全文获取类型
收费全文 | 2111篇 |
免费 | 245篇 |
国内免费 | 213篇 |
专业分类
化学 | 426篇 |
晶体学 | 5篇 |
力学 | 1041篇 |
综合类 | 24篇 |
数学 | 416篇 |
物理学 | 657篇 |
出版年
2023年 | 14篇 |
2022年 | 36篇 |
2021年 | 58篇 |
2020年 | 54篇 |
2019年 | 35篇 |
2018年 | 42篇 |
2017年 | 89篇 |
2016年 | 100篇 |
2015年 | 67篇 |
2014年 | 102篇 |
2013年 | 158篇 |
2012年 | 122篇 |
2011年 | 136篇 |
2010年 | 100篇 |
2009年 | 126篇 |
2008年 | 126篇 |
2007年 | 136篇 |
2006年 | 123篇 |
2005年 | 102篇 |
2004年 | 94篇 |
2003年 | 92篇 |
2002年 | 86篇 |
2001年 | 64篇 |
2000年 | 76篇 |
1999年 | 52篇 |
1998年 | 49篇 |
1997年 | 32篇 |
1996年 | 44篇 |
1995年 | 36篇 |
1994年 | 36篇 |
1993年 | 35篇 |
1992年 | 24篇 |
1991年 | 26篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 3篇 |
1967年 | 1篇 |
1957年 | 5篇 |
排序方式: 共有2569条查询结果,搜索用时 15 毫秒
61.
圆柱壳的动态塑性屈曲问题的研究主要是集中在屈曲模态方面,至于屈曲的临介载荷与临介时时间则研究的较少,SHPB用于研究材料在高应变率下动态力学性能已为大家所熟悉,但用于研究结构的动态屈曲则未见报道,本文利用一装置对柱壳的动态塑性屈曲进行了实验研究,测出了壳体屈曲过程的载荷,轴向缩短量与时间的关系曲线,得到屈曲时的临介载荷与临介时间,同时发现壳体屈曲变形的一些规律并与静态实验的结果进行了比较,为理论分 相似文献
62.
63.
利用模态综合法分析车辆与桥梁之间的相互作用时,合理地构造桥梁的插值振型函数可以大幅提高计算精度.其中,分段三次Hermite插值函数和三次样条插值函数较为常用.为研究二者的异同,以简支梁桥为例分别采用这两种插值函数构造结构梁单元模型的一维插值振型函数和板单元模型的二维插值振型函数.基于以上两类插值振型函数,分析单自由度簧上质量匀速过桥时,桥梁的跨中位移、跨中梁底正应力和轮-桥接触力时程响应.结果表明:无论是一维问题还是二维问题,由三次样条插值法构造的插值振型函数与结构的实际振型较为吻合,计算结果具有较高的收敛性和精度.而要达到相同的精度,分段三次Hermite插值法则须加密单元网格,但其误差仅存在于独立网格内,不会累积放大. 相似文献
64.
弹性圆柱壳冲击扭转屈曲的突变模型 总被引:2,自引:0,他引:2
本文将突变理论用于处理冲击载荷下弹性结构的屈曲问题,文中建立了结构冲击屈曲的突变准则,认为临界阶跃载荷位于所提出突变系统的分叉集之中,并由此对两端固支的弹性圆柱壳扭转屈曲进行了分析,给出了不同初缺陷时的临界阶跃扭矩计算公式,通过对临界静态扭矩的计算,表明临界阶跃扭矩小于临界静态扭矩. 相似文献
65.
ANALYTICAL EVALUATION OF PERMANENT DEFLECTION OF A THIN CIRCULAR PLATE STRUCK NORMALLY AT ITS CENTER BY A PROJECTILE 总被引:1,自引:0,他引:1
Chen Liebin Yang Jialing 《Acta Mechanica Solida Sinica》2007,20(2):117-122
The permanent deflection of a thin circular plate struck normally at its center by a projectile is studied by an approximate theoretical analysis,FEM simulation and experiment.The plate made of rate sensitive and strain-hardening material undergoes serious local deformation but is not perforated during the impact.The theoretical analysis is based on an energy approach, in which the Cowper-Symonds equation is used for the consideration of strain rate sensitive effects and the parameters involved are determined with the aid of experimental data.The maximum permanent deflections predicted by the theoretical model are compared with those of FEM sim- ulation and published papers obtained both by theory and experiment,and good agreement is achieved for a wide range of thickness of the plates and initial impact velocities. 相似文献
66.
