全文获取类型
收费全文 | 4582篇 |
免费 | 106篇 |
国内免费 | 20篇 |
专业分类
化学 | 3420篇 |
晶体学 | 36篇 |
力学 | 63篇 |
数学 | 271篇 |
物理学 | 918篇 |
出版年
2022年 | 20篇 |
2021年 | 29篇 |
2020年 | 46篇 |
2019年 | 37篇 |
2018年 | 38篇 |
2017年 | 39篇 |
2016年 | 70篇 |
2015年 | 48篇 |
2014年 | 81篇 |
2013年 | 193篇 |
2012年 | 186篇 |
2011年 | 232篇 |
2010年 | 118篇 |
2009年 | 127篇 |
2008年 | 235篇 |
2007年 | 249篇 |
2006年 | 262篇 |
2005年 | 242篇 |
2004年 | 207篇 |
2003年 | 172篇 |
2002年 | 182篇 |
2001年 | 99篇 |
2000年 | 98篇 |
1999年 | 82篇 |
1998年 | 56篇 |
1997年 | 49篇 |
1996年 | 51篇 |
1995年 | 52篇 |
1994年 | 48篇 |
1993年 | 53篇 |
1992年 | 70篇 |
1991年 | 72篇 |
1990年 | 46篇 |
1989年 | 47篇 |
1988年 | 69篇 |
1987年 | 56篇 |
1986年 | 54篇 |
1985年 | 88篇 |
1984年 | 76篇 |
1983年 | 48篇 |
1982年 | 72篇 |
1981年 | 77篇 |
1980年 | 61篇 |
1979年 | 57篇 |
1978年 | 50篇 |
1977年 | 46篇 |
1976年 | 56篇 |
1975年 | 37篇 |
1974年 | 47篇 |
1973年 | 41篇 |
排序方式: 共有4708条查询结果,搜索用时 281 毫秒
31.
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
32.
Small amounts of polycyclic aromatic hydrocarbons (PAHs) in aqueous solution were almost completely adsorbed on barium salts of copper (II) sulphophthalocyanines and cobalt (II) phthalocyanine, which were precipitated from the solution. Recoveries of the PAHs from the precipitates by thermal desorption gas chromatography were 71–95%. The method is useful for the concentration and analysis of medium molecular weight, thermally stable PAHs. 相似文献
33.
34.
35.
36.
37.
38.
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
39.
40.
The functionalized pyranosyl hetero-olefins , and received a remarkable diastereoselective addition of methyllithium to form adducts, one of which was introduced into a possible synthetic intermediate as for maytansine () along Scheme I. 相似文献