全文获取类型
收费全文 | 503篇 |
免费 | 49篇 |
国内免费 | 24篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 23篇 |
2016年 | 12篇 |
2015年 | 23篇 |
2014年 | 8篇 |
2013年 | 42篇 |
2012年 | 13篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 27篇 |
2008年 | 25篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 32篇 |
2004年 | 12篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有576条查询结果,搜索用时 31 毫秒
81.
Electronic and Defective Engineering of Electrospun CaMnO3 Nanotubes for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc–Air Batteries
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shengjie Peng Xiaopeng Han Linlin Li Shulei Chou Dongxiao Ji Huangjiao Huang Yonghua Du Jian Liu Seeram Ramakrishna 《Liver Transplantation》2018,8(22)
Rational design and massive production of bifunctional catalysts with superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are essential for developing metal–air batteries and fuel cells. Herein, controllable large‐scale synthesis of sulfur‐doped CaMnO3 nanotubes is demonstrated via an electrospinning technique followed by calcination and sulfurization treatment. The sulfur doping can not only replace oxygen atoms to increase intrinsic electrical conductivity but also introduce abundant oxygen vacancies to provide enough catalytically active sites, which is further demonstrated by density functional theory calculation. The resulting sulfur‐modified CaMnO3 (CMO/S) exhibits better electrocatalytic activity for ORR and OER in alkaline solution with higher stability performance than the pristine CMO. These results highlight the importance of sulfur treatment as a facile yet effective strategy to improve the ORR and OER catalytic activity of the pristine CaMnO3. As a proof‐of‐concept, a rechargeable Zn–air battery using the bifunctional catalyst exhibits a small charge–discharge voltage polarization, and long cycling life. Furthermore, a solid‐state flexible and rechargeable Zn–air battery gives superior discharge–charge performance and remarkable stability. Therefore, the CMO/S nanotubes might be a promising replacement to the Pt‐based electrocatalysts for metal–air batteries and fuel cells. 相似文献
82.
Review on Challenges and Recent Advances in the Electrochemical Performance of High Capacity Li‐ and Mn‐Rich Cathode Materials for Li‐Ion Batteries
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prasant Kumar Nayak Evan M. Erickson Florian Schipper Tirupathi Rao Penki Nookala Munichandraiah Philipp Adelhelm Hadar Sclar Francis Amalraj Boris Markovsky Doron Aurbach 《Liver Transplantation》2018,8(8)
Li and Mn‐rich layered oxides, xLi2MnO3·(1–x)LiMO2 (M=Ni, Mn, Co), are promising cathode materials for Li‐ion batteries because of their high specific capacity that can exceed 250 mA h g?1. However, these materials suffer from high 1st cycle irreversible capacity, gradual capacity fading, low rate capability, a substantial charge‐discharge voltage hysteresis, and a large average discharge voltage decay during cycling. The latter detrimental phenomenon is ascribed to irreversible structural transformations upon cycling of these cathodes related to potentials ≥4.5 V required for their charging. Transition metal inactivation along with impedance increase and partial layered‐to‐spinel transformation during cycling are possible reasons for the detrimental voltage fade. Doping of Li, Mn‐rich materials by Na, Mg, Al, Fe, Co, Ru, etc. is useful for stabilizing capacity and mitigating the discharge‐voltage decay of xLi2MnO3·(1–x)LiMO2 electrodes. Surface modifications by thin coatings of Al2O3, V2O5, AlF3, AlPO4, etc. or by gas treatment (for instance, by NH3) can also enhance voltage and capacity stability during cycling. This paper describes the recent literature results and ongoing efforts from our groups to improve the performance of Li, Mn‐rich materials. Focus is also on preparation of cobalt‐free cathodes, which are integrated layered‐spinel materials with high reversible capacity and stable performance. 相似文献
83.
84.
Effects of manganese toxicity on photosynthesis of white birch (Betula platyphylla var. japonica) seedlings 总被引:5,自引:0,他引:5
The effects of manganese (Mn) toxicity on photosynthesis in white birch ( Betula platyphylla var. japonica ) leaves were examined by the measurement of gas exchange and chlorophyll fluorescence in hydroponically cultured plants. The net photosynthetic rate at saturating light and ambient CO2 (Ca ) of 35 Pa decreased with increasing leaf Mn concentrations. The carboxylation efficiency, derived from the difference in CO2 assimilation rate at intercellular CO2 pressures attained at Ca of 13 Pa and O Pa, decreased with greater leaf Mn accumulation. Net photosynthetic rate at saturating light and saturating CO2 (5%) also declined with leaf Mn accumulation while the maximum quantum yield of O2 evolution at saturating CO2 was not affected. The maximum efficiency of PSII photochemistry (Fv /Fm ) was little affected by Mn accumulation in white birch leaves over a wide range of leaf Mn concentrations (2–17 mg g−1 dry weight). When measured in the steady state of photosynthesis under ambient air at 430 μmol quanta m−2 s−1 , the levels of photochemical quenching (qP) and the excitation capture efficiency of open PSII (F'v /F'm ) declined with Mn accumulation in leaves. The present results suggest that excess Mn in leaves affects the activities of the CO2 reduction cycle rather than the potential efficiency of photochemistry, leading to increases in QA reduction state and thermal energy dissipation, and a decrease in quantum yield of PSII in the steady state. 相似文献
85.
