全文获取类型
| 收费全文 | 400篇 |
| 免费 | 3篇 |
| 国内免费 | 2篇 |
专业分类
| 化学 | 285篇 |
| 晶体学 | 6篇 |
| 力学 | 9篇 |
| 数学 | 60篇 |
| 物理学 | 45篇 |
出版年
| 2024年 | 2篇 |
| 2023年 | 7篇 |
| 2022年 | 18篇 |
| 2021年 | 26篇 |
| 2020年 | 19篇 |
| 2019年 | 11篇 |
| 2018年 | 9篇 |
| 2017年 | 14篇 |
| 2016年 | 12篇 |
| 2015年 | 21篇 |
| 2014年 | 16篇 |
| 2013年 | 15篇 |
| 2012年 | 20篇 |
| 2011年 | 29篇 |
| 2010年 | 20篇 |
| 2009年 | 12篇 |
| 2008年 | 30篇 |
| 2007年 | 22篇 |
| 2006年 | 14篇 |
| 2005年 | 19篇 |
| 2004年 | 14篇 |
| 2003年 | 14篇 |
| 2002年 | 11篇 |
| 2001年 | 6篇 |
| 2000年 | 4篇 |
| 1999年 | 5篇 |
| 1998年 | 2篇 |
| 1997年 | 2篇 |
| 1996年 | 3篇 |
| 1993年 | 2篇 |
| 1991年 | 2篇 |
| 1990年 | 1篇 |
| 1985年 | 1篇 |
| 1984年 | 1篇 |
| 1974年 | 1篇 |
排序方式： 共有405条查询结果，搜索用时 15 毫秒
221.
Qing‐Qing Yang Marianna Marchini Prof. Dr. Wen‐Jing Xiao Prof. Dr. Paola Ceroni Prof. Dr. Marco Bandini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18052-18056
Photocatalysis enables the cascade reactions of indoles and CBr4 in MeOH through a C(sp2)?H functionalization/methanolysis sequence. The title reaction provides an efficient access to indole 2‐ and 3‐carboxylates in a single operation (no preinstallation of protecting as well as directing groups was required) with good yields under mild reaction conditions. 相似文献
222.
Pezzella A Panzella L Natangelo A Arzillo M Napolitano A d'Ischia M 《The Journal of organic chemistry》2007,72(24):9225-9230
Chemical or enzymatic oxidation of 5,6-dihydroxyindole (1) leads to the rapid deposition of a black solid resembling eumelanin pigments by way of a complex oligomerization/polymerization process that proceeds in the early stages via dimers 2-3 and trimers 5-6 characterized by 2,4'- and 2,7'-couplings. Despite extensive efforts, the structures of the higher oligomers, which define the structural architecture and physicochemical properties of the eumelanin particles, have so far defied elucidation. Using a dimer-dimer coupling strategy that has recently allowed the first successful entry to a tetramer of 1, we report now three additional tetramers obtained by oxidation of 5,5',6,6'-tetrahydroxy-2,7'-biindolyl (3) with the peroxidase/H2O2 system. On the basis of extensive 2D NMR and mass spectrometric analysis, the products were identified as 5,5',5',5',6,6',6',6'-octaacetoxy-7,2':3',3':2',7'-tetraindolyl (acetylated 8, 3%), 5,5',5',5',6,6',6',6' '-octaacetoxy-2,7':4',4':7',2'-tetraindolyl (acetylated 9, 4%), and 5,5',5',5',6,6',6',6'-octaacetoxy-2,7':2',3':2',7'-tetraindolyl (acetylated 10, 5%), in which the inner units are linked through unexpected 3,3'-, 4,4'-, and 2,3'-linkages. If verified in further studies, the newly uncovered coupling patterns would entail important consequences for current models of eumelanin structure based on one-dimensional structural chains with extended pi-electron conjugation or pi-stacked flat oligomer aggregates. 相似文献
223.
