全文获取类型
收费全文 | 63241篇 |
免费 | 6819篇 |
国内免费 | 4047篇 |
专业分类
电工技术 | 2702篇 |
技术理论 | 2篇 |
综合类 | 6470篇 |
化学工业 | 6818篇 |
金属工艺 | 5655篇 |
机械仪表 | 4170篇 |
建筑科学 | 10523篇 |
矿业工程 | 5212篇 |
能源动力 | 1866篇 |
轻工业 | 2998篇 |
水利工程 | 4083篇 |
石油天然气 | 5769篇 |
武器工业 | 516篇 |
无线电 | 2827篇 |
一般工业技术 | 7281篇 |
冶金工业 | 3714篇 |
原子能技术 | 476篇 |
自动化技术 | 3025篇 |
出版年
2024年 | 253篇 |
2023年 | 855篇 |
2022年 | 2443篇 |
2021年 | 2507篇 |
2020年 | 2178篇 |
2019年 | 1866篇 |
2018年 | 1753篇 |
2017年 | 2213篇 |
2016年 | 2389篇 |
2015年 | 2508篇 |
2014年 | 3876篇 |
2013年 | 3735篇 |
2012年 | 4433篇 |
2011年 | 4791篇 |
2010年 | 3653篇 |
2009年 | 3693篇 |
2008年 | 3507篇 |
2007年 | 4129篇 |
2006年 | 3686篇 |
2005年 | 3141篇 |
2004年 | 2648篇 |
2003年 | 2301篇 |
2002年 | 1987篇 |
2001年 | 1643篇 |
2000年 | 1405篇 |
1999年 | 1131篇 |
1998年 | 931篇 |
1997年 | 799篇 |
1996年 | 652篇 |
1995年 | 572篇 |
1994年 | 478篇 |
1993年 | 373篇 |
1992年 | 341篇 |
1991年 | 221篇 |
1990年 | 212篇 |
1989年 | 185篇 |
1988年 | 125篇 |
1987年 | 82篇 |
1986年 | 71篇 |
1985年 | 58篇 |
1984年 | 58篇 |
1983年 | 34篇 |
1982年 | 38篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 25篇 |
1964年 | 11篇 |
1961年 | 7篇 |
1959年 | 11篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
从材料的焊接性能、焊接结构、焊条、预热与焊后热处理、焊接工艺参数等角度对岸吊胎架焊缝裂纹进行了分析,提出了改进措施,取得了良好的效果。 相似文献
922.
S.A. Balogun D.E. Esezobor S.O. Adeosun 《Journal of Materials Engineering and Performance》2007,16(6):720-725
In the black world cup-shaped utensils cast or deep drawn are usually used for cooking purpose. The utensils are made from
deep drawn aluminum alloy of the 1xxx series and for cast 6xxx series. The cylindrical shape utensil is subjected to domestic
heating cycles and after a while, tiny hole-like features termed pits will appear. This development will eventually shorten
the service life of aluminum cooking utensils. This article examines the chemical response of deep drawn and cast utensils
made from 1017 and 6063 aluminum alloys, respectively, in solution of Lycopersicum esculentum at a temperature other than ambient temperature. The results show that cast cylindrical utensils pit much more readily than
deep drawn utensils. This occurrence is traceable to the presence of microcracks as a result of hydrogen embrittlement phase,
precipitation of brittle second phase particles and the fine texture in cast utensils. The aluminum alloy can fail by cracking
along grain boundaries when exposed to specific environments. 相似文献
923.
J.S. Huo J.T. Gou L.Z. Zhou X.Z. Qin G.S. Li 《Journal of Materials Engineering and Performance》2007,16(1):55-62
Creep properties of the experimental superalloy were investigated in the temperature range 1073–1223 K and stress range 110–550 MPa.
The observations of dislocation structures during different creep conditions reveal that in the high stress region, particle-shearing
mechanisms including stacking fault formation and antiphase boundary creation are operative and in the low stress region,
the dislocation climb mechanism is dominant. From the plot of minimum creep rate versus applied stress, a very low stress
region with exponent n < 2, which is related to diffusional creep, is found. Based on the experimental results, a stress–temperature creep deformation
mechanism map for the alloy is constructed. On the basis of particle hardening theories and various dislocation-creep theories,
the dislocation-creep transitions in terms of internal stress are discussed and calculated threshold stresses of various creep
deformation mechanisms indicates that the particle shearing is easier to operate than Orowan looping at high stresses, and
general climb is easy to happen at low stresses. 相似文献
924.
Flow behavior and microstructure evolution of TB8 alloy during hot deformation process 总被引:3,自引:0,他引:3
Hot compression tests of metastable β titanium alloy TB8 were carled out using a Gleeble-1500 thermal simulation testing machine in the temperature range of 750-1 100 ℃, at constant strain rate from 0.01 s^-1 to l S^-1 and with height direction reduction of 60%. Flow stress behavior and microstructure evolution during hot compression of TB8 alloy were investigated. The hyperbolic-sine-type constitutive model of TB8 alloy was obtained to provide basic data for determining reasonable forming process. The results indicate that hot deformation behavior of TB8 alloy is highly sensitive to the temperature and strain rate. An analysis of the flow stress dependence on strain rate and temperature gives a stress exponent of n=3.416 19 and a deformation activation energy of Ω=227.074 4 kJ/mol. According to the deformation microstructure, no dynamic recrystallization happens below r-phase transus temperature and as a result dynamic recovery is the predominant softening mechanism. On the other hand, the main softening mechanism is characterized as dynamic recrystallization at a slow strain rate above r-phase transus temperature. 相似文献
925.
The resistance of pipeline steel joint welded by submerged arc welding to stress corrosion cracking (SCC) at its different regions in boiling mixed nitrate solution and in H_2S saturated solution at room temperature is examined by the constant-load tension method. The result shows that when tested in nitrate, the weld metal may be the weakest link of the joint if the welding material doesn't match well. The resistance to SCC of the joint in H_2S is very low, especially at the bond and coarse grain zone and is closely dependent on the metallurgical quality of base metal. 相似文献
926.
从塑性力学应力Lode参数着手,深入研究了应力Lode参数与各应力参量之间的内在联系,并对塑性理论中屈服准则进行了合理推广。对塑性理论及其应用具有重要意义。 相似文献
927.
304不锈钢在室温HCl+NaCl溶液中可发生活化态下的应力腐蚀开裂(SCC).XPS成分分析表明:在酸性氯化物溶液中,试样表面形成了一层富铬的吸附产物膜,应力腐蚀裂纹的形核与这层膜的形成和Cl一局部富集有关. 相似文献
928.
929.
根据全息干涉法对板材轧制成形中的变形进行分析,假设三种典型轧制板的截面形状模型,计算了纵向非均匀应变分布,给出了其所产生的残余应力及其失稳起皱时的临界参数计算公式。与实测结果比较,变形的最大误差为11%。 相似文献
930.