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61.
62.
Catalysis of the electrochemical oxygen reduction reaction (ORR) on a pyrolytic graphite electrode (PGE) by iron-containing
superoxide dismutase (Fe-SOD) is investigated for the first time using cyclic voltammetry and electrochemical impedance spectroscopy.
The study is carried out in three room-temperature ionic liquids (RTILs), namely, 1-ethyl-3-methylimidazolium tetrafluoroborate
(EMIBF4), 1-propyl-3-methylimidazolium tetrafluoroborate (PMIBF4), and 1-butyl-3-methylimidazolium tetrafluoroborate (EMIBF4). The results demonstrate that in EMIBF4, Fe-SOD exhibits the most satisfactory catalysis for ORR, with the standard rate constant of ORR on bare PGE, k
s, increasing from 3.9 to 5.1 times 10−3 cm s−1, while in PMIBF4 and BMIBF4 containing Fe-SOD k
s increases from 2.6 to 3.6 and from 1.4 to 2.2 times 10−3 cm s−1, respectively. In addition to the increased k
s, adding Fe-SOD renders the formal potential of ORR more positive. To accelerate the electron transfer, multi-walled carbon
nanotubes (MWCNTs) are employed to modify PGE, consequently, yielding the dramatically increased peak current and k
s. For MWCNTs-modified PGE in EMIBF4 free of Fe-SOD, k
s increases from 3.9 to ∼7.1 times 10−3 cm s−1. The ORR catalysis by Fe-SOD in the presence of Fe-SOD is also evidenced by the formal-potential shift in the positive direction.
With MWCNTs accounting for the larger k
s and Fe-SOD being responsible for the formal-potential shift, the catalysis of ORR is satisfactory. Chronocoulmetry experiments
proved that some Fe-SOD could be adsorbed on PGE. After analyzing the results, dismutation of superoxide anion O
2
−
by Fe-SOD is thought to be the main reason for the formal-potential shift. The different polarity of RTILs is probably partly
responsible for different k
s obtained in different RTILs. Basing on an earlier proposition, the catalysis of ORR by MWCNTs in RTILs is discussed.
Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 9, pp. 1137–1146.
The text was submitted by the authors in English. 相似文献
63.
Tanveer Mahamadali Shaikh 《Tetrahedron letters》2009,50(23):2815-4239
A new facile procedure for the aminobromination of olefins in high yields has been described using p-toluene sulfonamide (p-TsNH2) and N-bromosuccinimide (NBS) as nitrogen and bromine sources, respectively, and titanium superoxide as a truly heterogeneous catalyst. The formation of anti-Markovnikov product exclusively in all the cases studied possibly proceeding through a free radical reaction pathway is remarkable. 相似文献
64.
Weizhou Fan Xiaohong Liu Jinsheng Wu Qian Liu Lan Ding Dr. Xiuhui Liu 《Electroanalysis》2022,34(6):987-994
Reactive oxygen species (ROS) have become the focus of research in recent years because they are closely related to many diseases, including cancer. Therefore, detection of ROS released from cells is of particular importance. In this work, the nanocomposites with uniform dispersion of silver nanoparticles were obtained through pyrolyzing a novel silver-based metal-organic framework. As the main active component of the composition, AgNPs can effectively catalyze the decomposition of hydrogen peroxide produced by superoxide anion (O2 ⋅ −) disproportionation. Then, we designed a superoxide anion sensor (AgNPs@C/GCE) using the above nanocomposite for the first time. The prepared sensor presented excellent catalytic ability and satisfactory detection performance towards O2 ⋅ − with a detection range as wide as eight orders of magnitude and a lower detection limit of 1.011×10−13 M (S/N=3). Furthermore, the sensor can directly measure O2 ⋅ − released by human cervical cancer cells (HeLa) under both the normal condition and the inducement by malonic acid. In addition, we explored the effects of different concentrations of stimuli on cells. The results illustrated the high dose malonic acid can cause oxidative stress on cells. Thus, this work has the tremendous potential applications to diagnosis of diseases related to ROS. 相似文献
65.
Debojyoti Lahiri Tuhin Bhowmick Bhabatosh Banik Reema Railkar Suryanarayanarao Ramakumar Rajan R. Dighe Akhil R. Chakravarty 《Polyhedron》2010
Dicobalt(II) complexes [{(B)CoII}2(μ-dtdp)2] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μB per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving Kb values within 4.3 × 105–4.0 × 106 M−1. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC50 value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC50 value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC50 = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC50 = 0.4 μM). 相似文献
66.
67.
冷应激对铜预投大鼠血清铜锌代谢、SOD活性及GSH含量的影响 总被引:7,自引:0,他引:7
为揭示应激对体内微量元素代谢的影响和机制,预先给予大鼠不同水平的铜3周后,采用冷束缚法使大鼠产生应激,测定了血清铜、锌水平及超氧化物歧化酶(SOD)活性、还原型谷胱甘肽(GSH)和丙二醛(MDA)含量。结果表明,高铜给予没有对清洁级大鼠生长产生明显的影响.血清铜、锌及铜锌比值变化不明显,但适量的铜给予能显著提高血清中SOD活性和GSH含量;冷应激处理后大鼠血清中Cu水平下降,Zn水平升高,同时SOD消耗降低,而GSH含量显著升高。表明冷应激可使大鼠体内铜锌代谢及SOD活性和GSH含量发生变化,适量的铜给予在应激状况下才发挥出积极的生理作用。 相似文献
68.
