全文获取类型
收费全文 | 2221篇 |
免费 | 90篇 |
国内免费 | 6篇 |
专业分类
化学 | 1814篇 |
晶体学 | 30篇 |
力学 | 25篇 |
数学 | 95篇 |
物理学 | 353篇 |
出版年
2023年 | 5篇 |
2021年 | 20篇 |
2020年 | 26篇 |
2019年 | 43篇 |
2018年 | 20篇 |
2017年 | 15篇 |
2016年 | 48篇 |
2015年 | 36篇 |
2014年 | 68篇 |
2013年 | 87篇 |
2012年 | 111篇 |
2011年 | 134篇 |
2010年 | 87篇 |
2009年 | 59篇 |
2008年 | 143篇 |
2007年 | 137篇 |
2006年 | 139篇 |
2005年 | 145篇 |
2004年 | 136篇 |
2003年 | 117篇 |
2002年 | 95篇 |
2001年 | 50篇 |
2000年 | 45篇 |
1999年 | 31篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 37篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 6篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 25篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 19篇 |
排序方式: 共有2317条查询结果,搜索用时 31 毫秒
21.
22.
23.
24.
The use of polyamines as electroosmotic modifiers has been shown to be effective in enhancing resolution of protein glycoforms in capillary zone electrophoresis (CZE) using a bare capillary tube. In this study, effectiveness was evaluated by using a polyacrylamide-coated capillary tube instead of a bare capillary tube. Electropherograms obtained in the presence of polyamines were inferior to those obtained in their absence with respect to resolution. Electrophoretic mobility of the proteins decreased and their peaks were broadened by polyamines bound to them. This unfavorable effect was dependent on both the species of polyamines and the pH values of the electrolyte buffer. The reduction of resolution caused by polyamines was in the following order: spermidine (SPD) approximately spermidine-tri-hydrochloride (SPD-HCI) > putrescine (PUT) > hexamethonium chloride (HMC). The observed effect can be ascribed to the formation of complexes between the proteins and the polyamines. In addition, for the bare capillary tube the complexes showed interaction with the inner surface, resulting in local suppression of electroosmosis and poor resolution. The high resolution obtained in the coated capillary tube was reduced in the presence of the polyamines. Thus, the use of the polyamines has a negative effect on the analysis of protein microheterogeneity as a result of protein-polyamine interaction. 相似文献
25.
The friction coefficient between the polymer network of an opaque poly(acrylamide) gel and water is measured as a function of the mole fraction of cross linker. The friction coefficients of opaque gels are 4 to 5 orders of magnitude smaller than those of the transparent gels. This drastic decrease in friction occurs when the mole fraction of cross linker is 0.2. In opaque gels, the friction coefficient of gels and the mole fraction of cross linker are related by a power law. The network structure of the opaque gels used in the friction measurements is examined with a confocal laser scanning microscope. The opaque gel network consists of a fractal aggregate of colloidal particles. The radius of particles and the volume occupied by the particles depend on the mole fraction of cross linker. Both relationships are well described by the power laws. The power law of the friction coefficient is well explained in terms of the power laws of the structural parameters and the Stokes equation of the hydrodynamic friction for the spherical particle. It indicates that the friction of the opaque gel is determined simply by the structure of the polymer network. 相似文献
26.
Mieko Urano Hitoshi Kagawa Yoshihiro Harigaya Shaoshun Li Masayuki Onda 《Journal of heterocyclic chemistry》1991,28(8):1845-1847
A total synthesis of optically pure (+)-catechin pentaacetate has been established using the (-)-chalcon epoxide (100% ee) derived from 3,4,2′,4′,6′-pentakis(methoxymethoxy)chalcon as the starting material. The optical purity of the product is confirmed by 1H nmr analysis in the presence of a shift reagent. 相似文献
27.
Yamamoto Y Hattori R Miwa T Nakagai YI Kubota T Yamamoto C Okamoto Y Itoh K 《The Journal of organic chemistry》2001,66(11):3865-3870
A monomeric titanocene(III) derivative, Cp(2)TiPh, effectively promoted the pinacol coupling of both an aromatic aldehyde, benzaldehyde, and an aliphatic aldehyde, 3-phenylpropionaldehyde. The same reactive complex was successfully generated by a catalytic amount of a precursor, Cp(2)Ti(Ph)Cl, and its stoichiometric amount of Zn. The Cp(2)TiPh-catalyzed pinacol coupling of benzaldehyde derivatives and aliphatic aldehydes afforded the corresponding 1,2-diols in high yields with moderate to good threo-selectivity. On the other hand, Cp(2)TiPh-catalyzed pinacol cyclization of dials gave cyclic 1,2-diols with excellent diastereoselectivity. The extension of this protocol to chiral dials demonstrated that the phenyltitanium complex catalytically transmitted an axial chirality or a central chirality of the starting dials to the central chirality of the resultant 1,2-diols. 相似文献
28.
Fluorescence quenching by molecular oxygen has been employed to estimate dynamic parameters and solubility characteristics of molecular oxygen in micelle forming detergent solutions. A kinetic model which assumes that oxygen quenching occurs only in the micellar phase is employed to analyze the data. 相似文献
29.
Matsuda H Morikawa T Toguchida I Harima S Yoshikawa M 《Chemical & pharmaceutical bulletin》2002,50(7):972-975
Two new flavanone glycosides, (2S)- and (2R)-eriodictyol 7-O-beta-D-glucopyranosiduronic acids, and a new phenylbutanoid glycoside, (2S, 3S)-1-phenyl-2,3-butanediol 3-O-beta-D-glucopyranoside, were isolated from the flowers of Chrysanthemum indicum L. cultivated in China together with eight flavonoids. The absolute stereostructures of the new compounds were determined on the basis of chemical and physicochemical evidence. Both of the new flavanone glycosides were found to show inhibitory activity for rat lens aldose reductase. 相似文献
30.
Hatsuhiko Hattori 《Tetrahedron letters》2005,46(35):5871-5875
Organozinc and a Pd catalyst promoted formation of dienes from allylic esters possessing a leaving group such as acyloxy and alkoxy groups next to the allyl moiety. The reaction proceeded with high regio- and stereoselectivity when applied to secondary allylic substrates. 相似文献