全文获取类型
收费全文 | 247891篇 |
免费 | 4462篇 |
国内免费 | 2869篇 |
专业分类
化学 | 117399篇 |
晶体学 | 3801篇 |
力学 | 13379篇 |
综合类 | 164篇 |
数学 | 38970篇 |
物理学 | 81509篇 |
出版年
2021年 | 1156篇 |
2020年 | 1388篇 |
2019年 | 1255篇 |
2018年 | 10692篇 |
2017年 | 11560篇 |
2016年 | 6424篇 |
2015年 | 2745篇 |
2014年 | 2441篇 |
2013年 | 6104篇 |
2012年 | 9589篇 |
2011年 | 19305篇 |
2010年 | 11510篇 |
2009年 | 11332篇 |
2008年 | 16426篇 |
2007年 | 20165篇 |
2006年 | 5281篇 |
2005年 | 12251篇 |
2004年 | 7860篇 |
2003年 | 7327篇 |
2002年 | 5109篇 |
2001年 | 4196篇 |
2000年 | 3369篇 |
1999年 | 2672篇 |
1998年 | 2240篇 |
1997年 | 2174篇 |
1996年 | 2310篇 |
1995年 | 2154篇 |
1994年 | 1909篇 |
1993年 | 1813篇 |
1992年 | 2009篇 |
1991年 | 1974篇 |
1990年 | 1880篇 |
1989年 | 1873篇 |
1988年 | 1880篇 |
1987年 | 1823篇 |
1986年 | 1724篇 |
1985年 | 2269篇 |
1984年 | 2394篇 |
1983年 | 2002篇 |
1982年 | 2306篇 |
1981年 | 2129篇 |
1980年 | 2163篇 |
1979年 | 2165篇 |
1978年 | 2295篇 |
1977年 | 2123篇 |
1976年 | 2182篇 |
1975年 | 2103篇 |
1974年 | 1944篇 |
1973年 | 2194篇 |
1972年 | 1322篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
M. D. Srinivas 《Pramana》2003,60(6):1137-1152
We derive an optimal bound on the sum of entropic uncertainties of two or more observables when they are sequentially measured
on the same ensemble of systems. This optimal bound is shown to be greater than or equal to the bounds derived in the literature
on the sum of entropie uncertainties of two observables which are measured on distinct but identically prepared ensembles
of systems. In the case of a two-dimensional Hilbert space, the optimum bound for successive measurements of two-spin components,
is seen to be strictly greater than the optimal bound for the case when they are measured on distinct ensembles, except when
the spin components are mutually parallel or perpendicular 相似文献
92.
For the decay of two identical particles with close momenta, the angular correlations between the directions of emission of decay products are considered on the basis of the model of independent single-particle sources emitting unstable unpolarized particles of nonzero spin. These correlations reflect spin correlations that are caused by quantum-statistics and final-state-interaction effects. A general theory of angular correlations in the decays of two arbitrarily polarized particles (resonances) is constructed. 相似文献
93.
94.
O. M. Ostrikov 《Mechanics of Solids》2008,43(5):793-797
We propose a dislocation model of a nanotwin, which is used to calculate the stress fields in the nanotwin. We consider the role of these stresses in the process of interdislocation interaction and nanotwin growth. 相似文献
95.
Some possible errors in determining the gravity anomalies are discussed. Such errors may be caused by an inaccurate calibration of the gravimeter used in an airborne survey system. An approach based on wavelet decompositions is proposed for its additional calibration with the use of flight data obtained during repeated flights. 相似文献
96.
We study parametric oscillations of linear systems with one degree of freedom for large values of the modulation coefficient. We use the classical analytic Lyapunov-Poincaré perturbation methods and an original numerically-analytic method of accelerated convergence to construct periodic solutions and the corresponding eigenvalues. We find the boundaries of stability and instability domains. We use specific models to illustrate the main properties of parametric oscillations of systems with singular character of the perturbation dependence on the modulation coefficient. We consider periodic boundary value problems for the modified Mathieu equation and the Kochin equation modeling crankshaft torsional vibrations and show that there are significant differences between weakly and essentially perturbed periodicmotions both for the lowest and arbitrary oscillation modes. We also describe the unusual properties of the boundaries in the domain of the system determining parameters. 相似文献
97.
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
98.
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
99.
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
100.
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