全文获取类型
收费全文 | 17504篇 |
免费 | 646篇 |
国内免费 | 90篇 |
专业分类
化学 | 10351篇 |
晶体学 | 234篇 |
力学 | 480篇 |
综合类 | 1篇 |
数学 | 1162篇 |
物理学 | 3587篇 |
无线电 | 2425篇 |
出版年
2024年 | 87篇 |
2023年 | 246篇 |
2022年 | 600篇 |
2021年 | 638篇 |
2020年 | 677篇 |
2019年 | 680篇 |
2018年 | 651篇 |
2017年 | 568篇 |
2016年 | 818篇 |
2015年 | 529篇 |
2014年 | 877篇 |
2013年 | 1456篇 |
2012年 | 1214篇 |
2011年 | 1225篇 |
2010年 | 837篇 |
2009年 | 668篇 |
2008年 | 819篇 |
2007年 | 805篇 |
2006年 | 654篇 |
2005年 | 575篇 |
2004年 | 436篇 |
2003年 | 366篇 |
2002年 | 286篇 |
2001年 | 195篇 |
2000年 | 171篇 |
1999年 | 128篇 |
1998年 | 98篇 |
1997年 | 129篇 |
1996年 | 132篇 |
1995年 | 95篇 |
1994年 | 90篇 |
1993年 | 118篇 |
1992年 | 117篇 |
1991年 | 89篇 |
1990年 | 88篇 |
1989年 | 80篇 |
1988年 | 59篇 |
1987年 | 56篇 |
1986年 | 51篇 |
1985年 | 80篇 |
1984年 | 78篇 |
1983年 | 57篇 |
1982年 | 52篇 |
1981年 | 53篇 |
1980年 | 55篇 |
1979年 | 65篇 |
1978年 | 58篇 |
1977年 | 59篇 |
1976年 | 46篇 |
1975年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Dhirendra Kumar Dr. K. R. Justin Thomas Ching‐Chiao Lin Prof. Jwo‐Huei Jou 《化学:亚洲杂志》2013,8(9):2111-2124
A series of pyrenoimidazoles that contained various functional chromophores, such as anthracene, pyrene, triphenylamine, carbazole, and fluorene, were synthesized and characterized by optical, electrochemical, and theoretical studies. The absorption spectra of the dyes are dominated by electronic transitions that arise from the pyrenoimidazole core and the additional chromophore. All of the dyes exhibited blue‐light photoluminescence with moderate‐to‐high quantum efficiencies. They also displayed high thermal stability and their thermal‐decomposition temperatures fell within the range 462–512 °C; the highest decomposition temperature was recorded for a carbazole‐containing dye. The oxidation propensity of the dyes increased on the introduction of electron‐rich chromophores, such as triphenylamine or carbazole. The application of selected dyes that featured additional chromophores such as pyrene, carbazole, and triphenylamine as blue‐emissive dopants into multilayered organic light‐emitting diodes with a 4,4′‐bis(9H‐carbazol‐9‐yl)biphenyl (CBP) host was investigated. Devices that were based on triphenylamine‐ and carbazole‐containing dyes exhibited deep‐blue emission (CIE 0.157, 0.054 and 0.163, 0.041), whereas a device that was based on a pyrene‐containing dye showed a bright‐blue emission (CIE 0.156, 0.135). 相似文献
95.
Oxidation of chromanones (1a-i) and 2-spiro-chromanones (j-m) using [hydroxy(tosyloxy)iodo] benzene in refluxing acetonitrile as well as using ultrasound via dehydrogenation and 2,3-alkyl migration provides a convenient route for the synthesis of chromones (2a-i), tetrahydroxanthones (2j,k) and their higher homologues (21,m). The ultrasound also enhances substantially the rate of above transformations. 相似文献
96.
97.
In order to establish a rapid conversion method of primary amides to nitriles, various types of carboxamides were treated with 2,2,2-trichloroethyl chloroformate and Et3N, as a dehydrating agent to obtain the desired nitriles in 82–95% yields. 相似文献
98.
A new three-component reaction of chalcones, ketones, and ammonia assisted by magnesium methoxide is described. The corresponding 2,4,6-triaryl pyridines (Kröhnke pyridines) are formed in fair to good yields (34–76%) within 3 h. The method also provides a facile way to synthesize 2(6)-difluoromethyl pyridines via an interesting mechanism. 相似文献
99.
Reaction of 2-pyridylmagnesium chlorides with N,N-dialkyl arylamides afford exclusively 2-(aroyl) pyridines in high yields and purity without the formation of any tertiary alcohol. This method employs easily available raw materials and avoids the use of hazardous lithium reagents and cryogenic conditions. Further, preferential reactivity of this Grignard reagent with N,N-dialkyl arylamides over its carbonitrile counterparts offers a variety of 2-(aroyl) pyridines including the ones containing carbonitrile groups on the aryl ring. 相似文献
100.
A convenient method has been developed for the conversion of indoles and indigos into anthranilic acids in good to excellent yields using a bromamine-B/PdCl2 system. The general process utilizes our efficient method for the oxidation of indoles and indigos in alkaline (pH 12) acetonitrile/water (1:1) at 60 °C. 相似文献