全文获取类型
收费全文 | 2892篇 |
免费 | 383篇 |
国内免费 | 163篇 |
专业分类
化学 | 268篇 |
晶体学 | 35篇 |
力学 | 1579篇 |
综合类 | 51篇 |
数学 | 489篇 |
物理学 | 1016篇 |
出版年
2024年 | 11篇 |
2023年 | 21篇 |
2022年 | 30篇 |
2021年 | 43篇 |
2020年 | 75篇 |
2019年 | 46篇 |
2018年 | 67篇 |
2017年 | 81篇 |
2016年 | 102篇 |
2015年 | 54篇 |
2014年 | 121篇 |
2013年 | 247篇 |
2012年 | 152篇 |
2011年 | 127篇 |
2010年 | 110篇 |
2009年 | 138篇 |
2008年 | 166篇 |
2007年 | 180篇 |
2006年 | 196篇 |
2005年 | 172篇 |
2004年 | 139篇 |
2003年 | 144篇 |
2002年 | 96篇 |
2001年 | 93篇 |
2000年 | 89篇 |
1999年 | 106篇 |
1998年 | 81篇 |
1997年 | 83篇 |
1996年 | 70篇 |
1995年 | 65篇 |
1994年 | 44篇 |
1993年 | 30篇 |
1992年 | 51篇 |
1991年 | 48篇 |
1990年 | 22篇 |
1989年 | 12篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3438条查询结果,搜索用时 31 毫秒
21.
A theoretical model for the evaluation of the elastic modulus in particulate composites has been developed. The method takes into account the existence of a mesophase between main phases, which constitutes an important parameter influencing the behaviour of a composite material. This layer between the matrix and filler develops different physico-chemical properties from those of the constituent phases and variable ones along its thickness. The effect of the progressive variation of the elastic modulus of the mesophase on the modulus of the composite was estimated by applying various simple laws of variation. Convenient laws of variation were introduced, varying from a simple one, assuming a linear law, to a more refined one using a parabolic law. Experimental results with particulates, based on iron-filled epoxy composites, compared satisfactorily with other models. However, the model based on a parabolic law was superior to all others on physical grounds.List of symbols
E
elastic modulus
-
v
Poisson's ratio
-
volume fraction
-
r
radius
-
V
volume
-
K
bulk modulus
-
r
thickness of mesophase
-
parameter which depends on the sudden changes of the heat capacity for the filled and unfilled polymer C
p
f
and C
p
0
相似文献
22.
A full field solution, based on small deformation, three-dimensional elastic–plastic finite element analysis of the centrally cracked thin disk under mode I loading has been performed. The solution for the stresses under small-scale yielding and lo!cally fully plastic state has been compared with the HRR plane stress solution. At the outside of the 3D zone, within a distance of rσo/J=18, HRR dominance is maintained in the presence of a significant amount of compressive stress along the crack flanks. Ahead of this region, the HRR field overestimate the stresses. These results demonstrate a completely reversed state of stress in the near crack front compared to that in the plane strain case. The combined effect of geometry and finite thickness of the specimen on elastic–plastic crack tip stress field has been explored. To the best of our knowledge, such an attempt in the published literature has not been made yet. For the qualitative assessment of the results some of the field parameters have been compared to the available experimental results of K, gives a fair estimate of the crack opening stress near the crack front at a distance of order 10−2 in. On the basis of this analysis, the Linear Elastic Fracture Mechanics approach has been adopted in analyzing the fatigue crack extension experiments performed in the disk (Part II). 相似文献
23.
含夹杂复合材料宏观性能研究 总被引:10,自引:1,他引:10
本文综述并评价了有关含夹杂复合材料的有效弹性模量研究的代表性工作,包括自洽理论,微分法,Eshelby-Mori-Tanaka法,Hashin和Shtrikman的变分法等。指出上述理论由于没有充分考虑复合材料内部的微结构特征,如夹杂的形状、几何尺寸、分布和夹杂间的相互影响,在夹杂的体积份数较大,如大于0.3时已不能有效地预报复合材料的有效弹性模量,随后介绍了近来才发展起来的一种新方法─—相关函数积分法,理论与实验的结果的比较表明,该方法在夹杂体积份数较大时仍然有效。 相似文献
24.
