全文获取类型
收费全文 | 837篇 |
免费 | 41篇 |
国内免费 | 20篇 |
专业分类
化学 | 106篇 |
晶体学 | 2篇 |
力学 | 510篇 |
综合类 | 4篇 |
数学 | 56篇 |
物理学 | 220篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 20篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 17篇 |
2016年 | 34篇 |
2015年 | 24篇 |
2014年 | 56篇 |
2013年 | 35篇 |
2012年 | 30篇 |
2011年 | 51篇 |
2010年 | 46篇 |
2009年 | 51篇 |
2008年 | 60篇 |
2007年 | 46篇 |
2006年 | 52篇 |
2005年 | 43篇 |
2004年 | 59篇 |
2003年 | 46篇 |
2002年 | 34篇 |
2001年 | 20篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有898条查询结果,搜索用时 0 毫秒
81.
Jialai Wang 《Journal of the mechanics and physics of solids》2004,52(4):891-905
An improved method based on the first-order shear deformable plate theory is developed to calculate the energy release rate and stress intensity factor for a crack at the interface of a bi-layer structure. By modeling the uncracked region of the structure as two separate Reissner-Mindlin plates bonded perfectly along the interface, this method is able not only to take into account the shear deformation in the cracked region, but also to capture the shear deformation in the uncracked region of the structure. A closed form solution of energy release rate and mode decomposition at the interface crack is obtained for a general loading condition, and it indicates that the energy release rate and stress intensity factor are determined by two independent loading parameters. Compared to the approach based on the classical plate theory, the proposed method provides a more accurate prediction of energy release rate as well as mode decomposition. The computational procedures introduced are relatively straightforward, and the closed form solution can be used to predict crack growth along the layered structures. 相似文献
82.
探讨了一种能够揭示三维复合型断裂现象并能记录这些现象的三维复合型断裂研究的实验方法,用此方法完成了LC4-CS航空结构铝合金不同厚度紧凑拉伸试样的I+Ⅱ复合型断裂试验。结果表明:此方法能够简便地确定出复合型裂纹的起裂载荷、破坏载荷、裂尖张开位移、滑移位移和起裂角,基本解决三维复合型断裂研究所需实验数据问题。同时发现此种材料试样的承载能力和超裂方向的确具有明显的厚度效应。 相似文献
83.
F. D. Fischer J. Predan O. Kolednik N. K. Simha 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(2-3):95-112
The material forces concept has become an elegant tool in continuum mechanics for the calculation of the thermodynamic driving
force of a defect. Based on this concept, we have recently shown that inhomogeneities essentially shield or anti-shield crack
tips from applied far-field stresses. The goal of this paper is to illustrate this by considering the model example of a crack
in a CT-type specimen that contains a bimaterial interface. The crack driving force is calculated as the sum of the far-field
driving force and the crack-tip shielding or anti-shielding. Several cases of inhomogeneity in either thermal or elastic properties
are considered. Rather simple hand calculations are provided in addition to numerical results to illustrate the advantages
of using the material forces concept. 相似文献
84.
A number of plane stress numerical analyses of the mode I elastoplastic fracture mechanics problem have been performed in the past using the Huber–Mises yield criterion. This study employs instead the Tresca yield condition using an incremental theory of plasticity for a stationary crack. A commercial finite element program is used to solve the opening mode of fracture problem (mode I) for a square plate containing a central crack under generalized plane stress loading conditions. A biaxial uniform tensile traction is applied to the edges of a thin plate composed of a linear elastic non-work hardening material under small strain assumptions. The finite element results are compared with the analytical predictions of the Dugdale plastic strip model for a crack in an infinite plate subject to a biaxial uniform load at infinity. 相似文献
85.
In this paper the Mode-I elastodynamic problem of a crack propagating in an orthotropic medium is studied under the condition that the matrix of elastodynamic coefficients has repeated eigenvalues. It is shown that the crack is constrained in an elastodynamic state which is defined through a compulsory condition coupling its velocity with the elastic parameters of the orthotropic medium. The dynamic stress and displacement components ahead of the crack tip as well as the energy release rate are explicitly obtained. 相似文献
86.
Considering a cohesive zone ahead of the crack tip, the linear elastic crack problem under Mode I, Mode II or mixed-mode conditions is formulated in an elliptic coordinate system, so that the cohesive surfaces are conveniently represented by straight line segments. It is shown that the displacement and stress fields around the crack tip and the cohesive zone, expressed in terms of elliptic coordinates, have a simple mathematical form, which does not contain a stress singularity at the crack tip due to the existence of the cohesive zone. 相似文献
87.
