全文获取类型
收费全文 | 66490篇 |
免费 | 4898篇 |
国内免费 | 3625篇 |
专业分类
化学 | 4592篇 |
晶体学 | 56篇 |
力学 | 2789篇 |
综合类 | 555篇 |
数学 | 9737篇 |
物理学 | 8828篇 |
综合类 | 48456篇 |
出版年
2024年 | 139篇 |
2023年 | 408篇 |
2022年 | 774篇 |
2021年 | 925篇 |
2020年 | 1001篇 |
2019年 | 835篇 |
2018年 | 855篇 |
2017年 | 1204篇 |
2016年 | 1355篇 |
2015年 | 1593篇 |
2014年 | 2982篇 |
2013年 | 2923篇 |
2012年 | 3502篇 |
2011年 | 4046篇 |
2010年 | 3311篇 |
2009年 | 3588篇 |
2008年 | 4033篇 |
2007年 | 5108篇 |
2006年 | 4559篇 |
2005年 | 4367篇 |
2004年 | 4008篇 |
2003年 | 3498篇 |
2002年 | 2981篇 |
2001年 | 2447篇 |
2000年 | 2018篇 |
1999年 | 1881篇 |
1998年 | 1485篇 |
1997年 | 1398篇 |
1996年 | 1250篇 |
1995年 | 1138篇 |
1994年 | 947篇 |
1993年 | 837篇 |
1992年 | 697篇 |
1991年 | 663篇 |
1990年 | 567篇 |
1989年 | 451篇 |
1988年 | 410篇 |
1987年 | 280篇 |
1986年 | 175篇 |
1985年 | 89篇 |
1984年 | 53篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 38篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
The turbulent flow in a compound meandering channel with a rectangular cross section is one of the most complicated turbulent flows, because the flow behaviour is influenced by several kinds of forces, including centrifugal forces, pressure‐driven forces and shear stresses generated by momentum transfer between the main channel and the flood plain. Numerical analysis has been performed for the fully developed turbulent flow in a compound meandering open‐channel flow using an algebraic Reynolds stress model. The boundary‐fitted coordinate system is introduced as a method for coordinate transformation in order to set the boundary conditions along the complicated shape of the meandering open channel. The turbulence model consists of transport equations for turbulent energy and dissipation, in conjunction with an algebraic stress model based on the Reynolds stress transport equations. With reference to the pressure–strain term, we have made use of a modified pressure–strain term. The boundary condition of the fluctuating vertical velocity is set to zero not only for the free surface, but also for computational grid points next to the free surface, because experimental results have shown that the fluctuating vertical velocity approaches zero near the free surface. In order to examine the validity of the present numerical method and the turbulent model, the calculated results are compared with experimental data measured by laser Doppler anemometer. In addition, the compound meandering open channel is clarified somewhat based on the calculated results. As a result of the analysis, the present algebraic Reynolds stress model is shown to be able to reasonably predict the turbulent flow in a compound meandering open channel. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
22.
23.
XU Xian-long 《广西民族大学学报》2007,(5)
论述了家族的概念及其特征、穆斯林家族社会组织的特点、穆斯林家族社会的信仰、穆斯林的习俗对家族的制度和维护,并就中国家族文化进行了讨论。 相似文献
24.
通过建立完善的教学质量监控机构、全程监控的教学质理管理制以及毕业生质量跟踪调查制度,使教学质量得到了很大的提高,为培养社会急需的、具有较高素质的技能型、应用性人才奠定了坚实的基础。 相似文献
25.
常金娥 《科技情报开发与经济》2007,17(30):238-239
论述了在教育领域中使用开源软件的必要性,介绍了几种应用于网络教育的开源软件,主要包括服务器软件、工作站软件和课程管理系统。 相似文献
26.
Jocelyn Sabatier Serge Poullain Patrick Latteux Jean Luc Thomas Alain Oustaloup 《Nonlinear dynamics》2004,38(1-2):383-400
Robust speed control of a low damped electromechanical system with backlash is studied, controlled load angular speed being not measured. The proposed control strategy combines a Luenberger observer (load angular speed and load torque disturbance estimations) and a robust CRONE controller. The observer provides estimation of the load angular speed and of the disturbance torque applied on the load. Through the computation of only three independent parameters (as many as a PID controller), the CRONE controller permits to ensure the robust speed control of the load in spite of plant parametric variations and speed observation errors. The proposed control strategy is applied to a four mass experimental test bench. 相似文献
27.
A new grid‐free upwind relaxation scheme for simulating inviscid compressible flows is presented in this paper. The non‐linear conservation equations are converted to linear convection equations with non‐linear source terms by using a relaxation system and its interpretation as a discrete Boltzmann equation. A splitting method is used to separate the convection and relaxation parts. Least squares upwinding is used for discretizing the convection equations, thus developing a grid‐free scheme which can operate on any arbitrary distribution of points. The scheme is grid free in the sense that it works on any arbitrary distribution of points and it does not require any topological information like elements, faces, edges, etc. This method is tested on some standard test cases. To explore the power of the grid‐free scheme, solution‐based adaptation of points is done and the results are presented, which demonstrate the efficiency of the new grid‐free scheme. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
28.
陈刚 《西北大学学报(自然科学版)》1995,(5)
运用深盆气圈闭的基本原理,综合分析了鄂尔多斯盆地下古生界天然气赋存的基本地质因素,论证并提出了盆地腹部下古生界深盆气圈闭的新认识,并依据盆地地质构造特征将其进一步划分为:西部前渊拗陷型和中东部复式向斜型两大深盆气赋存系统. 相似文献
29.
李梧生 《汕头大学学报(自然科学版)》1995,10(1):22-27
本文对一类对称的三次微分系统进行探讨,对每个奇点导出表示其鞍结性的型号公式。给出(K3)所有的六种全局相图。 相似文献
30.