全文获取类型
收费全文 | 289178篇 |
免费 | 30813篇 |
国内免费 | 10252篇 |
专业分类
电工技术 | 15113篇 |
技术理论 | 21篇 |
综合类 | 14658篇 |
化学工业 | 58752篇 |
金属工艺 | 13498篇 |
机械仪表 | 15654篇 |
建筑科学 | 21696篇 |
矿业工程 | 6350篇 |
能源动力 | 8122篇 |
轻工业 | 22322篇 |
水利工程 | 4525篇 |
石油天然气 | 13687篇 |
武器工业 | 1953篇 |
无线电 | 37153篇 |
一般工业技术 | 41717篇 |
冶金工业 | 14086篇 |
原子能技术 | 2752篇 |
自动化技术 | 38184篇 |
出版年
2024年 | 1097篇 |
2023年 | 4002篇 |
2022年 | 7387篇 |
2021年 | 10213篇 |
2020年 | 8564篇 |
2019年 | 8895篇 |
2018年 | 9455篇 |
2017年 | 10670篇 |
2016年 | 10442篇 |
2015年 | 12691篇 |
2014年 | 15260篇 |
2013年 | 19459篇 |
2012年 | 17696篇 |
2011年 | 19317篇 |
2010年 | 16921篇 |
2009年 | 16582篇 |
2008年 | 15503篇 |
2007年 | 14819篇 |
2006年 | 15012篇 |
2005年 | 13105篇 |
2004年 | 9445篇 |
2003年 | 8439篇 |
2002年 | 7946篇 |
2001年 | 7178篇 |
2000年 | 7058篇 |
1999年 | 7245篇 |
1998年 | 6364篇 |
1997年 | 5276篇 |
1996年 | 4694篇 |
1995年 | 3932篇 |
1994年 | 3228篇 |
1993年 | 2595篇 |
1992年 | 1998篇 |
1991年 | 1536篇 |
1990年 | 1196篇 |
1989年 | 1044篇 |
1988年 | 821篇 |
1987年 | 584篇 |
1986年 | 483篇 |
1985年 | 412篇 |
1984年 | 244篇 |
1983年 | 223篇 |
1982年 | 195篇 |
1981年 | 178篇 |
1980年 | 153篇 |
1979年 | 117篇 |
1978年 | 74篇 |
1977年 | 80篇 |
1976年 | 98篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
Interfacial segregation of Ti in the brazing of diamond grits onto a steel substrate using a Cu-Sn-Ti brazing alloy 总被引:1,自引:0,他引:1
Wen-Chung Li Shun-Tian Lin Cheng Liang 《Metallurgical and Materials Transactions A》2002,33(7):2163-2172
Diamond grits were brazed onto a steel substrate using a prealloyed Cu-10Sn-15Ti (wt pct) brazing alloy at 925 °C and 1050
°C. Due to the relatively high concentration of Ti in the brazing alloy, the braze matrix exhibited a composite structure,
composed of β-(Cu,Sn), a Cu-based solid solution, and various intermetallic compounds with different morphologies. The reaction of Ti with
diamond yielded a continuous TiC layer on the surfaces of the diamond grits. On top of the TiC growth front, an intermetallic
compound, composed of Sn and Ti, nucleated and grew into a randomly interwoven fine lacey structure. An interfacial structure
developed as the interwoven fine lacey phase was semicoherently bonded to the TiC layer, with the Cu-based braze matrix filling
its interstices. The thickness of such a composite layer was increased linearly with the square root of isothermal holding
time at 925 °C, complying with the law of a diffusion-controlled process. However, at 1050 °C, the segregation behavior of
Ti and Sn to the interfaces between the TiC layer and the braze matrix diminished, due to the increased solubility of Ti in
the Cu-based liquid phase. The enhanced dissolution of Ti in the Cu-based liquid phase at 1050 °C also caused the precipitation
of rod-like CuTi with an average diameter of about 0.2 μm during cooling. SnTi3 was the predominant intermetallic compound and existed in three different forms in the braze matrix. It existed as interconnected
grains of large size which either floated to the surface of the braze matrix or grew into faceted grains. It also exhibited
a nail-like structure with a mean diameter of about 1 μm for the rod section and a lamellar structure arising from a eutectic reaction during cooling. 相似文献
54.
Development of the Chinese Scientometric Indicators (CSI) 总被引:1,自引:0,他引:1
We describe the Chinese Scientometric Indicators (CSI), an indicator database derived from the Chinese Science Citation Database (CSCD). Its design is supported by the Natural Sciences Foundation of China (NSFC). In this indicator database data of a statistical nature are organized and categorized leading to ranked lists and providing bases for comparisons among Chinese institutions and regions. 相似文献
55.
Tsu-Hua Ai Jiann-Fuh Chen Tsorng-Juu Liang 《Industrial Electronics, IEEE Transactions on》2002,49(3):595-597
To overcome the problem of unequal switching loss in power switches, in conventional hybrid pulse width modulation (HPWM) full-bridge inverters, a random switching method for HPWM full-bridge inverters is proposed. The proposed method equalizes switching losses of the four switches, while also providing good output performance 相似文献
56.
行波热声驱动器的性能分析 总被引:1,自引:0,他引:1
在简单介绍行波热声驱动器的研究历史、工作机理及其与驻波型热声驱动器的区别之后,着重对环路部分的性能进行了预测分析,并给出一些有益的结论。 相似文献
57.
新型高k栅介质材料研究进展 总被引:5,自引:0,他引:5
随着半导体技术的不断发展,MOSFET(metal-oxide-semiconductor field effect transistor)的特征尺寸不断缩小,栅介质等效氧化物厚度已小至nm数量级。这时电子的直接隧穿效应将非常显著,将严重影响器件的稳定性和可靠性。因此需要寻找新型高k介质材料,能够在保持和增大栅极电容的同时,使介质层仍保持足够的物理厚度来限制隧穿效应的影响。本文综述了研究高k栅介质材料的意义;MOS栅介质的要求;主要新型高k栅介质材料的最新研究动态;展望了高k介质材料今后发展的主要趋势和需要解决的问题。 相似文献
58.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
59.
60.
The formula and program for calculating the total and negative first harmonic interaction impedance from the data of “large
perturbation measurement” are given. This program is a part of the programs for CCTWT design. 相似文献