全文获取类型
收费全文 | 658286篇 |
免费 | 5313篇 |
国内免费 | 1496篇 |
专业分类
化学 | 320430篇 |
晶体学 | 9250篇 |
力学 | 35763篇 |
综合类 | 24篇 |
数学 | 97156篇 |
物理学 | 202472篇 |
出版年
2021年 | 5634篇 |
2020年 | 6102篇 |
2019年 | 6969篇 |
2018年 | 13428篇 |
2017年 | 13728篇 |
2016年 | 15053篇 |
2015年 | 7276篇 |
2014年 | 11845篇 |
2013年 | 26656篇 |
2012年 | 22872篇 |
2011年 | 31031篇 |
2010年 | 22139篇 |
2009年 | 22320篇 |
2008年 | 28643篇 |
2007年 | 30437篇 |
2006年 | 21161篇 |
2005年 | 21504篇 |
2004年 | 18976篇 |
2003年 | 17765篇 |
2002年 | 16743篇 |
2001年 | 17194篇 |
2000年 | 13369篇 |
1999年 | 10177篇 |
1998年 | 8865篇 |
1997年 | 8675篇 |
1996年 | 8208篇 |
1995年 | 7381篇 |
1994年 | 7326篇 |
1993年 | 7125篇 |
1992年 | 7496篇 |
1991年 | 8093篇 |
1990年 | 7715篇 |
1989年 | 7698篇 |
1988年 | 7475篇 |
1987年 | 7276篇 |
1986年 | 6961篇 |
1985年 | 8880篇 |
1984年 | 9201篇 |
1983年 | 7794篇 |
1982年 | 8081篇 |
1981年 | 7586篇 |
1980年 | 7155篇 |
1979年 | 7831篇 |
1978年 | 8136篇 |
1977年 | 7994篇 |
1976年 | 8011篇 |
1975年 | 7685篇 |
1974年 | 7471篇 |
1973年 | 7866篇 |
1972年 | 5838篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
V.I. Kushch I. Sevostianov L. Mishnaevsky Jr 《International Journal of Solids and Structures》2008,45(18-19):5103-5117
The paper addresses the problem of calculation of the local stress field and effective elastic properties of a unidirectional fiber reinforced composite with anisotropic constituents. For this aim, the representative unit cell approach has been utilized. The micro geometry of the composite is modeled by a periodic structure with a unit cell containing multiple circular fibers. The number of fibers is sufficient to account for the micro structure statistics of composite. A new method based on the multipole expansion technique is developed to obtain the exact series solution for the micro stress field. The method combines the principle of superposition, technique of complex potentials and some new results in the theory of special functions. A proper choice of potentials and new results for their series expansions allow one to reduce the boundary-value problem for the multiple-connected domain to an ordinary, well-posed set of linear algebraic equations. This reduction provides high numerical efficiency of the developed method. Exact expressions for the components of the effective stiffness tensor have been obtained by analytical averaging of the strain and stress fields. 相似文献
982.
The aim of this paper is to investigate laminar-turbulent transition in a mixed convection phenomenon occurring in a horizontal rectangular duct. Indeed, laminar-turbulent transition is well known in the case of forced convection but the presence of secondary flow induced by natural convection on this transition is not well highlighted. In this study, we will not be concerned by determining a critical threshold value of a Reynolds number of transition but only to estimate the degree of turbulence in the transition regime, i.e. weak turbulence in the case of a mixed convection phenomenon. This is possible thanks to the application of the wavelet transform. The calculation of the Hölder exponent, associated with the maximum value of the singularity spectrum for various experimental conditions allows the degree of turbulence to be measured. The variation of the Hölder exponent versus heat flux and Reynolds number enables us to show that there are two ways to go towards turbulence: thermal by increasing heat flux and hydrodynamic by increasing fluid velocity. 相似文献
983.
A. V. Ivanov M. Yu. Tsentalovich E. G. Kogan L. G. Tomilova N. S. Zefirov 《Russian Chemical Bulletin》2008,57(8):1676-1679
The chlorination of benzene, toluene, and o-xylene with molecular chlorine in the presence of the phthalocyanine complexes of different structures was studied. The transformations
of the catalysts during the reaction were investigated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1644–1647, August, 2008. 相似文献
984.
985.
The kinetics of unhindered sedimentation of a titanium dioxide suspension (as model dispersed system) was studied, and the effect of the concentration and mode of addition of various formulations based on anionic and cationic acrylamide copolymers on their flocculation properties in aqueous salt (NaCl) solutions was evaluated. 相似文献
986.
A. Ya. Samuilov L. A. Zenitova I. N. Bakirova Ya. D. Samuilov 《Russian Journal of Applied Chemistry》2008,81(8):1419-1422
Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed. 相似文献
987.
M. K. Bratenko Yu. V. Kadel’nik V. A. Chornous M. V. Vovk 《Russian Journal of Organic Chemistry》2008,44(2):247-250
Oximes of 4-(4-pyrazolyl)-3-buten-2-onees obtained by successive reaction of 3-aryl-4-formylpyrazoles with acetone and hydroxylamine at the treatment with iodine suffered an oxidative cyclization yielding 3-aryl-4-(5-isoxazolyl)pyrazoles. 相似文献
988.
989.
K. S. Trofimova V. G. Dronov N. S. Shaglaeva R. G. Sultangareev 《Russian Journal of Applied Chemistry》2008,81(4):730-731
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested. 相似文献
990.