全文获取类型
收费全文 | 219篇 |
免费 | 5篇 |
专业分类
化学 | 211篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 5篇 |
物理学 | 6篇 |
出版年
2023年 | 1篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 13篇 |
2011年 | 21篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 13篇 |
2007年 | 26篇 |
2006年 | 21篇 |
2005年 | 8篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有224条查询结果,搜索用时 15 毫秒
211.
Ono M Takamura C Sugita F Masuoka C Yoshimitsu H Ikeda T Nohara T 《Chemical & pharmaceutical bulletin》2007,55(4):551-556
Two new steroid glycosides, named trikamsterosides A and B, and a new sesquiterpenoid glycoside named trikamsesuquiside A were isolated from the underground parts of Trillium kamtschaticum PALL. along with 18 known compounds comprising 12 steroids, one sesquiterpenoid glycoside, one phenylpropanoid, one flavonoid glycoside, and three phenylpropanoid sucrose esters. Their chemical structures were determined on the basis of spectroscopic data and chemical evidence. Among them, one phenylpropanoid sucrose ester showed almost the same radical-scavenging effect on 1,1-diphenyl-2-picrylhydrazyl as that of alpha-tocopherol. 相似文献
212.
Nagataki T Ishii K Tachi Y Itoh S 《Dalton transactions (Cambridge, England : 2003)》2007,(11):1120-1128
Nickel(ii) complexes supported by a series of pyridylalkylamine ligands [tris(2-pyridylmethyl)amine (TPA; complexes and ), tris[2-(2-pyridyl)ethyl]amine (TEPA; complexes and ), 6-[N,N-bis(2-pyridylmethyl)aminomethyl]-2,4-di-tert-butylphenol ((Dtbp)Pym2H; complexes and ), 6-[N,N-bis[2-(2-pyridyl)ethyl]aminomethyl]-2,4-di-tert-butylphenol ((Dtbp)Pye2H; complexes and ), N-benzyl-bis(2-pyridylmethyl)amine ((Bz)Pym2; complex ) and N-benzyl-bis[2-(2-pyridyl)ethyl]amine ((Bz)Pye2; complex )] have been synthesized and structurally characterized by X-ray crystallographic analysis [coordinating counter anion (co-ligand) of complexes n (n = 1-6) is AcO(-) and that of complexes n (n = 1-4) is NO(3)(-)]. All complexes, except , were obtained as a mononuclear nickel(ii) complex exhibiting a distorted octahedral geometry, whereas complex was isolated as a dinuclear nickel(ii) complex bridged by two nitrate anions. Catalytic activity of the nickel(ii) complexes were examined in the oxidation of cyclohexane with m-CPBA as an oxidant. In all cases, the oxygenation reaction proceeded catalytically to give cyclohexanol as the major product together with cyclohexanone as the minor product. The complexes containing the pyridylmethylamine (Pym) metal-binding group (, , ) showed higher turnover number (TON) than those containing the pyridylethylamine (Pye) metal-binding group (, , ), whereas the alcohol/ketone (A/K) selectivity was much higher with the latter (Pye system) than the former (Pym system). On the other hand, the existence of the NO(3)(-) co-ligand (, and ) caused a lag phase in the early stage of the catalytic reaction. Electronic and steric effects of the supporting ligands as well as the chemical behavior of the co-ligands on the catalytic activity of the nickel(ii) complexes have been discussed on the basis of their X-ray structures. 相似文献
213.
214.
A convergent asymmetric total synthesis of (+)-danicalipin A is accomplished, in which two chlorinated fragments are stereoselectively joined by 1,3-dipolar coupling, leading to the confirmation of the absolute configuration of the natural product. 相似文献
215.
216.
Three new 15-hydroxy-trinor type (1-3), a new tetranor type (4), and two new 3,15,23,24-tetrahydroxy-16-oxo type cycloartane glycosides (5, 6) were isolated from the rhizome of Cimicifuga heracleifolia KOMAROV. Their structures were determined by the use of the 2D-NMR techniques and chemical evidence. 相似文献
217.
Nohara T Okamoto K Matsushita S Fujiwara Y Ikeda T Miyashita H Ono M Yoshimitsu H Kansui H Kunieda T 《Chemical & pharmaceutical bulletin》2008,56(7):1015-1017
Previously, we reported an interesting reaction by which esculeogenin A [(5alpha,22S,23S,25S)-3beta,23,27-trihydroxyspirosolane], a sapogenol of tomato-saponin, esculeoside A, was easily converted into a pregnane derivative, 5alpha-pregn-16-en-3beta-ol-20-one, merely by refluxing with pyridine and water. Its chemical mechanism including air oxidation is here described. 相似文献
218.
Mori T Kodera T Yoshimine H Kakuta Y Sugiura N Kimata K Okahata Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(24):7388-7393
Using a highly sensitive flow-type 27?MHz quartz crystal microbalance, we could detect a small mass change during stepwise and alternating one-sugar transfer of glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) to an acceptor, catalyzed by chondroitin polymerase from Escherichia coli strain K4 (K4CP), and analyze the elongation mechanism of K4CP. K4CP was found to bind strongly to a chondroitin acceptor (K(d)=0.97?μM). Although the binding affinity and the catalytic rate constant for each monomer were considerably different, the apparent catalytic efficiency (k(cat)/K(m)) was similar (6.3×10(4) M(-1) s(-1) for GlcA transfer and 3.4×10(4) M(-1) s(-1) for the GalNAc transfer). This is reasonable for the smooth alternating elongation of GlcA and GalNAc on the acceptor. This is the first study to report the determination of kinetic parameters for enzymatic, alternated, sugar elongation. 相似文献
219.
Prof. Dr. Hiroaki Ohno Mutsumi Iuchi Dr. Naoto Kojima Prof. Dr. Takehiko Yoshimitsu Prof. Dr. Nobutaka Fujii Prof. Dr. Tetsuaki Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5352-5360
Palladium‐catalyzed cascade C? H alkenylation and arylation provides convenient access to polycyclic aromatic compounds. Treatment of 3‐bromoaniline derivatives bearing a bromocinnamyl group on the nitrogen atom with a catalytic amount of [Pd(OAc)2] and PCy3?HBF4 in the presence of Cs2CO3 in dioxane affords naphthalene‐fused indole derivatives in good yields. This double cyclization reaction is also applicable to heterocyclic substrates, giving fused indoles containing a heteroaromatic ring such as dibenzofuran, dibenzothiophene, carbazole, indole, or benzofuran through heterocyclic C? H arylation. When using a 2,6‐unsubstituted aniline derivative, the first C? H arylation preferentially proceeds at the more hindered position of the aniline ring. 相似文献
220.
The alkylation of dienolates generated from 3-methoxycycloalk-2-enones having a 3'-hydroxyl alkenyl chain provides the corresponding quaternized cycloalkenones in a highly diastereoselective manner. The high degree of stereocontrol in the α-quaternization possibly implies intervention of a rigid chelating transition state that allows an efficient 1,4-asymmetric induction to take place. 相似文献