全文获取类型
收费全文 | 31915篇 |
免费 | 4171篇 |
国内免费 | 2311篇 |
专业分类
电工技术 | 2235篇 |
综合类 | 3706篇 |
化学工业 | 4439篇 |
金属工艺 | 1705篇 |
机械仪表 | 2813篇 |
建筑科学 | 4248篇 |
矿业工程 | 1136篇 |
能源动力 | 1556篇 |
轻工业 | 919篇 |
水利工程 | 1757篇 |
石油天然气 | 1367篇 |
武器工业 | 376篇 |
无线电 | 3815篇 |
一般工业技术 | 4006篇 |
冶金工业 | 1309篇 |
原子能技术 | 634篇 |
自动化技术 | 2376篇 |
出版年
2024年 | 136篇 |
2023年 | 463篇 |
2022年 | 846篇 |
2021年 | 956篇 |
2020年 | 1164篇 |
2019年 | 987篇 |
2018年 | 969篇 |
2017年 | 1322篇 |
2016年 | 1321篇 |
2015年 | 1388篇 |
2014年 | 1814篇 |
2013年 | 2065篇 |
2012年 | 2329篇 |
2011年 | 2462篇 |
2010年 | 1786篇 |
2009年 | 1911篇 |
2008年 | 1868篇 |
2007年 | 2228篇 |
2006年 | 1940篇 |
2005年 | 1636篇 |
2004年 | 1386篇 |
2003年 | 1125篇 |
2002年 | 982篇 |
2001年 | 826篇 |
2000年 | 750篇 |
1999年 | 621篇 |
1998年 | 490篇 |
1997年 | 443篇 |
1996年 | 398篇 |
1995年 | 341篇 |
1994年 | 297篇 |
1993年 | 214篇 |
1992年 | 197篇 |
1991年 | 158篇 |
1990年 | 148篇 |
1989年 | 118篇 |
1988年 | 81篇 |
1987年 | 51篇 |
1986年 | 42篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1973年 | 2篇 |
1965年 | 2篇 |
1959年 | 5篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2020,40(8):3348-3353
Large transduction coefficient () is difficult to obtain in piezoelectric ceramics because these two parameters show opposite trends with compositional modifications. Herein, the Pb(Zr0.53Ti0.47)O3 ceramic powders were calcinated under different temperatures (A:830 °C, B:860 °C, and C:890 °C), and then mixed together according to different weight ratios (1A:1B:1C, 1A:2B:1C, 1A:2B:3C and 3A:2B:1C) for ceramics preparation. Both d33 and g33 are improved successfully, and the transduction coefficient with the weight ratio of 1A:2B:3C reaches up to 17,500 × 10−15 m2/N, which is 60 % higher than that with the powders calcinated under 830 °C, and at least twice those of commercial PZT-4, PZT-5A and PZT-8 ceramics. The improved transduction coefficient is owing to the enhanced piezoelectric constant and spontaneous polarization resulted from the increased grain size, relative density and the fraction of tetragonal phase. These results indicate that this is a simple but effective way to tailor the transduction coefficient in piezoelectric ceramics. 相似文献
2.
3.
讨论了输出终端带不等式约束情形的多输入多输出系统,说明了这些约束可以通过修改输入柔化系数而使其得以满足,在柔化系数的选择范围确定过程中,为了避免矩阵求逆,采用利用已知数据辨识参数的方法来确定柔化系数,从而使得问题简化。降低了计算量且加快了收敛速度。 相似文献
4.
为了提高非稳定渗流计算的计算精度 ,通过数学分析得到了水位传导系数随时间变化时 ,一类非稳定渗流井流模型的半解析解 ,并进行了计算比较 相似文献
5.
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
6.
7.
An experimental technique together with a numerical model is proposed with which the diffusion coefficient and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapour in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equilibrium. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theoretical/numerical model against the experimental values, follow the diffusion coefficient and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coefficient. 相似文献
8.
Cs-K混合蒸气中Cs(8D)+K(4S)碰撞能量转移 总被引:3,自引:3,他引:0
在Cs-K混合蒸气中,两步激发Cs原子到8D态,观察了Cs(8D) K(4S)→Cs(5D) K(4P)碰撞能量合并逆过程(REP,reverse energy pooling)。应用双调制技术探测K(4P)原子发射的荧光,基态K原子密度用光学吸收方法测量。得到了REP速率系数,讨论了其它过程对速率系数的影响. 相似文献
9.
10.