全文获取类型
收费全文 | 111138篇 |
免费 | 5761篇 |
国内免费 | 3527篇 |
学科分类
工业技术 | 120426篇 |
出版年
2023年 | 1192篇 |
2022年 | 2065篇 |
2021年 | 2846篇 |
2020年 | 2265篇 |
2019年 | 2116篇 |
2018年 | 2570篇 |
2017年 | 2856篇 |
2016年 | 2719篇 |
2015年 | 3157篇 |
2014年 | 4033篇 |
2013年 | 6204篇 |
2012年 | 5641篇 |
2011年 | 6343篇 |
2010年 | 5370篇 |
2009年 | 5455篇 |
2008年 | 5221篇 |
2007年 | 5358篇 |
2006年 | 5178篇 |
2005年 | 4521篇 |
2004年 | 3431篇 |
2003年 | 3051篇 |
2002年 | 2972篇 |
2001年 | 2842篇 |
2000年 | 2682篇 |
1999年 | 3004篇 |
1998年 | 3877篇 |
1997年 | 3110篇 |
1996年 | 2828篇 |
1995年 | 2046篇 |
1994年 | 1770篇 |
1993年 | 1477篇 |
1992年 | 1135篇 |
1991年 | 1007篇 |
1990年 | 844篇 |
1989年 | 737篇 |
1988年 | 602篇 |
1987年 | 547篇 |
1986年 | 468篇 |
1985年 | 457篇 |
1984年 | 342篇 |
1983年 | 336篇 |
1982年 | 341篇 |
1981年 | 318篇 |
1980年 | 363篇 |
1979年 | 346篇 |
1978年 | 295篇 |
1977年 | 415篇 |
1976年 | 630篇 |
1975年 | 308篇 |
1973年 | 311篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
In the literature the concept of representative volume element (RVE) was introduced to correlate the effective or macroscopic properties of materials with the properties of the microscopic constituents and microscopic structures of the materials. However, to date little quantitative knowledge is available about minimum RVE sizes of various engineering materials. In our recent paper [J. Mech. Phys. Solids 50 (2002) 881], a new definition of minimum RVE size was introduced based on the concept of nominal modulus. Numerical experiments using the finite element method (FEM) were then carried out for determining the minimum RVE sizes of more than 500 cubic polycrystals in the plane stress problem, under the assumption that all grains in a polycrystal have the same square shape––called the simple polycrystal model. The major finding is that the minimum RVE sizes for effective elastic moduli have a roughly linear dependence on crystal anisotropy degrees. The present paper takes into account the effect of grain sizes, shapes, and distribution on the minimum RVE sizes for real cubic polycrystals that are formed by crystallization processes. Similar roughly linear dependence is found again, with the slope about 19% lower than that in the simple polycrystal model. This finding is interesting and useful because numerical experiments on minimum RVE sizes for a large number of crystals are quite time-consuming and the simple polycrystal model reduces significantly the FEM pre- and post-processing works. This should be particularly true in numerically testing minimum RVE sizes for three-dimensional polycrystals and for nonelastic properties in future works. With a maximum relative error 5%, all the polycrystals tested have a minimum RVE size of 16 or less times the grain size. 相似文献
85.
A comparative study of numerical solutions to non-linear discrete crack modelling of concrete beams involving sharp snap-back 总被引:1,自引:0,他引:1
Numerical problems are often encountered in modelling crack propagation in concrete beams using non-linear finite element (FE) analysis, especially when sharp snap-back behaviour in load-displacement relations occurs. This paper firstly identifies 16 arc-length control based numerical strategies based on extensive literature review. They are then used to carefully model the structural behaviour of a four-point single notched shear beam using discrete crack modelling approach in which cracks are represented by interface elements with bilinear softening constitutive laws. Based on extensive FE analyses, detailed comparisons of the merits and demerits of these numerical algorithms are then made. The results indicate that the effectiveness and efficiency of different algorithms may vary considerably from one to another, with the local arc-length based procedures in conjunction with tangential stiffness strategy and reversible unloading model being the most robust. 相似文献
86.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
87.
V. N. Perevezentsev M. Yu. Shcherban’ M. Yu. Murashkin R. Z. Valiev 《Technical Physics Letters》2007,33(8):648-650
The structure and mechanical properties of nanocrystalline aluminum alloy 1570 obtained by means of severe plastic deformation have been studied. Being tested in a temperature range from 300 to 400°C, the alloy exhibits high-strain-rate superplasticity. At 400°C, the superplasticity is manifested in a very broad range of strain rates, extending from 5 × 10?3 to 1 s?1. 相似文献
88.
89.
90.
本文提出一种多输入多输出(MIMO)天线系统中简单的扩展空时块编码(SSTBC)分集技术,采用沃尔什码来区分各天线发送数据子流。采用这种方法,在系统带宽一定时,不降低发送信息速率,同时接收机简单。不同天线的发送信息经过了所有收一发天线对之间的空间子信道,获得了所有路径的部分空间分集增益,仿真结果表明,这种增益的获得不受限于接收分集阶数,并且随发射天线的增加以一定的线性关系增加。 相似文献