全文获取类型
收费全文 | 1179篇 |
免费 | 54篇 |
国内免费 | 361篇 |
专业分类
化学 | 1438篇 |
晶体学 | 2篇 |
力学 | 8篇 |
综合类 | 2篇 |
数学 | 1篇 |
物理学 | 143篇 |
出版年
2024年 | 4篇 |
2023年 | 96篇 |
2022年 | 29篇 |
2021年 | 43篇 |
2020年 | 56篇 |
2019年 | 25篇 |
2018年 | 36篇 |
2017年 | 35篇 |
2016年 | 44篇 |
2015年 | 53篇 |
2014年 | 54篇 |
2013年 | 72篇 |
2012年 | 53篇 |
2011年 | 63篇 |
2010年 | 60篇 |
2009年 | 67篇 |
2008年 | 68篇 |
2007年 | 81篇 |
2006年 | 70篇 |
2005年 | 86篇 |
2004年 | 73篇 |
2003年 | 53篇 |
2002年 | 38篇 |
2001年 | 38篇 |
2000年 | 45篇 |
1999年 | 24篇 |
1998年 | 20篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 30篇 |
1993年 | 22篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 1篇 |
排序方式: 共有1594条查询结果,搜索用时 171 毫秒
101.
Decorating Pt/C Nanoparticles with Ru by Wall‐Jet Configuration: The Role of Coverage Degree on the Catalyst Activity for Glycerol Electrooxidation 下载免费PDF全文
《Electroanalysis》2018,30(9):2167-2175
Here, we built Ru‐decorated Pt/C nanoparticles with different coverage degrees (θRu) by wall‐jet configuration for the first time, and we investigated their catalytic properties towards glycerol electrooxidation in acidic medium. Moreover, we used the most active catalysts as the anode in electrolysis to produce carbonyl compounds. The use of an electrochemical cell in wall‐jet configuration allows for the controlling of electrodeposition through easily handling parameters; namely, the θRu is controlled by changing the concentration of the metallic precursor, speed, and volume of injection onto a Pt/C‐modified glassy carbon electrode under applied potential. Excess of Ru on a Pt surface inhibits glycerol dissociative adsorption, which limits further electrooxidation; whereas low θRu do not provide surface oxygen species to the anodic reaction. Hence, intermediates θRu reveal active catalysts – namely, θRu=0.42 shifts the onset potential 170 mV towards lower values and increases 1.65‐fold the current density at 0.5 V. The stability of this catalyst is also enhanced by maintaining a more constant current density during successive potential cycles in the presence of glycerol and by avoiding Ru leaching from the surface. The electrolysis on Ru‐decorated Pt/C is shown to lead the reaction towards formic acid (‘high oxidation state’), decreasing the amounts of glyceradehyde, glycolic acid, and dihydroxyacetone, as a result of the improved catalytic properties. 相似文献
102.
It has been observed on the oxidized V2 O5/γ-Al2 O3 that C3H6 form alkoxides which were converted to acetone during the desorption of adsorbate phase at 373 K. C3 H8 may form π-complexes on the reduced form of the same catalyst. However, the intensities of the bands in the adadsorption of C3 H8 were very weak as compared with the case of C3 H6 adsorption. Therefore, it was not reasonable to assign these bands clearly as any of the surface type species. 相似文献
103.
<正>α-Aminonitriles were synthesized via a one-pot three-component condensation of aldehydes,amines,and trimethylsilyl cyanide using silica-bonded N-propylpiperazine sulfamic acid(SBPPSA) as a recyclable solid acid at room temperature.SBPPSA showed much the same efficiency when used in consecutive reaction runs. 相似文献
104.
《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2659-2661
Manganese dioxide was found to catalyze stereoselective conversion of dialkyl 2-(imido-N-yl)-3-(triphenylphosphoranylidene)butanedioates to electron-poor (Z)-N-vinylimides in solvent-free conditions at 95°C in high coversions. 相似文献
105.
