首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   181篇
  免费   17篇
  国内免费   35篇
电工技术   15篇
综合类   40篇
化学工业   6篇
金属工艺   1篇
机械仪表   1篇
建筑科学   26篇
能源动力   45篇
轻工业   1篇
水利工程   25篇
无线电   3篇
一般工业技术   24篇
冶金工业   27篇
自动化技术   19篇
  2023年   3篇
  2022年   1篇
  2020年   5篇
  2019年   2篇
  2018年   4篇
  2017年   3篇
  2016年   5篇
  2015年   5篇
  2014年   10篇
  2013年   10篇
  2012年   12篇
  2011年   11篇
  2010年   21篇
  2009年   10篇
  2008年   28篇
  2007年   41篇
  2006年   26篇
  2005年   8篇
  2003年   4篇
  2002年   3篇
  2001年   8篇
  2000年   2篇
  1999年   2篇
  1998年   3篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1989年   1篇
排序方式: 共有233条查询结果,搜索用时 15 毫秒
1.
Pullout resistance is one of the most important factors governing seismic stability of reinforced soil walls. The previous studies on the seismic stability of reinforced soil walls have focused on the axial resistance of the reinforcement against the pullout. However, the kinematics of failure causes the reinforcement to be subjected to the oblique pullout force and bending deformation. Considering the kinematics of failure and bending deformation of the reinforcement, this paper presents a pseudo-static seismic analysis for evaluating the pullout resistance of reinforcements in soil wall subjected to oblique pullout forces. A modified horizontal slice method (HSM) and Pasternak model are used to calculate the required force to maintain the stability of the reinforced soil wall and shear resistance mobilized in the reinforcements, respectively. In addition, this paper studies the effect of various parameters on the pullout resistance of the reinforcements in soil wall subjected to seismic loads. Results of this study are compared with the published data and their differences are analyzed in detail.  相似文献   
2.
对于裂纹等不连续问题,常规有限元法通常需对裂纹尖端进行局部网格加密,且在模拟裂纹扩展过程中需进行网格重构.扩展有限元法基于单位分解的思想,将一些加强函数加入到常规有限元法位移模式中,能有效地求解不连续问题.对于复合裂纹及裂纹受压的情况,通常需考虑裂纹面间的接触问题,以避免裂纹面发生相互嵌入.本文将砂浆法与罚函数法相结合,用于扩展有限元法中裂纹面之间摩擦接触条件的施加.数值结果表明,该方法能有效的阻止裂纹面间的相互嵌入,且与其它数值方法求解结果相一致.  相似文献   
3.
考虑初始缺陷的混凝土压缩试验   总被引:1,自引:0,他引:1  
以混凝土损伤理论为基础,通过进行混凝土单轴压缩试验,研究考虑初始缺陷的混凝土相关力学性能.通过对试验结果的分析,在此基础上提出较为合理的混凝土本构模型.文中混凝土损伤本构模型的建立,首先找出理想无损状态应力,即有效应力的表达式,然后根据试验结果求出损伤演化规律,最后得到最终的混凝土损伤本构方程.文中的混凝土本构模型可以较好地体现混凝土在各个阶段的受力特征.  相似文献   
4.
This paper summarizes the results of an experimental investigation into the bond behavior between recycled aggregate concrete (RAC) and deformed steel rebars, with the main variables being the recycled coarse aggregate replacement ratio (RCAr) and water-to-cement ratio of the concrete mixture. The investigation into splitting cracking strength indicates that the degradation of the bond splitting tensile stress of the cover concrete was affected by not only the roundness of the coarse aggregate particles but also the weak interfacial transition zone (ITZ) between the cement paste and the RCA that has a more porous structure in the ITZ than normal concrete. In this study, a linear relationship between the bond strength and the density of the RCA was found, but the high compressive strength reduced the effects of the parameters. To predict the bond strength of RAC using the main parameters, a multivariable model was developed using nonlinear regression analysis. It can be inferred from this study that the degradation characteristic of the bond strength of RAC can be predicted well, whereas other empirical equations and code provisions are very conservative.  相似文献   
5.
At the South Branch of the Changjiang Estuary near Baimao Shoal, two in situ approaches were used to estimate the settling velocity, ws, of suspended, fine-grained sediments. The first approach was used when the current was less than 1.5??m/s and was based on measurements from an optical backscatter sensor (OBS-3A) and a laser in situ scattering and transmissometer (LISST-100, Type C). A modification, using the measured ratio of volume concentration for each floc size class to the total volume concentration as a weighting factor. To improve a previously published approach, a better algorthim was implemented to estimate ws. Results of the modified approach (0.4 to 4.6??mm/s) are about twice those of the original approach, which assumes that all sizes of flocs have the same floc density. The second approach used the Rouse equation to estimate the depth-averaged ws when the current was strong and nearly steady around maximum ebb. Results from the second approach show a much greater depth-averaged ws (4–8.5??mm/s). This is attributed to the large bed shear stresses (between 3 and 3.6?Pa) bringing large sediments into the water column.  相似文献   
6.
