全文获取类型
收费全文 | 345篇 |
免费 | 16篇 |
专业分类
化学 | 290篇 |
晶体学 | 7篇 |
力学 | 3篇 |
数学 | 32篇 |
物理学 | 29篇 |
出版年
2023年 | 3篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 14篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 18篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 28篇 |
2012年 | 22篇 |
2011年 | 31篇 |
2010年 | 22篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 18篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 203 毫秒
271.
Aleksander Kufelnicki Jan Jaszczak Urszula Kalinowska-Lis Cecylia Wardak Justyn Ochocki 《Journal of solution chemistry》2006,35(5):739-751
Equilibrium studies have been carried out on complex formation of M2+ ions (M=Co, Ni, and Zn) with L = thymine, 6-chloromethyluracil, 5-hydroxymethyluracil, uracil, 6-methyluracil, and 6-umpm (dimethyl 6-uracilmethylphosphonate) in aqueous solution, at 25 ∘;C and an ionic strength of I=0.1 mol⋅L−1 (KNO3). Potentiometric results indicate the formation of ML species (coordination via N3) for Co(II) and Ni(II) as well as a hydroxo complex MLH−1—with a deprotonated water of the inner coordination sphere. Titrations of Zn(II) confirmed both the existence of ML and MLH−1 species with 6-chloromethyluracil as well as 5-hydroxymethyluracil, whereas for uracil, thymine, and 6-methyluracil the only species accepted pH-metrically was MLH−1. For all the ligands under study the complexation with Zn(II) was reinvestigated by means of ion-selective electrodes (ISE). The role of substituents is discussed. 相似文献
272.
273.
Anna Nowak Martyna Zagrska-Dziok Paula Ossowicz-Rupniewska Edyta Makuch Wiktoria Duchnik ukasz Kucharski Urszula Adamiak-Giera Piotr Prowans Norbert Czapla Piotr Bargiel Jan Petriczko Marta Markowska Adam Klimowicz 《Molecules (Basel, Switzerland)》2021,26(11)
Epilobium angustifolium L. is a popular and well-known medicinal plant. In this study, an attempt to evaluate the possibility of using this plant in preparations for the care and treatment of skin diseases was made. The antioxidant, antiaging and anti-inflammatory properties of ethanolic extracts from Epilobium angustifolium (FEE) were assessed. Qualitative and quantitative evaluation of extracts chemically composition was performed by gas chromatography with mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). The total polyphenol content (TPC) of biologically active compounds, such as the total content of polyphenols (TPC), flavonoids (TFC), and assimilation pigments, as well as selected phenolic acids, was assessed. FEE was evaluated for their anti-inflammatory and antiaging properties, achieving 68% inhibition of lipoxygenase activity, 60% of collagenase and 49% of elastase. FEE also showed high antioxidant activity, reaching to 87% of free radical scavenging using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 59% using 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Additionally, in vitro penetration studies were performed using two vehicles, i.e., a hydrogel and an emulsion containing FEE. These studies showed that the active ingredients contained in FEE penetrate through human skin and accumulate in it. The obtained results indicate that E. angustifolium may be an interesting plant material to be applied as a component of cosmetic and dermatological preparations with antiaging and anti-inflammatory properties. 相似文献
274.
Beata Michalkiewicz Joanna Sreńscek-Nazzal Piotr Tabero Barbara Grzmil Urszula Narkiewicz 《Chemical Papers》2008,62(1):106-113
The investigations of selective methane oxidation to formaldehyde over T-Nb2O5, the mixture of M-Nb2O5 and H-Nb2O5 as well as H-Nb2O5 were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as
the oxidizing agent. T-Nb2O5 samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h−1). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb2O5 displayed various formaldehyde and carbon dioxide yield. Using H-Nb2O5 and M-Nb2O5 phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared
to T-Nb2O5 (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of
formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb2O5 supported on SiO2.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
275.
276.
Urszula Domańska Piotr Morawski Maria Piekarska 《The Journal of chemical thermodynamics》2008,40(4):710-717
The (solid + liquid) phase equilibria (SLE) of binary mixtures containing 1-octanol and fragrance raw materials based on cyclohexane were investigated. The systems {1-octanol (1) + cyclohexyl carboxylic acid (CCA), or cyclohexyl acetic acid (CAA), or cyclohexyl acetate (CA), or 2-cyclohexyl ethyl acetate (2CEA), or 2-cyclohexyl ethanol (2CE)(2)} have been measured by a dynamic method in wide range of temperatures from (220 to 320) K and ambient pressure. For all systems SLE diagrams were detected as eutectic mixtures with complete miscibility in the liquid phase. The experimental data were correlated by means of the Wilson and NRTL equations, utilizing parameters derived from the (solid + liquid) equilibrium. The root-mean-square deviations of the solubility temperatures for all calculated data are dependent upon the particular system and the particular equation used.Additionally, the SLE in binary mixture that contain {1-octanol (1) + CCA (2)} has been measured under very high pressures up to about 900 MPa at the temperature range from T = (303.15 to 353.15) K. The thermostatted apparatus for the measurements of transition pressures from the (liquid + solid) state was used. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The high pressure experimental results obtained at isothermal conditions (p–x) were interpolated to more convenient T–x diagram. Data of the (pressure + temperature) composition relation at the high pressure (solid + liquid) phase equilibria was correlated by the polynomial based on the Yang model.The basic thermodynamic properties of pure substances viz. the melting point, enthalpy of fusion, enthalpy of solid–solid phase transition, and glass transition, have been determined by the differential scanning calorimetry (DSC). 相似文献
277.
