全文获取类型
收费全文 | 108889篇 |
免费 | 8441篇 |
国内免费 | 6995篇 |
专业分类
电工技术 | 8286篇 |
技术理论 | 2篇 |
综合类 | 7505篇 |
化学工业 | 22898篇 |
金属工艺 | 8144篇 |
机械仪表 | 7879篇 |
建筑科学 | 3939篇 |
矿业工程 | 1790篇 |
能源动力 | 3829篇 |
轻工业 | 6863篇 |
水利工程 | 695篇 |
石油天然气 | 4646篇 |
武器工业 | 970篇 |
无线电 | 12362篇 |
一般工业技术 | 12399篇 |
冶金工业 | 3842篇 |
原子能技术 | 1662篇 |
自动化技术 | 16614篇 |
出版年
2024年 | 261篇 |
2023年 | 1527篇 |
2022年 | 1995篇 |
2021年 | 3088篇 |
2020年 | 2727篇 |
2019年 | 2680篇 |
2018年 | 2512篇 |
2017年 | 3221篇 |
2016年 | 3514篇 |
2015年 | 3599篇 |
2014年 | 5053篇 |
2013年 | 6216篇 |
2012年 | 6367篇 |
2011年 | 7574篇 |
2010年 | 6213篇 |
2009年 | 7104篇 |
2008年 | 6844篇 |
2007年 | 7549篇 |
2006年 | 7171篇 |
2005年 | 5979篇 |
2004年 | 5243篇 |
2003年 | 4933篇 |
2002年 | 4084篇 |
2001年 | 3273篇 |
2000年 | 2900篇 |
1999年 | 2307篇 |
1998年 | 1697篇 |
1997年 | 1357篇 |
1996年 | 1264篇 |
1995年 | 1213篇 |
1994年 | 1048篇 |
1993年 | 902篇 |
1992年 | 701篇 |
1991年 | 474篇 |
1990年 | 318篇 |
1989年 | 302篇 |
1988年 | 208篇 |
1987年 | 143篇 |
1986年 | 129篇 |
1985年 | 111篇 |
1984年 | 98篇 |
1983年 | 60篇 |
1982年 | 72篇 |
1981年 | 64篇 |
1980年 | 36篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 27篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
The effects of welding on the tensile and fatigue properties of fully annealed and cold-worked Fe-12Cr-20Mn austenitic stainless
steel were evaluated. Room temperature and 500 °C tensile tests and room temperature cantilever beam fatigue tests were accomplished
on specimens that contained autogenous bead-on-plate welds. The tensile and fatigue properties of the fully annealed material
were not significantly influenced by welding. The tensile properties of the welded cold-worked material were also not significantly
affected by the presence of a weldment. However, welding caused a large reduction of the fatigue life of the cold-worked material.
Fatigue cracks preferentially initiated at large Mn-Si inclusions that formed in the fusion zones of the weldments. 相似文献
992.
晶化机制与激活能的晶化速率参比法确定 总被引:1,自引:0,他引:1
本文根据修正的Kissinger公式提出一种确定非晶材料晶化机制与激活能的最大晶化速率参比法。以Ar_(70)Cu_(30)非晶合金为例,研究了晶化机制与激活能及其与压力的关系。 相似文献
993.
Knowledge based approach is effective for renovating design and manufacturing processes. The objective of this paper is to investigate roles and usages of expert engineering knowledge in high-quality manufacturing, and to study a practical knowledge capturing method for realizing engineering support tools. An engineer oriented interface for a capturing method is proposed, and a flexible representation framework is studied for various types of expert knowledge. An integrated knowledge-based system has been developed for mold design support. The results have been evaluated by design and manufacturing of molds for cellular phones, and have shown substantial reduction of lead time for mold production. 相似文献
994.
Corrosion-Electrochemical behavior of a commercial API5CT grade L80 type 13Cr tubing enriched with microalloying elements
is studied in 6, 7.5, 9, 12 and 15% HCl solutions by electrochemical methods. The objective is to contribute to the comprehension
of corrosion phenomena caused by HCl of similar concentrations, generally used in acidizing job. The corrosion morphology
is examined by scanning electron microscopy (SEM) coupled with EDAX. The soluble corrosion products are analyzed by atomic
absorption spectroscopy and colorimetric methods. General, as well as localized, corrosion is present. The severest general
corrosion with a maximum rate of 26 mm/year is obtained at 15% HCl. The localized corrosion which morphologically differs
as function of HCl concentrations is revealed by SEM investigation. In all the above HCl solutions, the commercial 13% Cr
martensitic stainless steel tubing shows no passive state. Above 6% HCl, the microalloying elements promote forming a discontinuous
film of the corrosion products. The corrosion rate slightly decreases in 15% HCl compared to the published data on a conventional
13% Cr martensitic stainless steel tubing. This is due to both the chemical composition (silicon, manganese and vanadium)
and microstructural properties. Copper seems to additionally accelerate the corrosion of the alloy.
