全文获取类型
收费全文 | 5786篇 |
免费 | 570篇 |
国内免费 | 526篇 |
专业分类
化学 | 419篇 |
晶体学 | 5篇 |
力学 | 399篇 |
综合类 | 105篇 |
数学 | 4242篇 |
物理学 | 1712篇 |
出版年
2023年 | 45篇 |
2022年 | 64篇 |
2021年 | 69篇 |
2020年 | 109篇 |
2019年 | 117篇 |
2018年 | 105篇 |
2017年 | 127篇 |
2016年 | 159篇 |
2015年 | 124篇 |
2014年 | 213篇 |
2013年 | 475篇 |
2012年 | 276篇 |
2011年 | 329篇 |
2010年 | 279篇 |
2009年 | 380篇 |
2008年 | 409篇 |
2007年 | 389篇 |
2006年 | 402篇 |
2005年 | 307篇 |
2004年 | 274篇 |
2003年 | 261篇 |
2002年 | 250篇 |
2001年 | 224篇 |
2000年 | 199篇 |
1999年 | 205篇 |
1998年 | 168篇 |
1997年 | 123篇 |
1996年 | 132篇 |
1995年 | 72篇 |
1994年 | 76篇 |
1993年 | 63篇 |
1992年 | 44篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 24篇 |
1988年 | 41篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 33篇 |
1984年 | 34篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1970年 | 3篇 |
排序方式: 共有6882条查询结果,搜索用时 15 毫秒
181.
182.
The edge‐percolation and vertex‐percolation random graph models start with an arbitrary graph G, and randomly delete edges or vertices of G with some fixed probability. We study the computational complexity of problems whose inputs are obtained by applying percolation to worst‐case instances. Specifically, we show that a number of classical ‐hard problems on graphs remain essentially as hard on percolated instances as they are in the worst‐case (assuming ). We also prove hardness results for other ‐hard problems such as Constraint Satisfaction Problems and Subset‐Sum, with suitable definitions of random deletions. Along the way, we establish that for any given graph G the independence number and the chromatic number are robust to percolation in the following sense. Given a graph G, let be the graph obtained by randomly deleting edges of G with some probability . We show that if is small, then remains small with probability at least 0.99. Similarly, we show that if is large, then remains large with probability at least 0.99. We believe these results are of independent interest. 相似文献
183.
基于状态空间模型的许多传统滤波算法都基于Rn空间中的高斯分布模型,但当状态向量中包含角变量或方向变量时,难以达到理想的效果。针对J.T.Horwood等提出的nS?R流形上的Gauss Von Mises(GVM)多变量概率密度分布,扩展了狄拉克混合逼近方法,给出了联合分布的GVM逼近方法,推导了后验分布的GVM参数计算公式,设计了量测更新状态估计算法。将J.T.Horwood等的时间更新算法与所提出的量测更新算法相结合,可实现基于GVM分布的递推贝叶斯滤波器(GVMF)。仿真结果表明,当状态向量符合GVM概率分布模型时,GVMF对角变量的估计明显优于传统的扩展卡尔曼滤波器。 相似文献
184.
G. Apreutesei 《Journal of Difference Equations and Applications》2013,19(5):511-527
The continuous dependence on data is studied for a class of second order difference equations governed by a maximal monotone operator A in a Hilbert space. A nonhomogeneous term f appears in the equation and some bilocal boundary conditions a, b are added. One shows that the function which associates to {a, b, A, f} the solution of this boundary value problem is continuous in a specific sense. One uses the convergence of a sequence of operators in the sense of the resolvent. The problem studied here is the discrete variant of a problem from the continuous case. 相似文献
185.
186.
We study the frequency chirping signals arising from spontaneously excited toroidial Alfvén eigenmode (TAE) waves that are being driven by an inverted energetic particle distribution whose free energy is tapped from the generic particle/wave resonance interaction. Initially a wave is excited inside the Alfvén gap with a frequency determined from the linear tip model of Rosenbluth, Berk and Van dam (RBV) [1]. Hole/clumps structures are formed and are observed to chirp towards lower energy states. We find that the chirping signals from clump enter the Alfvén continuum which eventually produce more rapid chirping signals. The accuracy of the adiabatic approximation for the mode evolution is tested and verified by demonstrating that a WKB-like decomposition of the time response for the field phase and amplitude agree with the data. Plots of the phase space structure correlate well with the chirping dependent shape of the separatrix structure. A novel aspect of the simulation is that it performed close to the wave frame of the phase space structure, which enables the numerical time step to remain the same during the simulation, independent of the rest frame frequency. 相似文献
187.
Alexander Gluhovsky Christopher Tong 《Communications in Nonlinear Science & Numerical Simulation》2012,17(7):3112-3113
Extensive prior literature (not referenced in the paper) on links between mechanical gyrostats and nonlinear dynamical systems with strange attractors is called to the readers’ attention. 相似文献
188.
Farshad Merrikh-Bayat 《Communications in Nonlinear Science & Numerical Simulation》2012,17(4):1852-1861
Oustaloup recursive approximation (ORA) is widely used to find a rational integer-order approximation for fractional-order integrators and differentiators of the form sv, v ∈ (−1, 1). In this method the lower bound, the upper bound and the order of approximation should be determined beforehand, which is currently performed by trial and error and may be inefficient in some cases. The aim of this paper is to provide efficient rules for determining the suitable value of these parameters when a fractional-order PID controller is used in a stable linear feedback system. Two numerical examples are also presented to confirm the effectiveness of the proposed formulas. 相似文献
189.
We analyze the emission spectrum of a single organic quantum dot coupled to a microcavity in the strong coupling regime. We take into account non-linearities arising from both exciton–exciton interactions and the Pauli exclusion principle. We apply the recently developed Pade approximation for regular truncation of Green functions to calculate the emission spectrum. We show that as the number of excitations in the quantum dot increases the Rabi doublet evolves into a more complicated triplet structure. 相似文献
190.