全文获取类型
收费全文 | 392篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 302篇 |
力学 | 3篇 |
数学 | 72篇 |
物理学 | 37篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 8篇 |
2013年 | 26篇 |
2012年 | 36篇 |
2011年 | 34篇 |
2010年 | 22篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 18篇 |
2005年 | 27篇 |
2004年 | 23篇 |
2003年 | 21篇 |
2002年 | 16篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有414条查询结果,搜索用时 906 毫秒
91.
About the OH yield in the radiolysis of an aqueous/H2O2 system. Its optimisation for water treatment
Salvatore S. Emmi Serena Caminati Biagio Esposito Michela Saracino 《Radiation Physics and Chemistry》2012,81(9):1430-1433
Unless the radiolytic reducing species are neutralised or converted into oxidising species, an EB remediation system cannot be considered a true Advanced Oxidation Processes (AOP). A water/H2O2 system irradiated by UVC mercury lamps constitutes a widely used OH production method. Employing H2O2 in radiolysis as well, an enhancement of the oxidative efficiency of an EB treatment can be obtained. Pulse radiolysis measurements of an aerated aqueous/H2O2/KSCN system have been systematically undertaken to assess the optimal H2O2 concentration. By linearly fitting a competition kinetics relationship, it is found that the scavengeable extra-yield of OH is ΔG(OH)=0.24 μmol J?1 (R=0,9958), while the maximum experimental yield is measured G(OH)max=(0.52±0.02) μmol J?1 when [H2O2]=5–10 mM. Exceeding these concentrations the OH yield drops off. 相似文献
92.
Michela Ottobre 《Stochastic Processes and their Applications》2012,122(3):844-884
We study the long time behavior of a Brownian particle moving in an anomalously diffusing field, the evolution of which depends on the particle position. We prove that the process describing the asymptotic behavior of the Brownian particle has bounded (in time) variance when the particle interacts with a subdiffusive field; when the interaction is with a superdiffusive field the variance of the limiting process grows in time as t2γ−1, 1/2<γ<1. Two different kinds of superdiffusing (random) environments are considered: one is described through the use of the fractional Laplacian; the other via the Riemann-Liouville fractional integral. The subdiffusive field is modeled through the Riemann-Liouville fractional derivative. 相似文献
93.
Dr. Elena Ghedini Dr. Valentina Nichele Dr. Michela Signoretto Dr. Giuseppina Cerrato 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10653-10660
A series of titanium oxides was prepared by using a surfactant‐template method (STM) and used as a carrier for the sustained release of ibuprofen, which was chosen as a model drug. This STM provides an efficient route to TiO2 matrices with both high surface area (when compared with those that were obtained by using traditional synthetic approaches) and well‐defined mesoporous textures. Some parameters of the synthetic procedure were varied: pH value, surfactant, and thermal treatment. The physicochemical nature of the surface carriers were investigated by means of N2‐physisorption measurements and FTIR spectroscopy. The effect of the amount of drug on the release kinetics was also investigated. The drug delivery was evaluated in vitro in four different physiological solutions (that simulated the gastrointestinal tract) to analyze the behavior of the TiO2‐based systems if they were to be formulated as oral DDSs. Our optimized approach is a good alternative to the classical methods that are used to prepare efficient TiO2‐based drug‐delivery systems. 相似文献
94.
This paper consists of two results dealing with balanced metrics (in Donaldson terminology) on noncompact complex manifolds. In the first one we describe all balanced metrics on Cartan domains. In the second one we show that the only Cartan–Hartogs domain which admits a balanced metric is the complex hyperbolic space. By combining these results with those obtained in Loi and Zedda (Mathematische Annalen, 2011, to appear) we also provide the first example of complete, Kähler-Einstein and projectively induced metric g such that α g is not balanced for all α > 0. 相似文献
95.
In this paper we are concerned with the optimal control problem consisting in minimizing the time for reaching (visiting)
a fixed number of target sets, in particular more than one target. Such a problem is of course reminiscent of the famous “Traveling
Salesman Problem” and brings all its computational difficulties. Our aim is to apply the dynamic programming technique in
order to characterize the value function of the problem as the unique viscosity solution of a suitable Hamilton–Jacobi equation.
We introduce some “external” variables, one per target, which keep in memory whether the corresponding target is already visited
or not, and we transform the visiting problem in a suitable Mayer problem. This fact allows us to overcome the lacking of
the Dynamic Programming Principle for the originary problem. The external variables evolve with a hysteresis law and the Hamilton–Jacobi
equation turns out to be discontinuous 相似文献
96.