《Luminescence》2003,18(5):259-267
High‐valent oxo‐iron(IV) species are commonly proposed as the key intermediates in the catalytic mechanisms of iron enzymes. Water‐soluble iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)porphyrin (Fe(III)TMPyP) has been used as a model of heme‐enzyme to catalyse the hydrogen peroxide (H2O2) oxidation of various organic compounds. However, the mechanism of the reaction of Fe(III)TMPyP with H2O2 has not been fully established. In this study, we have explored the kinetic simulation of the reaction of Fe(III)TMPyP with H2O2 and of the catalytic reactivity of FeTMPyP in the luminescent peroxidation of luminol. According to the mechanism that has been established in this work, Fe(III)TMPyP is oxidized by H2O2 to produce (TMPyP)·+Fe(IV)=O (k1 = 4.5 × 104/mol/L/s) as a precursor of TMPyPFe(IV)=O. The intermediate, (TMPyP)·+Fe(IV)=O, represented nearly 2% of Fe(III)TMPyP but it does not accumulate in suf?cient concentration to be detected because its decay rate is too fast. Kinetic simulations showed that the proposed scheme is capable of reproducing the observed time courses of FeTMPyP in various oxidation states and the decay pro?les of the luminol chemiluminescence. It also shows that (TMPyP)·+Fe(IV)=O is 100 times more reactive than TMPyPFe(IV)=O in most of the reactions. These two species are responsible for the initial sharp and the sustained luminol emissions, respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
86.
Muhammad Arba Rahmana E. Kartasasmita 《Journal of biomolecular structure & dynamics》2016,34(2):427-438
A series of cationic porphyrin–anthraquinone hybrids bearing either pyridine, imidazole, or pyrazole rings at the meso-positions have been investigated for their interaction with DNA G-quadruplexes by employing molecular docking and molecular dynamics simulations. Three types of DNA G-quadruplexes were utilized, which comprise parallel, antiparallel, and mixed hybrid topologies. The porphyrin hybrids have a preference to bind with parallel and mixed hybrid structures compared to the antiparallel structure. This preference arises from the end stacking of porphyrin moiety following G-stem and loop binding of anthraquinone tail, which is not found in the antiparallel due to the presence of diagonal and lateral loops that crowd the G-quartet. The binding to the antiparallel, instead, occurred with poorer affinity through both the loop and wide groove. All sites of porphyrin binding were confirmed by 6 ns molecular dynamics simulation, as well as by the negative value of the total binding free energies that were calculated using the MMPBSA method. Free energy analysis shows that the favorable contribution came from the electrostatic term, which supposedly originated from the interaction of either cationic pyridinium, pyrazole, or imidazole groups and the anionic phosphate backbone, and also from the van der Waals energy, which primarily contributed through end stacking interaction. 相似文献
87.
The antenna proteins in photosystem II (PSII) not only promote energy transfer to the photosynthetic reaction center (RC) but provide also an efficient cation sink to re-reduce chlorophyll a if the electron transfer (ET) from the Mn-cluster is inhibited. Using the newest PSII dimer crystal structure (3.0 Å resolution), in which 11 β-carotene molecules (Car) and 14 lipids are visible in the PSII monomer, we calculated the redox potentials (Em) of one-electron oxidation for all Car (Em(Car)) by solving the Poisson-Boltzmann equation. In each PSII monomer, the D1 protein harbors a previously unlocated Car (CarD1) in van der Waals contact with the chlorin ring of ChlZ(D1). Each CarD1 in the PSII dimer complex is located in the interface between the D1 and CP47 subunits, together with another four Car of the other PSII monomer and several lipid molecules. The proximity of Car bridging between CarD1 and plastoquinone/QA may imply a direct charge recombination of Car+QA−. The calculated Em(CarD1) and Em(ChlZ(D1)) are, respectively, 83 and 126 mV higher than Em(CarD2) and Em(ChlZ(D2)), which could explain why CarD2+ and ChlZ(D2)+ are observed rather than the corresponding CarD1+ and ChlZ(D1)+. 相似文献
88.
