全文获取类型
收费全文 | 318篇 |
免费 | 9篇 |
专业分类
化学 | 257篇 |
力学 | 1篇 |
数学 | 33篇 |
物理学 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 23篇 |
2021年 | 21篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 20篇 |
2011年 | 31篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 16篇 |
2007年 | 16篇 |
2006年 | 19篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 3篇 |
1987年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
91.
Stare J Jezierska A Ambrozic G Kosir IJ Kidric J Koll A Mavri J Hadzi D 《Journal of the American Chemical Society》2004,126(13):4437-4443
2D free energy surfaces V = V(rOH, rO...O) for the intramolecular H-bond in the title compound were calculated by the DFT method and used in the calculation of primary and secondary chemical shifts of the compound dissolved in chloroform and acetonitrile. Solvent effects were accounted for by the SCRF/PCM method. The corresponding two-dimensional chemical shift surfaces with included solvent reaction field were obtained using the Continuous Set of Gauge Transformations approach at the B3LYP/6-311+G(2d,2p) level of theory. The chemical shifts were estimated as quantum averages along the two internal coordinates in the hydrogen bond and along several vibrational levels according to the Boltzmann distribution at room temperature. Fairly good agreement between the experimental and calculated isotope effects was obtained. 1D and 2D NMR spectra of solutions of picolinic acid N-oxide and its deuterated analogue were recorded and assigned. 相似文献
92.
Bojarski AJ Mokrosz MJ Duszyńska B Kozioł A Bugno R 《Molecules (Basel, Switzerland)》2004,9(3):170-177
Two sets of new o-methoxyphenylpiperazine (MPP; series a) and 1,2,3,4-tetrahydroisoquinoline (THIQ; series b) derivatives, containing various imide moieties derived from NAN190, were synthesized and evaluated in vitro for their ability to bind to the serotonin 5-HT(1A) and 5-HT(2A) receptors. All new derivatives from series a demonstrated high 5-HT(1A) affinities, whereas THIQ analogues were much less active. With respect to 5-HT(2A) receptors, three MPP derivatives presented moderate activity but the rest of the investigated compounds were practically inactive. The influence of changes in terminus geometry on 5-HT(1A) receptor affinity was analyzed in regard to model compounds NAN190and MM199. 相似文献
93.
Marta Vinha Vieira Igor Piotr Turkiewicz Karolina Tkacz Claudio Fuentes-Grünewald Lorenzo M. Pastrana Pablo Fucios Aneta Wojdyo Paulina Nowicka 《Molecules (Basel, Switzerland)》2021,26(24)
The functional food market has been in a state of constant expansion due to the increasing awareness of the impact of the diet on human health. In the search for new natural resources that could act as a functional ingredient for the food industry, microalgae represent a promising alternative, considering their high nutritional value and biosynthesis of numerous bioactive compounds with reported biological properties. In the present work, the phytochemical profile, antioxidant activity, and enzymatic inhibitory effect aiming at different metabolic disorders (Alzheimer’s disease, Type 2 diabetes, and obesity) were evaluated for the species Porphyridium purpureum, Chlorella vulgaris, Arthorspira platensis, and Nannochloropsis oculata. All the species presented bioactive diversity and important antioxidant activity, demonstrating the potential to be used as functional ingredients. Particularly, P. purpureum and N. oculata exhibited higher carotenoid and polyphenol content, which was reflected in their superior biological effects. Moreover, the species P. purpureum exhibited remarkable enzymatic inhibition for all the analyses. 相似文献
94.
Jarosław J. Panek Riccardo Mazzarello Marjana Novič Aneta Jezierska-Mazzarello 《Molecular diversity》2011,15(1):215-226
Mercury(II) has a strong affinity for the thiol groups in proteins often resulting in the disruption of their biological functions. In this study we present classical and first-principles, DFT-based molecular dynamics (MD) simulations of a complex of Hg(II) and proteinase K, a well-known serine protease with a very broad and diverse enzymatic activity. It contains a catalytic triad formed by Asp39, His69, and Ser224, which is responsible for its biological activity. It was found previously by X-ray diffraction experiments that the presence of Hg(II) inhibits the enzymatic action of proteinase K by affecting the stereochemistry of the triad. Our simulations predict that (i) the overall structure as well as the protein backbone dynamics are only slightly affected by the mercury cation, (ii) depending on the occupied mercury site, the hydrogen bonds of the catalytic triad are either severely disrupted (both bonds for mercury at site 1, and the His69–Ser224 contact for mercury at site 2) or slightly strengthened (the Asp39–His69 bond when mercury is at site 2), (iii) the network of hydrogen bonds of the catalytic triad is not static but undergoes constant fluctuations, which are significantly modified by the presence of the Hg(II) cation, influencing in turn the triad’s ability to carry out the enzymatic function—these facts explain the experimental findings on the inhibition of proteinase K by Hg(II). 相似文献
95.
Simulating the effect of carbon nanotube curvature on adsorption of polycyclic aromatic hydrocarbons
Radosław P. Wesołowski Sylwester Furmaniak Artur P. Terzyk Piotr A. Gauden 《Adsorption》2011,17(1):1-4
The results of Molecular Dynamics simulation of polycyclic aromatic hydrocarbons adsorption on single-walled (13,9) carbon nanotube are reported. We discuss the angular orientation and plausible adsorbed states of molecules. It is shown, that suggested by Gotovac et al. orientation of adsorbed molecules is correct. 相似文献
96.
