全文获取类型
收费全文 | 14094篇 |
免费 | 1319篇 |
国内免费 | 944篇 |
专业分类
电工技术 | 275篇 |
综合类 | 570篇 |
化学工业 | 2694篇 |
金属工艺 | 1767篇 |
机械仪表 | 2139篇 |
建筑科学 | 178篇 |
矿业工程 | 95篇 |
能源动力 | 248篇 |
轻工业 | 721篇 |
水利工程 | 34篇 |
石油天然气 | 167篇 |
武器工业 | 80篇 |
无线电 | 2838篇 |
一般工业技术 | 3265篇 |
冶金工业 | 341篇 |
原子能技术 | 716篇 |
自动化技术 | 229篇 |
出版年
2024年 | 18篇 |
2023年 | 251篇 |
2022年 | 287篇 |
2021年 | 404篇 |
2020年 | 420篇 |
2019年 | 444篇 |
2018年 | 405篇 |
2017年 | 501篇 |
2016年 | 482篇 |
2015年 | 451篇 |
2014年 | 566篇 |
2013年 | 835篇 |
2012年 | 789篇 |
2011年 | 1061篇 |
2010年 | 756篇 |
2009年 | 781篇 |
2008年 | 847篇 |
2007年 | 844篇 |
2006年 | 778篇 |
2005年 | 687篇 |
2004年 | 581篇 |
2003年 | 531篇 |
2002年 | 486篇 |
2001年 | 301篇 |
2000年 | 309篇 |
1999年 | 280篇 |
1998年 | 261篇 |
1997年 | 261篇 |
1996年 | 254篇 |
1995年 | 205篇 |
1994年 | 153篇 |
1993年 | 147篇 |
1992年 | 143篇 |
1991年 | 127篇 |
1990年 | 114篇 |
1989年 | 106篇 |
1988年 | 75篇 |
1987年 | 68篇 |
1986年 | 62篇 |
1985年 | 62篇 |
1984年 | 69篇 |
1983年 | 54篇 |
1982年 | 57篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
Yuhui ZHANG 《等离子体科学和技术》2019,21(7):74003-33
In this paper, a two-dimensional axisymmetric fluid model was established to investigate the influence of nitrogen impurity content on the discharge pattern and the relevant discharge characteristics in an atmosphere pressure helium dielectric barrier discharge (DBD). The results indicated that when the nitrogen content was increased from 1 to 100 ppm, the discharge pattern evolved from a concentric-ring pattern into a uniform pattern, and then returned to the concentricring pattern. In this process, the discharge mode at the current peak moment transformed from glow mode into Townsend mode, and then returned to glow mode. Further analyses revealed that with the increase of impurity level, the rate of Penning ionization at the pre-ionization stage increased at first and decreased afterwards, resulting in a similar evolution pattern of seed electron level. This evolution trend was believed to be resulted from the competition between the N2 partial pressure and the consumption rate of metastable species. Moreover, the discharge uniformity was found positively correlated with the spatial uniformity of seed electron density as well as the seed electron level. The reason for this correlation was explained by the reduction of radial electric field strength and the promotion of seed electron uniformity as pre-ionization level increases. The results obtained in this work may help better understand the pattern formation mechanism of atmospheric helium DBD under the variation of N2 impurity level, thereby providing a possible means of regulating the discharge performance in practical application scenarios. 相似文献
72.
73.
Marieke M. Hoog Antink Lisa Röpke Julia Bartels Christian Soltmann Andreas Kunzmann Kurosch Rezwan Stephen Kroll 《Ceramics International》2018,44(14):16561-16571
The growing demand for stony corals as ornamental aquarium animals requires defined aquacultural breeding strategies. For the sexual propagation of corals, material substrates are needed, that attract larvae and support their settlement and development. In this study, five types of highly porous ceramic materials were developed following the example of coral skeleton. The applicability of these settlement substrates was tested using larvae of the stony coral Pocillopora damicornis. Partial sintering of pressed clay pellets, freeze casting of clay and alumina-mullite based slurries and direct foaming of high alkane phase emulsified suspensions (HAPES) using alumina were employed. By the addition of mm-sized spherical polystyrene beads as sacrificial templates during freeze casting (alumina-mullite), superficial pores in the size of the larvae were created. The inorganic substrates featured open porosities between 35% (pressed clay) and 83% (foamed alumina), pore sizes ranging from nm to mm-scale and pore morphologies dominated by interparticle porosity (pressed), lamellar pores (freeze casting) and cellular pore types (direct foaming). The ceramic substrates were incubated in artificial sea water for 3 months to induce necessary biofilm formation and algae growth. Afterwards, individual substrates were exposed to 5 coral larvae, and their settlement behavior was monitored over 14 days. At the end of this period, all ceramic materials were successfully accepted as settlement substrates, with a mean settlement rate of 46.2%, and no significant differences between the substrate types. On samples with large surface superficial pores, a significantly reduced survival of settled larvae (79%) compared to the other porous materials (93–98%) was determined, suggesting a non-ideal surface topography. While alumina foam samples (HAPES) exhibit the most promising results in terms of settlement and survival of larvae, clay-based substrates provide a more economic solution for the sexual propagation of corals in aquaculture. 相似文献
74.