The accumulation and biocycle of Cu, Pb, Zn and Mn elements were studied in Kandelia candel (L.) Druce mangrove community of Jiulong River Estuary of Fujian. The pool amounts of Cu, Pb, Zn and Mn elements in the forest soil (0~30 cm in depth) were 6.86, 4.23, 25.64 and 134. 67 g · m-2, respectively. The respective element contents ranged from in different parts of the plant, 1.85~6.97, 0.37~3.74, 16.0~25.2 and 140~1405 μg· g-1 of Cu, Pb, Zn and Mn. The pool amounts of elements in standing crop of the community were 87.98, 40. 34, 335.34 and 8006.99 mg · m-2 for Cu, Pb, Zn and Mn respectively. The pool amounts of Cu, Pb, Zn and Mn elements in residues were: 593.06, 49.27, 2450.79 and 43486.70 μg · m-2 respectively. The biocycle of the elements in the community were described as follows: Annual uptake of Cu was 10. 17, Pb 4.32, Zn 49. 14 and Mn 2268. 16 mg · m-2; Annual return of Cu was 2.21, Pb 0.70, Zn 18.63 and Mn 1574.98 mg· m-2; Annual retention of Cu was 7.96, Pb 3.62, Zn 30. 51 and Mn 693.18 mg · m-2. The turnover periods of Cu, Pb, Zn and Mn were 40, 58, 18 and 5 year, respectively. The absorption, utilatizion and cycle coefficients were in the order of Mn〉Zn〉Cu〉Pb. 相似文献
89.
By treating the reduced MoFe protein from Azotobacter vinelandii with o-phenanthroline and O2, an inactive protein partially deficient in both FeMoco and P-cluster could be obtained. The inactive protein could be reactivated by the reconsfituent solutions of different colours which were prepared from mixture in different proportions of ferric homocitrate, Na2S and dithiothreitol (DTT) with K2CrO4, KMnO4 and Na2MoO4, respectively, the inactive protein could be somewhat reactivated by DTF but not by the other compounds or their mixtures which were deficient in one or two of the above compounds. 99Mo was found in the reconstituted protein of the inactive MoFe protein with a reconstituent solution containing 99Mo. Its measurement of differential perturbed angular correlation indicated that 41% of 99Mo in the reconstituted protein were in a state similar to that of 99Mo in 99MoFe protein from K. pneumoniae. The results showed that the reactivation of the inactive MoFe rotein was mainly based on the restoration of its metallocluster content. It seemed to be reasonable to postulate that Mn- or Cr-containing nitrogenase could be obtained likewise by the reconstitution of the inactive protein with the Mn- or Cr-containing reconstituent solution. 相似文献
90.
A new electron-deficient tentacle porphyrin meso-tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine)phenyl]porphyrin (TθF4TAP) has been synthesized. The binding interactions of TθF4TAP with DNA polymers were studied for comparison to those of an electron-deficient tentacle porphyrin and an electron-rich tentacle porphyrin; these previously studied porphyrins bind to DNA primarily by intercalative and outside-binding modes, respectively. The three tentacle porphyrins have similar size and shape. The basicity of TθF4TAP indicated that it has electronic characteristics similar to those of the intercalating electron-deficient tentacle porphyrin. However, TθF4TAP binds to calf thymus DNA, [poly(dA-dT)]2, and [poly(dG-dC)]2 in a self-stacking, outside-binding manner under all conditions. Evidence for this binding mode included a significant hypochromicity of the Soret band, a conservative induced CD spectrum, and the absence of an increase in DNA solution viscosity. As found previously for the electron-rich porphyrin, the results suggest that combinations of closely related self-stacked forms coexist. The mix of forms depended on the DNA and the solution conditions. There are probably differences in the detailed features of the self-stacking adducts for the two types of tentacle porphyrins, especially at high R (ratio of porphyrin to DNA). At low R values, the induced CD signal of TθF4TAP/CT DNA resembled that of TθF4TAP/[poly(dA-dT)]2, suggesting that TθF4TAP binds preferentially at AT regions. Competitive binding experiments gave evidence that TθF4TAP binds preferentially to [poly(dA-dT)]2 over [poly(dG-dC)]2. Thus, despite the long, positively charged, flexible substituents on the porphyrin, the binding of TθF4TAP is significantly affected by base-pair composition. Similar characteristics were found previously for the electron-rich tentacle porphyrin. Thus, significant changes in electron richness have relatively minor effects on this outside binding selectivity for AT regions. TθF4TAP is the first porphyrin with electron deficiency and shape similar to intercalating porphyrins that does not appear to intercalate. All porphyrins reported to intercalate have had pyridinium substituents. Thus, the electronic distribution in the porphyrin ring, not just the overall electron richness, may play a role in facilitating intercalation. © 1997 John Wiley & Sons, Inc. Biopoly 42: 203–217, 1997 相似文献