全文获取类型
收费全文 | 120411篇 |
免费 | 10939篇 |
国内免费 | 6223篇 |
专业分类
电工技术 | 8022篇 |
技术理论 | 6篇 |
综合类 | 9929篇 |
化学工业 | 19306篇 |
金属工艺 | 6675篇 |
机械仪表 | 6823篇 |
建筑科学 | 9773篇 |
矿业工程 | 2979篇 |
能源动力 | 3214篇 |
轻工业 | 11659篇 |
水利工程 | 2329篇 |
石油天然气 | 5307篇 |
武器工业 | 1085篇 |
无线电 | 13642篇 |
一般工业技术 | 13437篇 |
冶金工业 | 5120篇 |
原子能技术 | 1364篇 |
自动化技术 | 16903篇 |
出版年
2024年 | 608篇 |
2023年 | 2053篇 |
2022年 | 3777篇 |
2021年 | 5075篇 |
2020年 | 3780篇 |
2019年 | 3119篇 |
2018年 | 3354篇 |
2017年 | 3816篇 |
2016年 | 3477篇 |
2015年 | 4826篇 |
2014年 | 6180篇 |
2013年 | 7315篇 |
2012年 | 8130篇 |
2011年 | 8863篇 |
2010年 | 8061篇 |
2009年 | 7581篇 |
2008年 | 7779篇 |
2007年 | 7308篇 |
2006年 | 7028篇 |
2005年 | 5773篇 |
2004年 | 4183篇 |
2003年 | 3578篇 |
2002年 | 3729篇 |
2001年 | 3196篇 |
2000年 | 2647篇 |
1999年 | 2410篇 |
1998年 | 1802篇 |
1997年 | 1493篇 |
1996年 | 1409篇 |
1995年 | 1159篇 |
1994年 | 916篇 |
1993年 | 676篇 |
1992年 | 571篇 |
1991年 | 432篇 |
1990年 | 295篇 |
1989年 | 259篇 |
1988年 | 227篇 |
1987年 | 139篇 |
1986年 | 97篇 |
1985年 | 91篇 |
1984年 | 57篇 |
1983年 | 45篇 |
1982年 | 57篇 |
1981年 | 28篇 |
1980年 | 43篇 |
1979年 | 22篇 |
1977年 | 11篇 |
1976年 | 23篇 |
1974年 | 9篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Ying Ding Chunqing Wang Yanhong Tian Binbin Zhang 《Metallurgical and Materials Transactions A》2006,37(12):1017-1025
in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture
behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed
by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast
samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While
remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured
area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion
of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area
were also found. Under this condition, a new critical stress intensity factor K
c
′ to define the mutual dislocation emission was proposed. 相似文献
33.
34.
35.
Microstructure evolution of AZ31 magnesium alloy during equal channel angular extrusion 总被引:3,自引:0,他引:3
Li Yuanyuan Zhang Datong Chen Weiping Liu Ying Guo Guowen 《Journal of Materials Science》2004,39(11):3759-3761
36.
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
37.
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
38.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
39.
Generalized difference control of parallel streams temperatures 总被引:1,自引:0,他引:1
A furnace with multiple parallel passes and multiple burners is commonly seen in petroleum refineries. In order to maintain the furnace running in a safe, stable, and high-efficiency state it is necessary to control the outlet temperatures of the multiple passes to be the same. Due to the fact that the process of the oil heating in such furnace is nonlinear, multivariable, time varying, has serious coupling among passes, has frequent dynamic changes and a large time delay, traditional control methods have trouble in controlling these temperatures, and some advanced control methods, including predictive control, adaptive control, and robust control, are usually too complex for convenient use. In this paper, a control technique, called differences control technique (DsCT), is proposed to distribute the stream flowrates such that the stream temperatures are as identical as possible. The principle of the proposed technique is explained and demonstrated, and the results of its application to a real-life petroleum refinery furnace are also reported. The DsCT technique has the following advantages: it does not need complicated design procedures, the controller structure is simple, it is easy to apply, and it can be canonically applied to furnaces with different number of passes. 相似文献
40.
印染废水处理工艺研究及实例 总被引:1,自引:0,他引:1
本文简要介绍了印染废水水质特征,提出了处理工艺,并利用两个工程实例说明了该工艺的可行性. 相似文献