全文获取类型
收费全文 | 130898篇 |
免费 | 12786篇 |
国内免费 | 5788篇 |
专业分类
化学 | 92324篇 |
晶体学 | 1608篇 |
力学 | 5979篇 |
综合类 | 322篇 |
数学 | 13563篇 |
物理学 | 35676篇 |
出版年
2023年 | 749篇 |
2022年 | 1710篇 |
2021年 | 2241篇 |
2020年 | 3344篇 |
2019年 | 4753篇 |
2018年 | 3747篇 |
2017年 | 3409篇 |
2016年 | 6504篇 |
2015年 | 5588篇 |
2014年 | 6533篇 |
2013年 | 8546篇 |
2012年 | 7617篇 |
2011年 | 7197篇 |
2010年 | 6772篇 |
2009年 | 6766篇 |
2008年 | 6497篇 |
2007年 | 5665篇 |
2006年 | 5034篇 |
2005年 | 4771篇 |
2004年 | 4247篇 |
2003年 | 3856篇 |
2002年 | 4655篇 |
2001年 | 3792篇 |
2000年 | 3177篇 |
1999年 | 1926篇 |
1998年 | 1559篇 |
1997年 | 1349篇 |
1996年 | 1294篇 |
1995年 | 1078篇 |
1994年 | 1161篇 |
1993年 | 1097篇 |
1992年 | 1062篇 |
1991年 | 1124篇 |
1990年 | 1118篇 |
1989年 | 1040篇 |
1988年 | 917篇 |
1987年 | 916篇 |
1986年 | 884篇 |
1985年 | 924篇 |
1984年 | 919篇 |
1983年 | 823篇 |
1982年 | 800篇 |
1979年 | 802篇 |
1978年 | 812篇 |
1977年 | 806篇 |
1976年 | 919篇 |
1975年 | 813篇 |
1974年 | 845篇 |
1973年 | 849篇 |
1972年 | 752篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
E. M. Suleimenov O. V. Morozova V. A. Raldugin Yu. V. Gatilov T. V. Rybalova M. M. Shakirov R. Seidakhmetov R. M. Aksartov S. M. Adekenov 《Chemistry of Natural Compounds》2005,41(5):556-560
Four sesquiterpene lactones with the germacrane structure were isolated from the aerial part of Stizolophus balsamita. X-ray structure analyses showed that two of them were previously known balsamin derivatives. A third was a crystalline isomorphous
mixture of the known lactone stizolin and 11,13-dihydrostizolin in a 53:47 ratio. The biological activities of the balsamin
derivatives were investigated.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 454–457, September–October, 2005. 相似文献
992.
I. V. Aristov O. V. Bobreshova O. Yu. Strel'nikova 《Russian Journal of Electrochemistry》2002,38(5):567-569
In mixed aqueous solution of glycine and L-lysine the ionization of both amino acids increases due to the proton transfer from glycine zwitterion to lysine zwitterion. This is manifested by a considerable nonlinear (pairwise interaction of amino acids) increase in the mixed solution electroconductivity at high amino acid concentrations. The solution pH varies negligibly, as the amino acids in aqueous solutions demonstrate buffering. The refraction coefficient additively depends on glycine and L-lysine concentrations. 相似文献
993.
Yu. A. Davidovich N. N. Semenova K. K. Babievskii S. V. Rogozhin 《Russian Chemical Bulletin》1986,35(9):1951-1953
Conclusions -Amino acid esters are readily acylated by 2-ethoxy-4-thiolanones to form the corresponding -mercaptocarboxylic acid amides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2139–2140, September, 1986. 相似文献
994.
Summary The paper discusses the effect of the length and structure of the hydrocarbon chain connecting the nitrile group to the silica gel surface on the chromatographic properties of cyanoalkyl phases.When using non-polar and polar mobile phases, the selectivity of the cyanodecyl phases toward PAHs is higher than of the cyanopropyl phase and of hydroxylated silica gel.Polar additives to the mobile phase drastically decrease the retention on silica gel and on the cyanopropyl phase while affect the properties of cyanodecyl phases only to a considerably less degree. Newly synthesized phases with different structures of the hydrocarbon chain are compared with the commerical cyano-and ODS-phases. The retention mechanism on the cyanoalkyl phases is discussed. 相似文献
995.
