全文获取类型
收费全文 | 504篇 |
免费 | 45篇 |
国内免费 | 97篇 |
专业分类
化学 | 548篇 |
力学 | 7篇 |
综合类 | 5篇 |
数学 | 20篇 |
物理学 | 66篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 2篇 |
2014年 | 31篇 |
2013年 | 50篇 |
2012年 | 47篇 |
2011年 | 10篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 18篇 |
2004年 | 28篇 |
2003年 | 35篇 |
2002年 | 85篇 |
2001年 | 194篇 |
2000年 | 31篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 1篇 |
1995年 | 3篇 |
排序方式: 共有646条查询结果,搜索用时 15 毫秒
161.
Yang JIANG Bo TAN Yu Fen ZHAO* The Key Laboratory of Bioorganic Phosphorus Chemistry Ministry of Education Department of Chemistry School of Life Sciences Engineering Tsinghua University Beijing 《中国化学快报》2001,(9)
Mass spectrometry plays an important role in peptide sequencing since the invention of soft ionization techniques, such as fast atom bombardment (FAB), electrospray (ESI) and matrix-assisted laser desorption/ionization (MALDI). In our previous work, it was found that phosphorylation on the N-terminal of small peptides could enormously improve their sensitivity in FAB-MS1.To understand the sensitivity-improvement effect of phosphoryl group, the energies for the protonation of glycylglycin… 相似文献
162.
Jing Bo ZHANG Yuan LIN Yao LIU Xu Rui XIAO* Center of Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2001,(8)
Size quantized nanocrystalline semiconductor thin films have attracted considerable interest in the photoelectrochemical studies1,2. In this paper, we report a pronounced size quantization in nanocrystalline CdTe thin films which is less extensively studied.Nanocrystalline CdTe thin films were electrodeposited on conducting glass by asymmetric rectangular pulse in dimethylsulfoxide solution containing 6 mmol/L Te, 0.75 mmol/L Cd(ClO4)2, 18 mmol/L triphenylphosphine and 0.1 mol/L LiClO4 a… 相似文献
163.
Dong Mei HAN Xun Tian JIANG Jian Hong CHEN Bin WANG Dong Lu BAI* Shanghai Institute of Meteria Medica Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai 《中国化学快报》2001,(5)
Recently we reported that the diastereoselective intramolecular [4+3] cycloaddition of 4 led to the formation of cycloadduct 5 as the only isolated isomer in 50% yield. The chiral C-3 of compound 4 could be used to direct the stereochemical course of [4+3] cycloaddition enabling the control of the relative stereochemistry between three contiguous asymmetric centers in adduct 51. The stereogenic center at C-3 of 4 was constructed by the asymmetric Michael addition of (, (-unsaturated ester 2 w… 相似文献
164.
A New Ceramide from the Basidiomycetes Armillaria mellea 总被引:2,自引:0,他引:2
Jin Ming GAO Ze Jun DONG Ji Kai LIU* Kunming Institute of Botany Chinese Academy of Sciences Kunming Northwest Sci. 《中国化学快报》2001,(2)
As one part of our study on the bioactive metabolites of the higher fungi in Yunnan Province, the chemical constituents of Armillaria mellea (Tricholomataceae) collected at Zhong Dian in Yunnan Province have been investigated. The present report deals with the structural elucidation of a new ceramide 1, named armillaramide, isolated from the AcOEt extract of the fruiting bodies of this fungus.Figure 1 The structure of armillaramide 1Compound 1, white amorphous powder, mp 113(117(C, [(] + … 相似文献
165.
Surface Modification of Nanometer Silica by N, N''''-dicyclohexyl- carbodiimide Mediated Amidation 总被引:1,自引:0,他引:1
Zhao Xia GUO Jie YU Jian YU* Institute of Polymer Science Engineering Department of Chemical Engineering Tsinghua University Beijing 《中国化学快报》2001,(10)
Nanometer silica has gained ever more attention for its superior properties over conventional micrometer particles and has been widely used as a filler in the manufacture of paints, rubber, plastics and so on1. However it is difficult to get silica mono- dispersed in the matrix due to heavy agglomeration. Surface modification through organic reactions is an efficient way to improve the dispersibility and compatibility with the matrix, thus improving the mechanical properties of the composite… 相似文献
166.
Hong Chao GUO Shang Zhong LIU Xue Tai HOU Min WANG* Department of Applied Chemistry China Agricultural University Beijing 《中国化学快报》2001,(9)
4-Amino-6-tert-butyl-3-methylthio-1, 2, 4-triazin-5 (4H)-one I, named as Metribuzin1, is an excellent selective herbicide. In the course of studying the reaction of I, we have found an unexpected reaction. We have attempted to prepare 6-tert-butyl- 4-methylamino-3-methylthio-1, 2, 4-triazin-5 (4H)-one II from I with methyl iodide in the presence of sodium hydroxide in aqueous methanol, surprisingly, instead of II the product III 4-amino-6-tert-butyl-3, 4-dihydro-2-methyl-3-thioxo-1, 2, 4-… 相似文献
167.
Yu Xin LIU Xiao Tian LIANG* Institute of Materia Medica Chinese Academy of Medical Sciences &Peking Union Medical College Xian NongTan Street Beijing 《中国化学快报》2001,(1)
In our research on the ring enlargement of certain N-heterocycles, a general procedure for the ring enlargement with the insertion of an extra -CH2- was improved and shown in Scheme I1.Scheme IThe procedure had been carried out with such N-heterocycles as 2-methyl-1,2,3,4-tetrahydroisoquinoline2, tetrahydroberberine and strychnine3 with expected results. Thus, the procedure shown in Scheme I provides a new approach to the synthesis of larger N-heterocycles.Isoindolo[1,2-b][3]benzazepines a… 相似文献
168.
169.
Zhan Zhu LIU Shi Zhi CHEN* Institute of Materia Medica Chinese Academy of Medical Sciences & Peking Union Medical College Beijing 《中国化学快报》2001,(3)
1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid is a type of naturally occurring bio-active alkaloid1. Moreover, it can be used as building block for the synthesis of other natural products containing the 1,2,3,4-tetrahydroisoquinoline moiety2. Compound 2 was an intermediate in our attempt to the total synthesis of Ecteinascidin analogs. We employed the Bishler-Napieralski reaction to prepare this product and refluxed the N-acetyl phenylalanine compound 1 in POCl3/benzene. However, we fail… 相似文献
170.
Xiao Xia YE Ji Shuang CHEN Ming Kui WANG Ke Xin HUANG Li Sheng DING* Chengdu Institute of Biology Chinese Academy of Sciences Chengdu Department of Chemistry Wenzhou Medical College Wenzhou College of Life Science Zhejia 《中国化学快报》2000,11(11)
As a part of an investigation on plant of the genus Notoseris (Asteraceae), an endemic genus of seed plants of China1, we studied the chemical constituents of N. psololepis Shih. A new sesquiterpene lactone glucoside, named notoserolide C (1) was isolated from the methanolic extract of the whole plant of N. psilolepis by repeated column chromatography (MCI GEL, normal and reversed phase silica gel). This compound showed antibacterial activity against Bacillu cereus.Figure 1. The key HMB… 相似文献