全文获取类型
收费全文 | 179385篇 |
免费 | 17485篇 |
国内免费 | 10827篇 |
专业分类
电工技术 | 13317篇 |
技术理论 | 3篇 |
综合类 | 22093篇 |
化学工业 | 18015篇 |
金属工艺 | 9587篇 |
机械仪表 | 16116篇 |
建筑科学 | 23802篇 |
矿业工程 | 7827篇 |
能源动力 | 5863篇 |
轻工业 | 8841篇 |
水利工程 | 7524篇 |
石油天然气 | 7302篇 |
武器工业 | 2445篇 |
无线电 | 11423篇 |
一般工业技术 | 24762篇 |
冶金工业 | 7076篇 |
原子能技术 | 2688篇 |
自动化技术 | 19013篇 |
出版年
2024年 | 731篇 |
2023年 | 2103篇 |
2022年 | 4026篇 |
2021年 | 4802篇 |
2020年 | 5296篇 |
2019年 | 4517篇 |
2018年 | 4485篇 |
2017年 | 5683篇 |
2016年 | 6325篇 |
2015年 | 6819篇 |
2014年 | 10946篇 |
2013年 | 10509篇 |
2012年 | 13811篇 |
2011年 | 14167篇 |
2010年 | 10866篇 |
2009年 | 11319篇 |
2008年 | 10290篇 |
2007年 | 12814篇 |
2006年 | 11208篇 |
2005年 | 9389篇 |
2004年 | 7672篇 |
2003年 | 6597篇 |
2002年 | 5465篇 |
2001年 | 4498篇 |
2000年 | 4056篇 |
1999年 | 3468篇 |
1998年 | 2681篇 |
1997年 | 2384篇 |
1996年 | 2090篇 |
1995年 | 1829篇 |
1994年 | 1499篇 |
1993年 | 1115篇 |
1992年 | 980篇 |
1991年 | 699篇 |
1990年 | 587篇 |
1989年 | 553篇 |
1988年 | 402篇 |
1987年 | 236篇 |
1986年 | 183篇 |
1985年 | 88篇 |
1984年 | 90篇 |
1983年 | 41篇 |
1982年 | 53篇 |
1981年 | 68篇 |
1980年 | 43篇 |
1979年 | 43篇 |
1978年 | 21篇 |
1975年 | 20篇 |
1973年 | 13篇 |
1959年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
13.
Prediction of brittle-to-ductile transitions in polystyrene 总被引:1,自引:0,他引:1
In this study it is attempted to predict brittle-to-ductile transitions (BDTs) in polystyrene blends, induced either by an increase in temperature or by a decrease in inter-particle distance. A representative, two-dimensional volume element (RVE) of a polystyrene matrix with 20% circular voids, is deformed in tension. During deformation a hydrostatic-stress based craze-nucleation criterion [1] is evaluated. The simulations demonstrate that crazes initiate at low temperatures while a transition from crazing to shear yielding (BDT) is found around 75 °C. The numerical results correlate well with tensile tests on similar heterogeneous polystyrene. The presence of an absolute length, as experimentally found, is more difficult to explain. Near a free surface a Tg-depression is measured for polystyrene and also the resistance to indentation in polystyrene is lower than expected from bulk properties. Both observations are rationalised by an enhanced segmental mobility of chains near a free surface. As a consequence of these findings, an absolute length-scale could be incorporated in the numerical simulations. For simplicity, the length-scale is modelled by taking a temperature gradient over a thin layer near the internal free surfaces of the RVE. Deformation of the RVE with different absolute length-scales shows that indeed also the experimentally found brittle-to-ductile transition can be predicted if the ligament thickness between the inclusions (‘voids’) in polystyrene is below a critical value of ca. 15 nm. 相似文献
14.
电信企业信息化的实质就是赋予电信企业精细化的企业资源整合能力,本以此认识为出发点,通过定义基本的信息化业务元素,需求参数和基本信息处理机制,构建出带有行业共性的电信企业信息化统一模型,该模型针对目前电信企业信息化中常见的和潜在的问题提供了有效的解决措施。 相似文献
15.
16.
径向水平井弯曲转向机构影响因素仿真研究 总被引:3,自引:1,他引:2
针对径向水平井钻进中钻杆弯曲转向前进运动困难的问题,通过建立弯曲转向机构仿真有限元模型,对其主要影响因素:滑道轨迹曲率、间隙、工作压力、滚轮形状与位置和钻杆壁厚等用ANSYS软件进行仿真研究。研究表明:影响截面变形的主要因素是滑道曲率的改变和滑道摩擦因数,钻井失败时钻杆所受阻力的增大不是因为升高工作压力导致截面变形过大与滑道干涉所致,钻杆经校直段,钻头中轴线与校直中心线存在一定的角度,即钻杆的前进轨迹就会偏离理论值,或与地层干涉,或可能再次发生弯曲变形;另一主要原因是转向器滑道工作恶化。增加钻杆壁厚,降低工作压力和滑道摩擦因数,设计合理弯曲转向机构是解决问题的关键。 相似文献
17.
Ph. D. Candidate:Chen Xue-fengState Key Laboratory of Offshore Coastal Engineering Dalian University of Technology Dalian China e-mail: cxfeng @ student dlut. edu.cn 《水动力学研究与进展(B辑)》2003,15(6)
The reflection coefficient of perforated caissons and the total horizontal forces acting on them were experimentally and numerically analyzed and discussed when wave propagates normally. To consider the viscosity effect of fluid and nonlinear action of waves on structures, the VOF (Volume Of Fluid) method combined with the k-ε turbulence model was used to simulate the interaction between waves and structures. Governing equations were solved with the finite difference method. Through 2D experimental study in the wave flume, the empirical relationship between the reflection coefficient of perforated caissons and the main affecting factors were obtained from the experimental data using the least square method. Also the correlation between the ratio of the total horizontal force acting on perforated caisson and the force acting on solid caisson and the main affecting factors were regressed from the experimental data. 相似文献
18.
Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge 总被引:1,自引:0,他引:1
Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented. 相似文献
19.
求解二维结构-声耦合问题的一种直接方法 总被引:1,自引:1,他引:0
本文基于传递矩阵法(TMM)和虚拟边界元法(VBEM),提出了一种求解在谐激励作用下二维结构-声耦合问题的直接法。文中对任意形状的二维弹性环建立了一阶非齐次运动微分方程组,便于用齐次扩容精细积分法求解,对于含有任意形状孔穴的无穷域流体介质的Helmholtz外问题,采用复数形式的Burton-Miller型组合层势法建立了虚拟边界元方程,保证了声压在全波数域内存在唯一解。根据叠加原理并结合最小二乘法,提出了一种耦合方程的直接解法,由于该方法不存在迭代过程,因而具有较高的计算精度和效率。文中给出了二个典型弹性环在集中谐激励力作用下声辐射算例,计算结果表明本文方法较通常采用的混合FE/BE法更为有效。 相似文献
20.
分析光折变三维存储器的机理,探讨了光折变三维存储器的编码方式、光折变材料的选择及存储技术,阐述了其产业化进程. 相似文献