全文获取类型
收费全文 | 27008篇 |
免费 | 4353篇 |
国内免费 | 3477篇 |
专业分类
化学 | 13465篇 |
晶体学 | 307篇 |
力学 | 1177篇 |
综合类 | 203篇 |
数学 | 2597篇 |
物理学 | 7077篇 |
无线电 | 10012篇 |
出版年
2024年 | 98篇 |
2023年 | 606篇 |
2022年 | 914篇 |
2021年 | 1005篇 |
2020年 | 1056篇 |
2019年 | 1004篇 |
2018年 | 883篇 |
2017年 | 912篇 |
2016年 | 1181篇 |
2015年 | 1494篇 |
2014年 | 1746篇 |
2013年 | 2047篇 |
2012年 | 2496篇 |
2011年 | 2455篇 |
2010年 | 1976篇 |
2009年 | 1881篇 |
2008年 | 1943篇 |
2007年 | 1694篇 |
2006年 | 1615篇 |
2005年 | 1370篇 |
2004年 | 1032篇 |
2003年 | 812篇 |
2002年 | 772篇 |
2001年 | 587篇 |
2000年 | 464篇 |
1999年 | 458篇 |
1998年 | 296篇 |
1997年 | 239篇 |
1996年 | 252篇 |
1995年 | 257篇 |
1994年 | 204篇 |
1993年 | 154篇 |
1992年 | 121篇 |
1991年 | 117篇 |
1990年 | 123篇 |
1989年 | 81篇 |
1988年 | 75篇 |
1987年 | 36篇 |
1986年 | 54篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 11篇 |
1973年 | 10篇 |
1971年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
In this paper, the (2 + 1)-dimensional Korteweg-de Vries system is symbolically investigated. By the bilinear method, the N-soliton solution is presented. Then, based on the Bäcklund transformation in bilinear form, a new Bäcklund transformation is obtained and new representation of the N-soliton solution is derived. A class of novel multi-soliton solutions are obtained by the new Bäcklund transformation and the availability of symbolic computation is demonstrated. 相似文献
992.
This work develops asymptotically optimal dividend policies to maximize the expected present value of dividends until ruin.Compound Poisson processes with regime switching are used to model the surplus and the switching(a continuous-time controlled Markov chain) represents random environment and other economic conditions.Assuming the switching to be fast varying together with suitable conditions,it is shown that the system has a limit that is an average with respect to the invariant measure of a related Markov chain.Under simple conditions,the optimal policy of the limit dividend strategy is a threshold policy.Using the optimal policy of the limit system as a guide,feedback control for the original surplus is then developed.It is demonstrated that the constructed dividend policy is asymptotically optimal. 相似文献
993.
In this paper, we bring into the scheduling field a general learning effect model where the actual processing time of a job is not only a general function of the total actual processing times of the jobs already processed, but also a general function of the job’s scheduled position. We show that the makespan minimization problem and the sum of the kth power of completion times minimization problem can be solved in polynomial time, respectively. We also show that the total weighted completion time minimization problem and the maximum lateness minimization problem can be solved in polynomial time under certain conditions. 相似文献
994.
A hierarchy of new nonlinear evolution equations, which are composed of the positive and negative AKNS flows, is proposed. On the basis of the theory of algebraic curves, the corresponding flows are straightened using the Abel-Jacobi coordinates. The meromorphic function ?, the Baker-Akhiezer vector , and the hyperelliptic curve Kn are introduced and, by using these, quasi-periodic solutions of the first three nonlinear evolution equations in the hierarchy are constructed according to the asymptotic properties and the algebro-geometric characters of ?, and Kn. 相似文献
995.
In this paper, under some assumptions on the flow with a low Mach number, we study the nonexistence of a global nontrivial subsonic solution in an unbounded domain Ω which is one part of a 3D ramp. The flow is assumed to be steady, isentropic and irrotational, namely, the movement of the flow is described by the potential equation. By establishing a fundamental a priori estimate on the solution of a second order linear elliptic equation in Ω with Neumann boundary conditions on Ω and Dirichlet boundary value at some point of Ω, we show that there is no global nontrivial subsonic flow with a low Mach number in such a domain Ω. 相似文献
996.
We present an explicit expression of the anomaly formula for the Cappell-Miller holomorphic torsion for Khler manifolds. 相似文献
997.
Let R ∈ Cn×n be a nontrivial involution, i.e., R2 = I and R ≠ ±I. A matrix A ∈ Cn×n is called R-skew symmetric if RAR = −A. The least-squares solutions of the matrix inverse problem for R-skew symmetric matrices with R∗ = R are firstly derived, then the solvability conditions and the solutions of the matrix inverse problem for R-skew symmetric matrices with R∗ = R are given. The solutions of the corresponding optimal approximation problem with R∗ = R for R-skew symmetric matrices are also derived. At last an algorithm for the optimal approximation problem is given. It can be seen that we extend our previous results [G.X. Huang, F. Yin, Matrix inverse problem and its optimal approximation problem for R-symmetric matrices, Appl. Math. Comput. 189 (2007) 482-489] and the results proposed by Zhou et al. [F.Z. Zhou, L. Zhang, X.Y. Hu, Least-square solutions for inverse problem of centrosymmetric matrices, Comput. Math. Appl. 45 (2003) 1581-1589]. 相似文献
998.
Considered herein is the orbital stability of floating periodic peakons for the Camassa–Holm (CH) equation, which describes one-dimensional surface waves at a free surface of shallow water under the influence of gravity. The floating periodic peakons shift up or down according to the change of the parameter. The result shows that the floating periodic peakons are orbitally stable and their stability is independent of the parameter in the CH equation. 相似文献
999.
结合偏最小二乘法和支持向量机的优缺点,提出基于偏最小二乘支持向量机的天然气消费量预测模型。首先,利用偏最小二乘法确定影响天然气消费量的新综合变量,建立以新综合变量为输入,天然气消费量为输出的支持向量机模型,对天然气消费量进行了预测;然后,与多元回归、偏最小二乘回归、普通支持向量机做误差检验比较,验证该方法的可行性与正确性。结果表明,此天然气消费量预测模型具有较高的精确度和应用价值。 相似文献
1000.
Several authors have studied the uniform estimate for the tail probabilities of randomly weighted sumsa.ud their maxima. In this paper, we generalize their work to the situation thatis a sequence of upper tail asymptotically independent random variables with common distribution from the is a sequence of nonnegative random variables, independent of and satisfying some regular conditions. Moreover. no additional assumption is required on the dependence structureof {θi,i≥ 1). 相似文献