全文获取类型
收费全文 | 1167篇 |
免费 | 290篇 |
国内免费 | 115篇 |
专业分类
化学 | 188篇 |
晶体学 | 2篇 |
力学 | 404篇 |
综合类 | 20篇 |
数学 | 194篇 |
物理学 | 764篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 46篇 |
2020年 | 40篇 |
2019年 | 35篇 |
2018年 | 34篇 |
2017年 | 51篇 |
2016年 | 47篇 |
2015年 | 55篇 |
2014年 | 74篇 |
2013年 | 94篇 |
2012年 | 53篇 |
2011年 | 89篇 |
2010年 | 77篇 |
2009年 | 77篇 |
2008年 | 78篇 |
2007年 | 84篇 |
2006年 | 92篇 |
2005年 | 71篇 |
2004年 | 69篇 |
2003年 | 57篇 |
2002年 | 42篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1572条查询结果,搜索用时 15 毫秒
51.
The existence and multiplicity of positive solutions to a periodic boundary value problem for nonlinear third-order ordinary differential equation are established, based on the zero point theorem concerning cone expansion and compression of order type. Our main approach is different from the previous papers on the existence of multiple positive solutions to the similar problem. 相似文献
52.
53.
本文采用离散元方法,研究了双轴压缩的颗粒体系在刚性边界约束下,局部剪切带的形成和发展过程,注重分析了细观的体积分数、配位数、颗粒旋转角度等参数以及力链结构形态的演变.并从颗粒体系jamming 相图中J点附近的边壁压强和配位数随体积分数的标度规律出发,分析了剪切带内外的体积分数和配位数的变化.结果表明:剪切带形成于颗粒体系的塑性变形开始阶段,此时体系发生剪胀,颗粒体积分数减小,颗粒体系抵抗旋转的能力降低,开始出现细小剪切带,随着轴向应变的继续,细小剪切带发生连接,最终导致贯穿性优势剪切带形成
关键词:
颗粒物质
力链
双轴压缩
剪切带 相似文献
54.
55.
56.
对时间成像理论进行简要研究. 利用电光相位调制器进行光脉冲压缩实验,并分别对基于电光相位调制和交叉相位调制的时间透镜组成的时间成像系统进行了仿真和讨论. 实验结果表明,基于电光相位调制的时间透镜组成的时间成像系统可以有效压缩光脉冲,但是该系统受到了孔径限制,压缩系数较小,分辨率较低. 进一步的仿真分析结果表明,基于交叉相位调制的时间透镜组成的时间成像系统不受孔径限制,能够获得更大的压缩系数和更高的分辨率,但是该系统的实现难度较大.
关键词:
光脉冲压缩
时间透镜
电光相位调制
交叉相位调制 相似文献
57.
Piotr Kowalczyk 《Transport in Porous Media》1993,11(3):281-295
The anatomy and geometry of the lung at the micro- and macroscopic level have been described briefly. A notion of lung parenchyma — a macroscopically continuous medium whose mechanical properties result from those of microstructural components — has been adapted. Simplifying assumptions propounded in the constitutive model have been discussed. Two phases have been distinguished in the medium: the solid phase — a highly deformable, nonlinearly elastic skeleton in the form of a thin-walled tissue structure on the micro-scale — and the fluid phase — perfect gas (air) filterating through the structure. General constitutive relations for both phases and their mechanical interactions have ben formulated. Further, the fundamental set of differential equations of the quasi-static coupled problem has been developed. Large deformations, material nonlinearities, and dependence of permeability on skeleton deformation have been included. Matrix formulation of the problem has been presented from the point of view of the finite element method. An implicit iterative time integration scheme has been proposed. The algorithm has been illustrated with results of simple numerical tests. 相似文献
58.
Summary Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.With 16 figures and 2 tables 相似文献
59.
移动荷载作用下地基动力分析的有限元方法 总被引:3,自引:0,他引:3
通过对地基动力问题的基本方程进行变换,把基本方程变换到随荷载移动的运动坐标系中,通过加权残数法推导了相应的单元刚度矩阵,从而建立了移动问题的有限元格式,并发现移动荷载问题的单元刚度矩阵是对相应静力问题单元刚度矩阵的修正,在静力单元刚度矩阵的主对角元素上增加与移动速度有关的项,即可得到移动问题有限元的单元刚度矩阵,这样就将动力学问题转化为“拟静力”问题处理。文中用移动问题有限元方法计算了地基的动力响应,并与解析解进行了对比,以说明本方法具有较好的精度。 相似文献
60.
A novel dynamic compressive experimental technique has been developed based on a split Hopkinson pressure bar. This new method
dynamically loads the ceramic specimen by two consecutive stress pulses. The first pulse determines the dynamic response of
the intact ceramic materiaal and then crushes the specimen, and the second pulse determines the dynamic compressive constitutive
behavior of the ceramic rubble. Precise pulse shaping ensures that the specimen deforms at nearly constant strain rates under
dynamic stress equilibrium during the loading by both stress pulses. Pulse shaping also controls the amplitudes of loading
pulses, the values of strain rates, the maximum strains in the rubble specimens, and the proper separation time between the
two loading pulses. The feasibility of the new technique is demonstrated by the experimental results obtained on an AD995
alumina. 相似文献