全文获取类型
收费全文 | 159503篇 |
免费 | 8411篇 |
国内免费 | 5092篇 |
专业分类
电工技术 | 6619篇 |
技术理论 | 3篇 |
综合类 | 5237篇 |
化学工业 | 18967篇 |
金属工艺 | 8789篇 |
机械仪表 | 6942篇 |
建筑科学 | 6723篇 |
矿业工程 | 1987篇 |
能源动力 | 4690篇 |
轻工业 | 11863篇 |
水利工程 | 2097篇 |
石油天然气 | 3148篇 |
武器工业 | 723篇 |
无线电 | 22732篇 |
一般工业技术 | 27212篇 |
冶金工业 | 27177篇 |
原子能技术 | 1927篇 |
自动化技术 | 16170篇 |
出版年
2024年 | 432篇 |
2023年 | 1552篇 |
2022年 | 3149篇 |
2021年 | 4263篇 |
2020年 | 2960篇 |
2019年 | 2585篇 |
2018年 | 3146篇 |
2017年 | 3188篇 |
2016年 | 3001篇 |
2015年 | 3769篇 |
2014年 | 4869篇 |
2013年 | 8294篇 |
2012年 | 7088篇 |
2011年 | 8465篇 |
2010年 | 7078篇 |
2009年 | 7571篇 |
2008年 | 7539篇 |
2007年 | 7402篇 |
2006年 | 6604篇 |
2005年 | 5701篇 |
2004年 | 4960篇 |
2003年 | 4653篇 |
2002年 | 4480篇 |
2001年 | 4455篇 |
2000年 | 3673篇 |
1999年 | 3735篇 |
1998年 | 9806篇 |
1997年 | 6469篇 |
1996年 | 5005篇 |
1995年 | 3375篇 |
1994年 | 2961篇 |
1993年 | 2863篇 |
1992年 | 1729篇 |
1991年 | 1665篇 |
1990年 | 1570篇 |
1989年 | 1356篇 |
1988年 | 1207篇 |
1987年 | 887篇 |
1986年 | 910篇 |
1985年 | 926篇 |
1984年 | 809篇 |
1983年 | 703篇 |
1982年 | 717篇 |
1981年 | 690篇 |
1980年 | 589篇 |
1979年 | 485篇 |
1978年 | 415篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Xin Li Yurui Wang Minxuan Xu Yueqin Shi Hemiao Wang Xin Yang Haoting Ying Qi Zhang 《应用聚合物科学杂志》2021,138(19):50406
Polymer electrets have revealed great potential application in electromechanical devices because of the low weight, large quasi-piezoelectric sensitivity, and excellent flexibility. For an electret, a permanent and macroscopic electric field exists on the surface, principally led by a macroscopic electrostatic charge on the surface or a net orientation of polar groups inside the object. Here, progress in the development of polymer electrets is reviewed. After a brief retrospect of the research courses and those typical polymer electrets that are classified into fluorine polymer and nonfluorine polymer, we present a survey on the charging methods, including corona, soft X-ray, contact, thermal and monoenergetic particle beams. The latest representative applications (i.e., power harvesting, sensors, field effect transistors, and biomedicine) based on polymer electrets are also summarized. Finally, we complete this review with a discussion on perspectives and challenges in this field. 相似文献
3.
大气波导干扰是特定气象条件下发生的时分双工(time-division duplex,TDD)系统内干扰,是TDD移动通信系统大规模组网面临的顽疾。在总结分析大气波导干扰成因和分类等的基础上,对大气波导干扰进行建模和表征,验证了海量干扰源在时域和频域的功率集总特征,并结合大量4G/5G现网实测数据给出了典型条件下内陆波导和海面波导的量化干扰信号传播模型,对于干扰的预测和预防具有重要意义。基于干扰特征,给出了TDD系统预防大气波导干扰的帧结构与组网的4项设计原则,5G现网数据表明干扰控制方案有效,上行干扰下降10 dB以上,相关原则对于6G系统的设计也具有指导意义。 相似文献
4.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
5.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
6.
Shilin Du Yichen Dong Feiqiang Guo Beile Tian Songbo Mao Lin Qian Chengyun Xin 《International Journal of Hydrogen Energy》2021,46(27):14138-14147
The potential of using high metals containing coal gangue and lignite to prepare high-activity coal char-based catalysts is investigated for effective biomass tar decomposition. Loose structure and rough surface are formed for these char-based catalysts with heterogeneous distribution of a large number of inorganic particles. In the biomass tar decomposition, the performance of the coal char-based catalysts is significantly influenced by the content of the metals in the raw materials and coal gangue char (GC) with the ash content as high as 50.80% exhibits the highest activity in this work. A high biomass tar conversion efficiency of 93.5% is achieved at 800 °C along with a significant increase in the fuel gas product. During the five-time consecutive tests, the catalytic performance of GC increases a little at the second or third times reuse and remains relatively stable, showing the remarkable stability of the catalyst in biomass tar decomposition applications. 相似文献
7.
8.
Sun Xiaohao Miao Linchang Wang Hengxing Chen Runfa Guo Xin 《Bulletin of Engineering Geology and the Environment》2021,80(6):4957-4966
Bulletin of Engineering Geology and the Environment - Bio-cementation is currently applied to solidify sandy soils, but only few studies use it to cement loess soil particles. In this study, the... 相似文献
9.
Zhenkun Ke Xin Cao Chuanli Shan Lifen Shi Pingping Wang Yong Yang Fengyang Zhao Jiedong Cui Jinwei Li Gang Zhou Min Guan Tao Yu 《Ceramics International》2021,47(14):19605-19613
The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R2O–CaO–B2O3–SiO2) systematically. Because the glass would emulsify when Li2O was added to the glass batch, this article did not discuss Li2O. The results showed that when the amount of Na2O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na2O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased. 相似文献
10.
Yuzhu Su Junpu Wang Xin Li Qiqi Tang Jing Yang Li Lei Yi Tian Zhiwei Wang Duanwei He 《Ceramics International》2021,47(15):21077-21082
The in situ axial X-ray diffraction patterns of four ceramic powder samples (MgO, Al2O3, AlN, and cBN) that were compressed in a diamond anvil cell under uniaxial non-hydrostatic conditions were recorded. The microscopic deviatoric stress as a function of the pressure was determined from the X-ray diffraction peak broadening analysis: the curves increased approximately linearly with the pressure at the initial compression stage and then levelled off under further compression. Pressure-induced transparency was observed in all of the samples under compression, and the pressure at the turning point on the curves of the microscopic deviatoric stress versus pressure corresponded to the pressure at which the samples became transparent. Analysis of the microstructural features of the pressure-induced transparent samples indicated that the compression caused the grains to fracture, and the broken grains bonded with each other. We demonstrated that the ceramics’ pressure-induced transparency was a process during which the grains were squeezed and broken, the pores were close between the grains, and the broken grains were re-bonded under compression. 相似文献