射弹倾斜撞击带盖板炸药引发爆轰的条件 总被引:10,自引:0,他引:10
用二级轻气炮发射圆柱形、球形钢射弹以不同的角度撞击带不同厚度钢盖板的 TNT/RDX(40/60)炸药,得到了不同条件下引发炸药爆轰的阈值射弹速度。可以用vd~ (1/2)=(1 +k)[A+Bh/(dcos)]描述临界引爆条件。对于带钢盖板的TNT/RDX(40/60)炸药,A= 3.33.B=5.34;圆柱形平头射弹撞击,k/75,球形射弹撞击,k0.5+0.2(1/cos-1)。由 此,本研究将Jacobs 引爆判据推广到了斜碰撞条件。 相似文献
67.
The heat generated from dissipative mechanisms during shearing and opening dominated dynamic fracture of polymethyl methacrylate
and polycarbonate was measured with a remote sensing technique that utilizes the detection of infrared radiation. Significant
heating was detected for both materials and both modes of fracture. In the shear dominated experiments, the temperature increase
at the crack tip in polymethyl methacrylate was 85 K, the approximate increase necessary to reach the glass transition temperature.
An adiabatic shear band followed by a dynamically propagating crack were observed during the shear dominated experiments using
polycarbonate. The recorded shear band temperature increase was 45 K. This was followed by an additional 100 K temperature
increase from the ensuing crack, raising the temperature above glass transition. The maximum temperature increase recorded
for the opening mode experiments was 55 K for polymethyl methacrylate and 105 K for polycarbonate. The results of this study
show that temperature effects are significant during the dynamic fracture of polymers. The effects are especially important
in the shear dominated case where local temperatures approach or exceed the polymer glass transition temperature. 相似文献
68.
Nix and Gao established an important relation between the microindentation hardness and indentation depth. Such a relation
has been verified by many microindentation experiments (indentation depths in the micrometer range), but it does not always
hold in nanoindentation experiments (indentation depths approaching the nanometer range). Indenter tip radius effect has been
proposed by Qu et al. and others as possibly the main factor that causes the deviation from Nix and Gao's relationship. We
have developed an indentation model for micro- and nanoindentation, which accounts for two indenter shapes, a sharp, conical
indenter and a conical indenter with a spherical tip. The analysis is based on the conventional theory of mechanism-based
strain gradient plasticity established from the Taylor dislocation model to account for the effect of geometrically necessary
dislocations. The comparison between numerical result and Feng and Nix's experimental data shows that the indenter tip radius
effect indeed causes the deviation from Nix-Gao relation, but it seems not be the main factor.
The project supported by the National Natural Science Foundation of China (10121202) and the Ministry of Education of China
(20020003023) 相似文献
69.
Yu. I. Meshcheryakov A. K. Divakov N. I. Zhigacheva M. M. Myshlyaev 《Journal of Applied Mechanics and Technical Physics》2007,48(6):887-896
Shock tests of two lots of a 1420 aluminum-lithium alloy are performed. The mean grain size is 24 μm in the first lot and
1.6 μm in the second lot obtained by the method of equal-channel angular pressing. Two characteristics of dynamic strength
of the material were determined in experiments on the high-velocity impact of flat samples: threshold of dynamic stability
with respect to compression on the fore front of the compression pulse and spall strength of the material. The materials of
both types have an identical threshold of dynamic stability with respect to compression, whereas the spall strength of the
microcrystalline alloy is 20% greater than the spall strength of the polycrystalline alloy. The reason is the consumption
of energy on structure formation in the coarse-grain material in passing to a larger-scale structural level (in the case with
a fine-grain material, such a structure is available in the initial state). The experiments reveal the presence of a second
plastic front whose amplitude is approximately 10% of the first plastic front.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 135–146, November–December, 2007. 相似文献
70.