Marianna S. Safronova 《Annalen der Physik》2019,531(5)
In many theories beyond the Standard Model the quantities that we call “fundamental constants” become space‐time dependent, leading to corresponding variation of atomic and molecular spectra and clock frequencies. The extraordinary improvement of the atomic clock precision in the past fifteen years enabled testing the constancy of the fundamental constant at a very high level of precision. Herein, searches for the variation of fundamental constants with clocks are discussed, focusing on recent key results and future proposals, including highly charged ion, molecular, and nuclear clocks. The relevance of the recent searches for oscillatory and transient variation of fundamental constants to the major unexplained phenomena of our Universe, the nature of dark matter, is discussed. 相似文献
224.
Simon Vallières Jeffrey Powell Tanner Connell Michael Evans Marianna Lytova François Fillion-Gourdeau Sylvain Fourmaux Stéphane Payeur Philippe Lassonde Steve MacLean François Légaré 《Laser u0026amp; Photonics Reviews》2024,18(2):2300078
Ultrashort electron beams with femtosecond to picosecond bunch durations offer unique opportunities to explore active research areas ranging from ultrafast structural dynamics to ultra-high dose-rate radiobiological studies. It presents a straightforward method to generate relativistic electron beams in ambient air via the tight focusing of a few-cycle, mJ-class femtosecond infrared laser. It demonstrates experimentally that electrons can reach up to 1.4 MeV at a dose-rate of 0.15 Gy/s, providing enough dose rate for radiation therapy applications. 3D Particle-In-Cell simulations confirm that the acceleration mechanism is based on the relativistic ponderomotive force and show theoretical agreement with the measured electron energies and divergence. Relativistic peak intensities up to 1019 Wcm−2 are reached in ambient air due to a very low B-integral accumulation during focusing, which prevents intensity clamping. Furthermore, it discusses the scalability of this method with the continuing development of mJ-class high average power lasers, and providing a promising approach for FLASH radiation therapy. 相似文献
225.
Välikangas Juho Laine Petteri Hietaniemi Marianna Hu Tao Selent Marcin Tynjälä Pekka Lassi Ulla 《Journal of Solid State Electrochemistry》2023,27(3):641-654
Journal of Solid State Electrochemistry - This article presents a process for producing LiNi1-xAlxO2 (0 < × < 0.05) cathode material with... 相似文献
226.
Francesca Rigano Marianna Oteri Giuseppe Micalizzi Domenica Mangraviti Paola Dugo Luigi Mondello 《Journal of separation science》2020,43(9-10):1773-1780
In a previous article, Rigano et al. established a new linear retention index system for the identification of triacylglycerols by liquid chromatography methods only on the basis of the retention behavior and independently from many experimental parameters. In that work, a database of 209 compounds was built, but only 54 of them, typical of vegetable oils, were confirmed by mass spectrometry. The aim of the present research is to extend the applicability of the novel approach to more complex samples, such as fish lipid extracts, and assess the complementarity between mass spectromtery and retention information to achieve univocal identification. With this purpose, a new software was implemented to make the identification process easy and automatic as in gas chromatography‐mass spectrometry where the retention index filter is added in the spectral search to discriminate between compounds with similar mass spectrometry spectra. A total of 69 species were identified and, thanks to their baseline separation obtained by an ultra high performance liquid chromatography method, a semiquantification was also performed. The species under investigation were Dicentrarchus labrax, coming from aquaculture and the wild. Some differences in their native lipid composition were observed, probably related to a different diet. A major number of samples would be necessary to confirm such a preliminary finding. 相似文献
227.
Dr. Marianna Gambino Dr. Martin Veselý Dr. Matthias Filez Dr. Ramon Oord Dr. Dario Ferreira Sanchez Dr. Daniel Grolimund Dr. Nikolai Nesterenko Dr. Delphine Minoux Marianne Maquet Dr. Florian Meirer Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):3950-3955
Ni contamination from crude oil in the fluid catalytic cracking (FCC) process is one of the primary sources of catalyst deactivation, thereby promoting dehydrogenation–hydrogenation and speeding up coke growth. Herein, single-particle X-ray fluorescence, diffraction and absorption (μXRF-μXRD-μXAS) tomography is used in combination with confocal fluorescence microscopy (CFM) after thiophene staining to spatially resolve Ni interaction with catalyst components and study zeolite degradation, including the processes of dealumination and Brønsted acid sites distribution changes. The comparison between a Ni-lean particle, exposed to hydrotreated feedstock, and a Ni-rich one, exposed to non-hydrotreated feedstock, reveals a preferential interaction of Ni, found in co-localization with Fe, with the γ-Al2O3 matrix, leading to the formation of spinel-type hotspots. Although both particles show similar surface zeolite degradation, the Ni-rich particle displays higher dealumination and a clear Brønsted acidity drop. 相似文献
228.