MSc Daria B. Wojtala Sc.D. Urszula K. Komarnicka Sc.D. Agnieszka Kyzioł Dr. Sandra Kozieł BSc Magdalena Szmitka MSc Mateusz Słowikowski MSc Julia Kulczyńska Prof. Grażyna Stochel 《欧洲无机化学杂志》2023,26(33):e202300515
Two piano-stool ruthenium(II) complexes Ru(η6-p-cymene)Cl2PPh2CH2OH ( RuPOH ) and Ru(η6-p-cymene)Cl2P(p-OCH3Ph)2CH2OH ( RuMPOH ) and two half-sandwich iridium(III) complexes Ir(η 5-Cp*)Cl2PPh2CH2OH ( IrPOH ) and Ir(η 5-Cp*)Cl2P(p-OCH3Ph)2CH2OH ( IrMPOH ) have been studied in terms of potential anticancer activity on previously selected cell line (human lung adenocarcinoma). Based on experimental results obtained in monoculture in vitro model mechanistic considerations on the possible cellular modes of action have been carried out. ICP-MS analysis revealed the higher cellular uptake for less hydrophobic Ir(III) complexes in comparison to the corresponding Ru(II) compounds. Cytometric analysis showed a predominance of apoptosis over the other types of cell death for all complexes. The apoptotic pathway was confirmed by a decrease in mitochondrial membrane potential and the activation of caspases-3/9 for both Ru(II) and Ir(III) complexes. It was concluded that in the case of Ru(II) complexes the intense ROS generation is mainly responsible for the resulting cytotoxicity. The corresponding Ir(III) complexes trigger simultaneously at least three different cytotoxic pathways i. e., depletion of mitochondrial potential, activation of caspases-dependent apoptosis, and ROS-associated oxidation. Thus, it can be assumed that the final accumulation of toxic effects over time via parallel activation of different pathways results in the highest cytotoxicity in vitro exhibited by Ir(III) complexes when compared with Ru(II) complexes. 相似文献
278.
Tapan Chatterji Urszula D. Wdowik Grzegorz Jagło Stéphane Rols Frank R. Wagner 《Physics letters. A》2018,382(29):1937-1941
Results of inelastic neutron scattering experiments on SnSe single crystals at high temperatures along with theoretical studies based on the density functional theory are reported. Our experiments reveal significant softening of the transverse acoustic branch along the direction in the low-temperature α-SnSe of symmetry as temperature approaches K from below. This process is followed by a condensation of the zone-boundary Y-phonon of the high-temperature β-SnSe with symmetry at the onset of phase transition. The employed theoretical approach supports experimental observations and demonstrates that the phase change in SnSe is mediated by an unstable zone-boundary phonon with the irreducible representation within the symmetry space group of the high-temperature β-SnSe. The present work provides a detailed understanding of the soft-mode dynamics in SnSe and conclusively shows that the structural transformation in this currently topical thermoelectric material is of displacive type. 相似文献
279.
Summary. Various heteroaromatic N-oxides were efficiently deoxygenated to the corresponding bases under mild conditions using formamidinesulfinic
acid (thiourea S,S-dioxide).
Received March 24, 2000. Accepted April 18, 2000 相似文献
280.
Andelika Gsikiewicz-Puchalska Michal Zgrzebnicki Beata Michalkiewicz Agnieszka Kaamaga Urszula Narkiewicz Antoni W. Morawski Rafal Wrobel 《Molecules (Basel, Switzerland)》2021,26(24)
Zeolite 13X (NaX) was modified through ion-exchange with alkali and alkaline earth metal cations. The degree of ion exchange was thoroughly characterized with ICP, EDS and XRF methods. The new method of EDS data evaluation for zeolites was presented. It delivers the same reliable results as more complicated, expensive, time consuming and hazardous ICP approach. The highest adsorption capacities at 273 K and 0.95 bar were achieved for materials containing the alkali metals in the following order K < Na < Li, respectively, 4.54, 5.55 and 5.94 mmol/g. It was found that it is associated with the porous parameters of the ion-exchanged samples. The Li0.61Na0.39X form of zeolite exhibited the highest specific surface area of 624 m2/g and micropore volume of 0.35 cm3/g compared to sodium form 569 m2/g and 0.30 cm3/g, respectively. The increase of CO2 uptake is not related with deterioration of CO2 selectivity. At room temperature, the CO2 vs. N2 selectivity remains at a very high stable level prior and after ion exchange in co-adsorption process (XCO2 during adsorption 0.15; XCO2 during desorption 0.95) within measurement uncertainty. Additionally, the Li0.61Na0.39X sample was proven to be stable in the aging adsorption-desorption tests (200 sorption-desorption cycles; circa 11 days of continuous process) exhibiting the CO2 uptake decrease of about 6%. The exchange with alkaline earth metals (Mg, Ca) led to a significant decrease of SSA and micropore volume which correlated with lower CO2 adsorption capacities. Interestingly, the divalent cations cause formation of mesopores, due to the relaxation of lattice strains. 相似文献