全文获取类型
收费全文 | 1040篇 |
免费 | 53篇 |
国内免费 | 6篇 |
专业分类
化学 | 910篇 |
晶体学 | 3篇 |
力学 | 22篇 |
数学 | 27篇 |
物理学 | 137篇 |
出版年
2023年 | 13篇 |
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 29篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 31篇 |
2012年 | 47篇 |
2011年 | 67篇 |
2010年 | 26篇 |
2009年 | 33篇 |
2008年 | 47篇 |
2007年 | 48篇 |
2006年 | 62篇 |
2005年 | 66篇 |
2004年 | 49篇 |
2003年 | 30篇 |
2002年 | 48篇 |
2001年 | 44篇 |
2000年 | 29篇 |
1999年 | 19篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 6篇 |
1974年 | 15篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1967年 | 7篇 |
排序方式: 共有1099条查询结果,搜索用时 15 毫秒
1.
Dr. Nozomi Mihara Dr. Yasuyuki Yamada Dr. Hikaru Takaya Prof. Yasutaka Kitagawa Dr. Kazunobu Igawa Prof. Katsuhiko Tomooka Prof. Hiroshi Fujii Prof. Kentaro Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3369-3375
Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 5+, which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 5+ catalyzed ethane oxidation in the presence of H2O2 at a relatively low temperature. The site-selective complexation of 3 5+ with an additional anionic porphyrin (TPPS4−) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 5+ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS4− to 3 5+ enhanced the catalytic activity. 相似文献
2.
Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters. 相似文献
3.
4.
5.
6.
I Kitagawa A Matsuda T Nishimura S Hirai I Yoshioka 《Chemical & pharmaceutical bulletin》1967,15(9):1435-1437
7.
Caffeine concentration in human sweat was estimated by measuring separately the amounts of water and caffeine. After washing a finger with tap water for 15 s and waiting 2 min for drying, 70 microL aqueous ethanol solution in a small vial (0.6 mL) was used to sample for several minutes. Then 3 microL of the aliquot was used for GC/MS analysis of caffeine. As a first-order relationship between the sweat amount secreted on the left and right hands was obtained (correlation factor 0.848), the amount of sweat secretion during sampling on one hand was estimated by the value obtained on the other hand. This new indirect evaluation was used for the estimation of the amount of sweat secreted during sampling. Typical variations of caffeine concentration in sweat were demonstrated. Thirty minutes after the intake of caffeine, it was secreted in sweat, and the secretion had continued for more than 4 h. 相似文献
8.
9.
Racemic 2-amino-3-(heteroaryl)propanoic acids (1), mostly with a furan or thiophene nucleus as a heteroaryl group, were synthesized in 48-94% yield by the reduction of 3-(heteroaryl)-2-(hydroxyimino)propanoic acids (5) with zinc dust and formic acid in the presence of a catalytic amount of iron dust at 60 degrees C for 2 h. Under these conditions, unfavorable hydrogenolysis of bromine on the thiophene nucleus does not occur. Traditional N-formylation of the prepared 3-(heteroaryl)alanine (1) with a mixture of formic acid and acetic anhydride afforded 2-(formylamino)-3-(heteroaryl)propanoic acids (6) in 51-95% yield. 相似文献
10.
Radical iodine atom transfer [3 + 2] cycloaddition with various alkenes using dimethyl 2-(iodomethyl)cyclopropane-1,1-dicarboxylate and 1,1-bis(phenylsulfonyl)-2-(iodomethyl)cyclopropane as new precursors of a homoallyl radical species smoothly proceeds to give functionalized cyclopentane derivatives in good yields. 相似文献