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   3083篇
  免费   359篇
  国内免费   127篇
电工技术   183篇
综合类   267篇
化学工业   197篇
金属工艺   204篇
机械仪表   187篇
建筑科学   150篇
矿业工程   59篇
能源动力   127篇
轻工业   180篇
水利工程   200篇
石油天然气   70篇
武器工业   24篇
无线电   339篇
一般工业技术   907篇
冶金工业   157篇
原子能技术   81篇
自动化技术   237篇
  2024年   49篇
  2023年   50篇
  2022年   50篇
  2021年   72篇
  2020年   86篇
  2019年   69篇
  2018年   73篇
  2017年   124篇
  2016年   103篇
  2015年   102篇
  2014年   143篇
  2013年   205篇
  2012年   208篇
  2011年   207篇
  2010年   146篇
  2009年   172篇
  2008年   178篇
  2007年   211篇
  2006年   195篇
  2005年   135篇
  2004年   124篇
  2003年   125篇
  2002年   98篇
  2001年   80篇
  2000年   75篇
  1999年   68篇
  1998年   67篇
  1997年   64篇
  1996年   43篇
  1995年   44篇
  1994年   38篇
  1993年   21篇
  1992年   30篇
  1991年   15篇
  1990年   19篇
  1989年   18篇
  1988年   11篇
  1987年   8篇
  1986年   6篇
  1985年   6篇
  1984年   6篇
  1983年   3篇
  1982年   5篇
  1981年   6篇
  1980年   7篇
  1979年   1篇
  1978年   1篇
  1969年   1篇
  1956年   1篇
排序方式: 共有3569条查询结果,搜索用时 15 毫秒
1.
The dynamics of a thin liquid film falling down a uniformly heated wall is studied. The model introduced by Kalliadasis et al. [J. Fluid Mech. 475 (2003) 377] for the same problem is revisited and its deficiencies, namely the prediction of a critical Reynolds number with 20% error, cured. For the energy equation a high-order Galerkin projection in terms of polynomial test functions is developed. It is shown that not only does this more refined formulation correct the critical Reynolds number, but it also gives, with an appropriate expansion close to criticality, the long-wave theory. Bifurcation diagrams for permanent solitary waves are constructed and compared with the solution branches obtained from different models. It is shown that, in all cases, the long-wave theory exhibits limit points and branch multiplicity, while the other models predict the continuing existence of solitary waves. Time-dependent computations show that the free surface and interfacial temperature approach a train of coherent structures that resemble the infinite-domain stationary solitary pulses.  相似文献   
2.
Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics.  相似文献   
3.
A discontinuous Galerkin finite-element method (DG-FEM) solution to a set of high-order Boussinesq-type equations for modelling highly nonlinear and dispersive water waves in one horizontal dimension is presented. The continuous equations are discretized using nodal polynomial basis functions of arbitrary order in space on each element of an unstructured computational domain. A fourth-order explicit Runge-Kutta scheme is used to advance the solution in time. Methods for introducing artificial damping to control mild nonlinear instabilities are also discussed. The accuracy and convergence of the model with both h (grid size) and p (order) refinement are confirmed for the linearized equations, and calculations are provided for two nonlinear test cases in one horizontal dimension: harmonic generation over a submerged bar, and reflection of a steep solitary wave from a vertical wall. Test cases for two horizontal dimensions will be considered in future work.  相似文献   
4.
The Biot–Frenkel model of fluid-infiltrated material dynamics in its original linear form is adequate to solve many problems for soils and rocks mechanics saturated with fluids. The main interest to it was connected with applications in oil/gas production and the exploration industry and also in civil engineering and ecology. The model was developed and generalized successfully for the first half century. The input of the Russian writers was essential. A corresponding review of their published results is given in this paper.  相似文献   
5.
利用经典的质点网格法进行了含脱体激波的超音速流动的数值模拟,绘出了形象直观的超音速流动图画,且模拟流场中的各项参数与实验符合较好,为今后进一步探讨复杂形状物体的超音速运动提供了基础.  相似文献   
6.
Havelock’s type of expansion theorems, for an integrable function having a single discontinuity point in the domain where it is defined, are utilized to derive analytical solutions for the radiation or scattering of oblique water waves by a fully extended porous barrier in both the cases of finite and infinite depths of water in two-layer fluid with constant densities. Also, complete analytical solutions are obtained for the boundary-value problems dealing with the generation or scattering of axi-symmetric water waves by a system of permeable and impermeable co-axial cylinders. Various results concerning the generation and reflection of the axisymmetric surface or interfacial waves are derived in terms of Bessel functions. The resonance conditions within the trapped region are obtained in various cases. Further, expansions for multipole-line-source oblique-wave potentials are derived for both the cases of finite and infinite depth depending on the existence of the source point in a two-layered fluid.  相似文献   
7.
熊元新 《电力学报》2011,26(5):361-362,379
研究发现,麦克斯韦联立微分方程组不正确。一百多年来,电磁场、电磁波及相关专业科技人员应用麦克斯韦联立方程组求解闭合环路非均匀导体路径中的空间介质电容器电磁场和电磁波的问题是不正确的。因为在闭合环路非均匀导体路径中均匀导体电场强度、空间介质电容器电场强度和时变电源电场强度串联端点不连续,不连续电场强度不能求它的旋度。故麦克斯韦第二积分方程在闭合环路非均匀导体路径的情况下不能用斯托克斯公式化成微分方程。必须重新建立描述闭合环路非均匀导体路径电磁现象的联立方程组。  相似文献   
8.
利用激光激发声表面波及光差分技术研究激光源对声表面波的影响。实验中利用了Nd∶YAG脉冲激光器激发超声,采用632nm的He-Ne激光器基于光束偏转法的光差分检测系统,测量了铝样品表面的声表面波,获得了很好的信号。在此基础上研究了激发源的形状和能量对激发的声表面波幅度的影响。同时从热弹和融蚀机制下讨论激光声表面波的产生。在这两种机制下,声表面波的幅度发生了很大的变化。随着激光能量密度的增加,声表面波的幅度由线性变化转换为非线性变化。这一结果对激光激发声表面波理论研究有一定的指导意义。  相似文献   
9.
目的:观察半导体激光治慢性前列腺炎的临床疗效。方法:将患者140例随机分为2组.治疗组76例,采用半导体激光并体外短波对会阴部治疗;对照组64例,单纯采用体外短波治疗。结果:治疗组有效率为89.2%;对照组有效率为76.5%。两组比较差异显著(P<0.05)。结论:半导体激光照射治疗慢性前列腺炎可明豆糖高疗效。  相似文献   
10.
Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method (PWM). The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that the maximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of t rahertz (THz) devices.  相似文献   
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