Effective elastic moduli of two dimensional solids with distributed cohesive microcracks 总被引:1,自引:0,他引:1
Effective elastic properties of a defected solid with distributed cohesive micro-cracks are estimated based on homogenization of the Dugdale–Bilby–Cottrell–Swinden (Dugdale–BCS) type micro-cracks in a two dimensional elastic representative volume element (RVE).Since the cohesive micro-crack model mimics various realistic bond forces at micro-scale, a statistical average of cohesive defects can effectively represent the overall properties of the material due to bond breaking or crack surface separation in small scale. The newly proposed model is distinctive in the fact that the resulting effective moduli are found to be pressure sensitive. 相似文献
25.
Axisymmetric problem of a nonhomogeneous elastic layer 总被引:3,自引:0,他引:3
Summary The paper deals with a theoretical treatment of elastic behavior for a medium with nonhomogeneous materials property, which
is defined by the relation , i.e., shear modulus of elasticity G varies with the dimensionless axial coordinate by the power product form, arbitrarily. Fundamental differential equation for such nonhomogeneous medium has been already
proposed in [5]. It is given by a second-order partial differential equation. However, it was found that the fundamental equation
is not sufficient in general to solve several kinds of boundary-value problems. On the other hand, it is shown in the present
paper making use of the fundamental equations system for a nonhomogeneous medium, which has been proposed in our previous
paper [7], it is possible to solve axisymmetric problems for a thick plate (layer) subjected to an arbitrarily distributed
load or a concentrated load on its surfaces. Numerical calculations are carried out for several cases, taking into account
the variation of the nonhomogeneous parameter m. The numerical results for displacements stress and components are shown in graphical form.
Accepted for publication 25 March 1997 相似文献
26.
We propose an inverse method, using a circular disk in diametrical compression, for the simultaneous determination of two
elastic constants,E andv, from a single displacement map. Moiré interferometry combined with the phase-shifting technique provides a full-field displacement
field. An overdeterministic approach using the least-squares method is implemented to fit the experimentally determined displacements
to the theoretical solution. An implementation guideline is provided, considering the effects of accidental rigid-body motions,
random noise and imperfect position of the origin. Accuracy and repeatability of the proposed method are verified experimentally. 相似文献
27.
Single-walled carbon nanotubes (SWNTs) in crystalline bundles may exhibit a transition in which the cross-sections of tubes turn from perfectly circular to hexagonal, depending upon the tube diameter and externally applied pressure, and this structural instability leads to an abrupt change in the bulk elastic properties of SWNT bundles. This paper presents a hybrid atom/continuum model to study the bulk elastic properties of SWNT bundles, and the predicted characteristics of this structural instability agree well with the experimental observations available in the literature. Linearized bulk elastic properties of SWNT bundles with respect to a stable configuration are transversely isotropic and hence can be characterized by five independent elastic moduli. A complete set of these five moduli is predicted for the first time. It is found that the deformability of tube cross-sections play a dominant role in characterizing the transverse moduli. 相似文献
28.
29.
具有弹性支座杆件的动力稳定性研究 总被引:3,自引:0,他引:3
研究了杆件具有弹性支座时直杆的动力稳定性问题,推导出了杆件的临界频率和动力不稳定边界,分析了弹簧刚度和阻尼对杆件动力稳定性的影响,研究表明杆件的侧向刚度愈大其结构的动力稳定性愈好,阻尼对杆的振动起有利作用,并提出了在实际工程中减小杆件振动的一些措施. 相似文献
30.
In this paper, the dynamic interaction between two collinear cracks in a piezoelectric material plate under anti-plane shear
waves is investigated by using the non-local theory for impermeable crack surface conditions. By using the Fourier transform,
the problem can be solved with the help of two pairs of triple integral equations. These equations are solved using the Schmidt
method. This method is more reasonable and more appropriate. Unlike the classical elasticity solution, it is found that no
stress and electric displacement singularity is present at the crack tip. The non-local dynamic elastic solutions yield a
finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis.
The project supported by the Natural Science Foundation of Heilongjiang Province and the National Natural Science Foundation
of China(10172030, 50232030) 相似文献