全文获取类型
收费全文 | 1232篇 |
免费 | 25篇 |
国内免费 | 56篇 |
专业分类
化学 | 157篇 |
晶体学 | 7篇 |
力学 | 499篇 |
综合类 | 5篇 |
数学 | 59篇 |
物理学 | 231篇 |
综合类 | 355篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 26篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 30篇 |
2016年 | 45篇 |
2015年 | 37篇 |
2014年 | 65篇 |
2013年 | 68篇 |
2012年 | 36篇 |
2011年 | 75篇 |
2010年 | 51篇 |
2009年 | 85篇 |
2008年 | 100篇 |
2007年 | 65篇 |
2006年 | 64篇 |
2005年 | 51篇 |
2004年 | 44篇 |
2003年 | 40篇 |
2002年 | 48篇 |
2001年 | 16篇 |
2000年 | 13篇 |
1999年 | 32篇 |
1998年 | 29篇 |
1997年 | 34篇 |
1996年 | 23篇 |
1995年 | 35篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1313条查询结果,搜索用时 15 毫秒
1.
采用Agilent 81910A光子全参量测试仪,首次实验研究了InP/In1-xGaxAs1-yPy-MQW(Multiple-Quantum-Well,MQW)材料与衬底间因应力而产生的M-Z型光调制器的PDL影响以及由此引起的由差分群时延(Differential Group Delay,DGD)表征的偏振模色散(Polarization Mode Dispersion,PMD).研究结果表明,半导体MQW光调制器的PDL与DGD是一致的.因此在半导体光器件的制作过程中,应尽可能地减小衬底与波导芯层之间的因残存应力的存在造成对光器件的高速性能的不利影响. 相似文献
2.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
3.
The influence of pulse duration on the stress levels in ablation of ceramics: A finite element study
A. Vila Verde 《Applied Surface Science》2006,252(13):4511-4515
We present a finite element model to investigate the dynamic thermal and mechanical response of ceramic materials to pulsed infrared radiation. The model was applied to the specific problem of determining the influence of the pulse duration on the stress levels reached in human dental enamel irradiated by a CO2 laser at 10.6 μm with pulse durations between 0.1 and 100 μs and sub-ablative fluence. Our results indicate that short pulses with durations much larger than the characteristic acoustic relaxation time of the material can still cause high stress transients at the irradiated site, and indicate that pulse durations of the order of 10 μs may be more adequate both for enamel surface modification and for ablation than pulse durations up to 1 μs. The model presented here can easily be modified to investigate the dynamic response of ceramic materials to mid-infrared radiation and help determine optimal pulse durations for specific procedures. 相似文献
4.
V.I. Kushch I. Sevostianov L. Mishnaevsky Jr 《International Journal of Solids and Structures》2008,45(18-19):5103-5117
The paper addresses the problem of calculation of the local stress field and effective elastic properties of a unidirectional fiber reinforced composite with anisotropic constituents. For this aim, the representative unit cell approach has been utilized. The micro geometry of the composite is modeled by a periodic structure with a unit cell containing multiple circular fibers. The number of fibers is sufficient to account for the micro structure statistics of composite. A new method based on the multipole expansion technique is developed to obtain the exact series solution for the micro stress field. The method combines the principle of superposition, technique of complex potentials and some new results in the theory of special functions. A proper choice of potentials and new results for their series expansions allow one to reduce the boundary-value problem for the multiple-connected domain to an ordinary, well-posed set of linear algebraic equations. This reduction provides high numerical efficiency of the developed method. Exact expressions for the components of the effective stiffness tensor have been obtained by analytical averaging of the strain and stress fields. 相似文献
5.
宫立波 《广西民族大学学报》1996,(1)
作者认为,引起个体应激反应的因素来自内部和外部两个方面.就当代中国而言,青年的应激反应主要是适应性反应.这种适应性反应的外部因素则集中表现在新的价值观念的冲突,竞争加剧,社会分配不公,生活节奏加快,家庭与学校的精神保健职能出现偏差.以及科学和技术的变革速度加快等六个方面.为了培养和提高青年的应激反应能力,作者提出了五个方面的措施,以指导青年建立适宜应激水平. 相似文献
6.
