全文获取类型
收费全文 | 38112篇 |
免费 | 4773篇 |
国内免费 | 1882篇 |
专业分类
电工技术 | 1026篇 |
综合类 | 2226篇 |
化学工业 | 7691篇 |
金属工艺 | 5883篇 |
机械仪表 | 2043篇 |
建筑科学 | 1407篇 |
矿业工程 | 1329篇 |
能源动力 | 1153篇 |
轻工业 | 5160篇 |
水利工程 | 450篇 |
石油天然气 | 1572篇 |
武器工业 | 381篇 |
无线电 | 2758篇 |
一般工业技术 | 5744篇 |
冶金工业 | 3735篇 |
原子能技术 | 372篇 |
自动化技术 | 1837篇 |
出版年
2024年 | 225篇 |
2023年 | 1042篇 |
2022年 | 1135篇 |
2021年 | 1458篇 |
2020年 | 1654篇 |
2019年 | 1560篇 |
2018年 | 1312篇 |
2017年 | 1548篇 |
2016年 | 1393篇 |
2015年 | 1417篇 |
2014年 | 2008篇 |
2013年 | 2312篇 |
2012年 | 2424篇 |
2011年 | 2567篇 |
2010年 | 1899篇 |
2009年 | 1992篇 |
2008年 | 1750篇 |
2007年 | 2279篇 |
2006年 | 2098篇 |
2005年 | 1939篇 |
2004年 | 1563篇 |
2003年 | 1519篇 |
2002年 | 1246篇 |
2001年 | 1061篇 |
2000年 | 981篇 |
1999年 | 790篇 |
1998年 | 638篇 |
1997年 | 511篇 |
1996年 | 483篇 |
1995年 | 382篇 |
1994年 | 345篇 |
1993年 | 253篇 |
1992年 | 217篇 |
1991年 | 165篇 |
1990年 | 144篇 |
1989年 | 125篇 |
1988年 | 70篇 |
1987年 | 51篇 |
1986年 | 39篇 |
1985年 | 40篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Xueliang Wang Huiqin Yin Wenguan Liu Guojun Yu Jian He Zhongfeng Tang Long Yan 《工业材料与腐蚀》2020,71(6):931-937
Understanding the corrosion of molten ZnCl2 on metal surfaces is significant for the corrosion protection of metals, sustainable use of molten salts, preparation of ZnO coatings, and so on. In this paper, surfaces of pure Ni, Cr, and Fe corroded by molten ZnCl2 were investigated. The results show that Ni suffered very slight corrosion, while Cr experienced more serious corrosion than Ni, but lighter corrosion than Fe. The morphology of the corrosion of Cr and Fe, respectively, presented pitting and intergranular corrosion characteristics. Furthermore, nanostructured ZnO coatings were obtained on the surfaces of Ni and Fe, but not on the surface of Cr. The ZnO coating on the Ni surface was doped with a small amount of Zn5(OH)8Cl2, and the ZnO coating on the Fe surface was doped with ZnFe2O4 and Zn2OCl2. The coatings on the Ni and Fe surfaces had an average thickness of 1.5 and 50 μm, respectively. 相似文献
33.
34.
Wyatt L. Brown Douglas A. Day Harald Stark Demetrios Pagonis Jordan E. Krechmer Xiaoxi Liu Derek J. Price Erin F. Katz Peter F. DeCarlo Catherine G. Masoud Dongyu S. Wang Lea Hildebrandt Ruiz Caleb Arata David M. Lunderberg Allen H. Goldstein Delphine K. Farmer Marina E. Vance Jose L. Jimenez 《Indoor air》2021,31(1):141-155
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations. 相似文献
35.
The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system. 相似文献
36.
37.
X.W. Lou C. Yuan E. Rhoades Q. Zhang L.A. Archer 《Advanced functional materials》2006,16(13):1679-1684
We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth. 相似文献
38.
Service composition for generic service graphs 总被引:1,自引:0,他引:1
Service composition is a promising approach to multimedia service provisioning, due to its ability to dynamically produce new multimedia content, and to customize the content for individual client devices. Previous research work has addressed various aspects of service composition such as composibility, QoS-awareness, and load balancing. However, most of the work has focused on applications where data flow from a single source is processed by intermediate services and then delivered to a single destination. In this paper, we address the service composition problem for multimedia services that can be modeled as directed acyclic graphs (DAGs). We formally define the problem and prove its NP hardness. We also design a heuristic algorithm to solve the problem. Our simulation results show that the algorithm is effective at finding low-cost composition solutions, and can trade off computation overhead for better results. When compared with a hop-by-hop approach for service composition, our algorithm can find composition solutions that aress 10% smaller in cost, even when the hop-by-hop approach uses exhaustive searches. 相似文献
39.
40.
新型壳聚糖/纳米二氧化硅杂化材料的制备与性能 总被引:10,自引:5,他引:5
在纳米S iO2颗粒表面引入羟丙基氯活性基团,得到功能化S iO2颗粒,再将羟丙基氯化的S iO2颗粒交联固定在壳聚糖上,制备了一种新型的壳聚糖/纳米S iO2杂化材料(简称杂化材料);通过傅里叶变换红外光谱、透射电镜、扫描电镜方法对杂化材料进行表征,采用热重(TG)分析研究杂化材料的热性能;考察了杂化材料的沉降速率和对金属离子Ca2+和M g2+的吸附能力。电镜分析结果表明,杂化材料微粒为纳米尺度的无机S iO2加强化的微粒,S iO2颗粒分散在材料中,形成均匀的表面;TG分析结果表明,杂化材料的热性能有所提高;沉降实验测得壳聚糖和杂化材料作为吸附剂的沉降时间分别为130.3,68.5s,表明杂化材料的沉降速率比壳聚糖的沉降速率快了近一倍;杂化材料对金属离子Ca2+和M g2+的吸附量分别可达到0.289 3,1.445 6mm ol/g。 相似文献