine SA Lawrence MJ Hart SL Tabor AB Hailes HC 《Organic & biomolecular chemistry》2008,6(14):2554-2559
A range of monocationic and dicationic dioxyalkylglycerol cytofectins have been synthesised possessing methylene and short n-ethylene glycol spacers. The monocationic compounds were found to be effective in transfections when formulated as lipopolyplexes with peptide and DNA components, in particular with shorter PEG head groups which may have less effect on peptide targeting in the ternary complex. 相似文献
104.
Hughes AV Howse JR Dabkowska A Jones RA Lawrence MJ Roser SJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):1989-1999
Floating supported bilayers (FSBs) are new systems which have emerged over the past few years to produce supported membrane mimics, where the bilayers remain associated with the substrate, but are cushioned from the substrates constraining influence by a large hydration layer. In this paper we describe a new approach to fabricating FSBs using a chemically grafted phospholipid layer as the support for the floating membrane. The grafted lipid layer was produced using a Langmuir-Schaeffer transfer of acryloyl-functionalized lipid onto a pre-prepared substrate, with AIBN-induced cross-polymerization to permanently bind the lipids in place. A bilayer of DSPC was then deposited onto this grafted monolayer using a combination of Langmuir-Blodgett and Langmuir-Schaeffer transfer. The resulting system was characterized by neutron reflection under two water contrasts, and we show that the new system shows a hydrating layer of approximately 17.5 A in the gel phase, which is comparable to previously described FSB systems. We provide evidence that the grafted substrate is reusable after cleaning and suggest that this greatly simplifies the fabrication and characterization of FSBs compared to previous methods. 相似文献
105.
Haochen Qi Meiqi Zhao Huaguo Liang Jayne Wu Zhengfeng Huang Anming Hu Jian Wang Yingchun Lu Jian Zhang 《Electrophoresis》2019,40(20):2699-2705
Copper is an indispensable trace element for human health. Too much or too little intake of copper ion (Cu2+) can lead to its own adverse health conditions. Therefore, detection of Cu2+ is always of vital importance. In this work, a simple sensor was developed for rapid detection of trace Cu2+ in water, in which L‐cysteine (Cys) as a molecular probe was self‐assembled on a gold interdigital electrode to form a monolayer for specific capture of Cu2+. The interfacial capacitance of interdigital electrode was detected to indicate the target adsorption level under an AC signal working as the excitation to induce directed movement and enrichment of Cu2+ to the electrode surface. This sensor reached a limit of detection of 4.14 fM and a satisfactory selectivity against eight other ions (Zn2+, Hg2+, Pb2+, Cd2+, Mg2+, Fe2+, As3+, and As5+). Testing of spiked tap water was also performed, demonstrating the sensor's usability. This sensor as well as the detection method shows a great application potential in fields such as environmental monitoring and medical diagnosis. 相似文献
106.
Singh Y Sharpe PC Hoang HN Lucke AJ McDowall AW Bottomley SP Fairlie DP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):151-160
Transformation of proteins and peptides to fibrillar aggregates rich in β sheets underlies many diseases, but mechanistic details of these structural transitions are poorly understood. To simulate aggregation, four equivalents of a water‐soluble, α‐helical (65 %) amphipathic peptide (AEQLLQEAEQLLQEL) were assembled in parallel on an oxazole‐containing macrocyclic scaffold. The resulting 4α‐helix bundle is monomeric and even more α helical (85 %), but it is also unstable at pH 4 and undergoes concentration‐dependent conversion to β‐sheet aggregates and amyloid fibrils. Fibrils twist and grow with time, remaining flexible like rope (>1 μm long, 5–50 nm wide) with multiple strings (2 nm), before ageing to matted fibers. At pH 7 the fibrils revert back to soluble monomeric 4α‐helix bundles. During α→β folding we were able to detect soluble 310 helices in solution by using 2D‐NMR, CD and FTIR spectroscopy. This intermediate satisfies the need for peptide elongation, from the compressed α helix to the fully extended β strand/sheet, and is driven here by 310‐helix aggregation triggered in this case by template‐promoted helical bundling and by hydrogen‐bonding glutamic acid side chains. A mechanism involving α?α4?(310)4?(310)n?(β)n?m(β)n equilibria is plausible for this peptide and also for peptides lacking hydrogen‐bonding side chains, with unfavourable equilibria slowing the α→β conversion. 相似文献
107.
