全文获取类型
收费全文 | 80882篇 |
免费 | 8319篇 |
国内免费 | 4663篇 |
专业分类
电工技术 | 4955篇 |
技术理论 | 1篇 |
综合类 | 8741篇 |
化学工业 | 7392篇 |
金属工艺 | 5770篇 |
机械仪表 | 11274篇 |
建筑科学 | 9234篇 |
矿业工程 | 2403篇 |
能源动力 | 3161篇 |
轻工业 | 1875篇 |
水利工程 | 2515篇 |
石油天然气 | 3176篇 |
武器工业 | 1056篇 |
无线电 | 4354篇 |
一般工业技术 | 11953篇 |
冶金工业 | 2985篇 |
原子能技术 | 672篇 |
自动化技术 | 12347篇 |
出版年
2024年 | 125篇 |
2023年 | 914篇 |
2022年 | 1616篇 |
2021年 | 2181篇 |
2020年 | 2258篇 |
2019年 | 1998篇 |
2018年 | 2020篇 |
2017年 | 2552篇 |
2016年 | 2908篇 |
2015年 | 3374篇 |
2014年 | 4865篇 |
2013年 | 5027篇 |
2012年 | 5823篇 |
2011年 | 6847篇 |
2010年 | 4947篇 |
2009年 | 5397篇 |
2008年 | 5090篇 |
2007年 | 6117篇 |
2006年 | 5220篇 |
2005年 | 4444篇 |
2004年 | 3662篇 |
2003年 | 3137篇 |
2002年 | 2511篇 |
2001年 | 1942篇 |
2000年 | 1699篇 |
1999年 | 1297篇 |
1998年 | 1020篇 |
1997年 | 872篇 |
1996年 | 784篇 |
1995年 | 707篇 |
1994年 | 564篇 |
1993年 | 429篇 |
1992年 | 380篇 |
1991年 | 268篇 |
1990年 | 228篇 |
1989年 | 186篇 |
1988年 | 134篇 |
1987年 | 80篇 |
1986年 | 56篇 |
1985年 | 37篇 |
1984年 | 36篇 |
1983年 | 10篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1959年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
《International Journal of Hydrogen Energy》2022,47(77):33014-33026
The present study investigates the combined influence of Channel to Rib Width (CRW) ratio and clamping pressure on the structure and performance of High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) using a three-dimensional numerical model developed previously. It also considers the impact of interfacial contact resistance between the Gas Diffusion Layer (GDL) and Bipolar Plate (BPP). The structural analysis of the single straight channel HT-PEMFC geometry shows that the von-Mises stress greatly increases in the GDL under the ribs as the CRW ratio increases resulting in considerably high deformation. The cell performance analysis depicts the significance of ohmic resistance and concentration polarization for different CRW ratios, particularly at higher operating current densities. However, in low to medium current density regions, the CRW ratio has little influence on cell performance. A substantial impact on the species, overpotential, and current distributions is observed. The findings also reveal that the CRW ratio significantly affects the temperature distribution in the cell. 相似文献
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.
Rodrigo Montoya Allan G. Ruiz-García Alma Ortiz-Ozuna Blanca Ramírez-Barat Juan Genesca 《工业材料与腐蚀》2021,72(7):1259-1269
The electrochemical interactions between aluminum alloy 7075 and low-carbon steels under gelled electrolytes were studied. Such electrolytes provided the opportunity to investigate both thick and thin electrolyte systems. The electrolyte was chemically modified to visually track the acidic fronts during the anodic reaction and the subsequent hydrolysis process. Two mathematical models were validated for both thick and ultrathin electrolytes. The acidification of thick electrolytes was extended some millimeters beyond the aluminum alloy surface, whereas the acidic front was localized next to the metallic joint using ultrathin electrolytes. The combination of both numerical and experimental results allows proving (and explaining why) that the acidification process is more aggressive under dilute than under concentrated electrolytes. 相似文献
8.
Form selection of concomitant polymorphs: A case study informed by crystallization kinetics modeling
Weiwei Tang Yufeng Quan Junbo Gong Jingkang Wang Qiuxiang Yin Tonglei Li 《American Institute of Chemical Engineers》2021,67(4):e17129
Molecular mechanisms and process kinetics of crystallizing concomitant polymorphs remain poorly understood. Solvent-mediated phase transformation and concomitant crystallization are difficult to be distinguished in practice, as multiple forms can be detected at the same time. Herein, we developed a population balance model to simulate a concomitant crystallization process of two polymorphs of tolfenamic acid. Our kinetic modeling aims to understand concomitant crystallization and help guide form selection of such a molecular system. Crystallization kinetics of ethanolic solutions were uncovered from induction time measurements, as well as seeded and unseeded crystallization experiments. Experimental and simulation results demonstrate that the stable form I crystallizes concomitantly with the metastable form II. The faster growing form II results in an intermediate decline in the composition of form I in crystallized samples, a characteristic feature of the concomitantly crystallized system. A four-quadrant scheme of attainable polymorph outcome was simulated under various crystallization conditions. 相似文献
9.
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