全文获取类型
收费全文 | 32965篇 |
免费 | 2820篇 |
国内免费 | 1521篇 |
专业分类
电工技术 | 1058篇 |
综合类 | 1147篇 |
化学工业 | 12047篇 |
金属工艺 | 3090篇 |
机械仪表 | 449篇 |
建筑科学 | 365篇 |
矿业工程 | 1062篇 |
能源动力 | 3827篇 |
轻工业 | 743篇 |
水利工程 | 37篇 |
石油天然气 | 1026篇 |
武器工业 | 61篇 |
无线电 | 2453篇 |
一般工业技术 | 6509篇 |
冶金工业 | 2625篇 |
原子能技术 | 376篇 |
自动化技术 | 431篇 |
出版年
2024年 | 105篇 |
2023年 | 693篇 |
2022年 | 1005篇 |
2021年 | 1349篇 |
2020年 | 1236篇 |
2019年 | 1222篇 |
2018年 | 1165篇 |
2017年 | 1234篇 |
2016年 | 1107篇 |
2015年 | 1112篇 |
2014年 | 1628篇 |
2013年 | 1906篇 |
2012年 | 2071篇 |
2011年 | 2680篇 |
2010年 | 2016篇 |
2009年 | 1946篇 |
2008年 | 1677篇 |
2007年 | 1923篇 |
2006年 | 1678篇 |
2005年 | 1381篇 |
2004年 | 1192篇 |
2003年 | 1073篇 |
2002年 | 935篇 |
2001年 | 790篇 |
2000年 | 764篇 |
1999年 | 599篇 |
1998年 | 490篇 |
1997年 | 380篇 |
1996年 | 341篇 |
1995年 | 265篇 |
1994年 | 238篇 |
1993年 | 180篇 |
1992年 | 196篇 |
1991年 | 154篇 |
1990年 | 133篇 |
1989年 | 106篇 |
1988年 | 61篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 367 毫秒
991.
Tribological behavior of hydrogenated diamond-like carbon (DLC) films and Si incorporated DLC (Si-DLC) films deposited on Si (100) wafer by r.f.-plasma assisted chemical vapor deposition were investigated by ball-on-disk type tribometry in various environments. The friction tests were performed in ambient air of relative humidity ranging from 0% to 90% or dry oxygen environment. We focused on the tribochemical reactions by analyzing chemical composition, chemical bond structure and agglomerated shape of the debris. High and unstable friction behavior was observed in both humid air and dry oxygen environments. In these environments, Auger spectrum analysis showed that the debris contained large amounts of Fe. Significant incorporation of Fe in the debris resulted from the wear of the steel ball, which might be enhanced by the surface oxidation of the ball. These results show that the humidity dependence of friction coefficient is not an inherent tribological property of DLC films but results from the surface reaction of the steel ball in humid environments. Two possible reasons for the Fe rich debris affecting the friction behavior are presented. Reduced dependence of the friction coefficient on the relative humidity observed for Si-DLC films is discussed in terms of the two possible reasons. 相似文献
992.
High resolution electron microscopy has been used to examine both the similarities and differences in the growth morphologies of Fe2O3, Cr2O3 as formed on iron alloys, and MgO as formed by burning Mg in moist air. A general discussion is also given of the relative advantages and disadvantages of a variety of TEM techniques as applicable to the study of oxidation phenomena. 相似文献
993.
用Falex四球摩擦磨损试验机考察了金红石相与锐钛矿相TiO2、α-Al2O3和γ-Al2O3、钇稳四方相和单斜相ZrO2纳米粒子作为润滑脂添加剂的摩擦学行为。试验结果表明,这些纳米粒子均具有较好的减摩抗磨性能和较高的承载能力(pB值),其润滑性能与纳米粒子的结构和大小都有一定的关系,而且在添加浓度3%左右时具有最佳的效果。 相似文献
994.
