全文获取类型
收费全文 | 397164篇 |
免费 | 2026篇 |
国内免费 | 599篇 |
专业分类
化学 | 184467篇 |
晶体学 | 5916篇 |
力学 | 22768篇 |
综合类 | 20篇 |
数学 | 57964篇 |
物理学 | 128654篇 |
出版年
2021年 | 3949篇 |
2020年 | 4274篇 |
2019年 | 5166篇 |
2018年 | 7686篇 |
2017年 | 7884篇 |
2016年 | 9903篇 |
2015年 | 4654篇 |
2014年 | 8735篇 |
2013年 | 16319篇 |
2012年 | 13321篇 |
2011年 | 15479篇 |
2010年 | 13090篇 |
2009年 | 13231篇 |
2008年 | 14986篇 |
2007年 | 14742篇 |
2006年 | 13204篇 |
2005年 | 11429篇 |
2004年 | 10998篇 |
2003年 | 10104篇 |
2002年 | 10386篇 |
2001年 | 10536篇 |
2000年 | 8263篇 |
1999年 | 6269篇 |
1998年 | 5802篇 |
1997年 | 5585篇 |
1996年 | 5046篇 |
1995年 | 4481篇 |
1994年 | 4522篇 |
1993年 | 4509篇 |
1992年 | 4597篇 |
1991年 | 5081篇 |
1990年 | 5005篇 |
1989年 | 5052篇 |
1988年 | 4700篇 |
1987年 | 4779篇 |
1986年 | 4465篇 |
1985年 | 5355篇 |
1984年 | 5552篇 |
1983年 | 4730篇 |
1982年 | 4977篇 |
1981年 | 4637篇 |
1980年 | 4289篇 |
1979年 | 4927篇 |
1978年 | 5105篇 |
1977年 | 5298篇 |
1976年 | 5450篇 |
1975年 | 5058篇 |
1974年 | 4889篇 |
1973年 | 5132篇 |
1972年 | 4305篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper presents a quantum chemical calculation of native (2–7 fructoside residues) and chemically modified (2–4 fructoside residues) levan molecule models. A levan modification was carried out by oxidation and the following reduction or hyrdazonation of the fructoside rings. The conformational particularity and reaction ability was studied for the native and for the modified levan molecules. 相似文献
992.
Given one or more vibrational modes of a membrane, the free vibration equation can be applied to infer the mass surface density. This paper considers determining the surface density of an inhomogeneous membrane from digitized holographic projections (interferograms) of the modeshapes. Spatially discrete numerical models of the membrane surface are presented, which can be used to solve both forward and inverse vibration problems. The accuracy of the discrete models is examined for exactly solvable free vibration problems involving inhomogeneous membranes. For the solution of the inverse problem, error estimates are given for the mass surface density deduced from modeshape interferograms. The practicability of the method is investigated using simulated experimental data for membranes with composite and continuously inhomogeneous density profiles. Strategies are discussed for reducing errors in the reconstructed densities. 相似文献
993.
994.
995.
E. Yu. Daniyarova I. V. Kazatchkov V. N. Remeslennikov 《Journal of Mathematical Sciences》2005,131(6):6015-6022
This article is the fourth part of the series of papers whose aim is the construction of algebraic geometry over metabelian
Lie algebras.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 14, Algebra,
2004. 相似文献
996.
I.V. Markevich V.I. Kushnirenko L.V. Borkovska B.M. Bulakh 《Solid State Communications》2005,136(8):475-478
The mechanism of formation of a thin highly conductive layer, which is known to be present on ZnO surface, has been proposed. This process has been assumed to consist in accumulation of mobile shallow donors at crystal surface due to their drift in band-bending electric field caused by adsorbed oxygen. Experimental results that confirm this mechanism have been obtained. 相似文献
997.
P L Melgarejo M Ternero I Gracia 《International journal of environmental analytical chemistry》1986,24(4):283-295
A study of the atmospheric pollution by suspended particulate lead in the city of Seville, Spain, was carried out during the period between March 1983 and February 1984. The results obtained from seven sampling stations allowed us to study the site to site variations; there are two locations with average annual concentrations higher than 2 micrograms X m-3. In one station, the meteorological and traffic effects and relationship with other traffic-related pollutants, were investigated. The regression analyses performed on the average monthly data have shown an inverse correlation with wind speed and temperature and a direct correlation with carbon monoxide and smoke concentrations, but no significant correlation was found with the lead deposition levels. 相似文献
998.
999.
Statistical Analysis of the Effect of Mineral Admixtures on the Strength of the Interfacial Transition Zone 总被引:1,自引:0,他引:1
Microscopic evidence indicates that the thickness of the interfacial transition zone (ITZ) between the aggregate and the cement paste is modified when mineral admixtures partially replace portland cement. Unfortunately, there is limited information on the significance of these microscopic modifications to the mechanical properties of the ITZ. This research reports experimental results on the shear and tensile strength of the ITZ as affected by the addition of the following mineral admixtures: silica fume, fly ash, and natural pozzolan. Statistical analysis was used to identify the significant parameters affecting the tensile and shear strength of the ITZ. Experimental results indicate that not only does the incorporation of silica fume and fly ash increase the strength of the ITZ, these mineral admixtures have a greater influence on the strength increase of the ITZ than in the strength increase of the cement paste. 相似文献
1000.
Golovchenko A. V. Pil'o S. G. Brovarets V. S. Drach B. S. 《Russian Journal of General Chemistry》2003,73(11):1832-1833
Russian Journal of General Chemistry - 相似文献