全文获取类型
收费全文 | 56251篇 |
免费 | 7751篇 |
国内免费 | 1702篇 |
专业分类
电工技术 | 2156篇 |
综合类 | 2441篇 |
化学工业 | 14200篇 |
金属工艺 | 2581篇 |
机械仪表 | 1801篇 |
建筑科学 | 4362篇 |
矿业工程 | 6236篇 |
能源动力 | 1002篇 |
轻工业 | 7304篇 |
水利工程 | 990篇 |
石油天然气 | 1597篇 |
武器工业 | 225篇 |
无线电 | 4398篇 |
一般工业技术 | 5705篇 |
冶金工业 | 4794篇 |
原子能技术 | 541篇 |
自动化技术 | 5371篇 |
出版年
2024年 | 118篇 |
2023年 | 1024篇 |
2022年 | 2141篇 |
2021年 | 3931篇 |
2020年 | 1996篇 |
2019年 | 1969篇 |
2018年 | 2166篇 |
2017年 | 2744篇 |
2016年 | 3936篇 |
2015年 | 4354篇 |
2014年 | 4650篇 |
2013年 | 4512篇 |
2012年 | 3514篇 |
2011年 | 2808篇 |
2010年 | 2193篇 |
2009年 | 2196篇 |
2008年 | 2013篇 |
2007年 | 3135篇 |
2006年 | 3369篇 |
2005年 | 2806篇 |
2004年 | 1831篇 |
2003年 | 1808篇 |
2002年 | 1338篇 |
2001年 | 906篇 |
2000年 | 825篇 |
1999年 | 510篇 |
1998年 | 302篇 |
1997年 | 385篇 |
1996年 | 291篇 |
1995年 | 231篇 |
1994年 | 230篇 |
1993年 | 163篇 |
1992年 | 136篇 |
1991年 | 121篇 |
1990年 | 132篇 |
1989年 | 110篇 |
1988年 | 71篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 67篇 |
1983年 | 42篇 |
1982年 | 35篇 |
1981年 | 36篇 |
1980年 | 47篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 21篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
《Intermetallics》2015
Raney-type Ni precursor alloys containing 75 at.% Al and doped with 0, 0.75, 1.5 and 3.0 at.% Ti have been produced by a gas atomization process. The resulting powders have been classified by size fraction with subsequent investigation by powder XRD, SEM and EDX analysis. The undoped powders contain, as expected, the phases Ni2Al3, NiAl3 and an Al-eutectic. The Ti-doped powders contain an additional phase with the TiAl3 DO22 crystal structure. However, quantitative analysis of the XRD results indicate a far greater fraction of the TiAl3 phase is present than could be accounted for by a simple mass balance on Ti. This appears to be a (TixNi1−x)Al3 phase in which higher cooling rates favour small x (low Ti-site occupancy by Ti atoms). SEM and EDX analysis reveal that virtually all the available Ti is contained within the TiAl3 phase, with negligible Ti dissolved in either the Ni2Al3 or NiAl3 phases. 相似文献
54.
浮选机内各动力学分区的流动特征复杂。本文选取单槽容积0.2m3KYF型充气机械搅拌式浮选机为研究对象,采用PIV测试技术开展运输区的结构特征和动力学特征的研究。研究表明运输区在半个槽体的取截面内的轮廓形状整体呈现为左边为直线,右边折弯线,上下近似直线的近梯形结构,具有高度和宽度两个主要结构特征。运输区轮廓边界处的动力学特征存在明显差异。本研究加深了对浮选机运输区特征的理解,有助于通过调控运输区特征方法解决大型机械搅拌式浮选机粗粒矿物回收率低的难题。 相似文献
55.
Zhuang CHENG Jianfeng WANG Matthew Richard COOP Guanlin YE 《Frontiers of Structural and Civil Engineering》2020,14(2):357
The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of (diameter height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils. 相似文献
56.
V.I. Popkov O.V. Almjasheva V.N. Nevedomskiy V.V. Panchuk V.G. Semenov V.V. Gusarov 《Ceramics International》2018,44(17):20906-20912
Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formations of three structural yttrium orthoferrite modifications – amorphized hexagonal <h1>-YFeO3 (P63cm) and nanocrystalline hexagonal h2-YFeO3 (P63/mmc), as well as nanocrystalline orthorhombic o-YFeO3 (Pbnm), which are selectively formed depending on available three-dimensional confinements. Based on the analysis of changes in the fluid and size composition formulation, it has been proposed mechanism for formation and transformation of YFeO3 nanocrystals, including growth stage of h2-YFeO3 crystals due to amorphized phase of <h1>-YFeO3 up to critical size of about 15?nm and their subsequent transformation into orthorhombic form o-YFeO3. 相似文献
57.
针对郴州某复杂硫化铅锌矿资源的性质特点,采用铅快速浮选后尾矿再磨再选的阶磨阶选工艺,较好地实现了铅锌的高效浮选回收。研究了磨矿方式、捕收剂和调整剂种类及用量等因素对该矿石浮选的影响,确定了最佳浮选条件,通过小型闭路浮选试验,得到了铅品位60.05%、回收率89.63%的铅精矿和锌品位47.01%、回收率88.14%的锌精矿。 相似文献
58.
Mingzhi Zhao Jianwei Cao Zhi Wang Guohua Li 《Journal of the European Ceramic Society》2019,39(7):2427-2435
The crystallization phenomena of spinel in CaO-MgO-Al2O3-SiO2-Fe2O3 glass have received much attention due to the particular role in preparation of glass-ceramic materials, which represent an effective option to manage hazardous waste. In this study, both preliminary spinel and secondary spinel were precipitated in the precursor glass. The formation of these spinel was meticulously assessed by a combination of X-ray diffractometry and scanning electron microscopy. The structure of the microenvironment in the precursor glass was characterized by Raman spectrums. These advanced techniques highlight the potential for one-step crystallization of the glass. The investigation, which focused on one-step crystallization, demonstrated the growth of pyroxene on spinel accompanying a migration of chromium. The results also show the microstructure of the obtained glass-ceramic was very dependent on the heat-treat temperature. This study not only unambiguously reveals the precipitation mechanisms of spinel but also provides more documentation for one-step crystallization in the glass-ceramics field. 相似文献
59.
《Intermetallics》2015
Fine-grained fully-lamellar (FL) microstructure is desired for TiAl components to serve as compressor/turbine blades and turbocharger turbine wheels. This study deals with the process and phase transformation to produce FL microstructure for Mo stabilized beta-gamma TiAl alloys without single α-phase field. Unlike the α + γ two-phased TiAl or beta-gamma TiAl with single α-phase field, the wrought multi-phase TiAl–4/6Nb–2Mo–B/Y alloys exhibit special annealing process to obtain FL microstructure. Short-term annealing at temperatures slightly above β-transus is recommended to produce the desired FL microstructure. The related mechanism is to guarantee the sufficient diffusion homogenization of β stabilizers during single β-phase annealing, and further avoid α decomposition by α → γ + β when cooling through α + β + γ phase field. The colony boundary β phase contributes to fine-grained nearly FL microstructure, by retarding the coarsening of the α phase grains. 相似文献
60.