Małgorzata I. Szynkowska Aneta Węglińska Elżbieta Wojciechowska Tadeusz Paryjczak 《Chemical Papers》2009,63(2):233-238
Commercial hopcalite calcined at different temperatures and hopcalite modified with noble metals (Pt, Pd, and Au) were studied
in oxidation of thiophene. Surface and bulk properties of catalysts were studied using temperature-programmed reduction (TPRH2), X-ray diffraction method (XRD) and thermal analysis (TG-DTA-MS). It was shown that calcined samples displayed higher activity
in comparison with commercial untreated hopcalite; however, a lower temperature of calcination was favourable. High temperature
of thermal treatment induced an increase in the crystallinity and a decrease in the surface area of the samples, and, as a
consequence, the loss of catalysts activity. Moreover, marked improvement in the catalytic performance of platinum and palladium
modified catalysts in relation to base hopcalite was observed. The obtained results indicate that the higher activity of samples
containing Pt and Pd was accompanied by better reducibility of the catalysts.
Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May
2008. 相似文献
97.
M. Wesołowski W. Strupiński M. Motyka G. Sęk E. Dumiszewska P. Caban A. Jasik A. Wójcik K. Pierściński D. Pierścińska 《Opto-Electronics Review》2011,19(2):140-144
The antimonide laser heterostructures growth technology using MBE epitaxy is currently well-developed, while MOVPE method
is still being improved. It is known that the principal problem for MOVPE is the oxygen and carbon contamination of aluminium
containing waveguides and claddings. The solution would be to apply a proper aluminium precursor. In this study we present
the results of metal-organic epitaxy of In- and Al-containing layers and quantum well structures composing antimonide lasers
devices. Special emphasis was put on the aluminium precursor and its relation to AlGaSb and AlGaAsSb materials properties.
The crystalline quality of the layers grown with two different Al precursors was compared, very good structural quality films
were obtained. The results suggested a substantial influence of precursors pre-reactions on the epitaxial process. The oxygen
contamination was measured by SIMS, which confirmed its dependence on the precursor choice. We also optimised the GaSb substrate
thermal treatment to deposit high quality GaSb homoepitaxial layers. Quaternary InGaAsSb layers were obtained even within
the predicted miscibility gap, when arsenic content reached high above 10% values. InGa(As)Sb/AlGa(As)Sb quantum wells were
grown and their optical properties were characterised by photoluminescence and photoreflectance spectroscopy. Type-I quantum
wells showed a fundamental optical transition in the 1.9–2.1 μm range at room temperature. The epitaxial technology of the
structures was subjected to an optimisation procedure. The investigated layers and heterostructures can be considered for
application in laser devices. 相似文献
98.
Aneta Kolary-Zurowska Artur Zurowski Sonia Dsoke Beata Dembinska Sylwia Zoladek Malgorzata Kiliszek Roberto Marassi Pawel J. Kulesza 《Journal of Solid State Electrochemistry》2014,18(11):2993-3001
A unique preparation method of obtaining stable composite film (with ultra-low platinum content) highly active towards oxygen reduction and hydrogen oxidation is presented here. The matrix for platinum centers consists of high-surface-area zeolite-type acidic salt of cesium phosphododecatungstate (Cs2.5H0.5PW12O40) admixed with carbon (Vulcan XC-72) carriers. Platinum nanoparticles were deposited on the working electrode modified with matrix via corrosion of platinum counter electrode during cyclic voltammetry experiment conducted in acid electrolyte containing chloride ions. The results obtained from rotating disk voltammetry revealed that the composite film containing Pt nanoparticles at very low loadings (on the level of 2–5 μg cm?2) demonstrated remarkable electrocatalytic activity towards both oxygen reduction and hydrogen oxidation, particularly, when compared to the performance of the Cs2.5H0.5PW12O40-free system (i.e., containing only Vulcan support) prepared and examined under analogous conditions. The phenomenon should be primarily ascribed to the mesoporous nature of the matrix enabling immobilization and stabilization of small catalytic nanoparticles (1–2 nm diameters) inside the pores as well as to high surface acidity of the polyoxometalate-based salt providing proton-rich environment at the electrocatalytic interface. 相似文献
99.
Aneta M. Tomkiel Dorota Czajkowska-Szczykowska Ewa Olchowik-Grabarek Lucie Rrov Szymon Skowski Jacek W. Morzycki 《Molecules (Basel, Switzerland)》2023,28(1)
A chemoselective procedure for MCPBA oxidation of 26-thiodiosgenin to corresponding sulfoxides and sulfone was elaborated. An unusual equilibration of sulfoxides in solution was observed. Moreover, α-alkylation of sulfoxide and sulfone was investigated. Finally, the biological activity of obtained compounds was examined. 相似文献
100.
Bacterial adhesion to epithelial cells is a key step in infections, allowing subsequent colonization, invasion and internalization of pathogens into tissues. Anti-adhesive agents are therefore potential prophylactic tools against bacterial infections. The range of anti-adhesive compounds is largely confined to carbohydrate analogues. Tannins are generously recognized as potent antimicrobials, but little data exist on their anti-adherence potency. Using a model for mucosal pathogenesis with labeled group A-streptococci (GAS) and human laryngeal HEp-2 cells, a series of flavan-3-ols (epicatechin, epigallocatechin, epigallocatechin-3-O-gallate) and highly purified and chemically characterized proanthocyanidin samples including procyanidins based on epicatechin, catechin or 'mixed' constituent flavanyl units, prodelphinidins made up of (epi)gallocatechin monomeric unts as well as oligomers possessing A-type units in their molecules was evaluated for anti-adhesive effects. Reduced microbial adherence was observed exclusively for prodelphinidins, suggesting that pyrogallol-type elements, i.e., (epi)gallocatechin units are important structural features. This is the first report on structure-activity relationships regarding the anti-adhesive potency of proanthocyanidins. In addition, the structures of the first chemically defined proanthocyanidins from Pelargonium sidoides are disclosed. 相似文献