全文获取类型
收费全文 | 1131篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
化学 | 905篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 166篇 |
物理学 | 86篇 |
出版年
2023年 | 9篇 |
2022年 | 32篇 |
2021年 | 61篇 |
2020年 | 56篇 |
2019年 | 32篇 |
2018年 | 35篇 |
2017年 | 26篇 |
2016年 | 55篇 |
2015年 | 54篇 |
2014年 | 48篇 |
2013年 | 84篇 |
2012年 | 74篇 |
2011年 | 84篇 |
2010年 | 62篇 |
2009年 | 55篇 |
2008年 | 68篇 |
2007年 | 58篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 40篇 |
2003年 | 34篇 |
2002年 | 27篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1992年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1936年 | 2篇 |
1927年 | 2篇 |
1924年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有1167条查询结果,搜索用时 15 毫秒
991.
Gabriela Marcelino David Johane Machate Karine de Cssia Freitas Priscila Aiko Hiane Iriani Rodrigues Maldonade Arnildo Pott Marcel Arakaki Asato Camila Jordo Candido Rita de Cssia Avellaneda Guimares 《Molecules (Basel, Switzerland)》2020,25(24)
Carotenoids are vital antioxidants for plants and animals. They protect cells from oxidative events and act against the inflammatory process and carcinogenesis. Among the most abundant carotenoids in human and foods is β-carotene. This carotenoid has the highest level of provitamin A activity, as it splits into two molecules of retinol through the actions of the cytosolic enzymes: β-carotene-15,15′-monooxygenase (β-carotene-15,15′-oxygenase 1) and β-carotene-9′,10′-dioxygenase (β-carotene-9′,10′-oxygenase 2). The literature supports the idea that β-carotene acts against type 2 diabetes mellitus, cardiovascular diseases, obesity, and metabolic syndrome. Due to the many processes involved in β-carotene biosynthesis and metabolic function, little is known about such components, since many mechanisms have not yet been fully elucidated. Therefore, our study concisely described the relationships between the consumption of carotenoids, with emphasis on β-carotene, and obesity and type 2 diabetes mellitus and its associated parameters in order to understand the preventive role of carotenoids better and encourage their consumption. 相似文献
992.
Mariana G. Vallejo Marcos E. Corzo María Gabriela Ortega 《Natural product research》2020,34(9):1270-1275
Abstract12α-hydroxy-N-demethyl-sauroxine (1), another new Lycopodium alkaloid from the Lycodane group, was isolated from Phlegmariurus saururus (Lam.) B. Øllg. (Lycopodiaceae). Elucidation of the chemical structure and relative stereochemistry were stated by spectroscopic data and chemical correlation. In addition, the inhibitory activity on acetylcholinesterase for 1 was determined as well as for N-methyllycodine (2), a derivative with the same nucleus, previously identified in P. saururus (IC50 = 33.8?±?0.8?μM and 547.5?±?0.5?μM, respectively) and N-demethylsauroxine (3) whose inhibition in the actual conditions was better than the previously informed. 相似文献
993.
Tatiana V. Shishkanova Nina Habanov Michal ezanka Gabriela Broncov Pemysl Fitl Martin Vrata Pavel Matjka 《Electroanalysis》2020,32(4):767-774
We report the electrochemical deposition of a β‐cyclodextrin pyrrole conjugate (Py‐β‐CD) on an electrode surface including i) characterization based on surface‐enhanced Raman scattering and field‐emission scanning electron microscopy; ii) studies of the molecular recognition of enantiomers of phenylalanine methyl ester hydrochlorides (Phe) based on linear sweep voltammetry and a quartz crystal microbalance. The PPy‐β‐CD polymeric layer on a metallic substrate is distinguished by its inhomogeneity, in which both highly ordered β‐CD units and highly disordered polymer chains are observed. The voltammetric recognition results showed that PPy‐β‐CD exhibited a higher sensitivity for d ‐Phe (138±15)×103 than for l ‐Phe (6±1)×103 within the concentration range 0.1–0.75 mM (n=3) despite the differences in the polymer arrangement on the surface. A possible mechanism of molecular recognition of phenylalanine enantiomers is discussed. 相似文献
994.