The effect of hybrid fiber reinforcement on fracture energy and crack propagation in cement matrix composites is examined. The crack in cement matrix composites is allowed to fracture under mode-I loading with three-point bending beam specimens. The influence of fiber types and their combination is quantified by using the toughness index and fracture energy. A proper hybrid combination of steel fibers and polyvinyl alcohol microfibers enhances the resistance to both the nucleation and growth of the crack. The micromechanical model of hybrid composites by using a fiber bridging law is emphasized, and the numerical model prediction closely matches the behavior obtained from the experiment. The influencing role of the material parameters in the fracture tests (e.g., the fracture toughness index and fracture energy) becomes more apparent than ones used in some conventional strength-based or fiber pullout tests, and these fracture parameters could screen the effect of fiber/microfiber reinforcement in enhancing the crack growth resistance of cementitious composites. This study demonstrates that fundamental fracture tests are effective to characterize and develop high-performance hybrid fiber–reinforced cement matrix composites.  相似文献   
7.
The mechanisms of deformation and failure in face-centered cubic (FCC) nickel nanowires subjected to uniaxial tensile loading are investigated using molecular dynamics (MD) simulation, and the size effect on mechanical properties of FCC metal nanowires is studied. Simulation reveals that the surface free energy has great influence on the deformation and failure mechanism of metal nanowires. As a result of free surfaces and their reconstruction, the surface atoms depart from the perfect crystal lattice positions, leading to the appearance of nanocavities on the surfaces that are exposed to external load. The deformation process of nanowires undergoes expansion and connection of nanocavities from surface into inner lattices. Slip occurs during the deformation process, which is consistent with experimental phenomena. Elastic stiffness, yield, and fracture strength of nickel nanowires with various cross-sectional sizes are obtained, and the size effect on these mechanical properties is further analyzed. Based on numerical results, a set of quantitative prediction formulas are proposed, and they are capable of explaining the size sensitivity of nickel nanowires on the mechanical properties. Both the elastic modulus and yield strength of nickel nanowires are in a linear relationship with respect to the logarithm of their cross-sectional size, whereas the fracture strength exhibits an inverse relationship to the exponent of cross-sectional size of nickel nanowires. By using the MD simulation, the elastic modulus, yield strength, and fracture strength of a nickel nanowire in relationship to its cross-sectional size are well predicted, and they are in remarkable agreement with experimental and available numerical results. The present study demonstrates that the adopted MD simulation is capable of simulating the mechanical behavior of nanowires with respect to their geometrical size and providing numerical data that can be used to develop the empirical formulas on the effect of various physical and geometric parameters on their mechanical properties.  相似文献   
8.
In this study, we examine a method for estimating the setting time of concrete containing super retarding agent (SRA) under various curing temperatures. To estimate the setting time, the equivalent age method using the apparent activation energy (Ea), proposed by Pinto et al., is applied. Increasing the SRA content leads to considerable retardation of the initial and final sets of concrete, whereas increasing the curing temperature shortens the initial and final set times regardless of the SRA content. Ea values at the times of initial and final sets obtained using the Arrhenius function differ for different mixtures. They are estimated to be in the range 30–35 kJ/mol for the control mixture, which is similar to or slightly lower than the results of a previous study, but are in the range 20–40 kJ/mol in concrete containing SRA, which is lower than that for conventional concrete. We apply Ea according to the SRA content to Freisleben-Hansen and Pedersen’s equivalent age function and find that the equivalent age is nearly constant regardless of the curing temperature. This implies that the concept of maturity can be applied to the estimation of the setting time of concrete containing SRA. The setting time estimated using the equivalent age according to the SRA content and curing temperature is presented herein. A good agreement is observed between the estimated setting time and measured setting time. Thus, the method for estimating the setting time suggested by Pinto is applicable to the region of concrete containing SRA.  相似文献   
9.
Carbon nanotube (CNT) based continuous fiber, a CNT assembly that could retain the superb properties of individual CNTs on a macroscopic scale, has emerged as a promising candidate for reinforcement in multifunctional composites. While existing research has extensively examined their short-term mechanical properties based upon quasi-static measurements, the long-term durability of CNT fibers has been largely neglected. Here we report time-dependent behavior of CNT fibers, with a particular focus on tensile stress relaxation. Both the pure CNT fiber and the CNT/epoxy composite fiber exhibited significant stress decay during the relaxation process, and this time-dependent behavior became more significant at a higher initial strain level, a lower strain rate and a greater gauge length. The present approach signifies a fundamental difference in the load-bearing characteristics between CNT fibers and traditional advanced fibers, which has major implications for the long-term durability of CNT fibers in load-bearing multifunctional applications.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号