全文获取类型
收费全文 | 353篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 258篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 54篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 26篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 14篇 |
2012年 | 20篇 |
2011年 | 17篇 |
2010年 | 15篇 |
2009年 | 20篇 |
2008年 | 25篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有363条查询结果,搜索用时 15 毫秒
61.
Interaction of the Fungal Metabolite Harzianic Acid with Rare-Earth Cations (Pr3+, Eu3+, Ho3+, Tm3+)
Maria Michela Salvatore Antonietta Siciliano Alessia Staropoli Francesco Vinale Rosario Nicoletti Marina DellaGreca Marco Guida Francesco Salvatore Mauro Iuliano Anna Andolfi Gaetano De Tommaso 《Molecules (Basel, Switzerland)》2022,27(19)
Rare-earth elements (REEs) are in all respect a class of new contaminants that may have toxic effects on organisms and microorganisms and information on their interactions with natural ligands should be of value to predict and control their diffusion in natural environments. In the current study, we investigate interactions of tripositive cations of praseodymium, europium, holmium, and thulium with harzianic acid (H2L), a secondary metabolite produced by selected strains of fungi belonging to the Trichoderma genus. We applied the same techniques and workflow previously employed in an analogous study concerning lanthanum, neodymium, samarium, and gadolinium tripositive cations. Therefore, in the current study, HPLC-ESI-HRMS experiments, circular dichroism (CD), and UV-Vis spectrophotometric absorption data, as well as accurate pH measurements, were applied to characterize bonding interactions between harzianic acid and Pr3+, Eu3+, Ho3+, and Tm3+ cations. Problems connected to the low solubility of harzianic acid in water were overcome by employing a 0.1 M NaClO4/(CH3OH + H2O 50/50 w/w) mixed solvent. For Pr3+, Ho3+, and Tm3+, only the mono complexes PrL+, HoL+, and TmL+ were detected and their formation constant determined. Eu3+ forms almost exclusively the bis complex for which the corresponding formation constant is reported; under our experimental conditions, the mono complex EuL+ is irrelevant. Combining the results of the present and previous studies, a picture of interactions of harzianic acid with rare-earth cations extending over 8 of the 17 REEs can be composed. In order to complement chemical information with toxicological information, a battery of bioassays was applied to evaluate the effects of praseodymium, europium, holmium, and thulium tripositive cations on a suite of bioindicators including Aliivibrio fischeri (Gram-negative bacterium), Raphidocelis subcapitata (green alga), and Daphnia magna (microcrustacean), and median effective concentration (EC50) values of Pr3+, Eu3+, Ho3+, and Tm3+ for the tested species were assessed. 相似文献
62.
Dr. Ezhumalai David Dr. Alessia Colombo Prof. Dr. Claudia Dragonetti Prof. Dr. Nallasamy Palanisami 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(24):7124-7137
A series of new β-ketoimines containing a ferrocene moiety and their BF2 complexes have been synthesized and structurally characterized. The solvatochromism of the β-ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β-ketoimines exhibited weak emission, attributable to the excited-state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto-enamine tautomerism, induced upon addition of BF3 ⋅ OEt2, which afforded the related BF2 complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β-ketoimines and BF2 complexes exhibited significant aggregation-induced emission behavior in mixtures of CH3CN/H2O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground- and excited-state dipole moments (μg and μe), and the origin of electronic absorption spectra were studied by time-dependent DFT calculations. The second-order nonlinear optical (NLO) properties were determined by the electric-field-induced second-harmonic generation technique. The μβ1907 values of the β-ketoimines increased upon the formation of the related BF2 complexes, mainly due to an enhancement of the ground-state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications. 相似文献
63.
Alessia Petti Matthew C. Leech Anthony D. Garcia Iain C. A. Goodall Adrian P. Dobbs Kevin Lam 《Angewandte Chemie (International ed. in English)》2019,58(45):16115-16118
A new electrochemical methodology has been developed for the generation of oxycarbonyl radicals under mild and green conditions from readily available hemioxalate salts. Mono‐ and multi‐functionalised γ‐butyrolactones were synthesised through exo‐cyclisation of these oxycarbonyl radicals with an alkene, followed by the sp3–sp3 capture of the newly formed carbon‐centred radical. The synthesis of functionalised valerolactone derivatives was also achieved, demonstrating the versatility of the newly developed methodology. This represents a viable synthetic route towards pharmaceutically important fragments and further demonstrates the practicality of electrosynthesis as a green and economical method to activate small organic molecules. 相似文献
64.
