全文获取类型
收费全文 | 1743篇 |
免费 | 76篇 |
国内免费 | 923篇 |
专业分类
化学 | 2385篇 |
力学 | 20篇 |
综合类 | 2篇 |
物理学 | 335篇 |
出版年
2018年 | 10篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 22篇 |
2012年 | 16篇 |
2011年 | 316篇 |
2010年 | 107篇 |
2009年 | 237篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 47篇 |
2005年 | 135篇 |
2004年 | 367篇 |
2003年 | 160篇 |
2002年 | 151篇 |
2001年 | 120篇 |
2000年 | 69篇 |
1999年 | 53篇 |
1998年 | 44篇 |
1997年 | 43篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 34篇 |
1993年 | 123篇 |
1992年 | 156篇 |
1991年 | 114篇 |
1990年 | 113篇 |
1989年 | 115篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1978年 | 1篇 |
排序方式: 共有2742条查询结果,搜索用时 31 毫秒
911.
Peirong Chen Ly May Chew Aleksander Kostka Kunpeng Xie Martin Muhler Wei Xia 《天然气化学杂志》2013,(2):312-320
Oxygen-and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) were applied as metal-free catalysts in selective olefin hydrogenation. A series of NCNTs was synthesized by NH3 post-treatment of OCNTs. Temperature-programmed desorption, N2 physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygenand nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 C led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis. 相似文献
912.
4-Arylmethylidene-4,5-dihydro-3-phenylisoxazol-5-ones were synthesized by the convenient three-component reaction of ethyl benzoylacetate,hydroxylamine and aromatic aldehydes in the presence of pyridine.The target compounds were also obtained by the reaction between 3-phenylisoxazol-5-one and aromatic aldehydes at 105℃under solvent free condition.Yields of products depended considerably on the aldehyde used. 相似文献
913.
GU Fang WANG HaiJun & ZHAO ZuoFei College of Chemistry Environment Science Hebei University Baoding China International Centre for Materials Physics Chinese Academy of Sciences Shenyang China Key Laboratory of Medicinal Chemistry Molecular Diagnosis Ministry of Education China 《中国科学B辑(英文版)》2011,(3)
The thermodynamic properties of a binary self-condensing vinyl polymerization system consisting of monomers and inimers are investigated by the principle of statistical mechanics.In detail,in terms of two types of canonical partition functions constructed from different viewpoints,the equilibrium free energy,the law of mass action and the size distribution of hyperbranched polymers are obtained.As an application,the specific heat,equation of state and isothermal compressibility concerning the polymerization... 相似文献
914.
本文回顾唐敖庆先生的科教活动与事迹,从中展现他的学术思想、治学风格。上世纪中叶,他在国内环境中,独立自主地培养人才,开展研究,创建理论化学,并使之繁荣兴旺。他特别重视教学,视相关的课程学习为从业打好基础、开启智力、培植兴趣、进入研究的必经手段。据此,每招收新研究生和开办高层人才培训班时,必先系统授课。而在科研立项中,他... 相似文献
915.
LIN Feng LIU Lan-ying NI Jia-zuan .College of Life Science Jilin University Changchun P.R.China .Key Laboratory of Rare Earth of Chinese Academy Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun .College of Life Science Shenzhen University Shenzhen 《高等学校化学研究》2011,(4):619-622
Single-chain fragment variable(ScFv) antibodies with the substrate binding sites were obtained by repetitive selections from a semi-synthetic phage display antibody library against two haptens——thyroxine(T4) and O-methyl-T4(O-CH3-T4).The positive phage clones were determined by ELISA and then cloned into vector pET30a(+).The recombined plasmids were identified by DNA sequence analysis and transformed into E.coli BL21(DE3).The expressed proteins were isolated,purified,identified by Western blot analysis,and ... 相似文献
916.
