全文获取类型
收费全文 | 65463篇 |
免费 | 6454篇 |
国内免费 | 4361篇 |
专业分类
电工技术 | 5165篇 |
技术理论 | 3篇 |
综合类 | 6446篇 |
化学工业 | 9294篇 |
金属工艺 | 4235篇 |
机械仪表 | 4791篇 |
建筑科学 | 4916篇 |
矿业工程 | 2002篇 |
能源动力 | 1818篇 |
轻工业 | 6233篇 |
水利工程 | 1906篇 |
石油天然气 | 2502篇 |
武器工业 | 746篇 |
无线电 | 6926篇 |
一般工业技术 | 6091篇 |
冶金工业 | 2388篇 |
原子能技术 | 899篇 |
自动化技术 | 9917篇 |
出版年
2024年 | 202篇 |
2023年 | 663篇 |
2022年 | 1852篇 |
2021年 | 2440篇 |
2020年 | 1815篇 |
2019年 | 1421篇 |
2018年 | 1525篇 |
2017年 | 1762篇 |
2016年 | 1626篇 |
2015年 | 2598篇 |
2014年 | 3430篇 |
2013年 | 4178篇 |
2012年 | 5028篇 |
2011年 | 5368篇 |
2010年 | 5238篇 |
2009年 | 5096篇 |
2008年 | 5191篇 |
2007年 | 5071篇 |
2006年 | 4627篇 |
2005年 | 3789篇 |
2004年 | 2825篇 |
2003年 | 1991篇 |
2002年 | 2014篇 |
2001年 | 1818篇 |
2000年 | 1369篇 |
1999年 | 836篇 |
1998年 | 475篇 |
1997年 | 403篇 |
1996年 | 351篇 |
1995年 | 249篇 |
1994年 | 225篇 |
1993年 | 175篇 |
1992年 | 126篇 |
1991年 | 122篇 |
1990年 | 73篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 30篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1959年 | 5篇 |
1958年 | 2篇 |
1956年 | 2篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
934.
935.
The thermodynamic data of pure Ag and Y were calculated. The phase constitution, composition of micro-region and microstructures of Ag-Y alloy after internal oxidation were investigated by X-ray diffractometry(XRD), energy dispersion spectrometry(EDS) and scanning electron microscopy(SEM). The results show that the internal oxidation behavior of Ag-Y alloy is feasible from the view of thermodynamics. The upper limit of oxygen partial pressure of Ag-Y alloy oxidation is a function of temperature. Two phases (Ag and Y2O3) appear in Ag-Y alloy after the internal oxidation. The surface of Ag-Y alloy is convex because of the volume expansion of oxide in the alloy and the composition of the convex part is Ag. In Ag-Y2O3 sintered bulk Y2O3 particles are distributed inhomogeneously and conglomerated seriously, but they are dispersed uniformly in the Ag matrix after severe plastic deformation. 相似文献
936.
研究了合成镍硫化物的阳极过程。Ni_3S_2,Ni_7S_6和NiS的活性溶解伴随着生成表面产物层,其反应机理与电极电位有关。根据三种不同类型产物层生成规律的电化学研究,Ni溶出表观电子数的测定,以及产物层相组成分析和相的元素分析,认为存在三组平行反应:直接生成HSO_4~-或SO_(4-)~2的反应,生成中间硫化物的反应及生成元素硫的反应,每组反应具有不同的优势发展电位区。NiS_2阳极溶解时,基本上为生成HSO_(4-)或SO_(4-)~2的反应。 相似文献
937.
Ce0.8Ca0.2O1.8(CDC82) anode material was prepared by glycine-nitrate process(GNP). Thermogravimetric(TG) analysis and differential scanning calorimetric(DSC) methods were adopted to characterize the reaction process of CDC82 material. X-ray diffractometry(XRD), scanning electron microcopy(SEM), direct current four probe (four-probe DC) and temperature process reduce(TPR) techniques were adopted to characterize the properties of CDC82 material. After the precursor was sintered at 750℃ for 4 h, CDC82 material with pure-fluorite structure and nanometer size was obtained. The total conductivity of CDC82 changes little with temperature in air at 50-850℃, and the maximum value is 0.04 S/cm at 750 ℃. The total conductivity wholly becomes larger when the atmosphere changes from air to hydrogen, which greatly increases with increasing temperature and reaches the maximum value of 1.09 S/cm at 850 ℃. Some impurities such as CeMg and La203 exist after the mixture of CDC82 anode and La1-xSrxGa1-yMgyO3-δ (LSGM) electrolyte material is sintered at 1 200 ℃ for 15 h. The CDC82 material as anode material has excellent catalytic property for hydrogen and methane. 相似文献
938.
939.
Friction stir welding of AZ31 magnesium alloy 总被引:3,自引:0,他引:3
Friction stir welding (FSW) is an new solid-phase joining technology which has more advantages over fusion welding methods in welding of aluminum and other non-ferrous metals. The effects of welding parameters on mechanical properties and microstructure during friction stir welding of AZ31 magnesium alloy were studied in this paper. Microstructures and mechanical properties of the joints were investigated by means of optical microscopy, scanning electric microscopy ( SEM ) , micro-hardness analysis, and tensile test. Experimental results show that the magnesium alloy can be successfully welded by FSW method, and the ultimate tensile strength (UTS) of FSW joint reaches up to 90 percent of base metal. The microstructures of welded joints exhibit the variation from dynamically recrystallized fine grains to greatly deformed grains. Hardness in nugget zone was found lower than the base metal but not too obvious. 相似文献
940.