全文获取类型
收费全文 | 12771篇 |
免费 | 849篇 |
国内免费 | 667篇 |
专业分类
化学 | 981篇 |
晶体学 | 18篇 |
力学 | 876篇 |
综合类 | 94篇 |
数学 | 5676篇 |
物理学 | 949篇 |
综合类 | 5693篇 |
出版年
2024年 | 45篇 |
2023年 | 128篇 |
2022年 | 184篇 |
2021年 | 206篇 |
2020年 | 260篇 |
2019年 | 264篇 |
2018年 | 251篇 |
2017年 | 326篇 |
2016年 | 342篇 |
2015年 | 349篇 |
2014年 | 517篇 |
2013年 | 898篇 |
2012年 | 656篇 |
2011年 | 648篇 |
2010年 | 498篇 |
2009年 | 703篇 |
2008年 | 689篇 |
2007年 | 783篇 |
2006年 | 725篇 |
2005年 | 676篇 |
2004年 | 556篇 |
2003年 | 472篇 |
2002年 | 469篇 |
2001年 | 396篇 |
2000年 | 402篇 |
1999年 | 342篇 |
1998年 | 289篇 |
1997年 | 267篇 |
1996年 | 221篇 |
1995年 | 217篇 |
1994年 | 171篇 |
1993年 | 148篇 |
1992年 | 175篇 |
1991年 | 136篇 |
1990年 | 119篇 |
1989年 | 125篇 |
1988年 | 104篇 |
1987年 | 84篇 |
1986年 | 62篇 |
1985年 | 46篇 |
1984年 | 48篇 |
1983年 | 28篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 47篇 |
1979年 | 36篇 |
1978年 | 25篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
1.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献
2.
3.
Florence Drui Emmanuel Franck Philippe Helluy Laurent Navoret 《Comptes Rendus Mecanique》2019,347(3):259-269
The over-relaxation approach is an alternative to the Jin–Xin relaxation method in order to apply the equilibrium source term in a more precise way. This is also a key ingredient of the lattice Boltzmann method for achieving second-order accuracy. In this work, we provide an analysis of the over-relaxation kinetic scheme. We compute its equivalent equation, which is particularly useful for devising stable boundary conditions for the hidden kinetic variables. 相似文献
4.
建立了整车8-DOF系统动力学模型,考虑了主动悬架控制,并增设了主动座椅控制,设计了车辆主动悬架系统的LQG控制器。基于Matlab仿真平台建立了整车8-DOF系统动力学仿真模型,对所得最优控制策略下的动态响应进行了仿真验证。仿真结果表明:为了改善人椅系统质心及车身质心的跳振性能需要在一定程度上弱化各轮轮胎动位移性能。从控制效能上来看,该最优控制器能够满足各行驶状态下对悬架性能的要求,改善了车辆的行驶平顺性。 相似文献
5.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. 相似文献
6.
地表覆盖内业解译是地理国情普查的一道重要工序。地理国情地表覆盖内业解译现存图斑平面位置精度不足、分类错误多种多样等普遍问题,问题突出典型。文中针对这些问题图文并茂、清晰明了的进行了说明,并从多方面分析问题产生的原因,提出加强对技术指标和采集原则的学习和理解,加强内业与外业的结合,充分发挥解译样本的作用等建议,以有效提高内业解译的质量。 相似文献
7.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
8.
钱虹凌 《山西大同大学学报(自然科学版)》2015,(1):16-19
变压器的优化设计是变压器设计的核心,根据变压器自身的特征,通常采用遗传算法进行优化。本系统通过采用改进GA的父代参与竞争的最优保存遗传算法进行优化,得到了几乎必然收敛的优化效果。 相似文献
9.
Galia Pozina Elizaveta I. Girshova Konstantin M. Morozov Konstantin A. Ivanov Anton Yu. Egorov Mikhail A. Kaliteevski 《Annalen der Physik》2019,531(6)
Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures. 相似文献
10.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献