全文获取类型
收费全文 | 139篇 |
免费 | 2篇 |
专业分类
化学 | 98篇 |
数学 | 22篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 21篇 |
2011年 | 15篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 7篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1985年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有141条查询结果,搜索用时 15 毫秒
101.
We construct an additive category where objects are embedded graphs in the 3-sphere and morphisms are geometric correspondences given by 3-manifolds realized in different ways as branched covers of the 3-sphere, up to branched cover cobordisms. We consider dynamical systems obtained from associated convolution algebras endowed with time evolutions defined in terms of the underlying geometries. We describe the relevance of our construction to the problem of spectral correspondences in noncommutative geometry. 相似文献
102.
The methanolic extract of Verbascum thapsus was evaluated for its antiviral activity against the pseudorabies virus strain RC/79 (PrV), and also for its cytotoxic activity on Vero cells. The extract showed CC?? values of 1100?μg?mL?1 and 1426?μg?mL?1 by NRU and MTT assays, respectively. The 50% inhibitory concentration of the extract for PrV plaque formation was determined at 35?μg?mL?1, and selectivity indices were 31.4 (NRU) and 40.7 (MTT). When cells were pre-treated with the extract prior to virus infection, the inhibition in plaque formation was 70%. PrV was highly inhibited when it was incubated with plant extract or when the extract was added during the adsorption phase (99%). However, no inhibitory effect was observed when the extract was added to the cells after the adsorption period. Thus, these results suggest that the methanolic extract of Verbascum thapsus may contain bioactive compound(s) that affect PrV mostly in the adsorption phase. 相似文献
103.
Jakob Blom Gabriel J. Reyes‐Rodríguez Henriette N. Tobiesen Johannes N. Lamhauge Marc V. Iversen Casper L. Barlse Niels Hammer Matilde Rusbjerg Karl Anker Jrgensen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):18020-18026
Nucleophile–nucleophile coupling is a challenging transformation in organic chemistry. Herein we present a novel umpolung strategy for α‐functionalization of aldehydes with nucleophiles. The strategy uses organocatalytic enamine activation and quinone‐promoted oxidation to access O‐bound quinol‐intermediates that undergo nucleophilic substitution reactions. These quinol‐intermediates react with different classes of nucleophiles. The focus is on an unprecedented organocatalytic oxidative α‐thiolation of aldehydes. The reaction scope is demonstrated for a broad range of thiols and extended to chemoselective bioconjugation, and applicable to a large variety of aldehydes. This strategy can also encompass organocatalytic enantioselective coupling of α‐branched aldehydes with thiols forming quaternary thioethers. Studies indicate a stereoselective formation of the intermediate followed by a stereospecific nucleophilic substitution reaction at a quaternary stereocenter, with inversion of configuration. 相似文献
104.
Antonella Brizzolara Patrizia Garbati Serena Vella Matilde Calderoni Alessandro Quattrone Gian Paolo Tonini Mario Capasso Luca Longo Raffaella Barbieri Tullio Florio Aldo Pagano 《Molecules (Basel, Switzerland)》2020,25(22)
Despite significant improvement of neuroblastoma (NB) patients’ survival due to recent treatment advancements in recent years, NB is still associated with high mortality rate. In search of novel strategies to increase NB’s susceptibility to pharmacological treatments, we investigated the in vitro and in vivo effects of fendiline hydrochloride as an enhancer of cisplatin antitumor activity. To assess the modulation of fendiline treatment on cisplatin responses, we used in vitro (evaluating NB cell proliferation by XCELLigence technology and colony formation, and gene expression by RT-PCR) and in vivo (NB cell grafts in NOD-SCID mice) models of NB. NB cell treatment with fendiline induced the expression of the ncRNA NDM29, leading to cell differentiation and to the reduction of the expression of MDRs/ABC transporters linked to multidrug resistance. These events were correlated to higher NB cell susceptibility to cisplatin and, consequently, increased its cytotoxic potency. In vivo, this drug interaction causes an enhanced ability of cisplatin to induce apoptosis in NB masses, resulting in tumor growth reduction and prolonged animal survival rate. Thus, the administration of fendiline might be a possible novel therapeutic approach to increase cisplatin efficacy in aggressive and poorly responsive NB cases. 相似文献
105.
Lorenzo Navarro Elena Bilbao José Luis Vilas Matilde Rodríguez Luis Manuel León 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):718-728
In this study, the thermal behavior of polyacenaphthylene (PAcN) and partially modified polyacenaphthylene with Cl, Br, and H2PO3 groups, both under air and nitrogen atmosphere, have been investigated. The influence of the molecular weight, the heating rate, and the introduced substituent have been studied. Thermogravimetric Analysis combined with Fourier Transform Infrared Spectroscopy was used to determine the thermal stabilities and the degradation mechanism. All polyacenaphthylene samples degrade through a depolymerisation process under a nitrogen atmosphere, whereas in air, elimination and thermo-oxidation reactions take place. 相似文献
106.