为实现N_2O的减量化控制或资源化利用,接种普通活性污泥,以乙酸钠和硝酸盐为基质,通过淘洗反硝化聚磷菌,在SBR中以厌氧/缺氧交替运行的方式启动內源反硝化,单周期内约50%的NO-3-N转化为NO-2-N,N_2O释放速率随着亚硝酸的积累逐渐增大,N_2O转化率(释放量占TN去除的比例)为2.04%.在此基础上,分别取缺氧末和厌氧末污泥,对比研究胞内聚合物PHB合成前后,外碳源投加量(碳氮比为0,0.75和2.50)对亚硝酸型反硝化过程N_2O释放特性的影响,结果表明,外碳源存在时,N_2O释放量随总碳源的增加呈略微减少的趋势,转化率在0.24%~1.61%;而当仅利用內源物质进行反硝化时,N_2O的转化率高达15.90%,单位SS最大释放速率达71.29μg/(min·g),释放量是其余条件下的14~26倍.表明单独利用PHB进行亚硝酸型反硝化会大幅增加N_2O的释放. 相似文献
995.
The Raman scattering and photoluminescence (PL) spectra, PL temperature dependences and scanning electronic microscopy (SEM) images have been studied in the mixture of ZnO+1.0%C nanocrystals (NCs) before and after intensive mechanical processing (MP). The study reflects the diversity of physical processes occurring at MP: the amorphization of the ZnO NC surface, transforming an amorphous graphite into graphene monolayers covered of ZnO NCs, changing the ZnO NC shape owing to the plastic deformation and crushing the individual ZnO NCs, the partial oxidation of graphene layers with the formation of graphene oxide passivating ZnO NCs, the formation of graphite oxide when temperature increasing at MP, as well as the ZnO defect modification near the surface of ZnO NCs, etc. Additionally the new ‘blue” PL band peaked at 2.82–2.92 eV has been revealed in PL spectra after MP, which is assigned to emission of graphite (graphene) oxides. All mentioned processed have been studied and discussed in details. 相似文献
996.
997.
998.
Yihang Li Lixiang Yu Yingqin Yu Kristina Maliutina Qixing Wu Chuanxin He Liangdong Fan 《International Journal of Hydrogen Energy》2021,46(15):9646-9652
Electrochemical reduction reaction is an important approach to utilize CO2 and convert it into valuable products. Exceptional reaction kinetics at a high temperature of solid oxide electrolysis cells (SOECs) attracts particular attention. In this work, we propose to investigate CO2-RR kinetics using a new theoretical method based on the electrical conductivity relaxation (ECR) technique on a typical mixed-conducting Sr2Fe1.5Mo0.5O6-δ (SFM) electrode. Three kinetic parameters that are commonly adopted in the typical electrochemical test experiments consisting of overpotential, current density and area-specific resistance (ASR) are derived. The overpotential resulted from the difference in the oxygen partial pressure is caused by the change of CO2 partial pressure, while current density from the surface reaction rate constant. Accordingly, area-specific resistance, as well as overpotential-current density relationship, can be derived. We believe that this work brings a new method to study the kinetic process of CO2 electrolysis and to evaluate the electrocatalyst activity of developed new electrode materials as well as to benefit the designing of novel electrode electrocatalysts for highly efficient solid oxide electrolysis cells. 相似文献
999.
Tong Wei Bo Liu Lichao Jia Renhong Li 《International Journal of Hydrogen Energy》2021,46(48):24441-24460
SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH4 fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution. 相似文献
1000.
《Materials at High Temperatures》2013,30(3):261-271
AbstractA novel, two-stage oxidation experiment is described that enables the outward diffusion of cations in alumina scales during high-temperature oxidation to be analyzed on the basis of microstructural changes in the surface morphology of the scale. Using this technique, observations of aluminum out-diffusion along α-Al2O3 grain boundaries during oxidation of Fe–Cr–Al alloys, nickel aluminides and platinum-modified NiAl bond-coats are made. Although microstructural evidence for the inward grain boundary diffusion of oxygen is more difficult to obtain, it still can be demonstrated by the growth of the oxide above interface cavities on nickel aluminides and inside internal cracks in the alumina scales during cyclic oxidation of zirconia top-coated material. SEM examination of the crack surfaces after scale spallation provides a vivid illustration of two simultaneous processes, aluminum outward and oxygen inward diffusion along grain boundaries in the scale. 相似文献