全文获取类型
收费全文 | 62819篇 |
免费 | 5963篇 |
国内免费 | 3452篇 |
专业分类
电工技术 | 3518篇 |
技术理论 | 1篇 |
综合类 | 7449篇 |
化学工业 | 4403篇 |
金属工艺 | 5956篇 |
机械仪表 | 7568篇 |
建筑科学 | 9124篇 |
矿业工程 | 2344篇 |
能源动力 | 1654篇 |
轻工业 | 1357篇 |
水利工程 | 2482篇 |
石油天然气 | 1915篇 |
武器工业 | 765篇 |
无线电 | 2532篇 |
一般工业技术 | 10010篇 |
冶金工业 | 7348篇 |
原子能技术 | 615篇 |
自动化技术 | 3193篇 |
出版年
2024年 | 104篇 |
2023年 | 691篇 |
2022年 | 1255篇 |
2021年 | 1555篇 |
2020年 | 1654篇 |
2019年 | 1405篇 |
2018年 | 1408篇 |
2017年 | 1756篇 |
2016年 | 1987篇 |
2015年 | 2276篇 |
2014年 | 3509篇 |
2013年 | 3589篇 |
2012年 | 4589篇 |
2011年 | 5063篇 |
2010年 | 3859篇 |
2009年 | 4100篇 |
2008年 | 3799篇 |
2007年 | 4561篇 |
2006年 | 4323篇 |
2005年 | 3518篇 |
2004年 | 3044篇 |
2003年 | 2555篇 |
2002年 | 2097篇 |
2001年 | 1657篇 |
2000年 | 1491篇 |
1999年 | 1124篇 |
1998年 | 880篇 |
1997年 | 792篇 |
1996年 | 725篇 |
1995年 | 667篇 |
1994年 | 522篇 |
1993年 | 388篇 |
1992年 | 339篇 |
1991年 | 230篇 |
1990年 | 212篇 |
1989年 | 155篇 |
1988年 | 108篇 |
1987年 | 79篇 |
1986年 | 45篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1975年 | 2篇 |
1959年 | 4篇 |
1957年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 62 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.
《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
5.
6.
《中国稀土学报(英文版)》2022,40(7):1134-1147
In this study, the Bayan Obo rare earth concentrates mixed with Na2CO3 were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO2 react to form silicates, causing hardening. Further, REPO4 and NaF can directly generate CeF3 and CeF4 at high temperatures, and a part of CeF4 and NaF forms a solid solution substance Na3CeF7. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce0.6Nd0.4O1.8, Ce4O7, and LaPrO3+x. Then, BaSO4, Na2CO3, and Fe2O3 react to form barium ferrite BaFe12O19; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [?ln (1?α)]1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1?(1?α)1/3]2. Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry). 相似文献
8.
《Ceramics International》2021,47(23):32641-32647
Multi-components and equimolar rare earth monosilicates, (Y1/3Dy1/3Er1/3)2SiO5, (Y1/3Dy1/3Lu1/3)2SiO5, (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5, were prepared by solid-state reactions and the following hot-pressing. Dense microstructures with uniform elemental distributions were obtained for all samples. These investigated multi-components monosilicates exhibit low thermal conductivities and similar coefficients of thermal expansion with SiC. Moreover, they exhibit high corrosion resistances in 1400 °C water vapor, especially, four-components (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5 experienced almost invariable weights after small weight losses during the initial 0.5 h. All those results indicate that multi-components rare earth monosilicates are promising candidates of environmental barrier coatings for SiC/SiC composites. 相似文献
9.
《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
10.
梯度分层铝合金蜂窝板是一种有效的吸能结构,本工作在梯度铝蜂窝结构的基础上根据梯度率的概念,通过改变蜂窝芯层的胞壁长度,设计了4种质量相同、梯度率不同的铝蜂窝夹芯结构。通过准静态压缩实验,并结合非线性有限元模拟准静态及冲击态下梯度铝蜂窝夹芯结构的变形情况及其力学性能,分析对比了相同质量下梯度铝蜂窝夹芯结构在准静态下的变形模式以及冲击载荷下分层均质蜂窝结构和不同梯度率的分层梯度蜂窝结构的动态响应和能量吸收特性。结果表明:在准静态压缩过程中,铝蜂窝梯度夹芯板的变形具有明显的局部化特征,蜂窝芯的变形为低密度优先变形直至密实,层级之间的密实化应变差随芯层密度的增大而逐渐减小;在高速冲击下,梯度蜂窝板并非严格按照准静态过程中逐级变形直至密实,而是在锤头冲击惯性及芯层密度的相互作用下整体发生的线弹性变形、弹性屈曲、塑性坍塌及密实化;另外,在本工作所设计的梯度率中,当梯度率为γ1=0.0276时,梯度蜂窝夹芯板的吸能性达到最好,相较于同等质量下的均质蜂窝夹芯板,能量吸收提高了10.63%。 相似文献