全文获取类型
收费全文 | 11033篇 |
免费 | 1946篇 |
国内免费 | 837篇 |
专业分类
化学 | 2298篇 |
晶体学 | 86篇 |
力学 | 931篇 |
综合类 | 157篇 |
数学 | 4940篇 |
物理学 | 5404篇 |
出版年
2024年 | 14篇 |
2023年 | 111篇 |
2022年 | 241篇 |
2021年 | 305篇 |
2020年 | 332篇 |
2019年 | 364篇 |
2018年 | 358篇 |
2017年 | 438篇 |
2016年 | 475篇 |
2015年 | 380篇 |
2014年 | 552篇 |
2013年 | 983篇 |
2012年 | 623篇 |
2011年 | 727篇 |
2010年 | 657篇 |
2009年 | 662篇 |
2008年 | 736篇 |
2007年 | 670篇 |
2006年 | 619篇 |
2005年 | 531篇 |
2004年 | 458篇 |
2003年 | 483篇 |
2002年 | 439篇 |
2001年 | 365篇 |
2000年 | 338篇 |
1999年 | 303篇 |
1998年 | 218篇 |
1997年 | 240篇 |
1996年 | 182篇 |
1995年 | 160篇 |
1994年 | 126篇 |
1993年 | 87篇 |
1992年 | 76篇 |
1991年 | 67篇 |
1990年 | 55篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 53篇 |
1984年 | 34篇 |
1983年 | 19篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
A finite volume solver for the 2D depth‐integrated harmonic hyperbolic formulation of the mild‐slope equation for wave propagation is presented and discussed. The solver is implemented on unstructured triangular meshes and the solution methodology is based upon a Godunov‐type second‐order finite volume scheme, whereby the numerical fluxes are computed using Roe's flux function. The eigensystem of the mild‐slope equations is derived and used for the construction of Roe's matrix. A formulation that updates the unknown variables in time implicitly is presented, which produces a more accurate and reliable scheme than hitherto available. Boundary conditions for different types of boundaries are also derived. The agreement of the computed results with analytical results for a range of wave propagation/transformation problems is very good, and the model is found to be virtually paraxiality‐free. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
52.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
53.
In this paper, we examine a class of convex problems of Bolza type, involving a time delay in the state. It encompasses a variety of time-delay problems arising in the calculus of variations and optimal control. A duality analysis is carried out which, among other things, leads to a characterization of minimizers in terms of the Euler-Lagrange inclusion. The results obtained improve in significant respects on what is achievable by techniques previously employed, based on elimination of the time delay by introduction of an infinite-dimensional state space or on the method of steps. 相似文献
54.
Numerical analysis for stochastic age-dependent population equations with Poisson jumps 总被引:1,自引:0,他引:1
In this paper, stochastic age-dependent population equations with Poisson jumps are considered. In general, most of stochastic age-dependent population equations with jumps do not have explicit solutions, thus numerical approximation schemes are invaluable tools for exploring their properties. The main purpose of this paper is to develop a numerical Euler scheme and show the convergence of the numerical approximation solution to the true solution. 相似文献
55.
We consider a single machine scheduling problem with two min-sum objective functions: the sum of completion times and the sum of weighted completion times. We propose a simple polynomial time (1+(1/γ),1+γ)-approximation algorithm, and show that for γ>1, there is no (x,y)-approximation with 1<x<1+(1/γ) and 1<y<1+(γ-1)/(2+γ). 相似文献
56.
Karl Sigman 《Operations Research Letters》2007,35(5):581-583
In Mandelbaum and Yechiali [The conditional residual service time in the M/G/1 queue, http://www.math.tau.ac.il/∼uriy/publications (No. 30a), 1979] and in Fakinos [The expected remaining service time in a single-server queue, Oper. Res. 30 (1982) 1014-1018] a simple formula is derived for the (stationary) expected remaining service time in a M/G/1 queue, conditional on the number of customers in the system. We give a short new proof of the formula using Rate Conservation Law, and generalize to handle higher moments. 相似文献
57.
58.
We consider the M(t)/M(t)/m/m queue, where the arrival rate λ(t) and service rate μ(t) are arbitrary (smooth) functions of time. Letting pn(t) be the probability that n servers are occupied at time t (0≤ n≤ m, t > 0), we study this distribution asymptotically, for m→∞ with a comparably large arrival rate λ(t) = O(m) (with μ(t) = O(1)). We use singular perturbation techniques to solve the forward equation for pn(t) asymptotically. Particular attention is paid to computing the mean number of occupied servers and the blocking probability
pm(t). The analysis involves several different space-time ranges, as well as different initial conditions (we assume that at t = 0 exactly n0 servers are occupied, 0≤ n0≤ m). Numerical studies back up the asymptotic analysis.
AMS subject classification: 60K25,34E10
Supported in part by NSF grants DMS-99-71656 and DMS-02-02815 相似文献
59.
文章介绍2001年度国家自然科学奖二等奖获奖成果,在北京正负电子对撞机上采集了Ψ(2S)粒子大数据样本,开展了粲偶素物理的广泛研究:完成了6个粲偶素涉及质量,宽度和衰变化支比等大批重要参数的首次测量或高精度测量;通过对Ψ(2S)和J/Ψ强衰变性质的比较研究,观察到一系列反常现象,挑战现有理论图像。该项研究成果对量子色动力学的检验与发展具有重要意义,为我国粲偶素物理实验研究的继续发展并保持先进水平奠定坚实基础。 相似文献
60.
Online weighted flow time and deadline scheduling 总被引:1,自引:0,他引:1
Luca Becchetti Stefano Leonardi Alberto Marchetti-Spaccamela Kirk Pruhs 《Journal of Discrete Algorithms》2006,4(3):339
In this paper we study some aspects of weighted flow time. We first show that the online algorithm Highest Density First is an O(1)-speed O(1)-approximation algorithm for P|ri,pmtn|∑wiFi. We then consider a related Deadline Scheduling Problem that involves minimizing the weight of the jobs unfinished by some unknown deadline D on a uniprocessor. We show that any c-competitive online algorithm for weighted flow time must also be c-competitive for deadline scheduling. We then give an O(1)-competitive algorithm for deadline scheduling. 相似文献