Fondo M Ocampo N García-Deibe AM Corbella M El Fallah MS Cano J Sanmartín J Bermejo MR 《Dalton transactions (Cambridge, England : 2003)》2006,(41):4905-4913
The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium. 相似文献
107.
Dr. Alessandra Zanut Dr. Francesco Palomba Matilde Rossi Scota Sara Rebeccani Prof. Massimo Marcaccio Dr. Damiano Genovese Prof. Enrico Rampazzo Prof. Giovanni Valenti Prof. Francesco Paolucci Prof. Luca Prodi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22042-22047
The combination of highly sensitive techniques such as electrochemiluminescence (ECL) with nanotechnology sparked new analytical applications, in particular for immunoassay-based detection systems. In this context, nanomaterials, particularly dye-doped silica nanoparticles (DDSNPs) are of high interest, since they can offer several advantages in terms of sensitivity and performance. In this work we synthesized two sets of monodispersed and biotinylated [Ru(bpy)3]2+-doped silica nanoparticles, named bio-Triton@RuNP and bio-Igepal@RuNP, obtained following the reverse microemulsion method using two different types of nonionic surfactants. Controlling the synthetic procedures, we were able to obtain nanoparticles (NPs) offering highly intense signal, using tri-n-propylamine (TPrA) as coreactant, with bio-Triton@RuNps being more efficient than bio-Igepal@RuNP. 相似文献
108.
Efficient Deposition of Semiconductor Powders for Photoelectrocatalysis by Airbrush Spraying 下载免费PDF全文
Ramona Gutkowski Dominik Schäfer Tharamani C. Nagaiah Jorgé E. Yanez Heras Wilma Busser Martin Muhler Wolfgang Schuhmann 《Electroanalysis》2015,27(2):285-292
Powder catalysts were deposited as thin films on transparent conductive oxides (TCO) by means of an airbrush spray coating technique. Photoelectrocatalytic properties of the powder catalysts were characterized using photocurrent spectroscopy at different wavelengths demonstrating on the one hand the stability of the films and on the other hand the electrical connection with the electrode surface. The morphology and thickness of the deposited powder catalyst films on TCO were characterized using scanning electron microscopy. Aiming at photocatalytic water splitting, semiconductor powders like gallium oxide (Ga2O3) and zinc oxide (ZnO) were used as test samples to optimize the deposition technique resulting in thin homogeneous layers and good adhesion on the conductive substrate. The proposed airbrush deposition technique of powder catalysts allows closing an experimental gap between microheterogeneous systems and modified electrodes for finding suitable materials for photoelectrochemical water splitting. 相似文献
109.
Senatore M Lattanzi A Santoro S Santi C Della Sala G 《Organic & biomolecular chemistry》2011,9(18):6205-6207
The first example of meso-aziridine desymmetrization with selenium nucleophiles is reported. The reaction, promoted by VAPOL-hydrogen phosphate using (phenylseleno)trimethylsilane as the nucleophile, proves to be very general and highly enantioselective (84-99% ee). 相似文献
110.
Matilde S. Rodrigues Samira G. Ferreira Csar Quiroz Christopher J. Earley Diego García-Borreguero Rodrigo A. Cunha Francisco Ciruela Attila Kfalvi Sergi Ferr 《Molecules (Basel, Switzerland)》2022,27(5)
Brain iron deficiency (BID) constitutes a primary pathophysiological mechanism in restless legs syndrome (RLS). BID in rodents has been widely used as an animal model of RLS, since it recapitulates key neurochemical changes reported in RLS patients and shows an RLS-like behavioral phenotype. Previous studies with the BID-rodent model of RLS demonstrated increased sensitivity of cortical pyramidal cells to release glutamate from their striatal nerve terminals driving striatal circuits, a correlative finding of the cortical motor hyperexcitability of RLS patients. It was also found that BID in rodents leads to changes in the adenosinergic system, a downregulation of the inhibitory adenosine A1 receptors (A1Rs) and upregulation of the excitatory adenosine A2A receptors (A2ARs). It was then hypothesized, but not proven, that the BID-induced increased sensitivity of cortico-striatal glutamatergic terminals could be induced by a change in A1R/A2AR stoichiometry in favor of A2ARs. Here, we used a newly developed FACS-based synaptometric analysis to compare the relative abundance on A1Rs and A2ARs in cortico-striatal and thalamo-striatal glutamatergic terminals (labeled with vesicular glutamate transporters VGLUT1 and VGLUT2, respectively) of control and BID rats. It could be demonstrated that BID (determined by measuring transferrin receptor density in the brain) is associated with a selective decrease in the A1R/A2AR ratio in VGLUT1 positive-striatal terminals. 相似文献