Dr. Andrea Chiminazzo Dr. Giuseppe Borsato Alessia Favero Dr. Chiara Fabbro Prof. Dr. Charles E. McKenna Prof. Luca Giuseppe Dalle Carbonare Prof. Dr. Maria Teresa Valenti Prof. Dr. Fabrizio Fabris Prof. Dr. Alessandro Scarso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(14):3617-3626
The synthesis of a conjugate molecule between an unusual red-fluorescent diketopyrrolopyrrole (DPP) unit and a bis-phosphonate (BP) precursor by a click-chemistry strategy to target bone tissue and monitor the interaction is reported. After thorough investigation, conjugation through a triazole unit between a γ-azido rather than a β-azido BP and an alkyne-functionalized DPP fluorophore group turned out to be the winning strategy. Visualization of the DPP-BP conjugate on osteoclasts and specific antiresorption activity were successfully demonstrated. 相似文献
65.
Davide Balestri Paolo P. Mazzeo Claudia Carraro Nicola Demitri Paolo Pelagatti Alessia Bacchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17503-17511
The crystalline sponge method (CSM) is primarily used for structural determination by single‐crystal X‐ray diffraction of a single analyte encapsulated inside a porous MOF. As the host–guest systems often show severe disorder, reliable crystallographic determination is demanding; thus the dynamics of the guest entering and the formation of nanoconfined molecular aggregates has not been in the spotlight. Now, the concept is investigated of the CSM for monitoring the structural evolution of nanoconfined supramolecular aggregates of eugenol guests with displacement of DMF inside the cavities of the flexible MOF, PUM168. The interpretation of the electron density provides a series of unique detailed snapshots depicting the supramolecular guest aggregation, thus showing the tight interplay between the host flexible skeleton and the molecular guests through the DMF‐to‐eugenol exchange process. 相似文献
66.
67.
Dugo P Presti ML Ohman M Fazio A Dugo G Mondello L 《Journal of separation science》2005,28(11):1149-1156
Flavonoids are a large class of naturally occurring aromatic secondary plant metabolites. They constitute one of the most characteristic classes found in nature and more than 4000 flavonoids have been identified and divided into several subclasses. Flavonoids have several effects on human health, mainly related to their antioxidant activity. As a result of the increased interest in the biologically active compounds in food, many research studies have investigated the detection and quantification of antioxidants. Citrus plants are of great interest since they accumulate large amounts of flavonoids and fruit and juices of these species are consumed in large quantities. Despite the extensive research performed on Citrus flavonoids, many compounds still remain unidentified. In this work, flavonoids of five citrus juices: lemon, grapefruit, bergamot, orange, and mandarin were analyzed by microHPLC coupled on-line with an MS detector equipped with an ESI source operating in negative mode. The use of microcolumn HPLC greatly enhanced detection performance. In total, 20 flavonoids of two different subclasses (flavanone and flavone glycosides) were identified with the help of retention data and MS spectral information. 相似文献
68.
69.
70.
Francesco Caravenna Alessandro Garavaglia Remco van der Hofstad 《Random Structures and Algorithms》2019,54(3):444-498
It is well known that many random graphs with infinite variance degrees are ultra‐small. More precisely, for configuration models and preferential attachment models where the proportion of vertices of degree at least k is approximately k?(τ ? 1) with τ ∈ (2,3), typical distances between pairs of vertices in a graph of size n are asymptotic to and , respectively. In this paper, we investigate the behavior of the diameter in such models. We show that the diameter is of order precisely when the minimal forward degree dfwd of vertices is at least 2. We identify the exact constant, which equals that of the typical distances plus . Interestingly, the proof for both models follows identical steps, even though the models are quite different in nature. 相似文献