全文获取类型
收费全文 | 165篇 |
免费 | 5篇 |
专业分类
化学 | 114篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 12篇 |
物理学 | 40篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1970年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有170条查询结果,搜索用时 15 毫秒
51.
Aberration-corrected scanning transmission electron microscopy is used to determine the atomic structure of nanoclusters of cerium dopant atoms embedded in silicon. By channeling electrons along two crystallographic orientations, we identify a characteristic zinc-blende chemical ordering within CeSi clusters coherent with the silicon host matrix. Strain energy limits the size of these ordered arrangements to just above 1 nm. With the local order identified, we then determine the atomic configuration of an individual subnanometer cluster by quantifying the scattering intensity under weak channeling condition in terms of the number of atoms. Analysis based on single-atom visualization also evidences the presence of split-vacancy impurity complexes, which supports the hypothesis of a vacancy-assisted formation of these metastable CeSi nanophases. 相似文献
52.
Alessia Di Gilio Jolanda Palmisani Gianrocco Ventrella Laura Facchini Annamaria Catino Niccol Varesano Pamela Pizzutilo Domenico Galetta Massimo Borelli Pierluigi Barbieri Sabina Licen Gianluigi de Gennaro 《Molecules (Basel, Switzerland)》2020,25(24)
Despite promising results obtained in the early diagnosis of several pathologies, breath analysis still remains an unused technique in clinical practice due to the lack of breath sampling standardized procedures able to guarantee a good repeatability and comparability of results. The most diffuse on an international scale breath sampling method uses polymeric bags, but, recently, devices named Mistral and ReCIVA, able to directly concentrate volatile organic compounds (VOCs) onto sorbent tubes, have been developed and launched on the market. In order to explore performances of these new automatic devices with respect to sampling in the polymeric bag and to study the differences in VOCs profile when whole or alveolar breath is collected and when pulmonary wash out with clean air is done, a tailored experimental design was developed. Three different breath sampling approaches were compared: (a) whole breath sampling by means of Tedlar bags, (b) the end-tidal breath collection using the Mistral sampler, and (c) the simultaneous collection of the whole and alveolar breath by using the ReCIVA. The obtained results showed that alveolar fraction of breath was relatively less affected by ambient air (AA) contaminants (p-values equal to 0.04 for Mistral and 0.002 for ReCIVA Low) with respect to whole breath (p-values equal to 0.97 for ReCIVA Whole). Compared to Tedlar bags, coherent results were obtained by using Mistral while lower VOCs levels were detected for samples (both breath and AA) collected by ReCIVA, likely due to uncorrected and fluctuating flow rates applied by this device. Finally, the analysis of all data also including data obtained by explorative analysis of the unique lung cancer (LC) breath sample showed that a clean air supply might determine a further confounding factor in breath analysis considering that lung wash-out is species-dependent. 相似文献
53.
54.
55.
Gabriele Albertin Stefano Antoniutti Gianluigi Zanardo 《Journal of organometallic chemistry》2007,692(17):3706-3717
Mixed-ligand OsCl(Tp)L(PPh3) complexes 1 [Tp = hydridotris(pyrazolyl)borate; L = P(OMe)3, P(OEt)3 and PPh(OEt)2] were prepared by allowing OsCl(Tp)(PPh3)2 to react with an excess of phosphite. Treatment of chlorocomplexes 1 with NaBH4 in ethanol afforded hydride OsH(Tp)L(PPh3) derivatives 2. Stable dihydrogen [Os(η2-H2)(Tp)L(PPh3)]BPh4 derivatives 3 were prepared by protonation of hydrides 2 with HBF4 · Et2O at −80 °C. The presence of the η2-H2 ligand is supported by short T1 min values and JHD measurements on the partially deuterated derivatives. Treatment of the hydride OsH(Tp)[P(OEt)3](PPh3) complex with the aryldiazonium salt [4-CH3C6H4N2]BF4 afforded aryldiazene [Os(4-CH3C6H4NNH)(Tp){P(OEt)3}(PPh3)]BPh4 derivative 4. Instead, aryldiazenido [Os(4-CH3C6H4N2)(Tp)[P(OEt)3](PPh3)](BF4)2 derivative 5 was obtained by reacting the hydride OsH(Tp)[P(OEt)3](PPh3) first with methyltriflate and then with aryldiazonium [4-CH3C6H4N2]BF4 salt. Spectroscopic characterisation (IR, 15N NMR) by the 15N-labelled derivative strongly supports the presence of a near-linear Os-NN-Ar aryldiazenido group. Imine [Os{η1-NHC(H)Ar}(Tp){P(OEt)3}(PPh3)]BPh4 complexes 6 and 7 (Ar = C6H5, 4-CH3C6H4) were also prepared by allowing the hydride OsH(Tp)[P(OEt)3](PPh3) to react first with methyltriflate and then with alkylazides. 相似文献
56.
