全文获取类型
收费全文 | 1018篇 |
免费 | 90篇 |
国内免费 | 360篇 |
专业分类
化学 | 1144篇 |
晶体学 | 5篇 |
综合类 | 11篇 |
物理学 | 308篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 50篇 |
2019年 | 40篇 |
2018年 | 31篇 |
2017年 | 45篇 |
2016年 | 44篇 |
2015年 | 32篇 |
2014年 | 44篇 |
2013年 | 65篇 |
2012年 | 61篇 |
2011年 | 57篇 |
2010年 | 58篇 |
2009年 | 100篇 |
2008年 | 101篇 |
2007年 | 95篇 |
2006年 | 82篇 |
2005年 | 71篇 |
2004年 | 72篇 |
2003年 | 41篇 |
2002年 | 47篇 |
2001年 | 33篇 |
2000年 | 30篇 |
1999年 | 22篇 |
1998年 | 30篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1468条查询结果,搜索用时 31 毫秒
991.
负载Pt催化生物柴油加氢脱氧性能研究 总被引:1,自引:0,他引:1
采用XRD、BET、SEM、NH_3-TPD对Pt/Al_2O_3、Pt/Al_2O_3-ZSM-5、Pt/ZSM-5催化剂进行表征,在不同反应工艺条件下考察三种分子筛的酸性、孔径分布、外部形貌、晶体结构对其加氢脱氧性能的影响。结果表明,Br■nsted酸性位点和中孔体积占比对脂肪酸甲酯的加氢脱氧反应来说至关重要,其中,Br■nsted酸性位点在脱氧反应中的C-O键断裂发挥主要作用,中孔孔径则能提高整个反应的质量传递效率以及避免C_(12-18)长链烷烃发生裂解。三种催化剂的加氢脱氧催化效果大小为:Pt/Al_2O_3-ZSM-5Pt/Al_2O_3Pt/ZSM-5;适宜的反应工艺条件为:t=350℃,p=2 M Pa,H2/oil=1000,WHSV=0.5 h~(-1),在此条件下Pt/Al_2O_3-ZSM-5的脂肪酸甲酯转化率为99.4%,目标产物液体收率为86.8%。 相似文献
992.
Direct oxidation of methane at low temperature using Pt/C Pd/C Pt/C-ATO Pd/C-ATO electrocatalysts prepared by sodium borohydride reduction process 《燃料化学学报》2018,46(9):1137-1145
The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation. 相似文献
993.
Man Zhou Muhong Li Chujun Hou Zhongyu Li Yongzheng Wang Kun Xiang Xuefeng Guo 《中国化学快报》2018,29(6):787-790
Pt nanocrystallines (~3 nm) covered with controllable carbon layers were synthesized by photochemical reduction method which exhibited extraordinary anti-sintering properties and different CO oxidation activities. 相似文献
994.
Maryam Sadat Majdolashrafi 《Phosphorus, sulfur, and silicon and the related elements》2018,193(7):415-422
The complex [Pt2(μ-mtrzt)4(mtrzt)2] (1) was synthesized from the reaction of a mixture of 4-methyl-4H-1,2,4-triazole-3-thiol (Hmtrzt) and ethylenediamine (en) with K2PtCl4 in CH3OH/H2O (2:1) as solvent. The complex [Pt2(μ-mtrzt)4] (2) was synthesized by the same procedure as described for preparation of complex 1 but in the absence of ethylenediamine. Both complexes were characterized by elemental analysis, IR,1H NMR,13C{1H}NMR, UV-Vis, as well as luminescence spectroscopy and their structures were analyzed by single-crystal X-ray diffraction method. The X-ray structure determinations show that complexes of 1 and 2 have binuclear structures in a paddle-wheel fashion with Pt-Pt distances of 2.6628(7) and 2.7977(16)Å, respectively. In complex 1, each platinum(III) atom has a distorted octahedral coordination geometry with the sulfur atom and the second platinum subunit in axial positions and two nitrogen and two sulfur atoms in equatorial positions. Also, in complex 2, each platinum(II) atom has a distorted square-pyramidal coordination geometry with the second platinum subunit in axial position and two nitrogen and two sulfur atoms in equatorial positions. In addition, intermolecular C?H···N and C?H···S hydrogen bonds in 1 and 2 as well as intermolecular anagostic C?H···Pt and C?H···π interactions in 2 are effective in the stabilization of the crystal packing of these complexes. 相似文献
995.
Li-Juan Jia Chun-Yan Hua Li-Yi Dai Yong-Kui Shan 《Reaction Kinetics and Catalysis Letters》2004,81(2):235-240
Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst shows higher specific activity towards oxygen reduction reaction
as compared to Pt/MWNTs when employed as cathodic catalyst in direct methanol fuel cell.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
Jian Hua XIAO Xue Hui LI Sha DENG Fu Rong WANG Le Fu WANG 《中国化学快报》2006,17(10):1357-1360
The storage and reduction of nitrogen oxides has attracted much attention as an efficient way to reduce NOx emission of lean-burn gasoline and diesel engines1-5. At present, NOx storage and reduction (NSR) catalysts based on Pt and Ba have been extensivel… 相似文献
997.
998.
999.
1000.