全文获取类型
收费全文 | 26903篇 |
免费 | 2898篇 |
国内免费 | 2996篇 |
专业分类
化学 | 8953篇 |
晶体学 | 327篇 |
力学 | 3868篇 |
综合类 | 417篇 |
数学 | 14521篇 |
物理学 | 4711篇 |
出版年
2024年 | 66篇 |
2023年 | 275篇 |
2022年 | 433篇 |
2021年 | 597篇 |
2020年 | 811篇 |
2019年 | 724篇 |
2018年 | 700篇 |
2017年 | 845篇 |
2016年 | 975篇 |
2015年 | 689篇 |
2014年 | 1168篇 |
2013年 | 2165篇 |
2012年 | 1432篇 |
2011年 | 1552篇 |
2010年 | 1446篇 |
2009年 | 1658篇 |
2008年 | 1773篇 |
2007年 | 1892篇 |
2006年 | 1546篇 |
2005年 | 1395篇 |
2004年 | 1285篇 |
2003年 | 1247篇 |
2002年 | 1119篇 |
2001年 | 892篇 |
2000年 | 855篇 |
1999年 | 793篇 |
1998年 | 675篇 |
1997年 | 563篇 |
1996年 | 482篇 |
1995年 | 450篇 |
1994年 | 369篇 |
1993年 | 288篇 |
1992年 | 238篇 |
1991年 | 222篇 |
1990年 | 168篇 |
1989年 | 127篇 |
1988年 | 114篇 |
1987年 | 98篇 |
1986年 | 94篇 |
1985年 | 101篇 |
1984年 | 85篇 |
1983年 | 47篇 |
1982年 | 81篇 |
1981年 | 64篇 |
1980年 | 50篇 |
1979年 | 43篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper we provide an elementary proof of the existence of canard solutions for a class of singularly perturbed planar systems in which there occurs a transcritical bifurcation of the quasi steady states. The proof uses the one-dimensional result proved by V.F. Butuzov, N.N. Nefedov and K.R. Schneider, and an appropriate monotonicity assumption on the vector field. The result is applied to identify all possible predator–prey models with quadratic vector fields allowing for the existence of canard solutions. 相似文献
992.
m次幂等矩阵的等价条件 总被引:1,自引:0,他引:1
陈益智 《数学的实践与认识》2011,41(23)
利用矩阵的秩和齐次线性方程组解空间的维数,给出了m(m≥2)次幂等矩阵的一些等价条件,推广了2,3次幂等矩阵的相应结果.此外,所获结果还给推广到了m次幂等线性变换中. 相似文献
993.
We study quasi-periodic tori under a normal-internal resonance, possibly with multiple eigenvalues. Two non-degeneracy conditions play a role. The first of these generalizes invertibility of the Floquet matrix and prevents drift of the lower dimensional torus. The second condition involves a Kolmogorov-like variation of the internal frequencies and simultaneously versality of the Floquet matrix unfolding. We focus on the reversible setting, but our results carry over to the Hamiltonian and dissipative contexts. 相似文献
994.
J. Mecke 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2009,44(1):45-53
The paper deals with homogeneous random planar tessellations stable under iteration (random STIT tessellations). The length
distribution of the typical I-segment is already known in the isotropic case [8]. In the present paper, the anisotropic case
is treated. Then also the direction of the typical I-segment is of interest. The joint distribution of direction and length of the typical I-segment is evaluated.
As a first step, the corresponding joint distribution for the so-called typical remaining I-segment is derived.
Dedicated to the 80th birthday of Klaus Krickeberg 相似文献
995.
We consider a general Euler-Korteweg-Poisson system in R 3, supplemented with the space periodic boundary conditions, where the quantum hydrodynamics equations and the classical fluid dynamics equations with capillarity are recovered as particular examples. We show that the system admits infinitely many global-in-time weak solutions for any sufficiently smooth initial data including the case of a vanishing initial density - the vacuum zones. Moreover, there is a vast family of initial data, for which the Cauchy problem possesses infinitely many dissipative weak solutions, i.e. the weak solutions satisfying the energy inequality. Finally, we establish the weak-strong uniqueness property in a class of solutions without vacuum. In this paper we show that, even in presence of a dispersive tensor, we have the same phenomena found by De Lellis and Székelyhidi. 相似文献
996.
Minghua Min Yuyuan Shi Haiyou Ma Hongliang Huang Jiangao Shi Xiaoxue Chen 《Journal of Macromolecular Science: Physics》2015,54(4):411-423
The effects of addition of synthesized organic-suspension silver nanoparticles on the crystallization and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), UV-Vis absorption spectroscopy, polarized optical microscopy (POM), and thermal gravimetric analysis (TGA). The TEM images showed the average primary size of the as-synthesized silver nanoparticles, coated with a monolayer of the surfactants consisting of oleic acid and an alkylamine, was about 5 nm with narrow distribution, and that they were uniformly dispersed in n-heptane. PHBV/silver nanocomposites were prepared by melt mixing in an internal mixer and then injection molded into rectangle-shaped specimens by a labscale injection molding device. The coated silver nanoparticles showed a homogenuous dispersion in the PHBV matrix when the content of coated silver nanoparticles was about 1%. Both the DSC and POM data showed the efficient heterogeneous nucleation by the coated silver nanoparticles for facilitating PHBV crystallization. The thermal stability of the PHBV/silver nanocomposites improved with the increase in the content of the coated silver nanoparticles. 相似文献
997.
In this paper, we investigate a generalized nonautonomous nonlinear equation which describes the ultrashort optical pulse propagating in a nonlinear inhomogeneous fiber. By virtue of the generalized Darboux transformation, the first- and second-order rogue-wave solutions for the generalized nonautonomous nonlinear equation are obtained, under some variable–coefficient constraints. Properties of the first- and second-order rogue waves are graphically presented and analyzed: When the coefficients are all chosen as the constants, we can observe the some functions, the shapes of wave crests and troughs for the first- and second-order rogue waves change. Oscillating behaviors of the first- and second-order rogue waves are observed when the coefficients are the trigonometric functions. 相似文献
998.
In this article, we consider a continuous-time state-dependent jump linear system (SDJLS), a kind of stochastic hybrid system, with the presence of uncertainties in system parameters. In SDJLS, we consider that the transition rates of the underlying random jump process depend on the state variable. In particular, we assume the transition rates to have different values across suitably defined sets to which the state of the system belongs, and address a problem of robust stability and stabilization analysis. We obtain sufficient conditions for robust stability and state-feedback stabilization in terms of linear matrix inequalities (LMIs). We validate the obtained sufficient robust stability and stabilization conditions with numerical examples. 相似文献
999.
This paper mainly studies the problem of designing a hybrid state feedback D-admissible controller for a class of linear and nonlinear singular systems. Based on the relationship between singular discrete systems and singular delta operator systems, several necessary and sufficient conditions for a linear singular delta operator system to be D-admissible (i.e. regular, causal and all finite poles lie in a prescribed circular region) with different representations are derived. Then, the existence conditions and explicit expressions of a desirable D-admissible controller are given by means of matrix inequalities and strict linear matrix inequalities, respectively. We further extend the obtained results to singular delta operator systems with Lipschitz nonlinear perturbations, and the design methods of hybrid controller are presented for the nonlinear case as well. Finally, numerical examples as well as simulations are provided to illustrate the effectiveness of the theoretical outcomes obtained in the paper. 相似文献
1000.