全文获取类型
收费全文 | 7582篇 |
免费 | 1012篇 |
国内免费 | 895篇 |
专业分类
化学 | 2170篇 |
晶体学 | 44篇 |
力学 | 595篇 |
综合类 | 120篇 |
数学 | 4227篇 |
物理学 | 2333篇 |
出版年
2024年 | 8篇 |
2023年 | 85篇 |
2022年 | 128篇 |
2021年 | 189篇 |
2020年 | 258篇 |
2019年 | 216篇 |
2018年 | 228篇 |
2017年 | 252篇 |
2016年 | 290篇 |
2015年 | 207篇 |
2014年 | 311篇 |
2013年 | 729篇 |
2012年 | 390篇 |
2011年 | 449篇 |
2010年 | 404篇 |
2009年 | 511篇 |
2008年 | 511篇 |
2007年 | 550篇 |
2006年 | 461篇 |
2005年 | 396篇 |
2004年 | 342篇 |
2003年 | 376篇 |
2002年 | 347篇 |
2001年 | 274篇 |
2000年 | 210篇 |
1999年 | 188篇 |
1998年 | 217篇 |
1997年 | 177篇 |
1996年 | 132篇 |
1995年 | 93篇 |
1994年 | 76篇 |
1993年 | 63篇 |
1992年 | 51篇 |
1991年 | 51篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 36篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有9489条查询结果,搜索用时 151 毫秒
41.
42.
43.
A series of NiMnTi mixed metal oxides (Ni/Mn-TiO2, Mn/NiTi-LDO and TiO2/NiMn-LDO, NiMnTi-LDO) were synthesized via different assembling methods and evaluated in the selective catalytic reduction of NOx with NH3(NH3-SCR). As the results presented, catalysts via diverse assembling methods of LDHs templates afforded different catalytic denitrification (DeNOx) performance, which might be related to the exposure degree of active constituents and the interaction intensity between metal components. Noticeably, compared with Ni/Mn-TiO2, Mn/NiTi-LDO and TiO2/NiMn-LDO catalysts, the NiMnTi-LDO catalyst deriving from one step in-situ method NiMnTi-LDH precursor template exhibited the most desirable performance at temperature window of 150–360 °C in NH3-SCR (above 90% NOx conversion with 95% N2 selectivity). The specific structure and property of samples were correlated by means of a series of characterizations, where the results indicated that NiMnTi-LDO possessed the highest surface area, the strongest redox ability, the most abundant acid amount and the best dispersion. 相似文献
44.
The surface charge is a key concept in electrochemistry. Mathematically, the surface charge is obtained from a spatial integration of the volume charge along a particular direction. Ambiguities thus arise in choosing the starting and ending points of the integration. As for electrocatalytic interfaces, the presence of chemisorbates further complicates the situation. In this minireview, I adopt a definition of the surface charge within a continuum picture of the electric double layer. I will introduce surface charging behaviors of firstly ordinary electrochemical interfaces and then electrocatalytic interfaces featuring partially charged chemisorbates. Particularly, the origin of nonmonotonic surface charging behaviors of electrocatalytic interfaces is explained using a primitive model. Finally, a brief account of previous studies on the nonmonotonic surface charging behavior is presented, as a subline of the spectacular history of electric double layer. 相似文献
45.
Oxygen reduction reaction (ORR) is one of the most technologically relevant reactions. It occurs at the interface of the electrocatalyst and electrolyte, where oxygen reacts with protons and electrons to produce water. Because the electrocatalyst is dispersed on a high surface area support, morphological confinement becomes critical, as it dictates proton and oxygen transport. Furthermore, confinement is induced by ionomer, ionic liquids (ILs), or molecular additives, and their impact on electrocatalyst reactivity and transport properties is currently not well understood. We present an overview of electrostatics and mass transport–induced confinement and zoom in into ILs and molecular additives and try to unravel how local confinement induced by them impacts ORR. 相似文献
46.
Dr. Oumaïma Gharbi Dr. Mai T. T. Tran Prof. Mark E. Orazem Dr. Bernard Tribollet Dr. Mireille Turmine Dr. Vincent Vivier 《Chemphyschem》2021,22(13):1371-1378
The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer constant-phase elements. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution. 相似文献
47.
48.
NHC‐Pd complex‐catalyzed double carbonylation of aryl iodides with secondary amines to α‐keto amides 下载免费PDF全文
A series of palladium–NHC compounds were prepared and their catalytic activity in the double carbonylation of aryl iodides to synthesize α‐keto amides were examined. Palladium complexes bearing mixed NHC–phosphine exhibited high efficiency for the double carbonylation reaction. The effects of different solvents, base, temperature, carbon monoxide (CO), pressure, various amine and aryl iodides were investigated. Both electron‐rich and electron‐deficient aryl iodides afforded the corresponding substituted α‐keto amides in moderate to good yields. A possible mechanism was also proposed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
49.
A series of Mn(II) aminophosphonate complexes were successfully synthesized and intercalated into the hydroxy double salt [Zn5(OH)8]Cl2·yH2O. Complex incorporation led to an increase in the interlayer spacing from 7.8 to 10–12 Å. Infrared spectroscopy showed the presence of the characteristic vibration peaks of the Mn(II) complexes in the intercalates' spectra, indicating successful incorporation. The complex-loaded composites had somewhat lower proton relaxivities than the pure complexes. Nevertheless, these intercalates may have use as MRI contrast agents for patients with poor kidney function, where traditional Gd(III)-based contrast agents cause severe renal failure. 相似文献
50.
Wei Shi Jian‐Jun Liu Xiang‐Ping Ou Chang‐Cang Huang 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(4):289-293
A homochiral helical three‐dimensional coordination polymer, poly[[(μ2‐acetato‐κ3O,O′:O)(hydroxido‐κO)(μ4‐5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ido‐κ5N1,O:N2:N4:N5)(μ3‐5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ido‐κ4N1,O:N2:N4:N5)dicadmium(II)] 0.75‐hydrate], {[Cd2(C7H5N6O)2(CH3COO)(OH)]·0.75H2O}n, was synthesized by the reaction of cadmium acetate, N‐(1H‐tetrazol‐5‐yl)isonicotinamide (H‐NTIA), ethanol and H2O under hydrothermal conditions. The asymmetric unit contains two crystallographically independent CdII cations, two deprotonated 5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ide (NTIA−) ligands, one acetate anion, one hydroxide anion and three independent partially occupied water sites. The two CdII cations, with six‐coordinated octahedral and seven‐coordinated pentagonal bipyramidal geometries are located on general sites. The tetrazole group of one symmetry‐independent NTIA− ligand links one of the independent CdII cations into 61 helical chains, while the other NTIA− ligand links the other independent CdII cations into similar but unequal 61 helical chains. These chains, with a pitch of 24.937 (5) Å, intertwine into a double‐stranded helix. Each of the double‐stranded 61 helices is further connected to six adjacent helical chains through an acetate μ2‐O atom and the tetrazole group of the NTIA− ligand into a three‐dimensional framework. The helical channel is occupied by the isonicotinamide groups of NTIA− ligands and two helices are connected to each other through the pyridine N and carbonyl O atoms of isonicotinamide groups. In addition, N—H...O and O—H...N hydrogen bonds exist in the complex. 相似文献