全文获取类型
收费全文 | 1250篇 |
免费 | 12篇 |
国内免费 | 7篇 |
专业分类
化学 | 1089篇 |
晶体学 | 12篇 |
力学 | 9篇 |
数学 | 39篇 |
物理学 | 120篇 |
出版年
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 54篇 |
2012年 | 50篇 |
2011年 | 43篇 |
2010年 | 32篇 |
2009年 | 36篇 |
2008年 | 53篇 |
2007年 | 68篇 |
2006年 | 61篇 |
2005年 | 59篇 |
2004年 | 57篇 |
2003年 | 67篇 |
2002年 | 74篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 22篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 32篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 25篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 13篇 |
1967年 | 4篇 |
排序方式: 共有1269条查询结果,搜索用时 15 毫秒
11.
Rearrangement of Tertiary Allyl Alcohols Induced by Bromination: The Effect of a Fluorine Substituent on the Rate and the Outcome of the Reaction The allyl alcohol bearing a methyl and a t-butyl group at the hydroxylated position was found to undergo a rearrangement when treated with bromine (or N-bromosuccinimide) in an aqueous medium and to afford a product mixture containing two regioisomeric ketones and one oxirane. Introduction of an additional methyl group or a fluorine atom at the non-terminal olefinic center led to a more selective discrimination between potential migratory groups. As the result of an exclusive t-butyl shift only one product, a ketone, was formed in both cases. Whereas the reaction rate was only slightly affected by the additional methyl group, it was substantially decreased by the fluorine atom. 相似文献
12.
13.
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
14.
15.
Kakinoki K Yamane K Yamamoto M Teraoka R Sugimoto I Matsuda Y 《Chemical & pharmaceutical bulletin》2005,53(9):1092-1096
TiO(2) has been widely used in pharmaceutical products, and it also has been used as a photocatalyst. In this study, the influence of photocatalytic activity on the stability of solid-state mequitazine, an H(1)-blocker, was investigated. The photo-degradation of mequitazine with TiO(2) occurred under irradiation with both light sources. The degree of degradation of mequitazine with anatase was higher than that of rutile. The degradation was significantly enhanced with increasing relative humidity. The relationship between the apparent degradation rate constant and water vapor pressure could be clearly described by a simple power law. The major photo-degradation products of mequitazine, resulting from photocatalytic activity of TiO(2), were mequitazine-S-oxide and mequitazine-sulphone. A remarkable degradation of mequitadine occurred with addition of TiO(2), and its photocatalytic activity was controlled by water vapor pressure. The photo-degradation of mequitazine with TiO(2) is a different process from mequitazine without TiO(2), because mequitazine-S-oxide and mequitazine-sulphone are not formed with normal photo-degradation of mequitazine. 相似文献
16.
[structure: see text] New fluorescent compounds (1), lariat ethers having plural pyrenylmethyl groups on the sidearms, were prepared, and their complexation behavior with alkaline earth metal cations was examined by fluorescence spectrometry. The pyrene excimer emission decreased accompanied with an increase in the monomer emission upon complexation with the metal ion. This finding is ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion. 相似文献
17.
Vanadiuin(V) com: with an acidic hydroxy group attached to the metal form the crorrresponding.; with alcohols. These esters show a characteristic absorption at 445–480 that alcoholic hydroxy groups can be determined photometrically. The formation constant of the n-butanol esters of vanadium maltolate and 2-methyl-.S-hydroxyquinolinate Were determined in benzene or benzenechloroform (1:1). Simple methods are determined for the determination of alcohol in the concentration range 10-1–10-4M. 相似文献
18.
Treatment of alkyl allyl carbonates derived from various alcohols with a palladium catalyst in MeCN affords ketones and aldehydes in high yields. This new method of oxidation of alcohols can be applied to various alcohols except simple primary alcohols. 相似文献
19.
DESIGN AND PERFORMANCE OF THE OKAZAKI LARGE SPECTROGRAPH FOR PHOTOBIOLOGICAL RESEARCH 总被引:7,自引:1,他引:7
Masakatsu WatanabeMasaki Furuya†Yasuhiro Miyoshi†Yasunori Inoue†Isao Iwahashi‡Koichi Matsumoto‡ 《Photochemistry and photobiology》1982,36(4):491-498
A computer-operated spectrograph was recently built at Okazaki, Japan. Different specimens can be placed on a horseshoe-shaped focal curve (10 m long) covering a wavelength range of 250 to 1000 nm so they can be irradiated simultaneously. The linear dispersion is about 0.8 nm/cm. The photon fluence rate on the focal curve is 5 x 1015 . photons x cm-2 x s-1 at 300nm and 1 x 1016 photons x cm-2 x s-1 at 600 and at 900 nm. The spectral half width is 5.5 nm or less on the focal curve. The stray light content is about 10-5 of the main peak at the peak wavelength ± 100 nm. Specimens are set in microcomputer-controlled threshold boxes so that wavelengths, photon fluence rates, photon fluences and timing of irradiations are controlled automatically according to a pre-programmed schedule. An optical fiber system is also provided for remote irradiations. 相似文献
20.
The reaction of N-aryl-substituted ketenimines with N,N-disubstituted cyanamides or (MeS)2C=N-CN under high pressure afforded 4-(N,N-disubstituted amino) or 4-(MeS)2C=N-substituted quinazoline derivatives, respectively. These products were formed by [4+2] cycloaddition between the aza-diene moieties of the N-arylsubstituted ketenimines and cyano groups. A 4-(unsubstituted amino)quinazoline derivative was synthesized by hydrolysis of the latter product. 相似文献