Harvey RD Heenan RK Barlow DJ Lawrence MJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9282-9290
Surface pressure-area isotherm, neutron specular reflection, and small-angle neutron scattering studies have been carried out to determine the effects of added cholesterol and distearoylphosphatidylcholine (DSPC), on the molecular structures of monolayers and vesicles containing the dialkyl polyoxyethylene ether surfactant, 1,2-di-O-octadecyl-rac-glyceryl-3-(alpha-dodecaethylene glycol) (2C18E12). Previous neutron reflectivity studies on 2C18E12 monolayers at the air/water interface have shown them to possess a thickness of approximately 24 angstoms and highly disordered structure with significant intermixing of the polymer headgroups and alkyl chains. SANS studies of 2C18E12 vesicles gave a bilayer thickness of approximately 51 angstroms. Addition of cholesterol to 2C18E12 monolayers (1:1 molar ratio), produced a marked condensing effect coupled with an increased the layer thickness of approximately 7 angstroms, and in vesicles, increased bilayer thickness by approximately 16 angstroms. Monolayers consisting of 2C18E12:DSPC:cholesterol (1:1:2 molar ratio), showed a layer thickness of approximately 31 angstroms, whereas in vesicles, three-component bilayer was found to be only approximately 9 angstroms thicker than those possessed by vesicles composed solely of 2C18E12. Mixing between the molecules in three-component monolayers was shown to be ideal through analysis of the neutron reflectivity data. These findings are discussed in relation to increased ordering and decreased headgroup/hydrophobe intermixing within both monolayers and vesicle bilayers containing 2C18E12. The inferred increase in molecular order within vesicles composed of 2C18E12 with additional cholesterol and phospholipid is used as a model for explaining theoretical differences in bilayer permeability. 相似文献
108.
Hacker CA Batteas JD Garno JC Marquez M Richter CA Richter LJ van Zee RD Zangmeister CD 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6195-6205
Monolayers of oligo(phenylene-ethynylene) (OPE) molecules have exhibited promise in molecular electronic test structures. This paper discusses films formed from a novel molecule within this class, 2-fluoro-4-phenylethynyl-1-[(4-acetylthio)phenylethynyl]benzene (F-OPE). The conditions of self-assembled monolayer (SAM) formation were systematically altered to fabricate reproducible high-quality molecular monolayers from the acetate-protected F-OPE molecule. Detailed characterization of the F-OPE monolayers was performed by using an array of surface probes, including reflection absorbance infrared spectroscopy (RAIRS), contact angle (CA) measurements, spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and atomic force microscopy (AFM). XPS and RAIRS established that the SAM formed without removal of the F substituent and without oxidation of the thiol. The monolayer thickness, determined from SE and AFM based nanolithography, was consistent with the formation of a densely packed monolayer. The valence electronic structure of the SAM was consistent with an aromatic structure shifted by the electron-withdrawing fluorine substituent and intermolecular coupling within an oriented array of molecules. 相似文献
109.
Daniel S. Nielsen Dr. Huy N. Hoang Dr. Rink‐Jan Lohman Dr. Timothy A. Hill Dr. Andrew J. Lucke Prof. Dr. David J. Craik Dr. David J. Edmonds Dr. David A. Griffith Charles J. Rotter Dr. Roger B. Ruggeri Dr. David A. Price Dr. Spiros Liras Prof. Dr. David P. Fairlie 《Angewandte Chemie (International ed. in English)》2014,53(45):12059-12063
The use of peptides in medicine is limited by low membrane permeability, metabolic instability, high clearance, and negligible oral bioavailability. The prediction of oral bioavailability of drugs relies on physicochemical properties that favor passive permeability and oxidative metabolic stability, but these may not be useful for peptides. Here we investigate effects of heterocyclic constraints, intramolecular hydrogen bonds, and side chains on the oral bioavailability of cyclic heptapeptides. NMR‐derived structures, amide H–D exchange rates, and temperature‐dependent chemical shifts showed that the combination of rigidification, stronger hydrogen bonds, and solvent shielding by branched side chains enhances the oral bioavailability of cyclic heptapeptides in rats without the need for N‐methylation. 相似文献
110.
Eduardo J.M. Paiva Maria Lucia C.P. da Silva Jayne C.S. Barboza Pedro C. de Oliveira Heizir F. de Castro Domingos S. Giordani 《Ultrasonics sonochemistry》2013,20(3):833-838
Ethyl esters of babassu oil were synthesized by alkaline catalysis to make the green production of biodiesel feasible with simple methods and available technology. Babassu oil is a transparent, light yellow oil extracted from the seeds of the babassu palm (Orbinya sp), and due to its high saturated fatty acid composition (83%), it is considered a non-inedible oil. Transesterification using ethanol represents a valid alternative to using methanol because of ethanol’s lower toxicity and the higher yield on weight compared to methanol. Statistical methodology was applied to optimize the transesterification reaction, which was promoted by ultrasonic waves and mechanical agitation. Nuclear magnetic resonance spectroscopy was used to quantify the conversion attained. Alkaline transesterification assisted by ultrasound produced the best results with respect to reaction time and the phase separation step. The model obtained showed that conversions higher than 97% may be achieved in 10 min with correct tuning of the process variables. 相似文献