全文获取类型
收费全文 | 923篇 |
免费 | 41篇 |
国内免费 | 3篇 |
专业分类
化学 | 689篇 |
晶体学 | 9篇 |
力学 | 5篇 |
数学 | 59篇 |
物理学 | 205篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 30篇 |
2012年 | 42篇 |
2011年 | 61篇 |
2010年 | 33篇 |
2009年 | 41篇 |
2008年 | 59篇 |
2007年 | 50篇 |
2006年 | 45篇 |
2005年 | 46篇 |
2004年 | 43篇 |
2003年 | 63篇 |
2002年 | 31篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有967条查询结果,搜索用时 0 毫秒
11.
Simple and sensitive determination of methylglyoxal in biological samples by gas chromatography with electron-capture detection 总被引:1,自引:0,他引:1
Methylglyoxal was allowed to react with 4,5-dichloro-1,2-phenylenediamine, and the 6,7-dichloro-2-methylquinoxaline formed was determined by gas chromatography with electron-capture detection. The standard curve of the quinoxaline was linear up to 160 pmol/ml. The recoveries of methylglyoxal from coffee and rat liver homogenate were 84.1 and 77.6%, respectively. This procedure was very selective and so sensitive that as little as 9 fmol of the quinoxaline could be measured in biological and food samples. 相似文献
12.
Ogata H Mizoguchi Y Mizuno N Miki K Adachi S Yasuoka N Yagi T Yamauchi O Hirota S Higuchi Y 《Journal of the American Chemical Society》2002,124(39):11628-11635
The carbon monoxide complex of [NiFe]hydrogenase from Desulfovibrio vulgaris Miyazaki F has been characterized by X-ray crystallography and absorption and resonance Raman spectroscopy. Nine crystal structures of the [NiFe]hydrogenase in the CO-bound and CO-liberated forms were determined at 1.2-1.4 A resolution. The exogenously added CO was assigned to be bound to the Ni atom at the Ni-Fe active site. The CO was not replaced with H(2) in the dark at 100 K, but was liberated by illumination with a strong white light. The Ni-C distances and Ni-C-O angles were about 1.77 A and 160 degrees, respectively, except for one case (1.72 A and 135 degrees ), in which an additional electron density peak between the CO and Sgamma(Cys546) was recognized. Distinct changes were observed in the electron density distribution of the Ni and Sgamma(Cys546) atoms between the CO-bound and CO-liberated structures for all the crystals tested. The novel structural features found near the Ni and Sgamma(Cys546) atoms suggest that these two atoms at the Ni-Fe active site play a role during the initial H(2)-binding process. Anaerobic addition of CO to dithionite-reduced [NiFe]hydrogenase led to a new absorption band at about 470 nm ( approximately 3000 M(-1)cm(-1)). Resonance Raman spectra (excitation at 476.5 nm) of the CO complex revealed CO-isotope-sensitive bands at 375/393 and 430 cm(-1) (368 and 413 cm(-1) for (13)C(18)O). The frequencies and relative intensities of the CO-related Raman bands indicated that the exogenous CO is bound to the Ni atom with a bent Ni-C-O structure in solution, in agreement with the refined structure determined by X-ray crystallography. 相似文献
13.
Miyabe H Nishimura A Ueda M Naito T 《Chemical communications (Cambridge, England)》2002,(14):1454-1455
The indium-mediated allylation and alkylation reactions of the Oppolzer camphorsultam derivative of glyoxylic oxime ether proceeded with excellent diastereoselectivity in aqueous media, providing a variety of enantiomerically pure alpha-amino acids. 相似文献
14.
15.
Takashi Hirota Kenji Sasaki Yohsuke Tashima Taiji Nakayama 《Journal of heterocyclic chemistry》1991,28(2):263-267
Syntheses of 2,3-dihydrobenzofuro[2,3-e]imidazo[1,2-c]pyrimidine and its 5-substituted derivatives, corresponding to B-nor-6-oxa-11,13,15-triazasteroids, are described. These products and their precursors were screened to evaluate the antidepressive activity. 相似文献
16.
17.
In general, palladium-carbon (Pd/C) catalyzed hydrogenation of epoxides affords the corresponding primary and secondary alcohols as a mixture. It has been found that the catalytic activity of a Pd/C -ethylenediamine complex catalyst [Pd/C(en)] in the hydrogenolysis of epoxide functions is drastically reduced. Herein we describe a mild and chemoselective method for the hydrogenation of olefin, nitro, and azide functions with retention of the epoxide function. The chemoselectivity was accomplished by using a combination of 5% Pd/C(en) and THF as solvent. A significant drop in the chemoselectivity of the hydrogenation is observed with 5% Pd/C(en) in MeOH. These results reinforce the utility of epoxides as important precursors of alcohols in synthetic chemistry. 相似文献
18.
Kimura T Yoshino M Yamane T Yamato M Tobita M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5669-5672
A diamagnetic particle with magnetic susceptibilities chi3 < chi2 = chi1 < 0 was subjected to a rotating magnetic field to obtain an alignment of the chi3 axis (the smallest susceptibility axis) in the direction perpendicular to the plane of the rotating magnetic field. A polymer short fiber, whose fiber axis coincides with the chi3 axis, was suspended in a fluid with the same density, and then a rotating magnetic field generated by a rotation of a pair of permanent magnets was applied. The fiber axis, rotating following the applied field, finally ended up with an alignment perpendicular to the plane of the rotating magnetic field. The experimental data on the time course of the alignment was in good agreement with the numerical calculation based on the equation of rotation. 相似文献
19.
The binding constants of 1-alkanols with α-cyclodextrin (α-CD) were determined by indirect competitive potentiometry, although potentiometry is usually inapplicable to nonionic compounds. This novel method utilizes competitive binding of 1-alkanol and octyltrimethylammonium bromide (OTAB) to α-CD in aqueous media, where the concentration of free OTAB depending on the competitive binding is monitored with an OTAB-selective electrode. Therefore, the concentration of 1-alkanol is indirectly estimated from the observed electromotive force. The binding constants of 1-propapnol, 1-butanol, 1-hexanol, and 1-octanol with α-CD, obtained by this method, are close to the literature values. The implications and limitations of this indirect competitive potentiometry were discussed. 相似文献
20.
A critical review is presented on the studies of the internal rotation potential function which is indispensable in understanding rotational isomerism from a dynamical point of view. Molecules so far investigated are classified into a few groups to clarify what factors govern the potential function. As an application of these results, the molecular structures of some bicyclic compounds are discussed, where the internal rotation is shown to play an important role. The recent microwave studies on two molecules of fundamental importance in the internal rotation problem, namely ethane and dimethylacetylene, are briefly mentioned. 相似文献