Yu. B. Zelechonok L. P. Ivanova V. V. Zorin S. A. Kotlyar S. S. Zlotskii D. L. Rakhmankulov 《Chemistry of Heterocyclic Compounds》1988,24(1):64-65
Homolytic alkylation of protonated quinoxaline with 18-crown-6, initiated by the system pivalic acid-iron(II) sulfate at 20–25C, gives (quinoxalin-2-yl)-18-crown-6 in 85% yield. Under analogous conditions, the reaction with quinoline affords two isomers: (quinolin-4-yl)-18-crown-6 and (quinolin-2-yl)-18-crown-6, in yields of 20 and 30% respectively.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 75–76, January, 1988. 相似文献
996.
G.A. Tolstikov B.M. Lerman L.I. Umanskaya Yu.T. Struchkov A.A. Espenbetov A.L. Yanovsky 《Tetrahedron letters》1980,21(43):4189-4192
The interaction between SCl2 and adamantylideneadamantane produces epithiocompounds and or polychloroadamantylideneadamantanes – depending upon conditions. The structure of was determined by X-ray analysis. 相似文献
997.
K. A. Andrianov G. L. Slonimski
A. A. Zhdanov V. Yu. Levin Yu. K. Godovski
V. A. Moskalenko 《Journal of polymer science. Part A, Polymer chemistry》1972,10(1):1-22
Some physical properties of linear polydimethylsiloxanes have been studied. The states and transitions in polydimethylsiloxanes have been investigated by using the method of dynamic heat capacity and a thermomechanic method in the temperature range from ?150 to +200°C. The temperature dependence of primary and secondary crystallization has been studied by optical, calorimetric, and x-ray methods. 相似文献
998.
Yu. A. Mikheev L. N. Guseva E. Ya. Davydov Yu. A. Ershov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(12):1897-1913
A model of the hydration of hydrophobic substances in water is suggested. The models of fluctuation formation of empty cavities in water as a stage of hydration extensively used in the literature were shown to be at variance with experiment. The fundamental role played by the interphase boundary surface was emphasized. On this surface, the successive addition of water molecules with the formation of capsules around hydrophobic molecules occurred. The physical meaning of the Ostwald equation was revealed. This equation characterized the distribution of hydrophobic volatile substances between the gas and aqueous phases. The method of optical probes (hydrophobic aromatic molecules) was used to reveal the synergistic character of autocorrelation of dispersion interactions between water and hydrophobic substance molecules. This synergism was at variance with the Lennard-Jones potential. The synergism (superadditivity) of dispersion attraction forces, which strengthened their directional character, caused the self-organization and enhanced stability of hydration capsules with encapsulated hydrophobic molecules. Computer models were used to show that the spatially directional character of dispersion interactions necessary for the self-organization of hydrated aggregates could be simulated by the molecular mechanics method on the basis of orientational correlation of water molecules and hydrophobic substances in the starting system. 相似文献
999.
The velocity and velocity sign autocorrelation functions as well as the distribution of time intervals between velocity sign changes of a particle in a gas or fluid are studied within the framework of impact theory. The results of the uncorrelated successive velocity reversal model (USVRM), for which this approach provides a limiting case of infinitesimal collision time, are checked. It is shown with this simple model that the two approaches are equivalent in two special cases: either when there is no correlation between pre- and post-collision velocities, or when the only possible result of a collision is elastic back scattering. Otherwise, the USVRM leaves out the scope of its view the important correlations of velocity in course of collisions. 相似文献
1000.
L. A. Rodinovskaya Yu. A. Sharanin A. M. Shestopalov V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1988,24(6):658-665
The condensation of cyanothio- and cyanoselenoacetamide with 3-aryl-3-oxo-1-piperidino-1-propene or sodium 3-aryl-3-oxo-1-propen-1-olate takes place regioselectively with the formation of the 6-aryl-3-cyano-2(1H)-pyridinethiones or the corresponding selenones. Thieno[2,3-b]pyridines, thiazolo[3,2-a]pyridinium salts, and other annellated heterocycles were obtained from the 6-aryl-3-cyano-2(1H)-pyridinethiones.For Communication 28, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 805–812, June, 1988. 相似文献