全文获取类型
收费全文 | 687282篇 |
免费 | 6772篇 |
国内免费 | 2009篇 |
专业分类
化学 | 354462篇 |
晶体学 | 10057篇 |
力学 | 33157篇 |
综合类 | 19篇 |
数学 | 89858篇 |
物理学 | 208510篇 |
出版年
2021年 | 5897篇 |
2020年 | 6477篇 |
2019年 | 7422篇 |
2018年 | 9751篇 |
2017年 | 9800篇 |
2016年 | 13816篇 |
2015年 | 7864篇 |
2014年 | 12834篇 |
2013年 | 30930篇 |
2012年 | 23406篇 |
2011年 | 28262篇 |
2010年 | 20527篇 |
2009年 | 20371篇 |
2008年 | 26285篇 |
2007年 | 26221篇 |
2006年 | 23940篇 |
2005年 | 21592篇 |
2004年 | 19954篇 |
2003年 | 17912篇 |
2002年 | 17785篇 |
2001年 | 19005篇 |
2000年 | 14687篇 |
1999年 | 11467篇 |
1998年 | 9882篇 |
1997年 | 9780篇 |
1996年 | 9127篇 |
1995年 | 8345篇 |
1994年 | 8216篇 |
1993年 | 8070篇 |
1992年 | 8570篇 |
1991年 | 9095篇 |
1990年 | 8708篇 |
1989年 | 8613篇 |
1988年 | 8454篇 |
1987年 | 8192篇 |
1986年 | 7875篇 |
1985年 | 10221篇 |
1984年 | 10686篇 |
1983年 | 8972篇 |
1982年 | 9479篇 |
1981年 | 8932篇 |
1980年 | 8535篇 |
1979年 | 9041篇 |
1978年 | 9488篇 |
1977年 | 9211篇 |
1976年 | 9367篇 |
1975年 | 8758篇 |
1974年 | 8717篇 |
1973年 | 9171篇 |
1972年 | 6460篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
3-Hydroxy-4-hydroxymethyl pyrrolidin-2-ones, easily prepared from the Baylis–Hillman adduct 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate, are useful intermediates in the synthesis of bioactive compounds. In order to understand the mechanism involved in this reaction, vibrational and Montecarlo molecular mechanics conformational analysis on 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate were carried out, confirming the existence of a low energy intramolecular H-bonded five-member ring. 相似文献
943.
I. A. Uspenskaya Z. S. Vakhovskaya M. M. Efremova M. L. Kovba A. L. Emelina Zh. V. Dobrokhotova Yu. V. Goryushkina L. A. Tiflova A. A. Popova A. S. Monaenkova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):529-534
The thermodynamic properties of the Ln2BaO4 phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated. 相似文献
944.
Prashant M. Bhatt Gautam R. Desiraju 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):o362-o363
The title compound [systematic name: 8‐chloro‐11‐(piperidin‐4‐ylidene)‐6,11‐dihydro‐5H‐benzo[4,5]cyclohepta[2,1‐b]pyridine], C19H19ClN2, was crystallized from ethyl acetate. The interesting feature of the reported structure is that it does not contain any strong hydrogen bonds, although the molecule contains a secondary NH group, which is a good hydrogen‐bond donor. 相似文献
945.
946.
947.
948.
A. B. Mitkevich 《Mechanics of Composite Materials》2005,41(6):497-504
Errors in the programs of winding pressure vessels can lead to an asymmetric reinforcement structure, which affects the equilibrium
shape of their domes and the tension in the left and right families of filaments. In this paper, equations determining the
equilibrium shape of the domes, the tension in filaments, and the shear stresses between layers are obtained. Examples with
winding trajectories in the form of geodesics and constant-deviation lines are considered. It is found that, for pressure
vessels, in the absence of external torque, the tension levels in filaments of the left and right families differ considerably.
It is also revealed that, for actual friction coefficients in winding, the shear stresses taken up by the binder are insignificant.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 743–752, November–December, 2005. 相似文献
949.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance. 相似文献
950.