首页 | 官方网站   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   3459篇
  免费   304篇
  国内免费   77篇
工业技术   3840篇
  2025年   13篇
  2024年   47篇
  2023年   58篇
  2022年   80篇
  2021年   104篇
  2020年   97篇
  2019年   100篇
  2018年   88篇
  2017年   117篇
  2016年   147篇
  2015年   135篇
  2014年   190篇
  2013年   174篇
  2012年   232篇
  2011年   263篇
  2010年   184篇
  2009年   207篇
  2008年   195篇
  2007年   194篇
  2006年   188篇
  2005年   139篇
  2004年   124篇
  2003年   117篇
  2002年   82篇
  2001年   70篇
  2000年   58篇
  1999年   68篇
  1998年   53篇
  1997年   64篇
  1996年   60篇
  1995年   29篇
  1994年   40篇
  1993年   30篇
  1992年   17篇
  1991年   26篇
  1990年   17篇
  1989年   9篇
  1988年   9篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1983年   3篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1973年   1篇
排序方式: 共有3840条查询结果,搜索用时 15 毫秒
1.
现阶段地球物理三维勘探面临越来越复杂的问题,其要求更精细的三维网格剖分,现有的一些方法随着网格节点的增加其收敛速度相应减慢。对于应用中更复杂实际模型、更细密网格剖分以及更快收敛速度要求,难于有进一步提高。要有所突破,需借助计算数学最新进展,引入新的高效算法。多重网格法是近二十年迅速发展的一种求解微分方程近乎最优的新算法。本文首先简单介绍了多重网格法基本原理和运算格式,着重介绍了当前国内外多重网格法在地球物理正反演中的应用成果和发展现状。此外,对多重网格法在地球物理正反演中的应用前景及发展趋势进行了展望。  相似文献   
2.
The paper presents a formal methodology for the hull form optimization in calm and rough water using wash waves and selected dynamic responses, respectively. Parametric hull form modeling is used to generate the variant hull forms with some of the form parameters modified, which are evaluated in the optimization scheme based on evolutionary strategies. Rankine-source panel method and strip theories are used for the hydrodynamic evaluation. The methodology is implemented in the optimization of a double-chine, planing hull form. Furthermore, a dual-stage optimization strategy is applied on a modern fast displacement ferry. The effect of the selected optimization parameters is presented and discussed.  相似文献   
3.
In this paper, we consider the wave equation with internal distributed time delay and local damping in a bounded and smooth domain ΩRn. When the local damping acts on a neighborhood of a suitable part of the boundary of Ω, we show that an exponential stability result holds if the coefficient of the delay term is sufficiently small.  相似文献   
4.
论证ML9型配合物的立体构型,并运用群论方法,导出了该类型配合物中央体的σ杂化方式及杂化轨道的波函数.  相似文献   
5.
戴术辉 《铜业工程》2004,(3):41-42,13
由于供电线路故障、浪涌、断线或其它干扰都可能导致电力系统服务中断 ,而FCM2 0 0电力监控仪可在线进行谐波分量测量 ,具备数字波形高速采集功能 ,它的波形分析工具可诊断谐波等故障根源 ,并且有助于确定必要的保护措施。  相似文献   
6.
The influences of couplers on wave propagation and mode localization in simply supported multispan beams with couplers consisting of lumped rotational stiffness and mass on supports are studied. A transfer matrix equation governing the vibrational wave propagation in the simply supported multispan beams with couplers is newly derived and simplified. The eigenvalue of the simplified transfer matrix shows that the larger stiffness or the larger mass of the coupler makes the internal coupling between spans weaker and so it makes the system more sensitive to mode localization. As the wave frequency or the eigenvalues of the system increases, the mass effect is increased while the stiffness effect is decreased. In a case considering the large stiffness and mass at the same time, there is a region with relatively wider passbands and narrower stop bands having small attenuation rates and the normal modes in it become delocalized ones. As an example structure, a simply supported two span beam with a coupler at the midspan is considered.  相似文献   
7.
根据行波半导体放大器中载流子复合的实际过程,对放大器饱和参量的表达式作了适当的修正。  相似文献   
8.
This paper presents the results of a comparative study aiming to investigate the effect of reflective coatings on lowering surface temperatures of buildings and other surfaces of the urban environment, and thus test their suitability to lower ambient temperatures and fight the heat island effect. In total, 14 types of reflective coatings, selected from the international market were studied, from August to October 2004, on a 24 h basis. These coatings are used in buildings and some of them are used or could be used in the future in other surfaces of the urban environment (sidewalks, parking lots, etc.). In order to investigate the thermal performance of the reflective coatings, surface temperature sensors and a data logging system as well as infrared thermography procedures were used. The spectral reflectance and the infrared emittance of the samples were also measured. The collected data have been extensively analyzed. It was demonstrated that the use of reflective coatings can reduce a white concrete tile’s surface temperature under hot summer conditions by 4 °C and during the night by 2 °C. It can be warmer, than the ambient air by only 2 °C during the day and cooler than the ambient air by 5.9 °C during the night. “Cool” coatings present superior thermal performance even compared to other “cool” materials. This study can assist in choosing more appropriate coatings for building envelopes and other surfaces of the urban environment, and thus contribute to the mitigation of the heat island effect as well as the reduction of cooling loads and electricity consumption of buildings.  相似文献   
9.
Wells turbine is a self-rectifying airflow turbine capable of converting pneumatic power of the periodically reversing air stream in oscillating water column into mechanical energy. This paper reports the computational analysis on performance and aerodynamics of Wells turbine with the NACA 0021 constant chord blades. Studies have been made at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The present computational model can predict the performance and aerodynamics of the turbine quantitatively and qualitatively. The model also predicted the flow coefficient at which the turbine stalls, with reasonable accuracy.  相似文献   
10.
This paper presents the comparison of a three-dimensional Computational Fluid Dynamics (CFD) analysis with empirical performance data of a 0.6 m Impulse Turbine with Fixed Guide Vanes used for wave energy power conversion. Pro-Engineer, Gambit and Fluent 6 were used to create a 3-D model of the turbine. A hybrid meshing scheme was used with hexahedral cells in the near blade region and tetrahedral and pyramid cells in the rest of the domain. The turbine has a hub-to-tip ratio of 0.6 and results were obtained over a wide range of flow coefficients. Satisfactory agreement was obtained with experimental results. The model yielded a maximum efficiency of approximately 54% as compared to a maximum efficiency of around 49% from experiment. A degree of insight into flow behaviour, not possible with experiment, was obtained. Sizeable areas of separation on the pressure side of the rotor blade were identified toward the tip. The aim of the work is to benchmark the CFD results with experimental data and to investigate the performance of the turbine using CFD and to with a view to integrating CFD into the design process.  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

京公网安备 11010802026262号