全文获取类型
收费全文 | 339篇 |
免费 | 18篇 |
专业分类
化学 | 290篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 38篇 |
物理学 | 25篇 |
出版年
2023年 | 7篇 |
2022年 | 36篇 |
2021年 | 44篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 15篇 |
2016年 | 33篇 |
2015年 | 15篇 |
2014年 | 10篇 |
2013年 | 28篇 |
2012年 | 27篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 9篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有357条查询结果,搜索用时 15 毫秒
81.
Martyna N. Wieczorek Piotr Mariusz Pieczywek Justyna Cybulska Artur Zdunek Henryk H. Jele 《Molecules (Basel, Switzerland)》2022,27(2)
The storage of plant samples as well as sample preparation for extraction have a significant impact on the profile of metabolites, however, these factors are often overlooked during experiments on vegetables or fruit. It was hypothesized that parameters such as sample storage (freezing) and sample pre-treatment methods, including the comminution technique or applied enzyme inhibition methods, could significantly influence the extracted volatile metabolome. Significant changes were observed in the volatile profile of broccoli florets frozen in liquid nitrogen at −20 °C. Those differences were mostly related to the concentration of nitriles and aldehydes. Confocal microscopy indicated some tissue deterioration in the case of slow freezing (−20 °C), whereas the structure of tissue, frozen in liquid nitrogen, was practically intact. Myrosinase activity assay proved that the enzyme remains active after freezing. No pH deviation was noted after sample storage - this parameter did not influence the activity of enzymes. Tissue fragmentation and enzyme-inhibition techniques applied prior to the extraction influenced both the qualitative and quantitative composition of the volatile metabolome of broccoli. 相似文献
82.
Katarzyna Sukowska-Ziaja Gokhan Zengin Agnieszka Gunia-Krzyak Justyna Popi Agnieszka Szewczyk Magdalena Jaszek Jerzy Rogalski Boena Muszyska 《Molecules (Basel, Switzerland)》2022,27(1)
Fungal mycelium cultures are an alternative to natural sources in order to obtain valuable research materials. They also enable constant control and adaptation of the process, thereby leading to increased biomass growth and accumulation of bioactive metabolites. The present study aims to assess the biosynthetic potential of mycelial cultures of six Ganoderma species: G. adspersum, G. applanatum, G. carnosum, G. lucidum, G. pfeifferi, and G. resinaceum. The presence of phenolic acids, amino acids, indole compounds, sterols, and kojic acid in biomass extracts was determined by HPLC. The antioxidant and cytotoxic activities of the extracts and their effects on the inhibition of selected enzymes (tyrosinase and acetylcholinesterase) were also evaluated. The total content of phenolic acids in the extracts ranged from 5.8 (G. carnosum) to 114.07 mg/100 g dry weight (d.w.) (G. pfeifferi). The total content of indole compounds in the extracts ranged from 3.03 (G. carnosum) to 11.56 mg/100 g d.w. (G. lucidum) and that of ergosterol ranged from 28.15 (G. applanatum) to 74.78 mg/100 g d.w. (G. adspersum). Kojic acid was found in the extracts of G. applanatum and G. lucidum. The tested extracts showed significant antioxidant activity. The results suggest that the analyzed mycelial cultures are promising candidates for the development of new dietary supplements or pharmaceutical preparations. 相似文献
83.
Adam Bieniek Jan Epsztajn Justyna A Kowalska Zbigniew Malinowski 《Tetrahedron letters》2001,42(52):9293-9295
The transformation of the benzanilides 1 into 4-arylisochroman-3-acetic acids 8 applying the following sequence of reactions is described. At first, the 3-arylphthalides 3 were obtained via metallation [n-BuLi] of benzanilides 1 and subsequent treatment of the generated bis-lithiated anilides 2 with aromatic aldehydes. Next, the 3-arylphthalides 3 were reduced [LiBH4] to phthalanes 5 and then, via reductive metallation [Li/C10H8] and reaction of the generated bis-lithiated species 6 with dimethylformamide, 3-hydroxy-4-arylisochromans 7 were produced. In the final step the isochromans 7 were treated with 1-methoxy-1-trimethylsilyloxyethene in the presence of titanium tetrachloride and furnished 4-arylisochromans-3-acetic acid methyl esters 8 as trans stereoisomers (Ψ-e/e). 相似文献
84.
