全文获取类型
收费全文 | 28438篇 |
免费 | 3693篇 |
国内免费 | 3153篇 |
专业分类
化学 | 20742篇 |
晶体学 | 363篇 |
力学 | 1403篇 |
综合类 | 234篇 |
数学 | 3537篇 |
物理学 | 9005篇 |
出版年
2024年 | 47篇 |
2023年 | 438篇 |
2022年 | 523篇 |
2021年 | 764篇 |
2020年 | 906篇 |
2019年 | 926篇 |
2018年 | 788篇 |
2017年 | 751篇 |
2016年 | 1120篇 |
2015年 | 1140篇 |
2014年 | 1351篇 |
2013年 | 1901篇 |
2012年 | 2274篇 |
2011年 | 2509篇 |
2010年 | 1763篇 |
2009年 | 1734篇 |
2008年 | 1932篇 |
2007年 | 1759篇 |
2006年 | 1579篇 |
2005年 | 1392篇 |
2004年 | 1109篇 |
2003年 | 902篇 |
2002年 | 882篇 |
2001年 | 740篇 |
2000年 | 622篇 |
1999年 | 580篇 |
1998年 | 504篇 |
1997年 | 443篇 |
1996年 | 474篇 |
1995年 | 386篇 |
1994年 | 370篇 |
1993年 | 342篇 |
1992年 | 323篇 |
1991年 | 277篇 |
1990年 | 232篇 |
1989年 | 191篇 |
1988年 | 167篇 |
1987年 | 128篇 |
1986年 | 141篇 |
1985年 | 154篇 |
1984年 | 101篇 |
1983年 | 64篇 |
1982年 | 71篇 |
1981年 | 53篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 40篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sem DS Bertolaet B Baker B Chang E Costache AD Coutts S Dong Q Hansen M Hong V Huang X Jack RM Kho R Lang H Ma CT Meininger D Pellecchia M Pierre F Villar H Yu L 《Chemistry & biology》2004,11(2):185-194
Genomics-driven growth in the number of enzymes of unknown function has created a need for better strategies to characterize them. Since enzyme inhibitors have traditionally served this purpose, we present here an efficient systems-based inhibitor design strategy, enabled by bioinformatic and NMR structural developments. First, we parse the oxidoreductase gene family into structural subfamilies termed pharmacofamilies, which share pharmacophore features in their cofactor binding sites. Then we identify a ligand for this site and use NMR-based binding site mapping (NMR SOLVE) to determine where to extend a combinatorial library, such that diversity elements are directed into the adjacent substrate site. The cofactor mimic is reused in the library in a manner that parallels the reuse of cofactor domains in the oxidoreductase gene family. A library designed in this manner yielded specific inhibitors for multiple oxidoreductases. 相似文献
992.
To explore the properties of cyclodextrins (CDs) as an optical sensing phase, the behavior of immobilized CD in interaction with analytes was studied in this work. CDs having different cavity sizes were immobilized onto the surface of infrared (IR) internal reflection-sensing element (IRE) to kinetically monitor the behavior of CD in interaction with analytes. Several aromatic compounds having various molecular sizes and functional groups were used to characterize the interaction mechanism. A two-layer modification method was proposed in this work, which utilized a thin hydrophobic film (polyvinyl benzyl chloride) to stick on the IRE and to covalently bond to the CDs through an ethylene diamine linker. The synthesized CD phases exhibited high stability in aqueous solution. To analyze the behavior during the formation of complexes between the guest molecules and the CD phases, we modeled the interaction behavior and treated the kinetic data with the theoretical equations developed in this work. The results indicate that the behavior of the interaction between guest molecules and CDs was explained by considering the formation of two types of complexes: adsorbed complexes and inclusion complexes. The formation of the inclusion complexes was relatively fast, the time required to reach equilibrium could be shorter than a few minutes. The adsorbed complexes were also observed, but their rate of formation was relatively slow; equilibrium could be reached at times greater than 60 min. Based on the signals observed under equilibrium conditions, the concentration of inclusion complexes was approximately three times than that of the adsorbed complexes. 相似文献
993.
