全文获取类型
收费全文 | 604篇 |
免费 | 43篇 |
专业分类
化学 | 495篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 24篇 |
物理学 | 115篇 |
出版年
2023年 | 15篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 25篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 31篇 |
2013年 | 33篇 |
2012年 | 60篇 |
2011年 | 66篇 |
2010年 | 27篇 |
2009年 | 20篇 |
2008年 | 33篇 |
2007年 | 40篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 25篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有647条查询结果,搜索用时 15 毫秒
111.
Mehdi Asghari‐Khiavi Bayden R. Wood Pejman Hojati‐Talemi Andrew Downes Don McNaughton Adam Mechler 《Journal of Raman spectroscopy : JRS》2012,43(2):173-180
Tip‐enhanced Raman scattering (TERS) spectroscopy is a promising technique for nanoscale chemical analysis. However, there are several challenges preventing widespread application of this technology, including reproducible fabrication of efficient TERS probes. These problems reflect a lack of clear understanding of the origins of, and the parameters influencing TERS. It is believed that the coating characteristics at the apex of the tip have a major effect on the near‐field optical enhancement and thus the TERS activity of a metalized probe. Here we show that the aspect ratio of the tip can play a significant role in the efficiency of TERS probes. We argue that the electrostatic field arising from the lightning‐rod effect has a substantial role in the observed TERS effect. This argument is supported by ‘edge‐enhanced Raman scattering’ which is shown for a noble metal film. Furthermore, it is reported that an associated tip‐surface‐enhanced Raman scattering effect can be achieved by using a TERS‐inactive metalized probe on a surface‐enhanced Raman spectroscopy‐inactive roughened surface. This observation can be explained by an interparticle enhancement of the electromagnetic field. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
112.
A sensitive LC/MS/MS assay for determining zidovudine (ZDV) and lamivudine (3TC) in human plasma was validated to support antiretroviral pharmacology research programs. After addition of stable labeled isotopic zidovudine (ZDV‐IS) and lamivudine (3TC‐IS) as internal standard, a solid‐phase extraction was performed with an Oasis HLB 1 cm3 cartridge, with recoveries of 92.3% for ZDV and 93.9% for 3TC. A Phenomonex Synergi Hydro‐RP (2.0 × 150 mm) reversed‐phase analytical column was utilized for chromatographic separation. The mobile phase consisted of an aqueous solution of 15% acetonitrile and 0.1% acetic acid. Detection was accomplished by ESI/MS/MS in the positive ion mode, monitoring 268/127, 271/130, 230/112 and 233/115 transitions, for ZDV, ZDV‐IS, 3TC and 3TC‐IS, respectively. The method was linear from 1 to 3000 ng/mL with a minimum quantifiable limit of 1 ng/mL when 100 μL of plasma was analyzed. Validation results demonstrated high accuracy (≤8.3% deviation) and high precision (≤10% CV) for the quality control samples. The method was also shown to be specific and reproducible. The value of the high sensitivity was demonstrated by quantitation of approximately 100 existing samples that had ZDV below the limit of quantitation using a previously validated, less sensitive HPLC‐UV method utilized in the laboratory. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
113.
Zachary Nuño Brandon Hessler Bryan Heiberg Ralph Damato Terry Dunlap Young-Seok Shon Yohannes Abate 《Journal of nanoparticle research》2012,14(3):766
Spectroscopic near-field imaging of single silica-shell/Au-core and pure silica nanoparticles deposited on a silicon substrate
is performed in the infrared wavelength range (λ = 9–11 μm) using scattering-type scanning near-field optical microscopy (s-SNOM).
By tuning the wavelength of the incident light, we have acquired information on the spectral phonon–polariton resonant near-field
interactions of the silica-shell/Au-core and pure silica nanoparticles with the probing tip. We made use of the enhanced near-field
coupling between the high index Au-core and the probing tip to achieve spectral near-field contrast of the thin silica coating
(thickness < 10 nm). Our results show that spectroscopic imaging of thin coating layers and complex core–shell nanoparticles
can be directly performed by s-SNOM. 相似文献
114.
BM Kobilka AV Dubrovskiy MD Ewan AL Tomlinson RC Larock S Chaudhary M Jeffries-El 《Chemical communications (Cambridge, England)》2012,48(71):8919-8921
3,7-Diiodo-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b']difurans are efficiently prepared by an iodine-promoted double cyclization. This new heterocyclic core is readily modified by the attachment of alkyl chains for improved solubility. The use of these compounds for the synthesis of new conjugated polymers is also reported. 相似文献
115.
