全文获取类型
收费全文 | 2988篇 |
免费 | 81篇 |
国内免费 | 14篇 |
专业分类
化学 | 2083篇 |
晶体学 | 26篇 |
力学 | 43篇 |
数学 | 198篇 |
物理学 | 733篇 |
出版年
2022年 | 18篇 |
2021年 | 23篇 |
2020年 | 36篇 |
2019年 | 31篇 |
2018年 | 27篇 |
2017年 | 29篇 |
2016年 | 58篇 |
2015年 | 40篇 |
2014年 | 65篇 |
2013年 | 124篇 |
2012年 | 143篇 |
2011年 | 160篇 |
2010年 | 77篇 |
2009年 | 86篇 |
2008年 | 162篇 |
2007年 | 169篇 |
2006年 | 170篇 |
2005年 | 154篇 |
2004年 | 115篇 |
2003年 | 110篇 |
2002年 | 109篇 |
2001年 | 80篇 |
2000年 | 69篇 |
1999年 | 59篇 |
1998年 | 35篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 33篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 55篇 |
1991年 | 52篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 37篇 |
1986年 | 36篇 |
1985年 | 57篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 22篇 |
排序方式: 共有3083条查询结果,搜索用时 125 毫秒
21.
22.
K Ogawa M Nishii J Inagaki F Nohara T Saito T Itaya T Fujii 《Chemical & pharmaceutical bulletin》1992,40(5):1315-1317
The synthesis of 8-methylguanine 7-oxide (3) was accomplished via a "phenacylamine route", which started from condensation of alpha-(4-methoxybenzylamino)propiophenone (6), prepared by coupling of alpha-bromopropiophenone (4) and 4-methoxybenzylamine (5), with 2-amino-6-chloro-5-nitro-4(3H)-pyrimidinone (7) and proceeded through cyclization of the resulting phenacylaminopyrimidinone (8) and removal of the 4-methoxybenzyl group. The N-oxide 3 and its 9-arylmethyl derivatives 9 and 11 showed only very weak antileukemic activity and no antimicrobial activity. 相似文献
23.
24.
25.
26.
27.
28.
Minamide T Mitsubayashi K Jaffrezic-Renault N Hibi K Endo H Saito H 《The Analyst》2005,130(11):1490-1494
Methyl mercaptan (MM) is known as one of the major chemicals of halitosis (bad breath). In this study, a bioelectronic gas sensor (bio-detector) for gaseous MM was developed and was applied to measure halitosis in breath. The bio-detector consisted of a Clark-type dissolved oxygen electrode, a monoamine oxidase type-A (MAO-A) immobilized membrane and a reaction unit that had liquid and gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the electrode covered with MAO-A membrane was placed into the liquid compartment as touching to the PTFE diaphragm membrane. In order to amplify the bio-detector output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid as reducing reaction with reagent system, was applied. The results of MM vapor measurements showed the calibration range of the bio-detector for MM vapor was from 0.087 to 11.5 ppm (correlation coefficient: 0.993) and included the human sense of smell level 5 (0.2 ppm). The bio-detector had good selectivity being attributed to enzyme specificity was obtained for several substances (trimethyl amine, ammonia, dimethyl sulfide, etc.). The bio-detector was applied for halitosis measurement. Expired gases in five subjects were sampled every hour and the concentrations of MM in the expired gases were monitored. The output of bio-detector showed behaviour of halitosis level changes in a day such as increasing with passage of time and decreasing after eating. 相似文献
29.
30.
Oxidation of substituted thioanisoles by chemically generated singlet oxygen was investigated in polar aqueous media. The formation of the superoxide ion was observed during sulphoxidation of 4-hydroxythioanisole (4) in phosphate buffer at pH 7.5. Control experiments indicated that the superoxide ion was formed by a direct reaction between singlet oxygen and 4. The kinetics of the trapping reaction by diphenylsulphoxide indicated the involvement of a single intermediate. The overall rate constants of the reaction of thioanisoles with singlet oxygen in methanol-water (1:1) are one order of magnitude larger than those in benzene. On the basis of these results, a mechanism involving a charge-transfer complex has been proposed for the reaction of electron-rich thioanisoles with singlet oxygen, whereby the charge-transfer complex would produce persulphoxide directly or dissociate to the cation radical and superoxide ion in polar aqueous media. 相似文献