全文获取类型
收费全文 | 50819篇 |
免费 | 6121篇 |
国内免费 | 4868篇 |
专业分类
化学 | 13263篇 |
晶体学 | 983篇 |
力学 | 10493篇 |
综合类 | 772篇 |
数学 | 20941篇 |
物理学 | 15356篇 |
出版年
2024年 | 102篇 |
2023年 | 537篇 |
2022年 | 916篇 |
2021年 | 1126篇 |
2020年 | 1439篇 |
2019年 | 1289篇 |
2018年 | 1281篇 |
2017年 | 1734篇 |
2016年 | 2007篇 |
2015年 | 1523篇 |
2014年 | 2555篇 |
2013年 | 3801篇 |
2012年 | 2888篇 |
2011年 | 3453篇 |
2010年 | 2974篇 |
2009年 | 3327篇 |
2008年 | 3248篇 |
2007年 | 3272篇 |
2006年 | 2969篇 |
2005年 | 2751篇 |
2004年 | 2346篇 |
2003年 | 2156篇 |
2002年 | 1917篇 |
2001年 | 1591篇 |
2000年 | 1477篇 |
1999年 | 1322篇 |
1998年 | 1245篇 |
1997年 | 1024篇 |
1996年 | 853篇 |
1995年 | 716篇 |
1994年 | 641篇 |
1993年 | 531篇 |
1992年 | 531篇 |
1991年 | 418篇 |
1990年 | 313篇 |
1989年 | 254篇 |
1988年 | 210篇 |
1987年 | 156篇 |
1986年 | 117篇 |
1985年 | 146篇 |
1984年 | 137篇 |
1983年 | 67篇 |
1982年 | 91篇 |
1981年 | 70篇 |
1980年 | 42篇 |
1979年 | 65篇 |
1978年 | 46篇 |
1977年 | 50篇 |
1976年 | 20篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
设$ G $ 是一个$ n $ 阶$ k $ 圈图, $ k $ 圈图为边数等于顶点数加$ k-1 $ 的简单连通图。$ \mu_{1}(G) $ 、$ \mu_{2}(G) $ 分别记为图$ G $ 的Laplace矩阵的最大特征值和次大特征值, 图$ G $ 的Laplace分离度定义为$ S_{L}(G)=\mu_{1}(G)-\mu_{2}(G) $ 。本文研究了给定阶数的$ k $ 圈图的最大Laplace分离度, 并刻画了相应的极图, 其结果推广了已有当$ k=1, 2, 3 $ 时的结论。 相似文献
982.
针对传统的DEA模型在评估过程中并未考虑决策者对相关指标权重的偏好,将最优最差方法(BWM)嵌入到传统DEA模型中,基于决策者偏好排序的判断矩阵,构建一种含有偏好的DEA-BWM评价方法。首先在保持传统DEA方法的优势基础上,构建了CCR-BWM评价模型对各DMU进行评价。同时考虑为了便于各决策单元在统一权重基础上相互比较,构建了CSW-BWM公共权重模型。另外考虑决策单元自评和互评,构建了NCE-BWM中立型交叉效率。然后采用min-max方法分别将上述三种多目标评价模型转换为单目标线性规划进行求解。最后,选择一组算例对三种模型的有效性与合理性进行验证。 相似文献
983.
We consider the decay rate of energy of the 1D damped original nonlinear wave equation. We first construct a new energy function. Then, employing the perturbed energy method and the generalized Young’s inequality, we prove that, with a general growth assumption on the nonlinear damping force near the origin, the decay rate of energy is governed by a dissipative ordinary differential equation. This allows us to recover the classical exponential, polynomial, or logarithmic decay rate for the linear, polynomial or exponentially degenerating damping force near the origin, respectively. Unlike the linear wave equation, the exponential decay rate constant depends on the initial data, due to the nonlinearity. 相似文献
984.
Shutao Zhang & Yazhou Han 《分析论及其应用》2022,38(2):178-203
For conformal Hardy-Littlewood-Sobolev(HLS) inequalities [22] and reversed conformal HLS inequalities [8] on $\mathbb{S}^n,$ a new proof is given for the attainability
of their sharp constants. Classical methods used in [22] and [8] depends on rearrangement inequalities. Here, we use the subcritical approach to construct the extremal
sequence and circumvent the blow-up phenomenon by renormalization method. The
merit of the method is that it does not rely on rearrangement inequalities. 相似文献
985.
986.
This paper investigates input-to-state stability (ISS) and integral-input-to-state stability (iISS) of nonlinear impulsive systems with hybrid delayed impulses. Based on Lyapunov method, some sufficient conditions ensuring ISS and iISS of impulsive systems are obtained, where the time derivative of Lyapunov function is indefinite, and the hybrid effects of delayed impulses are also fully considered. It is shown that the impulsive system is ISS provided that the combined action of time delay existing in impulses, continuous dynamic, and the cumulative strength of hybrid impulses satisfies some conditions, even if the hybrid delayed impulses play a destabilizing effect on ISS. Examples and their simulations are presented to illustrate the applicability of the proposed results. 相似文献
987.
Linear systems whose associated block Jacobi iteration matrixB is weakly cyclic generated by the cyclic permutation = (1,2,...,
p
) in the spirit of Li and Varga are considered. Regions of convergence for the corresponding blockp-cyclic SOR method are derived and the exact convergence domains for real spectra, (B
p
), of the same sign are obtained. Moreover, analytical expressions for two special cases forp = 5 are given and numerical results are presented confirming the theory developed. The tools used for this work are mainly from complex analysis and extensive use of (asteroidal) hypocycloids in the complex plane is made to produce our results.This work was supported in part by AFOSR grant F49620-92-J-0069 and NSF grant 9202536-CCR. 相似文献
988.
Jean-Claude Yakoubsohn 《Numerical Algorithms》1995,9(2):223-244
We give a new theorem concerning the convergence of Newton's method to compute an approximate zero of a system of equations. In this result, the constanth
0=0.162434... appears, which plays a fundamental role in the localization of good initial points for the Newton iteration. We apply it to the determination of an appropriate discretization of the time interval in the classical homotopy method. 相似文献
989.
Xiaopu Yan 《Numerical Algorithms》1995,10(2):245-260
Multistep methods for the differential/algebraic equations (DAEs) in the form of
相似文献
990.
Schock (Ref. 1) considered a general a posteriori parameter choice strategy for the Tikhonov regularization of the ill-posed operator equationTx=y which provides nearly the optimal rate of convergence if the minimal-norm least-squares solution
belongs to the range of the operator (T
*
T)
v
, o<v1. Recently, Nair (Ref. 2) improved the result of Schock and also provided the optimal rate ifv=1. In this note, we further improve the result and show in particular that the optimal rate can be achieved for 1/2v1.The final version of this work was written while M. T. Nair was a Visiting Fellow at the Centre for Mathematics and Its Applications, Australian National University, Canberra, Australia. The work of S. George was supported by a Senior Research Fellowship from CSIR, India. 相似文献
|