Vassiliki G. Kontogianni Alexandra Primikyri Marianna Sakka Ioannis P. Gerothanassis 《Magnetic resonance in chemistry : MRC》2020,58(3):232-244
Artemisia annua is a promising and potent antimalarial herbal drug. This activity has been ascribed to its component artemisinin, a sesquiterpene lactone. The ability to determine artemisinin and its known analogs in plant extracts is an especially difficult task because the compounds are present in low concentrations, are thermolabile, and lack ultraviolet or fluorescent chromophores. We report herein a facile and rapid 1-D 1H, 1-D total correlation spectroscopy, 2-D 1H–13C heteronuclear single quantum coherence, and 1H–13C heteronuclear multiple bond correlation nuclear magnetic resonance techniques for the simultaneous identification and quantification of artemisinin and five of its analogs along with five flavonoids, an aromatic ketone, and camphor (in total, 13 compounds) in crude diethyl ether A. annua extract without the need of laborious isolation of the individual analytes. The above method was validated in terms of precision, linearity, and limit of detection. The analytical results were found to be in excellent agreement with those obtained with the use of the time consuming high-performance liquid chromatography with diode-array detection and liquid chromatography with tandem mass spectrometry for the compounds that standards were available. 相似文献
229.
Piotr Olejnik Marianna Gniadek Luis Echegoyen Marta E. Plonska-Brzezinska 《Electroanalysis》2021,33(4):1107-1114
Glassy carbon electrode (GCE) were modified with nanocomposites containing conductive polyaniline nanotubes (PANInt) and carbon nano-onions (CNOs). Herein we report a simple and sensitive way for daidzein (DA) determination at concentrations between 1 and 10 μM by linear sweep voltammetry using GCE/PANInt/CNOs system. The DA electrochemical behavior was examined in two buffer environments (pH 7.5 and 4.5) using electrodes modified with the oxidized CNOs or their derivatives containing carboxyl and benzylamino functional groups. The direct electrooxidation of DA was observed at +0.65 V and +0.8 V at pH 7.5 and at +0.7 V and +1.1 V vs. Ag/AgCl at pH 4.5. 相似文献
230.
Alexandra Primikyri Georgios Papamokos Themistoklis Venianakis Marianna Sakka Vassiliki G. Kontogianni Ioannis P. Gerothanassis 《Molecules (Basel, Switzerland)》2022,27(18)
Artemisinin is known to bind to the main plasma protein carrier serum albumin (SA); however, there are no atomic level structural data regarding its binding mode with serum albumin. Herein, we employed a combined strategy of saturation transfer difference (STD), transfer nuclear Overhauser effect spectroscopy (TR-NOESY), STD–total correlation spectroscopy (STD-TOCSY), and Interligand Noes for PHArmacophore Mapping (INPHARMA) NMR methods and molecular docking calculations to investigate the structural basis of the interaction of artemisinin with human and bovine serum albumin (HSA/BSA). A significant number of inter-ligand NOEs between artemisinin and the drugs warfarin and ibuprofen as well as docking calculations were interpreted in terms of competitive binding modes of artemisinin in the warfarin (FA7) and ibuprofen (FA4) binding sites. STD NMR experiments demonstrate that artemisinin is the main analyte for the interaction of the A. annua extract with BSA. The combined strategy of NMR and docking calculations of the present work could be of general interest in the identification of the molecular basis of the interactions of natural products with their receptors even within a complex crude extract. 相似文献