用循环伏安与现场可见紫外光谱电化学方法研究了氯化4-特丁基苯氧基铁酞菁[(TbPc)Fe(Ⅲ)Cl]电化学行为.结果表明,在四氢呋喃溶剂中其正电位区经历了两步氧化过程,对应于Fe(Ⅲ)/Fe(Ⅳ)以及Fe(Ⅳ)/阳离子自由基的生成反应,负电位区还原过程经历了Fe(Ⅲ)/Fe(Ⅱ),Fe(Ⅱ)/Fe(Ⅰ)和Fe(Ⅰ)/阴离子自由基生成的3个步骤,阐述了配位效应对氧化还原机理的影响.指出Fe(Ⅳ)不寻常价态的出现,是阴离子Cl-的轴向配位对超常价态起到稳定作用的结果. 相似文献
994.
995.
Two new C18-norditerpenoid alkaloids from Aconitum delavayi 总被引:2,自引:0,他引:2
Shan Hao Jiang Hai Qing Wang Yi Ming Li Shuang Jun Lin Jun Jie Tan Da Yuan Zhu 《中国化学快报》2007,18(4):409-411
Further phytochemical investigation of the unique C18-norditerpenoid alkaloids from the roots of Aconitum delavayi Franch ledto the isolation of two new norditerpenoid alkaloids,delavaconitine F 1 and delavaconitine G 2.Their structures were determinedfrom spectroscopic evidence. 相似文献
996.
LiLi Liu WanHong Ma WenJing Song ChunCheng Chen Jun Lin JinCai Zhao XinHua Qian ShiBo Zhang 《中国科学:化学(英文版)》2007,50(6):770-775
This study investigated the visible-light catalysis mediated by zeolite NaY on the oxidation of dyes with H2O2. The results demonstrated that zeolite NaY acts as a sink for the electron from the photo-excited dye in the heterogeneous catalysis. Furthermore, the electron can effectively activate H2O2 to produce ·OH radical that is a powerful oxidant for the oxidation of dye at room temperature. The effects of the framework topology, Si/Al ratio, and exchangeable cation of the zeolite on the oxidation of various dyes were also shown. 相似文献
997.
Hulin Li Boyan Zhang Lin Ma Liliu Wu James Q. Chambers 《Transition Metal Chemistry》1995,20(6):552-556
Summary The spectrochemical, electrochemical and electrocatalytic properties of Co[15]aneN4 ([15]aneN4 = 1,4,8,12-tetraazacyclopentadecane) have been investigated. The results show that, in aqueous solution, this compound mainly exists as three species whose axial coordination positions are occupied by water and/or hydroxy ligands; it is marginal whether other substrates such as Cl– and NO
inf3
sup–
interact with the central ion in acid-base solutions. The approximate Pourbaix diagram of CoIII/II[15]ane N4 was determined. There is an electrochemically-induced isomerization between two trans conformational isomers of the Co[15]aneN4 complexes in acid and netural solutions. The Co[15]aneN4 complex has electrocatalytic properties for reduction of nitrate and nitrite only in strong alkaline solution. 相似文献
998.
999.
A ligand-exchange capillary electrophoresis was explored, with L-ornithine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized and dansyl amino acids, a dipeptide, and drugs with amino alcohol structure. The enantioselectivity was found to be strongly dependent on pH and copper(II)-L-Orn complex concentration. Due to the adsorption of the positively charged species onto the capillary inner walls, the chiral separation selectivity is very high while the efficiency is relatively low. Permanent 1,3-propanediamine-coated capillaries show an improved separation efficiency and theoretical plate numbers increasing from 10(4) to 10(5). Similar phenomena were observed when sodium dodecyl sulfate (SDS) micelles were added to the copper(II) complex solution. The poor separation efficiency of chiral compounds in uncoated capillaries may result from the low rate of the ligand-exchange reactions, and the high enantioselectivity may derive from the complexing process in the adsorbed phase. 相似文献
1000.
Some novel beta-biarylacryl ferrocene derivatives were synthesized via Pd-catalytic Suzuki cross-coupling reactions of beta-(2-bromophenyl)acrylferrocene and arylboronic acids. The structures were determined with elemental analyses, IR spectra, and (1)H-NMR spectra. 相似文献