Giuseppe Squillaci Carla Zannella Virginia Carbone Paola Minasi Veronica Folliero Debora Stelitano Francesco La Cara Massimiliano Galdiero Gianluigi Franci Alessandra Morana 《Molecules (Basel, Switzerland)》2021,26(9)
The purpose of the current study was to determine the phenolic composition, antioxidant, and antimicrobial activities in grape cane extracts from typical cultivars of Southern Italy. Aqueous extracts at different pHs (1–13) were prepared from “Aglianico”, “Fiano”, and “Greco” grape canes. The results demonstrated that an alkaline pH (13.00) produced the best polyphenol-rich extracts, as the total phenolic content was more than double when compared to the respective extracts prepared at pH 1.00. “Greco” grape canes gave the highest quantity of phenolic compounds at each pH, ranging from 42.7 ± 0.4 to 104.3 ± 3.0 mg Gallic Acid Equivalents (GAE)/g Dry Extract (DE) from pH 1.00 to 13.00. The Radical Scavenging Activity (RSA) and the Ferric Reducing Antioxidant Power (FRAP) were measured. The highest antioxidant activity was showed by “Greco” extract at pH 7.00. Seventy-five compounds were identified in the extracts by HPLC-MS with six of them described for the first time in grape canes. Procyanidins were highly abundant in extracts at pH 7.00, whereas stilbenoids were the most represented compounds at pH 13.00. Very strong antiviral activity against herpes simplex viruses was recorded for the extracts at pH 7.00 and 13.00 that were active in the early stages of infection by acting directly against the viral particles. The overall results suggest that grape canes, currently underutilized, can be usefully valorised by providing active extracts to use as antioxidant and antiviral agents. 相似文献
57.
Gor'kov PL Chekmenev EY Li C Cotten M Buffy JJ Traaseth NJ Veglia G Brey WW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,185(1):77-93
RF heating of solid-state biological samples is known to be a destabilizing factor in high-field NMR experiments that shortens the sample lifetime by continuous dehydration during the high-power cross-polarization and decoupling pulses. In this work, we describe specially designed, large volume, low-E 15N-1H solid-state NMR probes developed for 600 and 900 MHz PISEMA studies of dilute membrane proteins oriented in hydrated and dielectrically lossy lipid bilayers. The probes use an orthogonal coil design in which separate resonators pursue their own aims at the respective frequencies, resulting in a simplified and more efficient matching network. Sample heating at the 1H frequency is minimized by a loop-gap resonator which produces a homogeneous magnetic field B1 with low electric field E. Within the loop-gap resonator, a multi-turn solenoid closely matching the shape of the sample serves as an efficient observe coil. We compare power dissipation in a typical lossy bilayer sample in the new low-E probe and in a previously reported 15N-1H probe which uses a double-tuned 4-turn solenoid. RF loss in the sample is measured in each probe by observing changes in the 1H 360 degrees pulse lengths. For the same values of 1H B1 field, sample heating in the new probe was found to be smaller by an order of magnitude. Applications of the low-E design to the PISEMA study of membrane proteins in their native hydrated bilayer environment are demonstrated at 600 and 900 MHz. 相似文献
58.
Dr. Biwei Xiao Dr. Hanshuo Liu Dr. Ning Chen Dr. Mohammad Norouzi Banis Prof. Haijun Yu Dr. Jianwen Liang Dr. Qian Sun Prof. Tsun-Kong Sham Ruying Li Dr. Mei Cai Prof. Gianluigi A. Botton Prof. Xueliang Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14419-14426
Li- and Mn-rich layered oxides are among the most promising cathode materials for Li-ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near-edge structure (FDMNES) code was combined with in situ X-ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn2O4-like sub-nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size-dependent. After prolonged cycling, the TMs displayed different levels of inactivity. 相似文献
59.
Airoldi C Colombo L Manzoni C Sironi E Natalello A Doglia SM Forloni G Tagliavini F Del Favero E Cantù L Nicotra F Salmona M 《Organic & biomolecular chemistry》2011,9(2):463-472
The antibiotic tetracycline was reported to possess an anti-amyloidogenic activity on a variety of amyloidogenic proteins both in in vitro and in vivo models. To unveil the mechanism of action of tetracycline on Aβ1-40 and Aβ1-42 at both molecular and supramolecular levels, we carried out a series of experiments using NMR spectroscopy, FTIR spectroscopy, dynamic laser light-scattering (DLS) and atomic force microscopy (AFM). Firstly we showed that the co-incubation of Aβ1-42 oligomers with tetracycline hinders the toxicity towards N2a cell lines in a dose-dependent manner. Therefore, the nature of the interaction between the drug and Aβ oligomers was investigated. To carry out NMR and FTIR studies we have prepared Aβ peptide solutions containing assemblies ranging from monomers to large oligomers. Saturation transfer difference (STD) NMR experiments have shown that tetracycline did not interact with monomers at variance with oligomers. Noteworthy, in this latter case we observed that this interaction was very peculiar since the transfer of magnetization from Aβ oligomers to tetracycline involved all drug protons. In addition, intermolecular cross-peaks between tetracycline and Aβ were not observed in NOESY spectra, indicating the absence of a specific binding site and suggesting the occurrence of a supramolecular interaction. DLS and AFM studies supported this hypothesis since the co-dissolution of Aβ peptides and tetracycline triggered the immediate formation of new aggregates that improved the solubility of Aβ peptides, preventing in this way the progression of the amyloid cascade. Moreover, competitive NMR binding experiments showed for the first time that tetracycline competes with thioflavin T (ThT) in the binding to Aβ peptides. Our data shed light on a novel mechanism of anti-amyloidogenic activity displayed by tetracycline, governed by hydrophobic and charge multiparticle interactions. 相似文献
60.