全文获取类型
收费全文 | 131834篇 |
免费 | 13386篇 |
国内免费 | 7571篇 |
专业分类
电工技术 | 9262篇 |
技术理论 | 11篇 |
综合类 | 9848篇 |
化学工业 | 20233篇 |
金属工艺 | 7979篇 |
机械仪表 | 8719篇 |
建筑科学 | 10726篇 |
矿业工程 | 4708篇 |
能源动力 | 4063篇 |
轻工业 | 8766篇 |
水利工程 | 2840篇 |
石油天然气 | 7836篇 |
武器工业 | 1369篇 |
无线电 | 15551篇 |
一般工业技术 | 14197篇 |
冶金工业 | 5995篇 |
原子能技术 | 1710篇 |
自动化技术 | 18978篇 |
出版年
2024年 | 689篇 |
2023年 | 2338篇 |
2022年 | 4518篇 |
2021年 | 6342篇 |
2020年 | 4789篇 |
2019年 | 3824篇 |
2018年 | 4257篇 |
2017年 | 4760篇 |
2016年 | 4175篇 |
2015年 | 6003篇 |
2014年 | 7559篇 |
2013年 | 8729篇 |
2012年 | 9917篇 |
2011年 | 10425篇 |
2010年 | 9410篇 |
2009年 | 8574篇 |
2008年 | 8259篇 |
2007年 | 7663篇 |
2006年 | 6977篇 |
2005年 | 5793篇 |
2004年 | 4005篇 |
2003年 | 3441篇 |
2002年 | 3637篇 |
2001年 | 2952篇 |
2000年 | 2358篇 |
1999年 | 2357篇 |
1998年 | 1664篇 |
1997年 | 1421篇 |
1996年 | 1418篇 |
1995年 | 1108篇 |
1994年 | 842篇 |
1993年 | 610篇 |
1992年 | 466篇 |
1991年 | 366篇 |
1990年 | 267篇 |
1989年 | 212篇 |
1988年 | 200篇 |
1987年 | 113篇 |
1986年 | 90篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 40篇 |
1979年 | 20篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1959年 | 14篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 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.
54.
55.
56.
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
57.
58.
三元复合驱油体系中驱油剂的协同效应,会使油水间的界面张力大幅度下降,原油采收率大幅度提高;但三元复合驱油体系的色谱分离现象也会破坏其协同效应和完整性,揭示色谱分离现象及其影响因素对于改善三元复合驱油效果具有十分重要意义。以油藏工程和分析化学理论为指导,以化学分析和物理模拟为技术途径,并以大庆喇嘛甸油田典型区块地质特征和流体性质为研究对象,开展强碱三元复合驱色谱分离现象及其影响因素研究。结果表明,采用前置高浓度聚合物段塞后,可以有效扩大波及体积,但表面活性剂与碱和聚合物之间无因次等浓距增加,色谱分离现象加剧。大庆油区喇嘛甸油田不同区块油水性质差异对色谱分离现象存在影响,原因在于部分重烷基苯石油磺酸进入油相,影响水相中浓度检测值。强碱三元复合驱油体系中表面活性剂与碱和聚合物之间色谱分离程度比较严重,碱与聚合物之间较弱。 相似文献
59.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors. 相似文献
60.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献