全文获取类型
收费全文 | 128822篇 |
免费 | 9300篇 |
国内免费 | 7675篇 |
专业分类
电工技术 | 8433篇 |
技术理论 | 3篇 |
综合类 | 8173篇 |
化学工业 | 30872篇 |
金属工艺 | 12719篇 |
机械仪表 | 8797篇 |
建筑科学 | 5081篇 |
矿业工程 | 2002篇 |
能源动力 | 4015篇 |
轻工业 | 9051篇 |
水利工程 | 770篇 |
石油天然气 | 5578篇 |
武器工业 | 1141篇 |
无线电 | 12830篇 |
一般工业技术 | 15305篇 |
冶金工业 | 3350篇 |
原子能技术 | 1287篇 |
自动化技术 | 16390篇 |
出版年
2024年 | 397篇 |
2023年 | 1735篇 |
2022年 | 2805篇 |
2021年 | 3530篇 |
2020年 | 3092篇 |
2019年 | 3143篇 |
2018年 | 3005篇 |
2017年 | 3847篇 |
2016年 | 3959篇 |
2015年 | 4127篇 |
2014年 | 6011篇 |
2013年 | 6958篇 |
2012年 | 7679篇 |
2011年 | 9096篇 |
2010年 | 7486篇 |
2009年 | 8270篇 |
2008年 | 7783篇 |
2007年 | 8729篇 |
2006年 | 8543篇 |
2005年 | 7072篇 |
2004年 | 6237篇 |
2003年 | 5767篇 |
2002年 | 4833篇 |
2001年 | 3878篇 |
2000年 | 3451篇 |
1999年 | 2703篇 |
1998年 | 2056篇 |
1997年 | 1630篇 |
1996年 | 1450篇 |
1995年 | 1383篇 |
1994年 | 1180篇 |
1993年 | 1019篇 |
1992年 | 816篇 |
1991年 | 486篇 |
1990年 | 316篇 |
1989年 | 314篇 |
1988年 | 192篇 |
1987年 | 123篇 |
1986年 | 126篇 |
1985年 | 94篇 |
1984年 | 79篇 |
1983年 | 55篇 |
1982年 | 58篇 |
1981年 | 64篇 |
1980年 | 37篇 |
1979年 | 23篇 |
1978年 | 25篇 |
1977年 | 21篇 |
1976年 | 28篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
991.
交直流混合电网的实时仿真既要考虑电力电子设备的开关特性,又要保证适应较大的电网规模,在实际工程中面临诸多困难.给子网络赋予动态可变的关注标志,对关注子网络采用存储压力小的节点消去法,对非关注子网络采用计算量少的线性组合法,从而保证骨架型节点电压法的实用性.在Xilinx公司的Virtex-7 FPGA VC709开发板中,采用无缝的并行化仿真计算程序对接方式和灵活的结构参数查询方法解决了现场可编程逻辑门阵列资源的紧缺问题,设计了一种关注区可变的实时数字仿真平台.以典型的交直流混合电网为例,仿真验证了所提方法的可行性与所研发平台的有效性. 相似文献
992.
G. Antou F. Hlawka A. Cornet G. Montavon C. Coddet F. Machi 《Journal of Thermal Spray Technology》2004,13(3):381-389
Several studies have been undertaken recently to adapt yttria partially stabilized zirconia (YPSZ) thermal barrier coating
(TBC) characteristics during their manufacturing process. Thermal spraying implementing laser irradiation appears to be a
possibility for modifying the coating morphology. This study aims to present the results of in situ (i.e., simultaneous treatment)
and a posteriori (i.e., post-treatment) laser treatments implementing a high-power laser diode. In both cases, the coatings
underwent atmospheric plasma spraying (APS). Laser irradiation was achieved using a 3 kW, average-power laser diode exhibiting
an 848 nm wavelength. Experiments were performed to reach two goals. First, laser post-treatments aimed at building a map
of the laser-processing parameter effects on the coating microstructure to estimate the laser-processing parameters, which
seem to be suited to the change into in situ coating remelting. Second, in situ coating remelting aimed at quantifying the
involved phenomena. In that case, the coating was treated layer by layer as it was manufactured. The input energy effect was
studied by varying the scanning velocity (i.e., between 35 and 60 m/min), and consequently the irradiation time (i.e., between
1.8 and 3.1 ms, respectively). Experiments showed that coating thermal conductivity was lowered by more than 20% and that
coating resistance to isothermal shocks was increased very significantly. 相似文献
993.
Microstructure evolution of cold-sprayed coating during deposition and through post-spraying heat treatment 总被引:2,自引:1,他引:2
The microstructural features of cold-sprayed coatings were investigated using Cu, Ti and Zn feedstocks by optical microscopy, scanning electron microscopy and transmission electron microscopy to reveal the microstructure evolution mechanisms in cold spray. Four typical effects including tamping, refinement, impact-induced fusion and annealing were examined on microstrueture. It is found that the microstructure of cold spray coating is remarkably influenced by spray materials. Ti coatings consist of evident porous layer and Cu coatings present a limited porous layer only near the surface. It is clear that the successive tamping effect and dynamic refinement of grains significantly influence the microstructure evolution of cold-sprayed coating. The tamping effect leads to the densification of porous coating layer gradually and the refinement effect leads to the formation of fine microstructure. It is considered that the large difference in the formation of porous layer is attributed to the dynamic impact pressure and hardenability of materials. It is also found that the impact-induced fusion during deposition of Zn coating can also modify the interfacial microstructure between particles in cold spray coating. Moreover, the nanocrystalline phase can be formed at the interfaces among particles resulting from the localized melting of the interfaces and tamping effect. Furthermore, the annealing treatment can modify the microstructure and property of a cold-sprayed coating. 相似文献
994.
