全文获取类型
收费全文 | 50712篇 |
免费 | 5048篇 |
国内免费 | 3334篇 |
专业分类
电工技术 | 973篇 |
综合类 | 4981篇 |
化学工业 | 8436篇 |
金属工艺 | 6644篇 |
机械仪表 | 2499篇 |
建筑科学 | 10179篇 |
矿业工程 | 2682篇 |
能源动力 | 727篇 |
轻工业 | 2208篇 |
水利工程 | 1782篇 |
石油天然气 | 3973篇 |
武器工业 | 453篇 |
无线电 | 900篇 |
一般工业技术 | 8440篇 |
冶金工业 | 3255篇 |
原子能技术 | 233篇 |
自动化技术 | 729篇 |
出版年
2024年 | 132篇 |
2023年 | 648篇 |
2022年 | 1317篇 |
2021年 | 1712篇 |
2020年 | 1654篇 |
2019年 | 1469篇 |
2018年 | 1494篇 |
2017年 | 1938篇 |
2016年 | 1944篇 |
2015年 | 2000篇 |
2014年 | 2843篇 |
2013年 | 3249篇 |
2012年 | 3526篇 |
2011年 | 3696篇 |
2010年 | 2743篇 |
2009年 | 2844篇 |
2008年 | 2642篇 |
2007年 | 3100篇 |
2006年 | 2928篇 |
2005年 | 2579篇 |
2004年 | 2144篇 |
2003年 | 1882篇 |
2002年 | 1695篇 |
2001年 | 1433篇 |
2000年 | 1235篇 |
1999年 | 1120篇 |
1998年 | 932篇 |
1997年 | 796篇 |
1996年 | 656篇 |
1995年 | 552篇 |
1994年 | 451篇 |
1993年 | 367篇 |
1992年 | 288篇 |
1991年 | 235篇 |
1990年 | 259篇 |
1989年 | 195篇 |
1988年 | 94篇 |
1987年 | 70篇 |
1986年 | 33篇 |
1985年 | 34篇 |
1984年 | 29篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 7篇 |
1980年 | 25篇 |
1979年 | 22篇 |
1975年 | 3篇 |
1964年 | 4篇 |
1959年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
It has been observed that the forming limit curve at fracture (FLCF) of steel sheets, with a relatively higher ductility limit
have linear shapes, similar to those of a bulk forming process. In contrast, the FLCF of sheets with a relatively lower ductility
limit have rather complex shapes approaching the forming limit curve at neck (FLCN) towards the equi-biaxial strain paths.
In this study, the FLCFs of steel sheets were measured and compared with the fracture strains predicted from specific ductile
fracture criteria, including a criterion suggested by the authors, which can accurately describe FLCFs with both linear and
complex shapes. To predict the forming limit for hydro-mechanical deep drawing of steel sheets, the ductile fracture criteria
were integrated into a finite element simulation. The simulation, results based on the criterion suggested by authors accurately
predicted the experimetal, fracture limits of steel sheets for the hydro-mechanical deep drawing process. 相似文献
952.
Mg-9Al-xRE magnesium alloys were studied, where, x is 0, 0.4. 0.8. 1.2 and 1.6% (in weight percent, wt%), respectively. Influence of rare earths (RE) on microstructure and strength in both T4 (solute heat treatment) and T6 (solute heat treatment and artificial ageing treatment) were investigated. Strength of specimen was tested at ambient temperature. The micro structure was analyzed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis. RE additions improved T4 tensile strength of the treated alloys. Small addition (0.4wt%) of RE greatly improved the strength of ageing treated (T6) Mg-9Al alloy, but further additions caused decreasing. 相似文献
953.
The heat treatment effect on the characteristics and tensile strength of plasma-sprayed alumina, yttria-stabilized zirconia
(YSZ), and mixtures of alumina and YSZ coatings on titanium was investigated. The as-sprayed structures of alumina and YSZ
coatings consists of a and y alumina phases, and cubic and tetragonal zirconia phases, respectively. The tensile strength
of the coatings containing a large amount of YSZ is increased from 25 to 50 MPa by heat treatment at 800 °C. The 60% YSZ-AI2O3 coating showed the highest tensile strength. The tensile strength increase of the YSZ-containing coating by heat treatment
is caused by formation of 10 to 100 nm wide microcracks. The interface adhesion strength between the heat-treated titanium
substrate and the alumina-containing coating is increased by chemical reaction at the in-terface. Thus, a heat-treated alumina
and zirconia mixture coating may be favorable in obtaining high tensile strength due to microcrack formation in the coating
and the chemical reaction at the interface.
During this work, S. Baba was a graduate student at Kyushu Institute of Technology, Sumitomo Metal Ind. Ltd., Osaka, Japan. 相似文献
954.
R. Dal Maschio V. M. Sglavo L. Mattivi L. Bertamini S. Sturlese 《Journal of Thermal Spray Technology》1994,3(1):51-56
The indentation technique has been used to measure the adhesion of plasma- sprayed ceramic coatings on metals intended for
thick thermal barrier coating ( TTBC) applications. This approach provides the adhesion value as the critical strain energy
release rate,Gc, of the interface, which also takes into account any residual stresses. The theoretical background of the method is outlined,
and specific examples are reported with respect to the effect of substrate temperature on the metal/ceramic adhesion of thick
TBCs. 相似文献
955.
Ti、Mo、W、Cr及其合金镀层与超硬磨料之间结合性能的研究 总被引:14,自引:6,他引:14
本文在研究金属与超硬磨料之间作用的基础上,讨论了实现镀层与磨料形成强力结合的条件,为高性能超硬工具的制造提供了理论和实践依据。 相似文献
956.
957.
辙叉是线路上工作条件最为严峻的轨道部件之一。用高强度复合材料整铸的辙叉替代普通辙叉的研究具有重要意义。以PD3钢轨钢作为基体材料,在其表面熔合上一层新型具有更好耐磨性能的材质。新材料1、新材料2分别在PD3基础上把V的含量提高到0.15%~0.25%和0.35%~0.45%。采用合适的工艺措施,使新材料1、2与PD3轨道钢很好地熔合在一起。它们的σb、ak、δ、τb均不低于PD3,而Hv却有了提高。 相似文献
958.
采用真空扩散焊技术对Mg/Al异种材料进行了焊接。采用金相显微镜、扫描电镜(SEM)、显微硬度计及X射线衍射(XRD)对扩散界面附近的显微组织及性能进行了试验研究。试验结果表明,Mg/Al异种材料真空扩散焊在加热温度Tp=450-490℃,压力强度P=0.08-0.10MPa,保温时间t=40-60min时能得到良好的扩散焊接头。扩散焊界面过渡区形成了致密的新相化合物层,断口形貌呈粗糙暗灰色,以解理断裂为主并伴有脆性的混合型断口,扩散界面过渡区生成了MgAl、Mg3Al2、Mg2Al3等金属间化合物。 相似文献
959.
960.