白杨素在汞电极上的电化学行为及其消除超氧阴离子自由基能力研究 总被引:2,自引:0,他引:2
The electrochemical behavior of chrysin in pH 2.0-9.0 Britton-Robinson (B-R) buffer solutions was studied by the means of linear sweep voltammetry and cyclic voltammetry at a static mercury drop electrode. In different pH range of B-R buffer solutions, chrysin could cause four reduction waves. In pH 2.0-5.8 B-R buffer solutions, wave P1 yielded by chrysin is a one-electron reduction wave, and wave P1 caused by further reduction of the products of wave P1 in pH〈3.0 B-R buffer solution is also a one-electron reduction wave. But in 3.0〈pH〈5.8 B-R buffer solution wave P1 was overlapped by the hydrogen wave. Between pH 5.8 and 9.0, chrysin could yield two reduction waves P2 and P3- The former is an irreversible adsorptive wave of ionized chrysin involving one electron and the latter is also an irreversible adsorptive wave of reduction intermediate radical of chrysin involving one electron and one proton. And a linear relationship between ip3 and the concentration of chrysin can be established from 1.0×10^-6 to 4.0×10^-5 mol·L^-1 (r=0.9924) with the detection limit of 5×10^-7 mol·L^-1. In addition, the antioxidant ability of chrysin was investigated by linear sweep voltammetry (LSV). The determination result of IC50 of chrysin showed that chrysin is a good antioxidant. 相似文献
69.
Valentin Gogonea 《International journal of quantum chemistry》2005,104(3):342-353
This article presents a theoretical investigation of the reaction mechanism of imidazole nitration by peroxynitrite using density functional theory calculations. Understanding this reaction mechanism will help in elucidating the mechanism of guanine nitration by peroxynitrite, which is one of the assumed chemical pathways for damaging DNA in cells. This work focuses on the analysis of the potential energy surface (PES) for this reaction in the gas phase. Calculations were carried out using Hartree–Fock (HF) and density functional theory (DFT) Hamiltonians with double‐zeta basis sets ranging from 6‐31G(d) to 6‐31++G(d,p), and the triple‐zeta basis set 6‐311G(d). The computational results reveal that the reaction of imidazole with peroxynitrite in gas phase produces the following species: (i) hydroxide ion and 2‐nitroimidazole, (ii) hydrogen superoxide ion and 2‐nitrosoimidazole, and (iii) water and 2‐nitroimidazolide. The rate‐determining step is the formation of a short‐lived intermediate in which the imidazole C2 carbon is covalently bonded to peroxynitrite nitrogen. Three short‐lived intermediates were found in the reaction path. These intermediates are involved in a proton‐hopping transport from C2 carbon to the terminal oxygen of the ? O? O moiety of peroxynitrite via the nitroso (ON? ) oxygen. Both HF and DFT calculations (using the Becke3–Lee–Yang–Parr functional) lead to similar reaction paths for proton transport, but the landscape details of the PES for HF and DFT calculations differ. This investigation shows that the reaction of imidazole with peroxynitrite produces essentially the same types of products (nitro‐ and nitroso‐) as observed experimentally in the reaction of guanine with peroxynitrite, which makes the former reaction a good model to study by computation the essential characteristics of the latter reaction. Nevertheless, the computationally determined activation energy for imidazole nitration by peroxynitrite in the gas phase is 84.1 kcal/mol (calculated at the B3LYP/6‐31++G(d,p) level), too large for an enzymatic reaction. Exploratory calculations on imidazole nitration in solution, and on the reaction of 9‐methylguanine with peroxynitrite in the gas phase and solution, show that solvation increases the activation energy for both imidazole and guanine, and that the modest decrease (15 kcal mol?1) in the activation energy, due to the adjacent six member ring of guanine, is counterbalanced by solvation. These results lead to the speculation that proton tunneling may be at the origin of experimentally observed high reaction rate of guanine nitration by peroxynitrite in solution. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
70.
K Papadopoulos T TriantisC.H Tzikis A NikokavouraD Dimotikali 《Analytica chimica acta》2002,464(1):135-140
A weak chemiluminescence (CL) emission was observed in commercial Greek extra virgin olive oils (Knossos, Spitiko, Ananias, Altis, Minerva, Xenia) and in refined seed oils such as sunflower oils (Marata, Sanola, Sun, Mana, Sol, Minerva) as well as in corn oils (Flora, Minerva, Marata Sun and Sol) with potassium superoxide in the aprotic solvent dimethoxyethylene.On measuring the CL of mixtures of extra virgin olive oils with the cheaper refined seed oils, calibrations were produced which can be used for the determination of the adulteration of olive oils with seed oils down to 3%. Furthermore, depending on the kind of oils, “low” authenticity-CL-factors for olive oils (0.8-2.15 μmol l−1 gallic acid) and “high” for seed oils (4.5-11.2 μmol l−1 gallic acid) were calculated. 相似文献