全文获取类型
收费全文 | 115080篇 |
免费 | 13940篇 |
国内免费 | 9380篇 |
专业分类
电工技术 | 10309篇 |
技术理论 | 1篇 |
综合类 | 12841篇 |
化学工业 | 14989篇 |
金属工艺 | 7781篇 |
机械仪表 | 7949篇 |
建筑科学 | 8871篇 |
矿业工程 | 4059篇 |
能源动力 | 3043篇 |
轻工业 | 12785篇 |
水利工程 | 3499篇 |
石油天然气 | 3922篇 |
武器工业 | 1604篇 |
无线电 | 12461篇 |
一般工业技术 | 10068篇 |
冶金工业 | 4311篇 |
原子能技术 | 2071篇 |
自动化技术 | 17836篇 |
出版年
2024年 | 406篇 |
2023年 | 2102篇 |
2022年 | 4744篇 |
2021年 | 6108篇 |
2020年 | 4348篇 |
2019年 | 3038篇 |
2018年 | 3308篇 |
2017年 | 3661篇 |
2016年 | 3218篇 |
2015年 | 4926篇 |
2014年 | 6400篇 |
2013年 | 7699篇 |
2012年 | 9114篇 |
2011年 | 9493篇 |
2010年 | 8999篇 |
2009年 | 8648篇 |
2008年 | 9286篇 |
2007年 | 8847篇 |
2006年 | 7763篇 |
2005年 | 6426篇 |
2004年 | 4608篇 |
2003年 | 3295篇 |
2002年 | 3176篇 |
2001年 | 2982篇 |
2000年 | 2270篇 |
1999年 | 1056篇 |
1998年 | 470篇 |
1997年 | 333篇 |
1996年 | 286篇 |
1995年 | 217篇 |
1994年 | 183篇 |
1993年 | 154篇 |
1992年 | 126篇 |
1991年 | 109篇 |
1990年 | 96篇 |
1989年 | 94篇 |
1988年 | 61篇 |
1987年 | 45篇 |
1986年 | 43篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 25篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 36篇 |
1979年 | 20篇 |
1976年 | 5篇 |
1970年 | 4篇 |
1959年 | 29篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
良好的负荷预测模型能够精准且快速地计算预测值,有利于合理地规划分配电能,提升电网运行稳定性.基于MATLAB搭建灰色Elman网络电力负荷预测模型,参考安徽省淮南市"十三五"能源规划[1],以对淮南市进行中长期电力负荷预测为例,同时设置基于MATLAB搭建的Elman网络和灰色理论中的GM(1,1)模型为对照组进行对比仿真实验.提出灰色Elman网络相比对照组具有更高的运算精度,灰色Elman网络对比Elman网络有更好的训练效果. 相似文献
4.
于潞璐 《辽东学院学报(自然科学版)》2021,28(3):207-210
运用八段锦进行女大学生篮球教学后疲劳恢复,并与传统恢复手段拉伸运动进行比较实验,探索快速消除运动性疲劳的方法.研究结果显示:女大学生运用八段锦进行篮球教学后的疲劳恢复,其心率恢复明显的优于传统拉伸运动;学生的主观感觉疲劳恢复程度也明显的优于传统拉伸运动.结果表明,八段锦能够有效促进女大学生生理和心理疲劳的恢复. 相似文献
5.
6.
Lindsey Yue Alicia Bayon Wojciech Lipiński 《American Institute of Chemical Engineers》2021,67(8):e17267
The effects of particle size and carbon dioxide concentration on chemical conversion in engineered spherical particles undergoing calcium oxide looping are investigated. Particles are thermochemically cycled in a furnace under different carbon dioxide concentrations. Changes in composition due to chemical reactions are measured using thermogravimetric analysis. Gas composition at the furnace exit is evaluated with mass spectroscopy. A numerical model of thermal transport phenomena developed previously is adapted to match the physical system investigated in the present study. The model is used to elucidate effects of reacting medium characteristics on particle temperature and reaction extent. Experimental and numerical results show that (1) an increase in particle size results in a decrease in carbonation extent, and (2) the carbonation step consists of fast and slow reaction regimes. The reaction rates in the fast and slow carbonation regimes increase with increasing carbon dioxide concentration. The effect of carbon dioxide concentration and the distinction between the fast and slow regimes become more pronounced with increasing particle size. 相似文献
7.
Mg(Ti1-xNbx)O3 (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti4+ replacement by Nb5+ in the formed solid solution Mg(Ti1-xNbx)O3 (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb5+ doping in Mg(Ti1-xNbx)O3 were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti1-xNbx)O3 (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti4+ by the high valence Nb5+ can improve the dielectric properties of Mg(Ti1-xNbx)O3 (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti1-xNbx)O3 (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb2O5, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb5+ to a certain extent to suppress Ti4+ to Ti3+, which was confirmed by XPS. The increase in τf from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τf is the reduction in the distortion degree of the [TiO6] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti0.95Nb0.05)O3 ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of εr = 18.12, Q × f = 163618 GHz and τf = ?40.1 ppm/°C. 相似文献
8.
建立高效液相色谱法检测伐地昔布的有关物质.采用α-酸性糖蛋白键合硅胶的手性色谱柱,以乙腈-醋酸铵缓冲液(0.01 mol/L,pH4.0)作为流动相进行梯度洗脱,检测波长215 nm.伐地昔布与5个已知杂质均可达到基线分离,在各自浓度范围内线性关系良好,平均回收率95.13%~99.77%,RSD1.10%~1.77%,检测限0.017 9~0.060 1 μg/mL,定量限0.059 7~0.200 0 μg/mL.方法专属性强,准确度好,灵敏度高,可为伐地昔布的质量控制及后续分离提纯和帕瑞昔布的质量控制提供指导. 相似文献
9.
10.
Yue Sheng Li Xiaolei Yu Huijun Tong Zongwei Liu Zhengdao 《Journal of Porous Materials》2021,28(3):651-659
Journal of Porous Materials - High-strength silica aerogels were prepared successfully by a new two-step surface modification (TSSM) method via ambient pressure drying (APD). Methyltrimethoxysilane... 相似文献