Walid M. Hikal Sanjoy K. Bhattacharia Mark W. Vaughn Brandon L. Weeks 《Molecules (Basel, Switzerland)》2022,27(17)
In this article, we report the in-situ nanoscale experimental measurement of sublimation rates, activation energy of sublimation, and diffusion coefficients of 2,4,6-trinitrotoluene (TNT) single crystals in air using atomic force microscopy (AFM). The crystals were prepared by slow evaporation at 5 °C using acetone-dissolved TNT. The mass loss was calculated by monitoring the shrinkage of the surface area of layered islands formed on the surface of the TNT crystals due to sublimation upon isothermal heating at temperatures below the melting point. The results suggest the sublimation process occurs via two-dimensional detachment of TNT molecules from the non-prominent facets on the crystal surface which imitates the nucleation and crystal growth process. Sublimation rates are one order of magnitude smaller than previously reported values. However, the calculated activation energy (112.15 ± 3.2 kJ/mol) and temperature-dependent sublimation rates agree well with the reported values for TNT thin films and microcrystals determined by UV-vis absorbance spectroscopy and quartz crystal microscopy (QCM) (90–141 kJ/mol). The average diffusion coefficient is (4.35 × 10–6 m2/s) which is within the range of the reported theoretical values with an average of 5.59 × 10–6 m2/s, and about 25% less than that determined using thermogravimetric analysis for powder TNT. 相似文献
116.
Dr. Kaveh Matinkhoo Antonio A. W. L. Wong Dr. Chido M. Hambira Brandon Kato Charlie Wei Dr. Christoph Müller Dr. Torsten Hechler Dr. Alexandra Braun Dr. Francesca Gallo Dr. Andreas Pahl Prof. David M. Perrin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10282-10292
Alpha-amanitin, an extremely toxic bicyclic octapeptide extracted from the death-cap mushroom, Amanita phalloides, is a highly selective allosteric inhibitor of RNA polymerase II. Following on growing interest in using this toxin as a payload in antibody-drug conjugates, herein we report the synthesis and biochemical evaluation of several new derivatives of this toxin to probe the role of the trans-hydroxyproline (Hyp), which is known to be critical for toxicity. This structure activity relationship (SAR) study represents the first of its kind to use various Hyp-analogs to alter the conformational and H-bonding properties of Hyp in amanitin. 相似文献
117.
A (4+1)‐cycloaddition is reported between 1,2‐dicarbonyls and aza‐o‐quinone methide precursors to access 2,3‐dihydroindoles bearing a tetra‐substituted carbon center. The utilization of dioxyphospholenes as carbene surrogates provided dihydroindoles in 20–90 % yield, wherein the electronic nature of the dioxyphospholene impacts its role in the reaction. 相似文献
118.
Brandon Carter Richard A. Battye Jean–Philippe Uzan 《Communications in Mathematical Physics》2003,235(2):289-311
The computation of long range linear self-interaction forces in string and higher dimensional brane models requires the evaluation
of the gradients of regularised values of divergent self-interaction potentials. It is shown that the appropriately regularised
gradient in directions orthogonal to the brane surface will always be obtainable simply by multiplying the regularised potential
components by just half the trace of the second fundamental tensor, except in the hypermembrane case for which the method
fails. Whatever the dimension of the background this result is valid provided the codimension is two (the hyperstring case)
or more, so it can be used for investigating brane-world scenarios with more than one extra space dimension.
Received: 15 April 2002 / Accepted: 23 October 2002 Published online: 25 February 2003
Communicated by H. Nicolai 相似文献
119.
Biotinylation permits recovery of a molecule from a complex mixture, with commercially available streptavidin containing products (such as streptavidin-coated beads). As part of a larger effort to evaluate reagents capable of degrading diazinon, a thiophosphate insecticide, we pursued biotinylation of this molecule. Our strategy focused on replacing a single thiophosphate ethyl ester with an ester linkage that contains biotin. Multiple approaches—using published methods—were unsuccessful and resulted in no reactivity, or degradation of starting material. Here, we report a successful strategy for the synthesis of biotinylated diazinon, which is likely applicable to alternative thiophosphate esters and other biotinylated molecules. 相似文献
120.
Brandon EF van Ooijen RD Sparidans RW Lázaro LL Heck AJ Beijnen JH Schellens JH 《Journal of mass spectrometry : JMS》2005,40(6):821-831
The cyclic depsipeptide aplidine is a new anti-cancer drug of marine origin. Four metabolites of this compound were found after incubation with pooled human microsomes using gradient high-performance liquid chromatography with ultraviolet detection. After chromatographic isolation, the metabolites have been identified using nano-electrospray triple quadrupole mass spectrometry. A highly specific sodium-ion interaction with the cyclic structure opens the depsipeptide ring, and cleavage of the amino acid residues gives sequence information when activated by collision-induced dissociation in the second quadrupole. The aplidine molecule could undergo the following metabolic reactions: hydroxylation at the isopropyl group (metabolites apli-h 1 and apli-h 2); C-dealkylation at the N(Me)-leucine group (metabolite apli-da); hydroxylation at the isopropyl group and C-dealkylation at the N(Me)-leucine group (metabolite apli-da/h), and C-demethylation at the threonine group (metabolite apli-dm). The identification of these metabolites formed in vitro may greatly aid the elucidation of the metabolic pathways of aplidine in humans. 相似文献