This work studies the asymptotic stress and displacement fields near the tip of a stationary crack in an elastic–plastic nonhomogeneous material with the emphasis on the effect of material nonhomogeneities on the dominance of the crack tip field. While the HRR singular field still prevails near the crack tip if the material properties are continuous and piecewise continuously differentiable, a simple asymptotic analysis shows that the size of the HRR dominance zone decreases with increasing magnitude of material property gradients. The HRR field dominates at points that satisfy |α−1 ∂α/∂xδ|1/r, |α−1 ∂2α/(∂xδ ∂xγ)|1/r2, |n−1 ∂n/∂xδ|1/[r|ln(r/A)|] and |n−1 ∂2n/(∂xδ ∂xγ)|1/[r2|ln(r/A)|], in addition to other general requirements for asymptotic solutions, where α is a material property in the Ramberg–Osgood model, n is the strain hardening exponent, r is the distance from the crack tip, xδ are Cartesian coordinates, and A is a length parameter. For linear hardening materials, the crack tip field dominates at points that satisfy |Etan−1 ∂Etan/∂xδ|1/r, |Etan−1 ∂2Etan/(∂xδ ∂xγ)|1/r2, |E−1 ∂E/∂xδ|1/r, and |E−1 ∂2E/(∂xδ ∂xγ)|1/r2, where Etan is the tangent modulus and E is Young’s modulus. 相似文献
88.
A set of cleavage experiments with strip-shaped single-crystal silicon specimens subjected to three-point bending is reported. The experiments enabled examination of the relationships between the dynamic energy release rate, the velocity, the orientation-dependent cleavage energy, and the cleavage plane of propagation.Dynamic crack propagation experiments show that when a [0 0 1] silicon single crystal is fractured under three-point bending at ‘parallel’ velocity (directly measured at the bottom surface of the specimen) of up to , it prefers to cleave along the vertical (1 1 0) plane, while when the specimen is fractured under the same conditions but at a velocity higher than , it cleaves along the inclined (1 1 1) plane. At intermediate velocities, the crack will deflect from the (1 1 0) plane to the (1 1 1) plane. Crack velocity was determined by the initial notch length. The local (calculated) velocity of deflection between the cleavage planes ranges from , for a crack propagating on the (1 1 0) plane in the direction, to about , for a crack on the (1 1 0) plane, but in the [0 0 1] direction.It is suggested that the cause of the deflection phenomenon is the anisotropic, velocity-dependent cleavage energy, resulted phonon radiation caused by anisotropic, velocity-dependent lattice vibrations. We have studied the effect of material properties and propose selection criteria to explain the deflection phenomenon: the crack will deflect to the plane of least-energy, for which G−Γi(V)=max, or to the plane with maximum crack tip velocity, Vi(Γ)=max. 相似文献
89.
Conventional electrospray ionization mass spectrometry (ESI-MS) is widely used for analysis of solution samples. The development of solid-substrate ESI-MS allows direct ionization analysis of bulky solid samples. In this study, we developed pipette-tip ESI-MS, a technique that combines pipette tips with syringe and syringe pump, for direct analysis of herbal powders, another common form of samples. We demonstrated that various herbal powder samples, including herbal medicines and food samples, could be readily online extracted and analyzed using this technique. Various powder samples, such as Rhizoma coptidis, lotus plumule, great burdock achene, black pepper, Panax ginseng, roasted coffee beans, Fructus Schisandrae Chinensis and Fructus Schisandrae Sphenantherae, were analyzed using pipette-tip ESI-MS and quality mass spectra with stable and durable signals could be obtained. Both positive and negative ion modes were attempted and various compounds including amino acids, oligosaccharides, glycosides, alkaloids, organic acids, ginosensides, flavonoids and lignans could be detected. Principal component analysis (PCA) based on the acquired mass spectra allowed rapid differentiation of closely related herbal species. 相似文献
90.
Kumazawa T Hasegawa C Uchigasaki S Lee XP Suzuki O Sato K 《Journal of chromatography. A》2011,1218(18):2521-2527
Solid-phase extraction (SPE) using micropipette tips is a useful technique to prepare samples prior to mass spectrometry. However, most commercial SPE tips have loading capacities that are insufficient for quantitative determination. In this paper, we describe a rapid method for quantitative microanalysis of five phenothiazine derivatives, chlorpromazine, levomepromazine, promazine, promethazine and trimeprazine, using a recently introduced C(18) monolithic silica SPE tip, the MonoTip C(18), for extraction from human plasma. The drugs could be extracted within 5 min from 0.1-mL plasma samples, eluted with methanol, and the eluate injected directly into a gas chromatograph prior to mass spectrometry analysis. Only 0.7 mL of solvent was required for each step of the extraction process. The recoveries of the five phenothiazines spiked into plasma were 91-95% and the limits of quantification for each drug were between 0.25 and 2.0 ng/0.1 mL. The maximum intra- and inter-day coefficient of variation was 11%. The validated method was successfully used to quantify the plasma concentration of levemepromazine in a human subject after oral administration of the drug. This new method is expected to have wide applications as a pretreatment for the rapid, quantitative determination of drug concentrations in plasma samples. 相似文献