全文获取类型
收费全文 | 97034篇 |
免费 | 18108篇 |
国内免费 | 11176篇 |
专业分类
化学 | 67636篇 |
晶体学 | 1135篇 |
力学 | 6188篇 |
综合类 | 712篇 |
数学 | 11290篇 |
物理学 | 39357篇 |
出版年
2024年 | 250篇 |
2023年 | 2145篇 |
2022年 | 2453篇 |
2021年 | 3428篇 |
2020年 | 4284篇 |
2019年 | 3877篇 |
2018年 | 3466篇 |
2017年 | 3189篇 |
2016年 | 4896篇 |
2015年 | 4658篇 |
2014年 | 5733篇 |
2013年 | 7359篇 |
2012年 | 8955篇 |
2011年 | 9326篇 |
2010年 | 6318篇 |
2009年 | 6124篇 |
2008年 | 6610篇 |
2007年 | 5771篇 |
2006年 | 5400篇 |
2005年 | 4315篇 |
2004年 | 3337篇 |
2003年 | 2622篇 |
2002年 | 2412篇 |
2001年 | 2097篇 |
2000年 | 1812篇 |
1999年 | 2012篇 |
1998年 | 1730篇 |
1997年 | 1663篇 |
1996年 | 1653篇 |
1995年 | 1393篇 |
1994年 | 1212篇 |
1993年 | 1047篇 |
1992年 | 898篇 |
1991年 | 823篇 |
1990年 | 679篇 |
1989年 | 532篇 |
1988年 | 386篇 |
1987年 | 315篇 |
1986年 | 332篇 |
1985年 | 271篇 |
1984年 | 151篇 |
1983年 | 122篇 |
1982年 | 103篇 |
1981年 | 59篇 |
1980年 | 43篇 |
1979年 | 13篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1959年 | 2篇 |
1957年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Recyclable antimicrobial magnetic nanoparticles, Fe3O4@P(St-co-AcQAC), were prepared through surfactantfree seeded emulsion polymerization involving a polymerizable, hydrophobic quaternary ammonium compound (QAC). These antimicrobial magnetic nanoparticles demonstrated excellent antimicrobial activities against both Grampositive and Gram-negative bacteria, and can be reused for multiple times. 相似文献
995.
996.
引入离子基团改善聚苯乙烯和热致液晶聚合物的相容性Ⅰ.热性能和形态 总被引:1,自引:0,他引:1
DSC和SEM研究结果表明聚苯乙烯与一种热致液晶聚合物完全不相容。共混体系具有与组分无关的Tg,并且表现出明显的两相结构。将PS进行化学改性,随中和盐离子的变化有;酸式,Li,Na,Zn和Mn盐五种形式。用DSC和SEM对LCP与SPS共混物的热性能和形态进行了分析和表征。 相似文献
997.
998.
999.
1000.
The separation of enantiomers and diastereomers of 8 commonly used pesticides was investigated by liquid chromatography (LC) using a Chiralcel OD column (cellulose tris-3,5-dimethylphenylcarbamate as the chiral stationary phase) and a Pirkle-type Chirex 3020 column (urea derivative from the reaction of (R)-1-(alpha-naphthyl)ethylamine with (S)-tert-leucine, chemically bonded to 3-aminopropylsilanized silica as the chiral stationary phase). The pesticides studied included one organophosphorus insecticide (phenthoate), 3 triazole fungicides (uniconazole, diniconazole, and propiconazole), and 4 pyrethroids (fenpropathrin, beta-cypermethrin, beta-cyfluthrin, and alpha-fenvalerate). The enantiomers were separated within 20 min with a resolution of > or = 1.5 using a mixture of n-hexane and 2-propanol as the mobile phase for all the pesticides studied except propiconazole, for which only the 2 diastereomers were baseline separated. This method allows determination of the enantiomers or stereoisomers of the above pesticides in soil. The strategy was as follows: (1) First, the total concentration(s) of the enantiomer pair(s) of a chiral pesticide in soil was (were) determined by a newly developed matrix solid-phase dispersion (MSPD) procedure, followed by silica-based LC quantification. The recoveries ranged from 76.5 to 93.6% with relative standard deviations of 6.0%. (2) Second, the enantiomeric ratio(s) (ER(s)) of the chiral pesticide was (were) determined by LC with a chiral stationary phase after fractionation of the MSPD extract by silica-based LC. The determined ERs or stereoisomeric ratio(s) (SR(s); for propiconazole, only the SR of the 2 diastereomers was determined) in soil samples spiked with the above 8 racemic pesticides agreed with those of the corresponding standard solutions. (3) Third, based on the total concentrations and the corresponding ERs, the concentration of each enantiomer in soil was calculated. The proposed method is rapid, precise, and sensitive, and is appropriate for the investigation of the stereo- and enantioselective degradation of pesticides in environmental media. 相似文献