全文获取类型
收费全文 | 1803篇 |
免费 | 42篇 |
国内免费 | 48篇 |
专业分类
系统科学 | 3篇 |
丛书文集 | 67篇 |
教育与普及 | 29篇 |
理论与方法论 | 7篇 |
现状及发展 | 4篇 |
综合类 | 1783篇 |
出版年
2024年 | 8篇 |
2023年 | 15篇 |
2022年 | 20篇 |
2021年 | 18篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 23篇 |
2016年 | 16篇 |
2015年 | 38篇 |
2014年 | 74篇 |
2013年 | 60篇 |
2012年 | 85篇 |
2011年 | 108篇 |
2010年 | 71篇 |
2009年 | 79篇 |
2008年 | 80篇 |
2007年 | 77篇 |
2006年 | 84篇 |
2005年 | 58篇 |
2004年 | 73篇 |
2003年 | 71篇 |
2002年 | 85篇 |
2001年 | 81篇 |
2000年 | 44篇 |
1999年 | 49篇 |
1998年 | 64篇 |
1997年 | 55篇 |
1996年 | 55篇 |
1995年 | 57篇 |
1994年 | 43篇 |
1993年 | 53篇 |
1992年 | 38篇 |
1991年 | 45篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有1893条查询结果,搜索用时 15 毫秒
991.
992.
热处理制度对Li2O-Al2O3-SiO2系统玻璃析晶及热膨胀系数的影响 总被引:1,自引:0,他引:1
采用传统熔融冷却法获得了以P2O5为成核剂的Li2O-Al2O3-SiO2系统基础玻璃,通过差热分析确定了使该玻璃微晶化的热处理条件,并获得了不同热处理温度下Li2O-Al2O3-SiO2系统低膨胀微晶玻璃;利用X射线衍射分析和扫描电子显微镜对晶化试样的物相和微观结构进行了研究;讨论了热处理制度对玻璃的析晶及热膨胀系数的影响.研究结果表明以P2O5为成核剂,采用不同热处理制度能获得Li2O-Al2O3-SiO2系统低膨胀微晶玻璃;在析晶初始温度下进行热处理,析出β-石英晶体,但晶体生长缓慢,结晶程度低;提高晶化温度,析出β-锂霞石和β-锂辉石晶体且晶体生长迅速. 相似文献
993.
采用形象思维法进行教学 ,能充分发挥教师的想象能力 ,培养学生的灵感、创造力和抽象思维能力 ,激发学生学习兴趣 ,加深课后印象。“金属材料与热处理”教学中 ,很多理论、概念均可以用形象的、具有个性的语言进行描述 ,进而取得较好的教学效果。 相似文献
994.
热轧钢材的淬火冷却是改善钢材质量和性能的重要措施,淬火过程的核心就是控制钢板的冷却速度。针对传统的淬火控冷模型的固有缺陷,为了满足扩展钢种、规格及淬火温度高精度的要求,利用神经网络技术建立了神经网络淬火控冷温度预报模型,该模型与回归数学模型相结合,完成淬火控冷现场控制。应用结果证明,该综合模型极大地提高了钢板淬火冷却的控制精度,提高了产品的成材率。 相似文献
995.
系统分析了铝箔轧机轧制:过程中热量转移及热量平衡的过程,提出了一种热量转移的观点,实际测量了三种不同喷嘴开放状态下分段冷却的轧件表面温度,采用理论分析与实验相结合的方法,求出了对应工况下轧件和工作辊所吸收热量的热功率,得到了生成热在轧件与轧辊间的分配系数,轧件分配系数大致为0.11~0.33,轧辊分配系数为0.67~0.89,随冷却能力的增强,轧辊分配系数增大,轧件分配系数减少。 相似文献
996.
Finite Element Simulation of Metal Quenching 总被引:3,自引:0,他引:3
The evolution of the phase transformation and the resulting internal stresses and strains in metallic parts during quenching were modeled numerically. The numerical simulation of the metal quenching process was based on the metallo-thermo-mechanical theory using the finite element method to couple the temperature, phase transformation, and stress-strain fields. The numerical models are presented for the heat treatment and kinetics of the phase transformation. The finite element models and the phase transition kinetics accurately predict the distribution of the microstructure volume fractions, the temperature, the distortion, and the stress-strain relation during quenching. The two examples used to validate the models are the quenching of a small gear and of a large turbine rotor. The simulation results for the martensite phase volume fraction, the stresses, and the distortion in the gear agree well with the experimental data. The models can be used to optimize the quenching conditions to ensure product quality. 相似文献
997.
Non-Fourier heat conduction induced by ultrafast heating of metals with a high-energy density beam was analyzed. The non-Fourier effects during high heat flux heating were illustrated by comparing the transient temperature response to different heat flux and material relaxation times. Based on the hyperbolic heat conduction equation for the non-Fourier heat conduction law, the equation was solved using a hybridmethod co mbining an analytical solution and numerical inversion of the Laplace transforms for a semiinfinite body with the heat flux boundary. Analysis of the temperature response and distribution led to a criterion for the applicability of the non-Fourier heat conduction law. The results show that at a relatively large heat flux, such as greater than 108 W/cm2, the heat-affected zone in the metal material experiences a strong thermal shock as the non-Fourier effects cause a large step increase in the surface temperature. The results provide a method for analyzing transient heat conduction problems using a high-energy density beam, such as electron beam deep penetration welding. 相似文献
998.
Effects of heat treatment temperature and time on hardness and wear resistance of RE-Ni-W-P-SiC-PTFE and RE-Ni-W-P-SiC composite coatings were studied. The results indicated that the hardness of the composite coatings as-deposited was lower and the mass loss (i.e. rate of abrasion) was higher, while the hardness increased and the rate of abrasion decreased with the increase of heat treatment temperature. The rate of abrasion was the lowest and hardness was the highest at 400℃ . The hardness decreased and the rate of abrasion increased with the temperature increasing continuously. Both the hardness and wear resistance also increased with the prolongation of heat treatment time, reaching their peak values when the heat treatment time was 2 h. The experimental results also showed that the hardness of the coatings decreased with PTFE quantity enhancing, but the wear rate diminished correspondingly. X-ray diffraction analysis indicated that the structure of RE-Ni-W-P-SiC-PTFE composite coating as-deposited is amorphous, and it partly became crystal when heat treatment temperature was over 3000℃. 相似文献
999.
40Cr钢亚温淬火强韧化机理的试验研究 总被引:3,自引:0,他引:3
研究40Cr钢亚温淬火热处理的强韧化机理,并与40Cr钢常规热处理后的机械性能进行比较。结果表明,亚温淬火热处理提高40Cr钢的冲击韧性,降低40Cr钢的韧脆转变温度。抑制40Cr钢的回火脆性。 相似文献
1000.
刘学东 《河北理工大学学报(自然科学版)》2004,26(2)
讨论了焊管轧辊CAD系统(简称RCAD)的原理和关键技术,该系统以Visual Basic5.0为开发语言,以AutoCAD R14为绘图支撑平台,采用基于焊管轧辊形状特征技术的参数化绘图方法,完成了轧辊孔型设计及轧辊零件参数化绘图. 相似文献