全文获取类型
收费全文 | 285577篇 |
免费 | 76781篇 |
国内免费 | 52970篇 |
专业分类
电工技术 | 33753篇 |
技术理论 | 11篇 |
综合类 | 30660篇 |
化学工业 | 38927篇 |
金属工艺 | 32480篇 |
机械仪表 | 12753篇 |
建筑科学 | 19486篇 |
矿业工程 | 16249篇 |
能源动力 | 11101篇 |
轻工业 | 28293篇 |
水利工程 | 9278篇 |
石油天然气 | 19332篇 |
武器工业 | 4528篇 |
无线电 | 40350篇 |
一般工业技术 | 39961篇 |
冶金工业 | 11322篇 |
原子能技术 | 3566篇 |
自动化技术 | 63278篇 |
出版年
2024年 | 3010篇 |
2023年 | 5613篇 |
2022年 | 7121篇 |
2021年 | 8675篇 |
2020年 | 10963篇 |
2019年 | 19908篇 |
2018年 | 21659篇 |
2017年 | 23140篇 |
2016年 | 22682篇 |
2015年 | 22468篇 |
2014年 | 22199篇 |
2013年 | 22098篇 |
2012年 | 21849篇 |
2011年 | 22352篇 |
2010年 | 18730篇 |
2009年 | 14412篇 |
2008年 | 12485篇 |
2007年 | 11175篇 |
2006年 | 10209篇 |
2005年 | 9446篇 |
2004年 | 12557篇 |
2003年 | 10263篇 |
2002年 | 10273篇 |
2001年 | 8657篇 |
2000年 | 7349篇 |
1999年 | 7619篇 |
1998年 | 6300篇 |
1997年 | 5660篇 |
1996年 | 5112篇 |
1995年 | 4890篇 |
1994年 | 3954篇 |
1993年 | 4526篇 |
1992年 | 4023篇 |
1991年 | 2940篇 |
1990年 | 2402篇 |
1989年 | 2112篇 |
1988年 | 1617篇 |
1987年 | 676篇 |
1986年 | 552篇 |
1985年 | 331篇 |
1984年 | 229篇 |
1983年 | 155篇 |
1982年 | 191篇 |
1981年 | 185篇 |
1980年 | 173篇 |
1976年 | 234篇 |
1975年 | 208篇 |
1972年 | 239篇 |
1971年 | 129篇 |
1960年 | 213篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Weikang Dong Ruishi Qi Tiansheng Liu Yi Li Ning Li Ze Hua Zirui Gao Shuyuan Zhang Kaihui Liu Jiandong Guo Peng Gao 《Advanced materials (Deerfield Beach, Fla.)》2020,32(46):2002014
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide (α-MoO3) show in-plane hyperbolicity, great wavelength compression, and ultralong lifetime, therefore holding great potential in nanophotonic applications. However, its polaritonic response in the far-infrared (FIR) range remains unexplored due to challenges in experimental characterization. Here, monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) is used to probe HPhPs in α-MoO3 in both mid-infrared (MIR) and FIR frequencies and correlate their behaviors with microstructures and orientations. It is found that low structural symmetry leads to various phonon modes and multiple Reststrahlen bands (RBs) over a broad spectral range (over 70 meV) and in different directions (55–63 meV and 119–125 meV along the b-axis, 68–106 meV along the c-axis, and 101–121 meV along the a-axis). These HPhPs can be selectively excited by controlling the direction of swift electrons. These findings provide new opportunities in nanophotonic and optoelectronic applications, such as directed light propagation, hyperlenses, and heat transfer. 相似文献
52.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献
53.
中国的菊花主题花展(菊花展览)是最重要的赏菊形式,对我国3种主要类型的菊花展览,即综合性菊花展览(中国菊花展览会、国际博览会菊花专项展和各级城市菊花展)、菊花专类园和菊花花田花海的发展现状进行了研究,并分析了菊花展览在促进菊花产业发展、弘扬菊花文化、服务生态文明及美丽乡村建设、加强菊花非物质文化遗产保护中的重要作用,为推动我国菊花展览水平的提高提供借鉴。 相似文献
54.
积分中值屈服准则解析厚板轧制椭圆速度场 总被引:1,自引:0,他引:1
为解决非线性Mises比塑性功率积分困难以及由此导致的轧制功率解析式难以获得的问题,本文通过建立并利用线性比塑性功率表达式对提出的椭圆速度场进行能量分析,得到了轧制力能参数的解析解.文中通过对变角度屈服函数求积分中值,构建了一个新的屈服准则,它是主应力分量的线性组合,在π平面上的轨迹是逼近Mises圆的等边非等角的十二边形,其基于Lode参数表达式的理论结果也与实验数据吻合较好.同时,根据厚板轧制时金属流动速度从入口到出口逐渐增大的特点,提出了水平速度分量满足椭圆方程的速度场,该速度场满足运动许可条件.通过相应的轧制能量分析,获得了基于线性屈服准则的内部变形功率以及基于应变矢量内积法上的摩擦功率与剪切功率.在此之上,通过泛函的极值变分导出了轧制力矩、轧制力以及应力状态系数的解析解,并与现场实测数据进行了对比,结果表明利用本文提出的屈服准则与速度场所建立的轧制力矩与轧制力模型与实测值吻合较好,其中轧制力误差小于5.3%,轧制力矩误差在6%左右. 相似文献
55.
56.
57.
58.
Meifang Luo Chaozhong Guo Xinyi Luo Zhaoxu Li Yuan Qin Weizhong Zhang 《International Journal of Hydrogen Energy》2021,46(2):2117-2127
It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm?2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices. 相似文献
59.
60.