High temperature GaN layers have been grown on Si (1 1 1) substrate by metalorganic vapor phase epitaxy (MOVPE). AlN was used as a buffer layer and studied as a function of thickness and growth temperature. The growth was monitored by in situ laser reflectometry. High resolution X-ray diffraction (HRXRD) revealed that optimized monocrystalline GaN was obtained for a 40 nm AlN grown at 1080 °C. This is in good agreement with the results of morphological study by scanning electron microscopy (SEM) and also confirmed by atomic force microscopy (AFM) observations. The best morphology of AlN with columnar structure and lower rms surface roughness is greatly advantageous to the coalescence of the GaN epilayer. Symmetric and asymmetric GaN reflections were combined for twist and stress measurements in monocrystalline GaN. It was found that mosaicity and biaxial tensile stress are still high in 1.7 μm GaN. Curvature radius measurement was also done and correlated to the cracks observations over the GaN surface. 相似文献
7.
通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。 相似文献
8.
The paper addresses the problem of a semi-infinite plane crack along the interface between two isotropic half-spaces. Two methods of solution have been considered in the past: Lazarus and Leblond [1998a. Three-dimensional crack-face weight functions for the semi-infinite interface crack-I: variation of the stress intensity factors due to some small perturbation of the crack front. J. Mech. Phys. Solids 46, 489-511, 1998b. Three-dimensional crack-face weight functions for the semi-infinite interface crack-II: integrodifferential equations on the weight functions and resolution J. Mech. Phys. Solids 46, 513-536] applied the “special” method by Bueckner [1987. Weight functions and fundamental fields for the penny-shaped and the half-plane crack in three space. Int. J. Solids Struct. 23, 57-93] and found the expression of the variation of the stress intensity factors for a wavy crack without solving the complete elasticity problem; their solution is expressed in terms of the physical variables, and it involves five constants whose analytical representation was unknown; on the other hand, the “general” solution to the problem has been recently addressed by Bercial-Velez et al. [2005. High-order asymptotics and perturbation problems for 3D interfacial cracks. J. Mech. Phys. Solids 53, 1128-1162], using a Wiener-Hopf analysis and singular asymptotics near the crack front.The main goal of the present paper is to complete the solution to the problem by providing the connection between the two methods. This is done by constructing an integral representation for Lazarus-Leblond's weight functions and by deriving the closed form representations of Lazarus-Leblond's constants. 相似文献
9.
Summary Thermopiezoelastic materials have recently attracted considerable attention because of their potential use in intelligent
or smart structural systems. The governing equations of a thermopiezoelastic medium are more complex due to the intrinsic
coupling effects that take place among mechanical, electrical and thermal fields. In this analysis, we deal with the problem
of a crack in a semi-infinite, transversely isotropic, thermopiezoelastic material by means of potential functions and Fourier
transforms under steady heat-flux loading conditions. The problem is reduced to a singular integral equation that is solved.
The thermal stress intensity factor for a crack situated in a cadmium selenide material is calculated.
Received 20 March 2001; accepted for publication 18 October 2001 相似文献
10.
R. D. Peindl M. E. Harrow P. M. Connor D. M. Banks D. F. D'Alessandro 《Experimental Mechanics》2004,44(3):228-234
Photoelastic stress freezing analyses in the orthopaedic literature have, in the past, been limited to studies where bone-on-bone,
bone-on-metal or ultra-high molecular weight polyethylene (UHMWPE)-on-metal constructs are modeled. In these cases photoelastic
plastics are used to simulate either bone or UHMWPE as it interacts with a metal implant. In joints such as the shoulder,
a UHMWPE component is often cemented directly into the scapula's glenoid concavity using polymethylmethacrylate (PMMA). While
a photoelastic material can be used to simulate bone with proper load scaling, UHMWPE and PMMA have very different mechanical
properties at elevated stress freezing temperatures as compared within vivo body temperature. In this study, materials were identified such that proper scaling of elastic properties at elevated temperatures
was utilized to simulate the metal-UHMWPE-PMMA-bone construct. Stresses on orthogonal planes throughout the glenoid were compared
for two different UHMWPE component anchoring geometries (keeled and pegged). High stresses were found at the neck of the glenoid
and also at the component-bone interface beneath simulated PMMA inclusions. 相似文献