全文获取类型
收费全文 | 942篇 |
免费 | 41篇 |
国内免费 | 1篇 |
专业分类
化学 | 655篇 |
晶体学 | 5篇 |
力学 | 28篇 |
数学 | 170篇 |
物理学 | 126篇 |
出版年
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 52篇 |
2020年 | 25篇 |
2019年 | 32篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 41篇 |
2015年 | 46篇 |
2014年 | 38篇 |
2013年 | 63篇 |
2012年 | 74篇 |
2011年 | 90篇 |
2010年 | 60篇 |
2009年 | 40篇 |
2008年 | 45篇 |
2007年 | 45篇 |
2006年 | 32篇 |
2005年 | 38篇 |
2004年 | 29篇 |
2003年 | 24篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 13篇 |
1992年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1958年 | 1篇 |
1954年 | 2篇 |
1935年 | 1篇 |
1892年 | 1篇 |
排序方式: 共有984条查询结果,搜索用时 15 毫秒
911.
912.
913.
Gioele Colombo Prof. Dr. G. Attilio Ardizzoia Prof. Dr. Julien Furrer Prof. Dr. Bruno Therrien Prof. Dr. Stefano Brenna 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12380-12387
Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1H, 13C, 11B, 19F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant. 相似文献
914.
In this study, a RP-HPLC method for the analysis of polyacetylenes and polyenes in Echinacea pallida roots and phytopharmaceuticals was developed. The reference compounds used for quantification were isolated from the plant material and their structures were determined on the basis of the analysis of UV, IR, NMR and MS data. The complete structure elucidation of three compounds, namely 8-hydroxy-tetradec-(9E)-ene-11,13-diyn-2-one (1), tetradec-(8Z)-ene-11,13-diyn-2-one (6) and pentadec-(8Z)-en-2-one (9) is described. In the analysis of the n-hexane extracts of E. pallida roots, the comparison between conventional and monolithic columns showed that the elution order in both cases is identical and the selectivity is equivalent. However, the retention times achieved by the monolithic column are shorter, resulting in a faster separation (20 min). Therefore, the analyses were carried out on a Chromolith Performance RP-18e (100 mm x 4.6 mm i.d.), with a gradient mobile phase composed by H(2)O and ACN at the flow rate of 2 mL/min. The column was thermostatted at 20 degrees C. The photodiode array detector monitored the eluent at 210 nm. The validation procedure confirmed that this technique affords reliable analysis of these components and is appropriate for the quality control of complex matrices, such as E. pallida roots and phytopharmaceuticals. 相似文献
915.
Magazù S Migliardo F Malomuzh NP Blazhnov IV 《The journal of physical chemistry. B》2007,111(32):9563-9570
The main aim of the present work is to show, for the case of glycerol, the connection between the macroscopic fragility parameter, defined as m = (d log eta)/(d(Tg/T))|T=Tg+, and the average number of H-bonds per molecule. Furthermore, the relation between the macroscopic and microscopic definitions of fragility, which takes into account the temperature dependence of the atomic mean square displacement, is discussed. 相似文献
916.
Obermajer N Sattin S Colombo C Bruno M Svajger U Anderluh M Bernardi A 《Molecular diversity》2011,15(2):347-360
In this article, we describe the design, synthesis and activity evaluation of glycomimetic DC-SIGN antagonists, that use a
mannose residue to anchor to the protein carbohydrate recognition domain (CRD). The molecules were designed from the structure
of the known pseudo-mannobioside antagonist 1, by including additional hydrophobic groups, which were expected to engage lipophilic areas of DC-SIGN CRD. The results demonstrate
that the synthesized compounds potently inhibit DC-SIGN-mediated adhesion to mannan coated plates. Additionally, in silico
docking studies were performed to rationalize the results and to suggest further optimization. 相似文献
917.
Colombo C Bevilacqua F Brambilla L Conti C Realini M Striova J Zerbi G 《Analytical and bioanalytical chemistry》2011,401(2):757-765
The potential of non-invasive in situ analytical techniques such as portable Raman, portable X-ray fluorescence, portable
optical microscope and fibre optics reflectance spectroscopy has been shown studying painted layers of Renaissance terracotta
polychrome sculptures belonging to the statuary of Santo Sepolcro Church in Milan. The results obtained allowed pointing out
the contribution of these techniques to the compositional diagnostic, providing complete information, in some cases, better
than micro-destructive techniques, on the kind of pigments used on the external painted layers. Moreover, a comparison with
the results obtained before the last conservation work (2009) with micro-destructive techniques allowed ascertaining the removal
of the external painted layers during the conservation operations. 相似文献
918.
919.
Todescato F Fortunati I Carlotto S Ferrante C Grisanti L Sissa C Painelli A Colombo A Dragonetti C Roberto D 《Physical chemistry chemical physics : PCCP》2011,13(23):11099-11109
The possibility to exploit a bottom-up approach to design and synthesize multichromophoric structures from a single molecular unit is strategic for the targeted synthesis of molecular compounds with well defined linear and nonlinear absorption properties. In this view, it is important to be able to predict the properties of multichromophoric units, based on the knowledge of the properties of the individual chromophores and their mutual arrangement. To this end, we present a combined experimental and theoretical study on 4-(para-di-n-butylaminostyryl)-pyridine, a push-pull molecule, and its dimer, 4,4'-bis(para-di-n-butylaminostyryl)-2,2'-bipyridine, formed by connecting the two pyridine groups into a bipyridine structure. One photon absorption and fluorescence spectra are measured in solvents of different polarity, and two-photon absorption spectra are recorded in dichloromethane. Experimental results are compared with results of TDDFT (Time-Dependent Density Functional Theory) and CIS (Configuration Interaction with Single excitation) methods implemented in the Gaussian03 program suite. An essential-state analysis of optical spectra is used to rationalize the observed behavior. 相似文献
920.
Gemma S Colombo L Forloni G Savini L Fracasso C Caccia S Salmona M Brindisi M Joshi BP Tripaldi P Giorgi G Taglialatela-Scafati O Novellino E Fiorini I Campiani G Butini S 《Organic & biomolecular chemistry》2011,9(14):5137-5148
Here we describe the identification and preliminary characterization of a new class of pyrrolo(imidazo)quinoxaline hydrazones as florescent probes for Aβ(1-42) fibrils. All the newly developed compounds were able to bind amyloid fibrils formed in vitro and some of them displayed an increase of their fluorescence upon binding. When tested on brain tissue preparations presenting Aβ deposits, the described hydrazones selectively stained amyloid structures and did not display aspecific binding. The hydrazones did not show antifibrillogenic activity and electron microscopy analysis revealed that they do not interfere with fibrils structure. The described pyrrolo(imidazo)quinoxalines could be useful for studying amyloid structures in vitro. Moreover, their experimentally proven ability to cross the blood-brain barrier in mouse opens the possibility of developing these compounds as potential amyloid imaging agents for in vivo applications. 相似文献