全文获取类型
收费全文 | 703篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
化学 | 608篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 74篇 |
物理学 | 52篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 55篇 |
2021年 | 45篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 31篇 |
2015年 | 23篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 44篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 49篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 29篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有743条查询结果,搜索用时 31 毫秒
691.
Pietro Celada Stefania Perrotta 《Calculus of Variations and Partial Differential Equations》2001,12(4):371-398
We consider the problem of minimizing multiple integrals of product type, i.e.
where is a bounded, open set in , is a possibly nonconvex, lower semicontinuous function with p-growth at infinity for some and the boundary datum is in (or simply in if ). Assuming that the convex envelope off is affine on each connected component of the set , we prove attainment for () for every continuous, positively bounded below function g such that (i) every point is squeezed between two intervals where g is monotone and (ii) g has no strict local minima. This shows in particular that the class of coefficents g that yield existence to () is dense in the space of continuous, positive functions on . We present examples which show that these conditions for attainment are essentially sharp.
Received April 12, 2000 / Accepted May 9, 2000 / Published online November 9, 2000 相似文献
692.
693.
Gaelle Derrien Jusef Hassoun Simone Sacchetti Stefania Panero 《Solid State Ionics》2009,180(23-25):1267-1271
In this work we report a new composite, PEO-based lithium polymer electrolyte containing a micro-sized, nanoporous zirconium–oxide–sulfate (Zr–O–SO4) filler synthesized by a surfactant templating sol–gel route. By thermal and transport studies, we show that the particular morphology of the filler enhances the properties of the material leading to a solvent-free electrolyte having unique features in terms of ionic conductivity, lithium ion transference number and thermal behaviour. Finally, the galvanostatic test of the lithium battery prepared using lithium iron phosphate, LiFePO4, as the cathode, lithium metal as the anode and the studied membrane as the electrolyte, shows enhanced performances also at the medium–low temperatures. 相似文献
694.
Stefania Barzaghi Lucia Monti Laura Marinoni Tiziana M. P. Cattaneo 《Molecules (Basel, Switzerland)》2021,26(16)
Proteomics and metabolomics are analytic tools used in combination with bioinformatics to study proteins and metabolites which contribute to describing complex biological systems. The growing interest in research concerning the resolution of these systems has stimulated the development of sophisticated procedures and new applications. This paper introduces the evolution of statistical techniques for the treatment of data, suggesting the possibility to successfully characterize the milk-whey syneresis process by applying two-dimensional correlation analysis (2DCOR) to a series of CE electropherograms referring to milk-whey samples collected during cheese manufacturing. Two cheese-making processes to produce hard cheese (Grana type) and fresh cheese (Crescenza) were taken as models. The applied chemometric tools were shown to be useful for the treatment of data acquired in a systematically perturbed chemical system as a function of time. 相似文献
695.
Stefania Cometa Maria Addolorata Bonifacio Caterina Licini Annalisa Bellissimo Loris Pinto Federico Baruzzi Monica Mattioli-Belmonte Elvira De Giglio 《Molecules (Basel, Switzerland)》2021,26(16)
Hydrogel formulations (masks or patches, without tissue support) represent the new frontier for customizable skin beauty and health. The employment of these materials is becoming popular in wound dressing, to speed up the healing process while protecting the affected area, as well as to provide a moisturizing reservoir, control the inflammatory process and the onset of bacterial development. Most of these hydrogels are acrylic-based at present, not biodegradable and potentially toxic, due to acrylic monomers residues. In this work, we selected a new class of cellulose-derived and biodegradable hydrogel films to incorporate and convey an active compound for dermatological issues. Films were obtained from a combination of different polysaccharides and clays, and berberine hydrochloride, a polyphenolic molecule showing anti-inflammatory, immunomodulatory, antibacterial and antioxidant properties, was chosen and then embedded in the hydrogel films. These innovative hydrogel-based systems were characterized in terms of water uptake profile, in vitro cytocompatibility and skin permeation kinetics by Franz diffusion cell. Berberine permeation fitted well to Korsmeyer–Peppas kinetic model and achieved a release higher than 100 µg/cm2 within 24 h. The latter study, exploiting a reliable skin model membrane, together with the biological assessment, gained insights into the most promising formulation for future investigations. 相似文献
696.
697.