LI GuangShe LI LiPing & ZHENG Jing State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou China 《中国科学B辑(英文版)》2011,(6)
This work presents a critical review on the studies of defect chemistry of oxide nanoparticles for creating new functionalities pertinent to energy applications including dilute-magnetic semiconductors,giant-dielectrics,or white light generation.Emphasis is placed on the relationships between the internal structure and defective surfaces of oxide nanoparticles and their synergy in tailoring the materials properties.This review is arranged in a sequence:(1) structural fundamentals of bulk oxides,using TiO2 a... 相似文献
917.
新型磺酸功能化吡啶盐酸盐离子液体催化剂用于六氢喹啉合成(英文) 总被引:1,自引:0,他引:1
Ardeshir Khazaei Mohammad Ali Zolfigol Ahmad Reza Moosavi-Zare Javad Afsar Abdolkarim Zare Vahid Khakyzadeh Mohammad Hassan Beyzavi 《催化学报》2013,34(10):1936-1944
Sulfonic acid functionalized pyridinium chloride [pyridine-SO3 H]Cl has been synthesized as a novel Brnsted acidic ionic liquid and characterized on the basis of its FT-IR,1H and 13C NMR,MS,ther-mogravimetry,and derivative thermogravimetry data.The material has also been used as a highly efficient,homogeneous,and reusable catalyst for the preparation of hexahydroquinolines according to the one-pot multi-component condensation of arylaldehydes,dimedone(5,5-dimethylcyclohexane-1,3-dione),β-ketoesters,and ammonium acetate under solvent-free conditions. 相似文献
918.
Using a click reaction between alkynylthiacalix[4]arene and ethyl 2-azidoacetate followed by an ammonolysis with ethanolamine,leucinol and hydrazine hydrate,respectively,three novel thiacalix [4]arene derivatives 4,5 and 6 with triazolyl and hydrogen bonding groups(NH and OH) were synthesized in high yields.They exhibited excellent extraction capability for six anionic and cationic dyes.The flexible cavity,π-triazole rings and hydrogen bonding groups all play crucial roles in dye complexation. 相似文献
919.
Seven square planar bis(o-diiminobenzosemiquinonato)nickel(II) complexes, [Ni(o-C6H4(NH)(NAr))2] (Ar= Mes, 1; p-F-C6H4, 2; p-CI-C6H4, 3), [Ni(o-4,5-F2-C6H2(NH)(NPh))2] (4), and [Ni(o-4,5-CIz-C6H2(NH)(NAr))2] (Ar =Ph, 5; 2,6-F2-C6H3, 6; 2,6-C12-C6H3, 7), have been synthesized and characterized by 1H NMR, 13C NMR, 19F NMR, IR, UV-Vis-NIR, elemental analyses, HRMS, as well as single-crystal X-ray diffraction studies (1 and 7). The cyclic voltammograms of these complexes exhibit two reversible redox processes of [NiLe]0n- and [NIL2]l /2 , and one irreversible process of [NiL2]~n+. Substituent effects on the redox properties of these complexes, in addi- tion with those of the known complexes [Ni(o-C6Ha(NH)(NPh))2] (8) and [Ni(o-3,5-Butz-C6Hz(NH)2)2] (9), are identified by comparing the half-wave potentials of the reduction waves, as 1 ~ 9 〈 8 ~ 2 〈 3 〈 4 〈 5 〈 7 〈 6, reflect- ing the ease of reduction of [NIL2] parallels the electron-donating and -withdrawing ability of the substituent group. Reduction of 1 with one or two equivalents of sodium metal in THF has led to the isolation of [Na(THF)3][I] and [Na(THF)3]2[1]. The structure data of these two complexes revealed by low-temperature X-ray crystallography suggest their corresponding electronic structures of [Nill(lL-1 )(IL2-)]1- and [Ni1](1L2 )212-, which are in line with those of [9]n (n = 1-, 2-) suggested by spectroelectrochemical study. 相似文献
920.