Păușescu Iulia Todea Anamaria Badea Valentin Peter Francisc Medeleanu Mihai Ledeți Ionuț Vlase Gabriela Vlase Titus 《Journal of Thermal Analysis and Calorimetry》2020,141(3):999-1008
Journal of Thermal Analysis and Calorimetry - Intelligent food packaging systems register and monitor food quality through data carriers, sensors or indicators. Food spoilage often leads to pH... 相似文献
995.
Luisa Bataglin Avila Elis Regina Correa Barreto Paloma Krolow de Souza Brbara De Zorzi Silva Thamiris Renata Martiny Caroline Costa Moraes Marcilio Machado Morais Vijaya Raghavan Gabriela Silveira da Rosa 《Molecules (Basel, Switzerland)》2020,25(23)
This research investigated the bioactive potential of jaboticaba peel extract (JPE) and proposed an innovative material for food packaging based on carrageenan films incorporated with JPE. The extract was obtained through microwave assisted extraction (MAE) according to central composite rotational design and the optimized conditions showed a combined antimicrobial and antioxidant actions when the extraction process is accomplished at 80 °C and 1 min. The carrageenan film incorporated with JPE was manageable, homogeneous and the presence of JPE into film increased the thickness and improved the light barrier of the film. The results of solubility and mechanical properties did not show significant differences. The benefit of using MAE to improve the recovery of bioactive compounds was demonstrated and the carrageenan film with JPE showed a great strategy to add additives into food packaging. 相似文献
996.
Pavel Jáč Zuzana Bubáková David Moreno-González Gabriela Kováčová Marcel Špulák Miroslav Polášek 《Electrophoresis》2020,41(18-19):1557-1563
The stability of α-bromophenylacetic acid (BPAA) in 50% aqueous methanol solution has been tested. CE in different running buffers was used to separate BPAA from the decomposition reaction products α-hydroxyphenylacetic (mandelic) acid and α-methoxyphenylacetic acid. Suitable CE separation of all three compounds and other product, bromide, was achieved in 60 mmol/L formate buffer (pH 3.0) at −30 kV in 50 μm (i.d.) poly(vinyl alcohol)-coated fused silica capillary (30 cm/24.5 cm) with UV detection at 200 nm. The CE method was applied to determine the reaction order of the decomposition of BPAA (0.47 mmol/L) via nucleophilic substitution in 50% aqueous methanol. The first-order reaction kinetics was confirmed by linear and non-linear regression, giving the rate constants 1.52 × 10−4 ± 2.76 × 10−5 s−1 and 7.89 × 10−5 ± 5.02 × 10−6 s−1, respectively. Additionally, the degradation products were identified by CE coupled to mass spectrometric (MS) detection. The CE–MS experiments carried out in 60 mmol/L formate buffer (pH 3.0) and in 60 mmol/L acetate buffer (pH 5.0) confirmed the results obtained by CE–UV. Furthermore, the stability of BPAA in polar solvents was tested by 1H NMR experiments. Our results provide strong evidence of the instability and fast degradation of BPAA in 50% aqueous methanol indicating that BPAA is not suitable as the model analyte for chiral separations. 相似文献
997.
Katarzyna Wińska Małgorzata Grabarczyk Wanda Mączka Barbara Żarowska Gabriela Maciejewska Mirosław Anioł 《Journal of Saudi Chemical Society》2018,22(3):363-371
Ten new derivatives of isophorone were obtained through a five-step synthesis. Among the products were several unsaturated, bicyclic lactones with three or four methyl groups. These lactones were used as the substrates for biotransformation mediated by selected fungal strains (Fusarium species, Syncephalastrum racemosum, Cunninghamella japonica, Penicillium species, Absidia species, and Pleurotus ostreatus). Four new hydroxylactones were obtained as a result of biotransformation. Because the unsaturated lactone with four methyl groups was a diastereoisomeric mixture, a structural analysis was conducted. The hydroxylactones were also included in this analysis. Both the unsaturated lactones and hydroxylactones were examined for their antimicrobial activity. It was found that some of these compounds exhibited growth inhibition against pathogenic strains of bacteria (Staphylococcus aureus, Pseudomonas fluorescens), yeasts (Candida albicans) and filamentous fungi (Alternaria sp., Penicillium sp.). All obtained compounds were also subjected to scent analysis. 相似文献
998.
