全文获取类型
收费全文 | 813篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 582篇 |
晶体学 | 7篇 |
力学 | 3篇 |
数学 | 23篇 |
物理学 | 160篇 |
无线电 | 53篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 73篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 25篇 |
2007年 | 36篇 |
2006年 | 29篇 |
2005年 | 37篇 |
2004年 | 29篇 |
2003年 | 33篇 |
2002年 | 30篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 26篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1973年 | 9篇 |
1969年 | 3篇 |
排序方式: 共有828条查询结果,搜索用时 15 毫秒
11.
12.
13.
Terai T Araho D Osakabe K Katai M Narama I Matsuura T Katakawa J Tetsumi T Sato M 《Chemical & pharmaceutical bulletin》2000,48(1):142-144
The structure of iso-grayanotoxin II, a new diterpenoid from Leucothoe grayana MAX., has been determined as 3 beta,5 beta,6 beta,14 beta,16 alpha-pentahydroxygrayanotox-9(10)-ene by spectroscopic and X-ray crystallographic analysis. The lethal dosage level of iso-grayanotoxin II in mice was lower than that of grayanotoxin III. 相似文献
14.
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
15.
16.
Tokita S Frigaard NU Hirota M Shimada K Matsuura K 《Photochemistry and photobiology》2000,72(3):345-350
The quenching of bacteriochlorophyll (BChl) c fluorescence in chlorosomes isolated from Chloroflexus aurantiacus was examined by the addition of various benzoquinones, naphthoquinones (NQ), and anthraquinones (AQ). Many quinones showed strong quenching in the micromolar or submicromolar range. The number of quinone molecules bound to the chlorosomes was estimated to be as small as one quinone molecule per 50 BChl c molecules. Quinones which exhibit a high quenching effect have sufficient hydrophobicity and one or more hydroxyl groups in the alpha positions of NQ and AQ. Chlorobiumquinone has been suggested to be essential for the endogenous quenching of chlorosome fluorescence in Chlorobium tepidum under oxic conditions. We suggest that the quenching effect of chlorobiumquinone in chlorosomes from Chl. tepidum is related to the 1'-oxo group neighboring the dicarbonyl group. 相似文献
17.
The oxygenation of 4-(N-arylmethyleneamino)-2,6-di--butylphenols with Co(Salpr), a five coordinate Co(II0 Schiff base complex, in CH2Cl2 results in the regioselective hydroperoxylation at the imino carbon to give N-(l-aryl-l-hydroperoxymethyl)-3,5-di--butyl--benzoquinone monoimines, which give exclusively the corresponding amides and 2,6-di--butyl--benzoquinone in an aerobic solution of KOH in 90% EtOH. 相似文献
18.
Yoshikatsu Ito Meng Ji-Ben Shin Suzuki Yoshitaka Kusunaga Teruo Matsuura Keiichi Fukuyama 《Tetrahedron letters》1985,26(17):2093-2096
In contrast to simple imidazoles, 1-methy1–2,4,5-triphenylimidazole () produced stable oxetane photoadducts - with good efficiency upon irradiation in the presence of benzophenone derivatives - in acetonitrile solution. Irradiation in the solid-phase was also studied. The oxetanes - readily underwent cycloreversion by acid catalysis or by heating. 相似文献
19.
Masaaki Sakakibara Yoko Yonemura Zenzo Tanaka Hiroatsu Matsuura Hiromu Murata 《Journal of Molecular Structure》1981
The Raman and IR spectra of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes have been measured. The normal coordinates have been calculated for these molecules using a consistent set of force constants and the molecular conformations studied by analysing the spectra with reference to the results of the calculations. In the crystalline solid state, 1,5-dichloropentane assumes the trans-trans-trans-gauche form and 1,5-dibromopentane, 1,6-dichloro- and 1,6-dibromohexanes assume the all-trans form. The normal coordinate treatment with the well-established force field was of great help in determining the whole molecular form of the relatively large chain molecules. 相似文献
20.
[reaction: see text] Base-promoted cyclocondensation of C-chloro oximes with cyclic 1,3-diketones affords functionalized isoxazoles in good yield and under convenient reaction conditions. This process enables the synthesis of highly substituted products with notable functional group tolerance. The products obtained are directly converted to a variety of polyketide-derived polycyclic structures including xanthenes, anthracenes, and benzophenones. 相似文献