106.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1173-1184
Copolymerization of 1-[3,5-bis(trimethylsilyl)phenyl]-2-phenylacetylene (m,m-(Me3Si)2DPA) with other diphenylacetylene derivatives and their copolymer properties were investigated. Homopolymerization of m,m-(Me3Si)2DPA by TaCl5─n-Bu4Sn (1:2) did not give the polymer due to steric hindrance. However, m,m-(Me3Si)2DPA copolymerized with diphenylacetylene (DPA), 1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene (p-Me3Si DPA), and 1-phenyl-2-[m-(trimethylsilyl)phenyl]acety-lene (m-Me3SiDPA) in the presence of TaCl5─n-Bu4Sn at various feed ratios to give copolymers in moderate yields. The formed copolymers were yellow to orange solids, which were soluble in common organic solvents such as toluene and CHCl3. The highest weight-average molecular weights (Mw) of these copolymers reached ca. 6 × 105 and tough films could be obtained by solution casting. Their onset temperatures of weight loss in air were observed around 400°C, indicating high thermal stability. The oxygen permeability coefficients at 25°C of copoly(m,m-(Me3Si)2 DPA/DPA) (feed ratio 1:1) and copoly(m,m-(Me3Si)2DPA/p-Me3SiDPA) (feed ratio 1:2) were 21 and 100 barrers, respectively, medium in magnitude among polymers from substituted acetylenes. 相似文献
107.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1437-1445
The kinetics of free radical polymerization of methylacrylate (MA) was investigated using benzyltributylammonium chloride (BTBAC) as phase transfer catalyst and potassium peroxydisulfate as initiator at aconstant temperature, 60°C, in an inert atmosphere under unstirred condition. The effect of concentrations of the monomer, initiator and the catalyst on polymerization was discussed and a mechanism of polymerization has been proposed. The order with respect to the monomer, initiator, and phase transfer catalyst was found to be 2, 0.5, and 0.5, respectively. 相似文献
108.
采用沉淀法和浸渍法制备了2种铬基(Cr2O3和CrO3/Cr2O3)催化剂,用于气相氟化2-氯-1,1,1-三氟乙烷合成1,1,1,2-四氟乙烷。研究发现含有低价铬(Cr3+)物种的Cr2O3催化剂上2-氯-1,1,1-三氟乙烷的稳态转化率为18.5%,而含有高价铬(Cr6+)物种和低价铬(Cr3+)物种的CrO3/Cr2O3催化剂初始转化率达到30.6%,然而存在明显的失活。含有Cr6+物种的CrO3/Cr2O3催化剂的2-氯-1,1,1-三氟乙烷氟化反应初始TOF值为1.71×10-4 molHCFC-133a·molCr(Ⅵ)-1·s-1,高于含有Cr3+物种的Cr2O3催化剂(4.16×10-5 molHCFC-133a·molCr(Ⅲ)-1·s-1)。Cr2O3催化剂在氟化反应前后催化剂的物相结构保持不变;而含有高价铬物种的CrO3/Cr2O3催化剂经HF反应后生成了CrOxFy活性物种。然而,CrOxFy物种在反应中挥发或转化成稳定但无活性的CrF3,从而导致催化剂失活。 相似文献
109.
Qian‐Lin Tang 《International journal of quantum chemistry》2013,113(16):1992-2001
Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H2S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H2S → H2S* → SH* → S* and (2) 2H2S → 2H2S* → 2SH* → S* + H2S* → S* + H2S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H2S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H2S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H2S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc. 相似文献
110.
By tracing the chlorine concentrations in the aqueous solutions containing the catalyst precursors, Pd/Fe(OH)x catalysts with different activities can be controllably prepared. For the hydrogenation of nitrobenzene, the active Pd/Fe(OH)x catalysts were obtained from aqueous solutions with chlorine concentrations below 18 ppm and above 8 ppm. 相似文献