全文获取类型
收费全文 | 30688篇 |
免费 | 2865篇 |
国内免费 | 5723篇 |
专业分类
化学 | 16717篇 |
晶体学 | 521篇 |
力学 | 1940篇 |
综合类 | 550篇 |
数学 | 11911篇 |
物理学 | 7637篇 |
出版年
2024年 | 49篇 |
2023年 | 270篇 |
2022年 | 455篇 |
2021年 | 502篇 |
2020年 | 708篇 |
2019年 | 698篇 |
2018年 | 699篇 |
2017年 | 949篇 |
2016年 | 1113篇 |
2015年 | 798篇 |
2014年 | 1252篇 |
2013年 | 2486篇 |
2012年 | 1878篇 |
2011年 | 1842篇 |
2010年 | 1640篇 |
2009年 | 1868篇 |
2008年 | 2068篇 |
2007年 | 2141篇 |
2006年 | 1873篇 |
2005年 | 1726篇 |
2004年 | 1510篇 |
2003年 | 1274篇 |
2002年 | 1279篇 |
2001年 | 1048篇 |
2000年 | 1773篇 |
1999年 | 1370篇 |
1998年 | 1274篇 |
1997年 | 645篇 |
1996年 | 620篇 |
1995年 | 566篇 |
1994年 | 469篇 |
1993年 | 415篇 |
1992年 | 351篇 |
1991年 | 254篇 |
1990年 | 204篇 |
1989年 | 148篇 |
1988年 | 127篇 |
1987年 | 106篇 |
1986年 | 93篇 |
1985年 | 98篇 |
1984年 | 82篇 |
1983年 | 53篇 |
1982年 | 88篇 |
1981年 | 96篇 |
1980年 | 58篇 |
1979年 | 60篇 |
1978年 | 54篇 |
1977年 | 39篇 |
1976年 | 25篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
This paper describes the theory of liquid adsorption chromatography (LSC) with mixed mobile phase, involving formation of multilayer surface phases. An equation describing the dependence of the capacity ratio upon the mobile phase composition is derived and theoretical curves illustrating the same dependence are calculated accordingly by assuming different thicknesses of the surface phase. 相似文献
992.
993.
本文介绍了尼龙1010的结晶过程与动力学、晶体的熔融与转化;并论述了其稀溶液、热降解与动态力学性质及共聚、共混、填充、增强、交联改性方面的研究进展。 相似文献
994.
Dewen Dong 《Tetrahedron letters》2005,46(43):7331-7335
A novel and facile synthesis of substituted 2,3-dihydro-1,4-dithiins and 6,7-dihydro-5H-1,4-dithiepins based on the reactions of α-bromo/hydroxy ketones with α-oxo ketene cyclic dithioacetals has been developed. A general mechanism for the reactions is proposed. 相似文献
995.
Lanying?Yang Yi?Zhang Qingqi?Chen Jin Shi?MaEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(2):223-229
Summary. 1-(Dipyrrin-2-yl)-1-(dipyrrin-3-yl)methane, the N-confused analog of biladiene-ac, is prepared by condensation of 2,3-dipyrromethane with two molecules of 2-formylpyrrole in dichloromethane in the presence of hydrogen bromide. Self-assembly of the ligand with Zn(II) in dichloromethane and methanol offers a dinuclear dimeric complex with a ligand:metal ratio of 2:2. X-Ray crystal structure analysis reveals two ligands bound through a head-to-tail pattern to two zinc centers to form a severely distorted helical conformation, which has the shape of a rectangle. 相似文献
996.
DFT Study on the (S)-Proline-catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde
1 INTRODUCTION Aldol reaction, one of the most important C–C bond-formation reactions, is widely utilized in orga- nic synthesis[1]. Extensive efforts have been donated to the development of catalytic stereo-selective va- riants of this reaction[2]. However, the direct aldol reaction between unmodified carbonyles would be the most attractive synthetic alternative. Proline-catalyzed intermolecular direct aldol reac- tion between acetone and 4-nitrobenzaldehyde was first reported by List… 相似文献
997.
VPI-5是具有十八元环超大孔道的磷酸铝分子筛,在加热过程中,随着孔道中的水分子的脱除,其骨架结构转化成具有十四元环孔道的AlPO_4-8分子筛。采用XRD及骨架结构模型计算等方法研究了这一相变过程,并对相变机理进行了探讨。 相似文献
998.
999.
O. V. Gusev L. N. Morozova T. A. Peganova P. V. Petrovskii N. A. Ustynyuk 《Russian Chemical Bulletin》1994,43(3):474-477
A mixture ofendo-H andexo-H isomers (1a and1b) of the (4-C5Me5H)PtCl2 complex was prepared by the reaction of K2PtCl4 with C5Me5H in MeOH. The mixture of isomers reacts with CpTl in the presence of TiBF4 to give a novel complex, [(4-C5Me5H)Pt(5-C5H5)]+BF4
–, as a mixture ofendo-H- andexo-H-isomers (2a and2b). The data of1H and13C NMR spectroscopy of the resulting complexes are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–517, March, 1994. 相似文献
1000.
J. P. Dassaud B. Gallot A. Guyot R. Spitz J. P. Beautemps C. Williams C. Bourgaux A. Eisenberg 《先进技术聚合物》1994,5(2):79-89
Polypropylene ionomers have been prepared by sulfonation of copolymers of propene and 7 methyl, 1-6 octadiene, followed by neutralization to cesium salts. Both WAXS and SAXS were used to study the morphology of the samples, while their thermal properties were studied by DSC and their mechanical properties by DMTA. The sulfonation process is shown to cause a further drop in crystallinity in addition to the effect of comonomer incorporation. Ion clustering is observed when the extent of sulfonation is high enough, the limit being dependent on the copolymer composition. The ion pairs which are not incorporated into the cluster cause a small-angle upturn in the WAXS pattern. The mechanical properties are strongly affected by the drop in crystallinity, but may be partly recovered due to ion clustering. No disruption of the ion clusters is observed before thermal decomposition of the polymer. 相似文献