Enrico Monzani Stefania Nicolis Simone Dell'Acqua Andrea Capucciati Chiara Bacchella Fabio A. Zucca Eugene V. Mosharov David Sulzer Luigi Zecca Luigi Casella 《Angewandte Chemie (International ed. in English)》2019,58(20):6512-6527
Dopamine (DA) is the most important catecholamine in the brain, as it is the most abundant and the precursor of other neurotransmitters. Degeneration of nigrostriatal neurons of substantia nigra pars compacta in Parkinson's disease represents the best‐studied link between DA neurotransmission and neuropathology. Catecholamines are reactive molecules that are handled through complex control and transport systems. Under normal conditions, small amounts of cytosolic DA are converted to neuromelanin in a stepwise process involving melanization of peptides and proteins. However, excessive cytosolic or extraneuronal DA can give rise to nonselective protein modifications. These reactions involve DA oxidation to quinone species and depend on the presence of redox‐active transition metal ions such as iron and copper. Other oxidized DA metabolites likely participate in post‐translational protein modification. Thus, protein–quinone modification is a heterogeneous process involving multiple DA‐derived residues that produce structural and conformational changes of proteins and can lead to aggregation and inactivation of the modified proteins. 相似文献
698.
Stefania Garzoli Valentina Laghezza Masci Giovanni Turchetti Lorenzo Pesci Antonio Tiezzi 《Natural product research》2019,33(13):1980-1983
The pepper-tree Schinus molle is an evergreen ornamental plant with various and diversified list of medical uses. In this article we analysed the chemical composition of male and female leaves of this plant during the off-flowering and flowering seasons. The leaf extracts were obtained by using a sequential extraction with solvents of different polarities and the chemical composition was investigated by GC-MS. The results showed a total of twenty-three components, in which elemol is the most abundant constituent followed by bicyclogermacrene, γ-eudesmol, α-eudesmol, β-eudesmol and isocalamendiol. The petroleum ether and diethyl ether extracts from male and female flowering and off-flowering leaves consisted of sesquiterpene hydrocarbons as a major constituent followed by monoterpene hydrocarbons, while the acetone extracts showed a different composition. The obtained results show differences in the chemical composition between male and female and flowering and not flowering. 相似文献
699.
Stefania Pragliola Chiara Costabile Mariagrazia Napoli Gaetano Guerra Pasquale Longo 《Macromolecular Symposia》2006,234(1):128-138
Olefin-diene copolymerizations in the presence of C2 symmetric zirconocene rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2/MAO catalytic system have been reported and rationalized by experimental and molecular modeling studies. Ethene gives 1,2-cyclopropane and 1,2-cyclopentane, 1,3-cyclobutane, and 1,3-cyclopentane units in copolymerization with 1,3-butadiene, 1,4-pentadiene, and 1,5-hexadiene, respectively. Propene-1,3-butadiene copolymerizations lead to 1,2 and 1,4 butadiene units and to a low amount of 1,2-cyclopropane units. 相似文献
700.
Eleonora Truzzi Lucia Marchetti Stefania Benvenuti Valeria Righi Maria Cecilia Rossi Vito Gallo Davide Bertelli 《Molecules (Basel, Switzerland)》2021,26(18)
Essential oils (EOs) are more and more frequently adulterated due to their wide usage and large profit, for this reason accurate and precise authentication techniques are essential. This work aims at the application of qNMR as a versatile tool for the quantification of vegetable oils potentially usable as adulterants or diluents in EOs. This approach is based on the quantification of both 1H and 13C glycerol backbone signals, which are actually present in each vegetable oil containing triglycerides. For the validation, binary mixtures of rosemary EO and corn oil (0.8–50%) were prepared. To verify the general feasibility of this technique, other different mixtures including lavender, citronella, orange and peanut, almond, sunflower, and soy seed oils were analyzed. The results showed that the efficacy of this approach does not depend on the specific combination of EO and vegetable oil, ensuring its versatility. The method was able to determine the adulterant, with a mean accuracy of 91.81 and 89.77% for calculations made on 1H and 13C spectra, respectively. The high precision and accuracy here observed, make 1H-qNMR competitive with other well-established techniques. Considering the current importance of quality control of EOs to avoid fraudulent practices, this work can be considered pioneering and promising. 相似文献