Karolina Soczyska Justyna Popi Agnieszka Gunia-Krzyak Paulina Koczurkiewicz-Adamczyk Pawe mudzki Elbieta Pkala 《Molecules (Basel, Switzerland)》2022,27(6)
This study aimed to assess two novel 5-arylideneimidazolidine-2,4-dione (hydantoin) derivatives (JH3 and JH10) demonstrating photoprotective activity using the reconstructed human skin model EpiskinTM. The skin permeability, irritation, and phototoxicity of the compounds was evaluated in vitro. Moreover, the in vitro genotoxicity and human metabolism of both compounds was studied. For skin permeation and irritation experiments, the test compounds were incorporated into a formulation. It was shown that JH3 and JH10 display no skin irritation and no phototoxicity. Both compounds did not markedly enhance the frequency of micronuclei in CHO-K1 cells in the micronucleus assay. Preliminary in vitro studies with liver microsomes demonstrated that hydrolysis appears to constitute their important metabolic pathway. EpiskinTM permeability experiments showed that JH3 permeability was lower than or close to currently used UV filters, whereas JH10 had the potential to permeate the skin. Therefore, a restriction of this compound permeability should be obtained by choosing the right vehicle or by optimizing it, which should be addressed in future studies. 相似文献
85.
Bert Vissers Joseph Everaert Justyna Sekula Anna Malak Hugo Bohets Grzegorz Bazylak Luc J. Nagels 《Journal of separation science》2009,32(2):167-179
Isocratic HPLC with potentiometric detection is used for the determination of some 17‐ketosteroids (17‐KS), e.g., androsterone, dehydroepiandrosterone and estrone, and their respective sulfated conjugates (17‐KSS). Glassy carbon or composite electrodes containing a mixture of graphite and poly(vinyl chloride), PVC, were used as substrate electrodes. These substrates were covered either by montmorillonite or potassium tetrakis(p‐chlorophenyl) borate containing PVC‐based rubber phase membranes. The neutral 17‐KS compounds were derivatized with Girard's reagent P (GP) to obtain cationic pyridinium acetohydrazones prior to the HPLC/potentiometric detection assay. No side reactions were observed, and the GP itself was not interfering. The method yielded accurate and reproducible results and was applicable to samples containing down to micromolar concentrations. Next, the 17‐KSS compounds, acting as anionic charged molecules, were determined directly in human urine samples with the HPLC/potentiometry combination without preliminary derivatization. For this purpose, a new anion‐sensitive potentiometric electrode was developed using a macrocyclic polyamine containing, PVC‐based, rubber phase membrane. The three 17‐KSS compounds were also determined accurately down to micromolar concentrations. Especially, the main androgen metabolites as dehydroepiandrosterone sulfate and androsterone sulfate could be selectively determined with a developed potentiometric sensor in human urine samples without time‐consuming cleanup and preconcentration step. 相似文献
86.
Daniel Długosz Malgorzata Pach Anna Zabrzeńska Monika Zegar Barbara J. Oleksyn Justyna Kalinowska-Tłuścik Katarzyna Ostrowska 《Monatshefte für Chemie / Chemical Monthly》2008,139(5):543-548
Bis(cycloamidine-2-yl)alkanes easily form bromide tribromide salts in the reduction-oxidation processes with bromine. Bis(tetrahydroimidazolium-2-yl)ethane
and bis(hexahydropyrimidinium-2-yl)-ethane bromide tribromides are such new convenient brominating agents for aromatic amides
in chemo- and regioselective electrophilic substitutions and α-bromination reactions.
Correspondence: Katarzyna Ostrowska, Department of Organic Chemistry, Jagiellonian University, R. Ingardena 3, PL-30060 Kraków,
Poland. 相似文献
87.
Justyna Sikorska 《Journal of Mathematical Analysis and Applications》2005,311(1):209-217
We study the stability problem for mappings satisfying the equation
‖f(x−y)‖=‖f(x)−f(y)‖. 相似文献
88.
89.
Let E be a Euclidean space,
dim E 2. We say that
f : E
E preserves equilateral triangles if for all triples of
points x, y, z E
we have
We show that if E is a finite-dimensional Euclidean space,
dim E 2,
f:E
E is measurable and preserves
equilateral triangles, then it is a similarity transformation (an isometry
multiplied by a positive constant). Moreover, in spaces at least
three-dimensional we get a similarity transformation without any
regularity assumption. Some generalizations as well as some interesting examples are also
presented in the paper. 相似文献
90.