995.
La2Ce2O7(LC) 和 LaMgAl11O19(LMA) 是两种新型热障涂层材料。 LC 具有优良的热物理及抗腐蚀性能, 但
其断裂韧性差。 LMA 具有良好的综合性能, 特别是力学性能优良。 基于复合材料设计理念, 为充分利用 LC 和
LMA 的优势, 本文探究了制备 LMA-LC 双相复合陶瓷的可行性。 采用高温固相法合成了 LMA 和 LC 粉末, 重
点研究了 LMA 和 LC 的高温稳定性, 初步研究了 LMA-LC 复合陶瓷块材的力学性能。 结果表明: LMA 和 LC 在
高温下发生了化学反应, 反应程度随温度升高而加剧, 主要反应产物为 LaAlO3, 其在低温下的铁弹性可能是复
合陶瓷在室温下具有良好力学性能的原因。 相似文献
996.
This paper investigates the interfacial structure in hot-wall CVD TiN/κ-Al2O3 multilayer coatings using both HREM and DFT modeling. Two multilayers with different thicknesses of the TiN layers (50 and 600 nm) separating the κ-Al2O3 layers are analyzed. The general microstructure of the two multilayers is relatively similar. The TiN layer in the thicker TiN/κ-Al2O3 coating is thick enough to be several TiN grains high. This means that epitaxial columns, which are often found in the thinner TiN/κ-Al2O3 coatings, are not present. However, the orientation relationships at the TiN/κ-Al2O3 interfaces are the same in both multilayers. The HREM investigations show that κ-Al2O3 (001) planes can grow directly on flat (111) TiN faces, without any other phases or detectable amounts of impurities, such as sulphur, present. Where the TiN layers are more curved, γ-Al2O3 can be grown, at least partly stabilized by the cube-on-cube orientation relationship between γ-Al2O3 and the underlying TiN. The DFT calculations show very similar adsorption strengths for an O monolayer positioned on Ti-terminated TiC(111) and TiN(111) surfaces, with preferred adsorption in the fcc site. O adsorption on N-terminated TiN(111) is much weaker, with preferred adsorption in the top site. Calculated elastic-energy contributions yield a higher stability for κ-Al2O3 on TiN(111) than on TiC(111) and a higher stability for κ-Al2O3 than for α-Al2O3 on both TiC and TiN. This indicates that the observed higher stability of κ-Al2O3 on TiC(111) than on TiN(111) is not due to the lattice mismatch, while the preferred epitaxial growth of κ-Al2O3 over α-Al2O3 can be partly attributed to the mismatch. 相似文献
997.
Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys 总被引:2,自引:0,他引:2
The corrosion protection afforded by a cerium conversion coating, formed by immersion in a solution containing rare earth salt and hydrogen peroxide, on pure magnesium and two magnesium alloys, AZ91 and AM50, has been studied. The effect of HCl pre-treatments on the morphology and on the corrosion resistance of the cerium conversion layer was investigated. A thicker and more homogeneous distribution of the conversion coating was obtained when the sample surface was pre-treated with acid. Higher amounts of cerium on the surface of the pre-treated samples were detected. The cerium conversion coating increased the corrosion resistance of the alloys because it ennobled the corrosion potential and decreased both the anodic and cathodic current. The acid pre-treatment further increased the corrosion resistance of the coated alloys. After five days of immersion in chloride environment the untreated samples showed localized corrosion while the chemical conversion coated samples appeared unaffected. 相似文献
998.
S. C. Kung 《Oxidation of Metals》1994,42(3-4):191-203
The formation of a chromium-carbide conversion coating on SiC was achieved using the pack-cementation technique. The conversion coating is intended to improve the corrosion resistance of SiC and its derivatives, such as SiC-base continuous fibers and composites, by forming a protective Cr2O3 scale upon exposure to high-temperature corrosive environments. Different pack chemistry and processing parameters were evaluated in the laboratory. Results indicated that the coating morphologies and compositions achieved were significantly affected by variation of these processing factors. In this paper, the conversion coating obtained from one of the systems investigated is reported. The coating consists of a multilayered structure with each of the sublayers containing a high-Cr concentration. In addition, the coating surface is relatively dense and pore free compared to the underlying SiC substrate material. A dense and pore-free morphology is highly desirable for coating applications, especially on porous substrates. The multilayered coating structure consists of the following sublayers: Cr23C6/Cr7C3/Cr7C3+Cr3Si/Cr5Si3Cx/SiC substrate. 相似文献
999.
ZENG Yanping ZHANG Maicang DONG Jianxin ZHANG Lina XIE Xishan 《稀有金属(英文版)》2005,24(3):298-300
1 IntroductionRecently the key components in advanced aircraftengines are widely made of nickel-base P/M super-alloy. However, non-metallic inclusions are intro-duced into this material during powder metallurgyprocessing. In industry, although many method… 相似文献
1000.
液压机本体柔性化设计相关技术的研究 总被引:3,自引:0,他引:3
针对液压机本体设计特点,在液压机本体CAD应用系统的开发中,引入了柔性化设计的概念,以Pro/E为建模后台、VB6.0为操作语言,研究了柔性化设计的相关技术,并提出了相关解决方案,并为以:Pro/E为后台的应用系统的开发提供了一种可行方案。 相似文献