Crisan Manuela Vlase Gabriela Plesu Nicoleta Petric Mihaela Croitor Lilia Kravtsov Victor Chumakov Yurii Bourosh Paulina Vlase Titus 《Journal of Thermal Analysis and Calorimetry》2018,132(1):353-364
Journal of Thermal Analysis and Calorimetry - The temperature dependence of molar heat capacity of Ba1.5Fe2(PO4)3 phosphate was investigated between T = 6 and 670 K with... 相似文献
999.
José Alfredo Del-Oso Bernardo Antonio Frontana-Uribe José-Luis Maldonado Margarita Rivera Melina Tapia-Tapia Gabriela Roa-Morales 《Journal of Solid State Electrochemistry》2018,22(7):2025-2037
In this article, controlled changes on morphology, thickness, and band gap of poly[ethylenedioxythiophene] (PEDOT) polymer films fabricated by electrochemical polymerization (potentiostatically) are analyzed. Electropolymerization of the monomer ethylenedioxythiophene (EDOT) was carried out on indium tin oxide (ITO) electrodes, in different dry organic electrolytic media, such as acetonitrile, acetonitrile–dichloromethane, and toluene–acetonitrile mixtures. It was found that electropolymerization kinetics can be controlled by changing the polarity of the electrolytic media, and kinetics is slower for those with low polarity. This fact combined with an accurate control of EDOT monomer concentration and electropolymerization at Epeak/2 potential, allows to control the morphology and thickness of the electropolymerized PEDOT films (E-PEDOT:ClO4); toluene/ACN (4:1, v/v) and [EDOT]?=?0.3 mM gave the best films for application in organic photovoltaic (OPV) cells. The performance of the E-PEDOT:ClO4 films was tested on ITO electrodes as anode buffer layer in OPV cells with the configuration ITO/E-PEDOT:ClO4/P3HT:PC61BM/Field’s metal, where Field’s metal (cathode) is a eutectic alloy that lets to fabricate OPV devices easily and in a fast and economical way at free vacuum conditions. The performance of these devices was compared with an OPV device constructed with a buffer layer anode, prepared using the classical spin coating of PEDOT:PSS on ITO. Results showed that OPV cells fabricated with E-PEDOT:ClO4 have a slightly increased PV performance. 相似文献
1000.
Tiago Fidemann Gabriela Aparecida de Araujo Pereira Lia Bossard Nascimento Milena Cristina Moraes Mônica Rosa Bertão Regildo Márcio Gonçalves da Silva 《Natural product research》2018,32(9):1109-1117
Plants endue a key role against illnesses caused by oxidative stress. These attributes are frequently associated with polyphenolic compounds. However, presence and concentration of secondary metabolites are affected by abiotic factors. The in vitro culture techniques can solve these drawbacks. Peppers can be a suitable alternative to obtain polyphenols. Aiming to optimise the callus culture stage from Capsicum baccatum to produce polyphenols, this work evaluated systemically the effects of the explant’s origin (root, hypocotyl and cotyledon), growth hormone type (2,4-dichlorophenoxyacetic acid (2,4-D), benzylaminopurine (BAP) and a combination of 2,4-D/BAP at five-to-one ratio) and concentration (0.023–10.000 mg L?1) on callus culture efficiency parameters using a multilevel factorial design. The root explant in combination with BAP at 1.138 mg L?1 ensured the optimal values of the assessed responses; ?callus mass (225.03 mg), antioxidant activity (35.95%), total phenols (11.48 mg of GAE/g DE) and flavonoids (15.92 mg of RU/g DE) production. 相似文献