75.
本实验通过采用电子探针显微分析和X-ray衍射分析方法实验研究了Co-Cu-Zn三元体系在800°C和1000°C时的相平衡。在这两个等温截面中均未发现三元化合物。在800°C等温截面,Co在β-CuZn相中的固溶度为32.36%,Cu在β1-CoZn相中的固溶度为5.28%。除此之外,γ-Co5Zn21和γ-Cu5Zn8具有相同的晶体结构,因此,它们之间形成了一个贯穿连续固溶体相。1000°C的等温截面中,β-CuZn相、β1-CoZn相、γ-Co5Zn21相、γ-Cu5Zn8相都消失了。随着温度从800°C上升到1000°C,液相区域增大。 相似文献
76.
77.
Martin G. Bakker Benjamin Fowler Michael K. Bowman Gregory S. Patience 《加拿大化工杂志》2020,98(8):1668-1681
Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance spectroscopy (ESR), utilizes absorption of microwave radiation by unpaired electrons in a magnetic field. The interaction between the unpaired electron(s) and nearby magnetic nuclei helps identify paramagnetic species and can provide information about the motion of the molecule and the local polarity, pH, viscosity, concentration, and accessibility to other paramagnetic species. This mini-review discusses the fundamental underpinnings of EPR needed to correctly interpret EPR spectra. We describe various types of EPR spectra encountered by chemical engineers, and use application examples drawn from the chemical engineering literature to illustrate the information available from the technique. Few chemical engineering departments or even chemistry departments have EPR instruments, which contributes to the significant barrier that prevents this being adopted as a routine measurement technique. However, in 2016 and 2017, Web of Science indexed 7000 articles that applied EPR spectroscopy. A bibliometric map categorized the keywords in four categories based on co-occurrences: magnetic properties, films, and luminescence; crystal structure, complexes, and ligands; nanoparticles, oxidation, and degradation; and, systems, radicals, and H2 O2 . 相似文献
78.
ABSTRACTIn the present paper, the mechanical properties and the scratch failure mechanisms of Ni–P electroless coatings are described. The material microstructure was studied in as-deposited and annealed conditions through SEM and EDS analyses. Nanoindentation measurements on the coatings showed a remarkable hardening due to the crystallization and precipitation behaviour produced by annealing. The scratch tests, conducted by increasing the load during scratch, revealed the coating failure mechanisms in a broad range of applied stresses up to delamination. 相似文献
79.
Dbora Drummond Hauss Monteiro Henrique Limboro Rodrigo Guimares Porto Allyson Nogueira Moreira Wagner Nunes Rodrigues Cludia Silami de Magalhes 《Microscopy research and technique》2020,83(6):597-603
The MeX? software is a useful tool for tridimensional data collection for surface evaluation and could be relevant to evaluate the same specimen in different phases of the study, assuming repeated measures of dental enamel roughness. The aim of this study was to evaluate the influence of sample metallization for dental enamel roughness analysis with 3D images reconstructed using MeX? software from Scanning Electron Microscopy (SEM) images. The influence of 74.98% (%mol/mol) argon?oxygen plasma for carbon layer removal on surface roughness of the metallized specimen was also evaluated. Dental enamel specimens were prepared for SEM analysis with and without carbon metallization using conventional or environmental modes. Argon?oxygen plasma for carbon layer removal was used and surface roughness was re‐evaluated. Roughness obtained by SEM and MeX? reconstructed images, with or without metallization, did not differ. No significant alteration on surface roughness after carbon layer removal using plasma was found. SEM baseline evaluation using conventional mode without sample preparation and in environmental mode were not comparable. Roughness of enamel 3D images reconstructed with MeX? software from SEM images, with or without metallization was similar. The 74.98% (%mol/mol) argon?oxygen plasma removed the carbon layer with no effect on enamel roughness. 相似文献
80.
Weibing Guo Haitao Xue Xin Wei Xiaoming Zhang 《International Journal of Applied Ceramic Technology》2020,17(3):1286-1292
Ti element is an important active element in brazing Zirconia ceramic (ZrO2) ceramic. Therefore, the interface bonding mechanism of Ti and ZrO2 was studied by using first principles calculation. Two kinds of interfaces with different termination and stacking sequence were established, and the interfacial bonding mechanism was studied using work of adhesion (Wad), electronic behavior and interface energy. The results show that in the O-terminated interface, Ti and O form a strong ion-covalent bond at the interface, and the Wad can reach 13.61 J/m2. In the Zr-terminated interface, Ti and Zr form a metal-covalent bond, and the Wad is 5.56 J/m2. At a temperature of 1123K, when the lnPO2 is larger than e−17, the O-rich interface is more stable in thermodynamics. Therefore, under the experimental condition, the interface tends to form Ti-O compounds when ZrO2 is brazed using Ag(Ti) filler metal. 相似文献