全文获取类型
收费全文 | 71965篇 |
免费 | 6925篇 |
国内免费 | 4244篇 |
专业分类
电工技术 | 6043篇 |
技术理论 | 1篇 |
综合类 | 9259篇 |
化学工业 | 4245篇 |
金属工艺 | 5292篇 |
机械仪表 | 8372篇 |
建筑科学 | 11393篇 |
矿业工程 | 2666篇 |
能源动力 | 2775篇 |
轻工业 | 1387篇 |
水利工程 | 3473篇 |
石油天然气 | 3197篇 |
武器工业 | 1092篇 |
无线电 | 3436篇 |
一般工业技术 | 10997篇 |
冶金工业 | 2763篇 |
原子能技术 | 1145篇 |
自动化技术 | 5598篇 |
出版年
2024年 | 91篇 |
2023年 | 748篇 |
2022年 | 1450篇 |
2021年 | 1799篇 |
2020年 | 1961篇 |
2019年 | 1583篇 |
2018年 | 1518篇 |
2017年 | 2025篇 |
2016年 | 2226篇 |
2015年 | 2570篇 |
2014年 | 4262篇 |
2013年 | 4178篇 |
2012年 | 5534篇 |
2011年 | 5947篇 |
2010年 | 4414篇 |
2009年 | 4734篇 |
2008年 | 4276篇 |
2007年 | 5247篇 |
2006年 | 4692篇 |
2005年 | 3955篇 |
2004年 | 3312篇 |
2003年 | 2763篇 |
2002年 | 2306篇 |
2001年 | 1955篇 |
2000年 | 1719篇 |
1999年 | 1373篇 |
1998年 | 1074篇 |
1997年 | 1022篇 |
1996年 | 843篇 |
1995年 | 823篇 |
1994年 | 633篇 |
1993年 | 483篇 |
1992年 | 411篇 |
1991年 | 267篇 |
1990年 | 268篇 |
1989年 | 215篇 |
1988年 | 148篇 |
1987年 | 82篇 |
1986年 | 43篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1959年 | 14篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
《Advanced Powder Technology》2022,33(8):103664
Powder transport systems are ubiquitous in various industries, where they can encounter single powder flow, two-phase flow with solids carried by gas or liquid, and gas–solid–liquid three-phase flow. System geometry, operating conditions, and particle properties have significant impacts on the flow behavior, making it difficult to achieve good transportation of granular materials. Compared to experimental trials and theoretical studies, the numerical approach provides unparalleled advantages over the investigation and prediction of detailed flow behavior, of which the discrete element method (DEM) can precisely capture complex particle-scale information and attract a plethora of research interests. This is the first study to review recent progress in the DEM and coupled DEM with computational fluid dynamics for extensive powder transport systems, including single-particle, gas–solid/solid–liquid, and gas–solid–liquid flows. Some important aspects (i.e., powder electrification during pneumatic conveying, pipe bend erosion, non-spherical particle transport) that have not been well summarized previously are given special attention, as is the application in some new-rising fields (ocean mining, hydraulic fracturing, and gas/oil production). Studies involving important large-scale computation methods, such as the coarse grained DEM, graphical processing unit-based technique, and periodic boundary condition, are also introduced to provide insight for industrial application. This review study conducts a comprehensive survey of the DEM studies in powder transport systems. 相似文献
2.
3.
4.
5.
《Soils and Foundations》2022,62(3):101156
In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses. 相似文献
7.
《Ceramics International》2022,48(11):15525-15532
In this paper, by simulating the gas phase conditions inside the MgO–Al2O3–C refractories during continuous casting process and combining with thermodynamic analysis, as well as SEM analysis, the gas-gas and gas-solid formation of MA spinel were clarified in carbon containing refractories. Thermodynamic calculations showed that gas partial pressure of CO, O2 and Mg could meet the formation and stable existence conditions of MA spinel in MgO–Al2O3–C refractories under service environment, and nitrogen could not affect the formation of MA spinel at 1550 °C in the thermodynamic condition. The formation processes of MA spinel were analyzed experimentally under embedding carbon atmosphere. The carbon-coated alumina powders in MgO–Al2O3–C refractories prevented the direct contact between magnesia and alumina. Mg gas was formed by carbon thermal reaction, then reacted with alumina (gas-solid) and gas containing aluminum (gas-gas) to generate MA spinel. Through gas-gas or gas-solid reaction, the formation of MA spinel was effectively controlled. By means of SEM analysis, a two-layer structure with dense outer spinel layer and loose inner layer was formed in MgO–Al2O3–C refractories. 相似文献
8.
为了实现在工业化生产中对α钛富氧层厚度预测和控制,通过实验研究α钛富氧层在高温空气环境中的形成及增厚过程,讨论热处理温度和时间的影响作用,建立高温(750~850℃)空气环境下关于温度、时间的富氧层增厚动力学模型。结果表明:当恒温热处理温度为750~850℃时,α钛富氧层厚度x与保温时间t0.5呈正比例关系,且升高热处理温度可显著提高富氧层增厚速度。在此温度范围内,氧原子的扩散激活能约为203473 J/mol,计算曲线与实验数据吻合性较好。结合文献中已有的扩散系数方程和实验测得的富氧层厚度数据,推导得到5个富氧层增厚动力学方程,其中3个方程的计算曲线与实验数据吻合性较好,可为实际生产中预估富氧层厚度提供理论支持。 相似文献
9.
在总结前人钨中空位及其团簇的能量学和动力学行为的研究成果基础上,采用第一性原理方法系统计算了钨中空位及其团簇的结合能和扩散能垒。研究发现,交换关联泛函PW91和PBE较PBEsol、AM05和LDA更适合用于计算钨空位的能量学性质。基于第一性原理计算结果对文献中单空位形成能、双空位作用性质等争议性问题进行了讨论,并对钨经验势进行了评估。研究结果表明,钨中孤立单空位间总是相互排斥,而空位团簇(Vn>3)对单空位具有很强的吸引作用,其结合能随着所含空位个数增多呈现波动性增大的趋势。空位团簇稳定结构可通过最小化Wigner-Seitz表面积来确定,其结合能与Vn与Vn-1之间的Wigner-Seitz面积之差呈正比。 相似文献
10.
《中国有色金属学会会刊》2021,31(11):3530-3548
In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements. Three generations of pyrite (Py I, Py II, and Py III) in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central, western, and northern (C_Py, W_Py, and N_Py) mining districts are selected for comparison. Compared with Py I and Py III, the contents of most elements in Py II are apparently higher. The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py. The highest As, Se, and Pb contents were found in W_Py and N_Py. These results indicate the drastic changes in the temperature and fluid mixing during the mineralization. The occurrence of fluctuation and change in temperature and f(O2) was triggered by intermittent pulses of magmatic-hydrothermal fluids, mixing with meteoric water, and water−rock interactions. The sulfur isotopes of all species of pyrite indicated the magmatic source. The change in the f(O2) conditions caused slight differences in the sulfur isotope compositions. Consequently, a metallogenic model was proposed to explain the ore-forming processes. 相似文献