Published in Russian in Zashchita Metallov, 2007, Vol. 43, No. 4, pp. 372–380.
The article was translated by the authors in English. 相似文献
995.
Angular-dependent magnetic Barkhausen noise measurements were performed on ASTM 36 steel samples for various values of applied uniaxial stress. The maximum differential permeability and the coercive field are obtained from this Barkhausen signals. The angular dependence of these macroscopic magnetic properties is studied. The tension for which the magneto-elastic energy balances the anisotropic energy is estimated. The results are discussed based on the domain wall theory. 相似文献
996.
Thermal stability behaviors of Cr(N,O)/CrN double-layered coatings by TGA/DTA analysis 总被引:1,自引:0,他引:1
In this study, Cr(N,O)/CrN double-layered coatings were synthesized using the cathodic arc deposition (CAD) process. CrN film was first deposited onto a substrate as an interlayer to ensure better adhesion, and Cr(N,O) film was subsequently deposited on top of the CrN layer as the surface layer. Variation in the Cr(N,O) coating composition was achieved through changing the O2/N2 flow ratio during the last stage of processing. Phase structure, chemical composition, and morphology of the resulting coatings were analyzed and observed using the X-ray diffractometer, Auger electron spectrometer and SEM. In addition, oxidation behavior of the coatings was investigated using TGA/DTA methods. The tests were carried out by increasing temperature up to 1000 °C in ambient air. With the introduction of oxygen gas during the CAD process, a superficial layer was produced in the Cr(N,O) constituent containing CrN and Cr2O3 phases. The formation of the oxide phase attributed to the reaction of chromium and oxygen was more favorable than that of chromium and nitrogen. The results also showed that Cr(N,O)/CrN double-layered coatings exhibited superior oxidation resistance at elevated temperature than that of CrN single-layer coated specimen (870 °C vs. 750 °C). 相似文献
997.
998.
离心成型法制备Al2O3/Ni功能梯度材料及性能表征 总被引:1,自引:0,他引:1
用离心成型法制备了Al2O3/Ni功能梯度材料,并研究了料浆调制工艺、制备参数和梯度材料的力学性能.结果表明,良好的料浆的最佳流动性配比为粘结剂(聚乙二醇)含量为2 mass%、固相含量为63 vol.%、球磨时间为36 h.经离心成型-真空烧结(1400℃,2 h)可获得致密、组元宏观连续过渡的Al2O3/Ni梯度材料.该复合材料孔隙率低,力学性能好,抗弯强度可达321 MPa. 相似文献
999.
A study was undertaken in an attempt to quantitatively describe the rolling process of eutectoid steel rods. Finite element method was employed to model plastic flow and heat transfer in the deformed material, and heat transfer during cooling to ambient temperature. The numerical calculation gave an assessment of the strain, strain rate and temperature distributions in the work piece. This allowed the prediction of the austenite microstructure evolution during the process. Finally, the relationships describing the microstructure-mechanical properties were used to quantitatively characterize the influence of processing parameters on strength of rods after rolling. 相似文献
1000.
Effects of sintering pressure and temperature on microstructure and tribological characteristic of Cu-based aircraft brake material 总被引:3,自引:0,他引:3
A novel Cu-based P/M aircraft brake material was prepared and the effects of sintering pressure and temperature on microstructure and tribological characteristic were investigated. For the constant sintering temperature, when the sintering pressure increases from 0.5 MPa to 1.5 MPa, the porosity, wear loss and friction coefficient decrease remarkably. When the sintering pressure increases from 1.5 MPa to 2.5 MPa, the porosity further decreases but in a little degree and wear behaviors are improved slightly. However, once the sintering pressure is larger than 2.5 MPa, it has no obvious effect on microstructure and tribological characteristic. For the constant sintering pressure, when the sintering temperature increases from 900 ℃ to 930 ℃, the sintered density remarkably-increases, and wear behaviors are obviously improved. For further increasing sintering temperature to l 000 ℃, the density keeps on increasing, but wear behaviors change slightly. 相似文献