Local branching is a general purpose heuristic method which searches locally around the best known solution by employing tree
search. It has been successfully used in Mixed-Integer Programming where local branching constraints are used to model the
neighborhood of an incumbent solution and improve the bound. We propose the integration of local branching in Constraint Programming
(CP). This integration is not simply a matter of implementation, but requires a number of significant extensions. The original
contributions of this paper are: the definition of an efficient and incremental bound computation for the neighborhood, a
cost-based filtering algorithm for the local branching constraint and a novel diversification strategy that can explore arbitrarily
far regions of the search tree w.r.t. the already found solutions. We demonstrate the practical value of local branching in
CP by providing an extensive experimental evaluation on the hard instances of the Asymmetric Traveling Salesman Problem with
Time Windows. 相似文献
97.
Federica Mastroiacovo Francesca Biagioni Paola Lenzi Gloria Lazzeri Michela Ferrucci Stefano Puglisi-Allegra Alessandro Frati Ferdinando Nicoletti Francesco Fornai 《Molecules (Basel, Switzerland)》2022,27(10)
The brain area which surrounds the frankly ischemic region is named the area penumbra. In this area, most cells are spared although their oxidative metabolism is impaired. area penumbra is routinely detected by immunostaining of a molecule named Heat Shock Protein 70 (HSP70). Within the area penumbra, autophagy-related proteins also increase. Therefore, in the present study, the autophagy-related microtubule-associated protein I/II-Light Chain 3 (LC3) was investigated within the area penumbra along with HSP70. In C57 black mice, ischemia was induced by permanent occlusion of the distal part of the middle cerebral artery. Immunofluorescence and electron microscopy show that LC3 and HSP70 are overexpressed and co-localize within the area penumbra in the same cells and within similar subcellular compartments. In the area penumbra, marked loss of co-localization of HSP70 and LC3-positive autophagy vacuoles, with lysosomal-associated membrane protein 1 (LAMP1) or cathepsin-D-positive lysosome vacuoles occurs. This study indicates that, within the area penumbra, a failure of autophagolysosomes depends on defective compartmentalization of LC3, LAMP1 and cathepsin-D and a defect in merging between autophagosomes and lysosomes. Such a deleterious effect is likely to induce a depletion of autophagolysosomes and cell clearing systems, which needs to be rescued in the process of improving neuronal survival. 相似文献
98.
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
99.
Raluca Maria Pop Ioana Corina Bocsan Anca Dana Buzoianu Veronica Sanda Chedea Sonia Ancua Socaci Michela Pecoraro Ada Popolo 《Molecules (Basel, Switzerland)》2020,25(22)
Natural products black cumin—Nigella sativa (N. sativa) and wild garlic—Allium ursinum (AU) are known for their potential role in reducing cardiovascular risk factors, including antracycline chemotherapy. Therefore, this study investigates the effect of N. sativa and AU water and methanolic extracts in a cellular model of doxorubicin (doxo)-induced cardiotoxicity. The extracts were characterized using Ultraviolet-visible (UV-VIS) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, Liquid Chromatography coupled with Mass Spectrometry (LC-MS) and Gas Chromatography coupled with Mass Spectrometry (GC-MS) techniques. Antioxidant activity was evaluated on H9c2 cells. Cytosolic and mitochondrial reactive oxygen species (ROS) release was evaluated using 2′,7′-dichlorofluorescin-diacetate (DHCF-DA) and mitochondria-targeted superoxide indicator (MitoSOX red), respectively. Mitochondrial membrane depolarization was evaluated by flow cytometry. LC-MS analysis identified 12 and 10 phenolic compounds in NSS and AU extracts, respectively, with flavonols as predominant compounds. FT-IR analysis identified the presence of carbohydrates, amino acids and lipids in both plants. GC-MS identified the sulfur compounds in the AU water extract. N. sativa seeds (NSS) methanolic extract had the highest antioxidant activity reducing both intracellular and mitochondrial ROS release. All extracts (excepting AU methanolic extract) preserved H9c2 cells viability. None of the investigated plants affected the mitochondrial membrane depolarization. N. sativa and AU are important sources of bioactive compounds with increased antioxidant activities, requiring different extraction solvents to obtain the pharmacological effects. 相似文献
100.
Giuseppe Romanazzi Valentina Petrelli Ambra Maria Fiore Piero Mastrorilli Maria Michela DellAnna 《Molecules (Basel, Switzerland)》2021,26(4)
Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C–N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features. 相似文献