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991.
NING Yuantao LI Yongnian Kunming Institute of Precious Metals China Ning Yuantao Professor Institute of Precious Metals Kunming Yunnan China 《金属学报(英文版)》1990,3(7):43-48
The influence of rare-earth elements,La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Ho,Er and Yb onthe thermal stability of PdSi_(16.5) glass was studied systematically by means of DSC.Allrare-earth elements,especially heavy ones,increase obviously the thermal stabilityparameters,including T_θ(T_g ,T_x ,T_g),T_(rg) and ΔE etc.The crystallization temperaturesT_(p1) and T_(p2) increase linearly with the lanthanide constriction increasing,but Eu shows ananomalous influence:Pd-Si-Eu metallic glass possesses the highest thermal stability and thelowest concentration limit of glass forming among Pd-Si-R glasses. 相似文献
992.
L. Xie M.R. Dorfman A. Cipitria S. Paul I.O. Golosnoy T.W. Clyne 《Journal of Thermal Spray Technology》2007,16(5-6):804-808
It has been found that reducing the level of impurity oxides (particularly SiO2 and Al2O3) in 7YSZ, from about 0.2 wt% to below 0.1 wt% raises the sintering resistance and the phase stability of plasma-sprayed coatings.
The implications for the usage of these coatings at elevated temperatures are examined. It is concluded that using relatively
high-purity powder of this type is likely to confer substantial benefits in terms of the thermomechanical stability of the
coatings under service conditions.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
993.
Isothermal oxidation of physical vapor deposited partially stabilized zirconia thermal barrier coatings 总被引:1,自引:0,他引:1
Y. H. Sohn R. R. Biederman R. D. Sisson 《Journal of Materials Engineering and Performance》1994,3(1):55-60
Thermal barrier coatings (TBCs), consisting of physical vapor deposited (PVD) partially stabilized zirconia (PSZ, 8 wt.%Y2O3) and a diffusion aluminide bond coat, were characterized as a function of time after oxidative isothermal heat treatment
at 1373 K in air. The experimental characterizations was conducted by X-ray diffraction analysis and scanning electron microscopy
(SEM) with energy-dispersive spectroscopy. During cooling to room temperature, spallation of the PSZ ceramic coatings occurred
after 200 and 350 h of isothermal heat treatment. This failure was always sudden and violent, with the TBC popping from the
substrate. The monoclinic phase of zirconia was first observed on the bottom surface of the PVD PSZ after 200 h of isothermal
heat treatment. The failure of TBCs occurred either in the bond coat oxidation products of αAl2O3 and rutile TiO2 or at the interface between the oxidation products and the diffusion aluminide bond coat or the PSZ coating. 相似文献
994.
The effects of long-term aging on microstructures and their influence on tensile and stress-rupture behavior of a corrosion
resistant nickel-base superalloy are investigated. Samples are aged isothermally at 1073, 1123, or 1173 K for different times
of up to 10,000 h and mechanical tests are performed on samples in both standard heat treatment (SHT) and aged conditions.
Scanning electron microscopy (SEM) studies reveal that the coarsening kinetics of γ′ follows a linear law at different temperatures
with the calculated activation energy, i.e., 255 kJ/mol, for γ′ growth according to Lifshitz-Slyozof-Wagner (LSW) theory.
After long-term aging for more than 1 khours, σ phase appears in the alloy. The kinetics of σ formation can be described by
the Johnson-Avrime-Mehl equation. Tensile experiments at room temperature and 1173 K and endurance experiments at 1173 K/274
MPa are performed to test the effect of σ phases on these properties and no remarkable harmful effect is found. γ′ coarsening
can be used to explain the reduction of yield stress, which is tested by the Labusch-Schwarz hardening theory. Although the
presence of the σ phase clearly does affect the fracture process, the σ phase does not embrittle the alloy. 相似文献
995.
铸造镍基高温合金K445的热疲劳行为 总被引:1,自引:0,他引:1
利用开有V形缺口的平板试样,研究了新型铸造镍基高温合金K445在最高温度分别为800,850,900℃,最低温度为室温的热循环下的热疲劳行为.通过光学显微镜和扫描电镜观察合金的组织和热疲劳裂纹形貌,研究热疲劳损伤机制.结果表明,热疲劳主裂纹主要从V形缺口处萌生,沿晶界扩展,而二次裂纹则穿晶扩展.当最高循环温度为800℃时,碳化物的组成和分布起主要作用,(Ti,Ta)C型碳化物的开裂处以及碳化物与基体的界面处是裂纹优先扩展区域.当最高循环温度为900℃时,高温氧化起重要作用,应力辅助作用下的晶界氧脆是主要损伤机制. 相似文献
996.
针对当前无法分析MEMS多层薄膜结构中热应力的现状,通过修正Suhir.E提出的双金属带热应力分布理论,提出了MEMS多层薄膜结构的热应力分布模型,该模型适用于评估MEMS多层结构中热应力分布规律,同时为采取合理措施减小应力提供了理论支持。在温度载荷作用下,多层薄膜结构中将产生正应力、剪应力和剥离应力的作用,应力变化主要集中在界面端处。其中,正应力分布于各层内,随与中心点距离的增大呈指数减小,在端面处急剧减小至最小值;剪应力和剥离应力则主要分布于各层界面上,随与中心点距离的增大呈指数增大,在界面端处达到最大值。最后,开展了由四种材料(玻璃、铬、铜、镍)组成的多层薄膜结构的热力学仿真分析,验证了所建立解析模型的正确性,以及各应力在多层结构中的分布规律。 相似文献
997.
998.
This paper presents a new perspective on the stability problem for uncertain LTI feedback systems with actuator input amplitude saturation. The solution is obtained using the quantitative feedback theory and a 3 DoF non‐interfering control structure. Describing function (DF) analysis is used as a criterion for closed loop stability and limit cycle avoidance, but the circle or Popov criteria could also be employed. The novelty is the combination of a controller parameterization from the literature and describing function‐based limit cycle avoidance with margins for uncertain plants. Two examples are given. The first is a benchmark problem and a comparison is made with other proposed solutions. The second is an example that was implemented and tested on an X‐Y linear stage used for nano‐positioning applications. Design and implementation considerations are given. An example is given on how the method can be extended to amplitude and rate saturation with the help of the generalized describing function, and a novel anti‐windup compensation structure inspired by previous contributions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
999.
热强度试验现场环境复杂,会对热电偶、热流等微弱电压信号产生较大电磁干扰,影响测量精度甚至控制信号精度。本文描述了热电偶调理模块的设计,对小信号进行隔离放大,有效抑制热强度试验存在的干扰,提高了系统的精度。 相似文献
1000.
目前,针对肿瘤的治疗,非血管介入技术已经成为了常规手段,但是,其治疗方法和原理各不相同。总结了各种治疗手段的原理,介绍和比较了最新的不可逆电穿孔技术的优点和缺点,以期为其今后的应用提供必要的参考。 相似文献