全文获取类型
收费全文 | 13229篇 |
免费 | 1006篇 |
国内免费 | 855篇 |
专业分类
化学 | 1959篇 |
晶体学 | 148篇 |
力学 | 875篇 |
综合类 | 146篇 |
数学 | 9694篇 |
物理学 | 2268篇 |
出版年
2024年 | 21篇 |
2023年 | 148篇 |
2022年 | 145篇 |
2021年 | 175篇 |
2020年 | 296篇 |
2019年 | 326篇 |
2018年 | 334篇 |
2017年 | 370篇 |
2016年 | 406篇 |
2015年 | 310篇 |
2014年 | 640篇 |
2013年 | 1200篇 |
2012年 | 519篇 |
2011年 | 744篇 |
2010年 | 748篇 |
2009年 | 862篇 |
2008年 | 925篇 |
2007年 | 908篇 |
2006年 | 731篇 |
2005年 | 634篇 |
2004年 | 576篇 |
2003年 | 540篇 |
2002年 | 493篇 |
2001年 | 382篇 |
2000年 | 327篇 |
1999年 | 308篇 |
1998年 | 267篇 |
1997年 | 242篇 |
1996年 | 204篇 |
1995年 | 150篇 |
1994年 | 135篇 |
1993年 | 103篇 |
1992年 | 99篇 |
1991年 | 66篇 |
1990年 | 57篇 |
1989年 | 49篇 |
1988年 | 54篇 |
1987年 | 29篇 |
1986年 | 50篇 |
1985年 | 60篇 |
1984年 | 68篇 |
1983年 | 44篇 |
1982年 | 57篇 |
1981年 | 50篇 |
1980年 | 46篇 |
1979年 | 57篇 |
1978年 | 37篇 |
1977年 | 27篇 |
1976年 | 25篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 113 毫秒
41.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.
42.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 相似文献
43.
44.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
45.
Donghyun Cho Taihyun Chang Apostolos Avgeropoulos Nikos Hadjichristidis 《European Polymer Journal》2003,39(11):2155-2160
Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species. 相似文献
46.
提出了一种比较系统的求解非线性发展方程精确解的新方法, 即试探方程法. 以一个带5阶 导数项的非线性发展方程为例, 利用试探方程法化成初等积分形式,再利用三阶多项式的完 全判别系统求解,由此求得的精确解包括有理函数型解, 孤波解, 三角函数型周期解, 多项 式型Jacobi椭圆函数周期解和分式型Jacobi椭圆函数周期解
关键词:
试探方程法
非线性发展方程
孤波解
Jacobi椭圆函数
周期解 相似文献
47.
Svitlana P. Rogovchenko 《Journal of Mathematical Analysis and Applications》2003,279(1):121-134
In this paper, we are concerned with a class of nonlinear second-order differential equations with a nonlinear damping term. Passage to more general class of equations allows us to remove a restrictive condition usually imposed on the nonlinearity, and, as a consequence, our results apply to wider classes of nonlinear differential equations. Two illustrative examples are considered. 相似文献
48.
变系数(2+1)维Broer-Kaup方程的精确解 总被引:19,自引:4,他引:15
利用齐次平衡原则,导出了变系数(2+1)维Broer-Kaup方程的B?cklund变换(BT),并由该BT,求出了(2+1)维Broer-Kaup方程的各种形式的精确解. 相似文献
49.
Influence of the Type of a Ligand on the Intensity of Luminescence of Ln3+ Ions in Aqueous Solutions
I. V. Barsukov E. N. Kabaeva V. V. Syt'ko S. D. Umreiko 《Journal of Applied Spectroscopy》2003,70(3):470-473
The luminescence characteristics of hydrated Ln3+ ions and their complexes with some acidic ligands have been investigated. The possibility of determining the stability of the complexes of lanthanides in solutions from the intensity of luminescence bands is shown. The influence of the characteristic features of the f-electron shell of Ln3+ on the formation of the spectrochemical series is discussed. 相似文献
50.
一类含有P-Laplacian算子的奇异边值问题解的确切个数 总被引:2,自引:0,他引:2
讨论了一类p-L ap lac ian算子型的奇异边值问题正解的确切个数以及解的性质. 相似文献