全文获取类型
收费全文 | 341546篇 |
免费 | 22642篇 |
国内免费 | 12055篇 |
专业分类
电工技术 | 16818篇 |
技术理论 | 18篇 |
综合类 | 18451篇 |
化学工业 | 54248篇 |
金属工艺 | 18654篇 |
机械仪表 | 18755篇 |
建筑科学 | 23025篇 |
矿业工程 | 7176篇 |
能源动力 | 8480篇 |
轻工业 | 22707篇 |
水利工程 | 5946篇 |
石油天然气 | 13796篇 |
武器工业 | 2103篇 |
无线电 | 40427篇 |
一般工业技术 | 47208篇 |
冶金工业 | 15437篇 |
原子能技术 | 3045篇 |
自动化技术 | 59949篇 |
出版年
2024年 | 912篇 |
2023年 | 3949篇 |
2022年 | 7267篇 |
2021年 | 10322篇 |
2020年 | 7563篇 |
2019年 | 6344篇 |
2018年 | 20441篇 |
2017年 | 20420篇 |
2016年 | 16567篇 |
2015年 | 10505篇 |
2014年 | 13006篇 |
2013年 | 16378篇 |
2012年 | 19972篇 |
2011年 | 27923篇 |
2010年 | 24097篇 |
2009年 | 21137篇 |
2008年 | 21871篇 |
2007年 | 22095篇 |
2006年 | 14673篇 |
2005年 | 13714篇 |
2004年 | 9764篇 |
2003年 | 8638篇 |
2002年 | 7491篇 |
2001年 | 6289篇 |
2000年 | 6039篇 |
1999年 | 6375篇 |
1998年 | 5736篇 |
1997年 | 4710篇 |
1996年 | 4248篇 |
1995年 | 3533篇 |
1994年 | 2928篇 |
1993年 | 2306篇 |
1992年 | 1778篇 |
1991年 | 1371篇 |
1990年 | 1070篇 |
1989年 | 899篇 |
1988年 | 700篇 |
1987年 | 498篇 |
1986年 | 391篇 |
1985年 | 327篇 |
1984年 | 204篇 |
1983年 | 184篇 |
1982年 | 159篇 |
1981年 | 147篇 |
1980年 | 150篇 |
1979年 | 102篇 |
1977年 | 65篇 |
1976年 | 81篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
王虔虔在上任中建材(合肥)粉体科技装备有限公司(简称粉体公司)总经理之前,和分管部门的所有同事坐在同一间大办公室内。之所以和大家在同一个空间内工作,王虔虔是想更进一步拉近彼此之间的距离,以身作则潜移默化,传承公司文化,建立相互信任的团队。2012年,粉体公司决定向"提供系统解决方案的综合服务商"转变。 相似文献
102.
103.
ABSTRACT This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared. 相似文献
104.
105.
106.
107.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
108.
不同折流板结构螺旋折流板换热器传热性能的比较(英文) 总被引:1,自引:0,他引:1
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
109.
粤港澳大湾区世界城市群与世界机场群相伴而生、联动发展.建设世界级机场群,需要5大机场错位发展和良性互动.澳门国际机场是澳门融入粤港澳大湾区重要一极,但机场发展存在与澳门定位、香港珠海空域空运矛盾、澳门土地和环境现状等相关的问题.因此,澳门国际机场今后发展需在葡语国家航线、珠澳密切合作、公务机产业方面努力实现跨越式发展.然而,澳门国际机场改扩建问题争议不断,本文就原址扩建、填海区新建、飞地黄茅岛新建3种模式进行比较分析,探索符合澳门长远利益之方案. 相似文献
110.
Ting Liu Huimin Zhang Panfei Ma Aimin Chang Hui Jiang 《Journal of the American Ceramic Society》2019,102(8):4393-4398
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics. 相似文献