全文获取类型
收费全文 | 37327篇 |
免费 | 2739篇 |
国内免费 | 2151篇 |
专业分类
电工技术 | 1450篇 |
综合类 | 2120篇 |
化学工业 | 11849篇 |
金属工艺 | 3577篇 |
机械仪表 | 1043篇 |
建筑科学 | 2564篇 |
矿业工程 | 494篇 |
能源动力 | 1101篇 |
轻工业 | 1511篇 |
水利工程 | 99篇 |
石油天然气 | 1252篇 |
武器工业 | 304篇 |
无线电 | 4255篇 |
一般工业技术 | 5149篇 |
冶金工业 | 1409篇 |
原子能技术 | 663篇 |
自动化技术 | 3377篇 |
出版年
2024年 | 77篇 |
2023年 | 508篇 |
2022年 | 740篇 |
2021年 | 1184篇 |
2020年 | 985篇 |
2019年 | 869篇 |
2018年 | 760篇 |
2017年 | 1034篇 |
2016年 | 1326篇 |
2015年 | 1285篇 |
2014年 | 1776篇 |
2013年 | 1990篇 |
2012年 | 2249篇 |
2011年 | 2944篇 |
2010年 | 2201篇 |
2009年 | 2737篇 |
2008年 | 2147篇 |
2007年 | 2625篇 |
2006年 | 2430篇 |
2005年 | 1906篇 |
2004年 | 1578篇 |
2003年 | 1574篇 |
2002年 | 1250篇 |
2001年 | 964篇 |
2000年 | 861篇 |
1999年 | 691篇 |
1998年 | 532篇 |
1997年 | 377篇 |
1996年 | 343篇 |
1995年 | 281篇 |
1994年 | 258篇 |
1993年 | 227篇 |
1992年 | 183篇 |
1991年 | 174篇 |
1990年 | 122篇 |
1989年 | 96篇 |
1988年 | 69篇 |
1987年 | 71篇 |
1986年 | 82篇 |
1985年 | 76篇 |
1984年 | 69篇 |
1983年 | 56篇 |
1982年 | 59篇 |
1981年 | 54篇 |
1979年 | 46篇 |
1978年 | 46篇 |
1977年 | 53篇 |
1976年 | 58篇 |
1975年 | 69篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Plasma surface nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 350 °C, 420 °C and 500 °C for 10 h using a DC plasma nitriding unit, and the surface properties of the plasma surface engineered samples were systematically evaluated. Experimental results have shown that the surface properties of the plasma nitrided layers in terms of hardness, wear resistance, corrosion behaviour and corrosion-wear resistance are highly process condition dependent, and it is feasible to provide considerable improvement in wear, corrosion and corrosion-wear resistance of 17-4PH steel using optimised plasma treatment conditions. All three treatments can effectively improve the surface hardness and the sliding wear resistance under unlubricated conditions; high temperature (420 °C and 500 °C) treated materials revealed improved corrosion and corrosion-wear properties due to the formation of surface compound layers. 相似文献
952.
电沉积-烧结制备Co3O4锂离子电池负极及电性能 总被引:4,自引:1,他引:4
摘要:采用电沉积一烧结方法制备Co3O4锂离子电池负极。X射线衍射XRD分析表明,电沉积的物质是Co(OH)2相,300℃烧结后均转变为Co3O4相。扫描电镜SEM观察发现获得的Co3O4具有花瓣形貌,其花瓣厚度约20nm。在300℃分别烧结30、45、60min制备的Co3O4组装的Co3O4/Li电池,在充放电循环中的首次嵌锂比容量分别为1361.7、1457.6和1345.0mAh/g,首次脱锂比容量分别为757.7、905.0和794.8mAh/g,10次循环后,脱锂比容量分别上升到815.5、969.0和890.1mAh/g。 相似文献
953.
Mixture of green petroleum coke, B4 C and SiC together with short carbon fiber were employed as starting materials, the mixture was press formed without any binder after grinding, dense and homogeneous binderless SiC-B4 C-C(carbon/ceramic) composites were then obtained after sintering. Composites thus prepared possess excellent anti-oxidation property, that is, mass loss less than IG within the temperature range from 900 to 1 100 ℃ for 10 h. Anti-oxidation mechanism was also discussed from the viewpoint of thermodynamics, excellent anti-oxidation property of materials thus prepared can be discribed to 1) solid SiO2 formed from SiC, which restrains the filtering of oxygen and simultaneously, its volume expansion brought about by the reaction takes roles both walling up the original pores and making the material more compact; 2) liquid B2O3 from the reaction of B4C not only makes the combination with C, B4 C and SiC tighter through forming solid solution, but also effect of reaction SiC(s)+2CO(g) =SiO2 (s)+3C(s) is an expansive process, which improves the microstructure of the material. 相似文献
954.
X70管线钢在近中性及高pH值溶液中的电化学行为和SCC敏感性 总被引:1,自引:0,他引:1
采用动电位极化曲线测试法研究了温度、通气条件和pH值对X70管线钢在NS4溶液和0.5 mol/LNa2CO3 1 mol/L NaHCO3溶液中的电化学极化行为的影响,并用慢应变速率试验(SSRT)研究了X70管线钢在这些溶液中的应力腐蚀破裂(SCC)敏感性。结果表明,X70管线钢在NS4溶液中不出现活化—钝化转变区,随外加电位负移,SCC敏感性增加,表现出氢致破裂(HIC)的特征;在0.5 mol/L Na2CO3 1 mol/L NaHCO3高pH值溶液中出现活化—钝化转变区,在阴极极化区,也表现出氢致破裂(HIC)的特征,但在阳极极化区,发生的是阳极溶解型应力腐蚀破裂(ADSCC)。 相似文献
955.
956.
对锆-4合金低周疲劳裂纹扩展过程进行了探索性的研究。通过分析锆-4合金低周疲劳断口在裂纹扩展方向上能量及分形维数变化趋势,发现锆-4合金动态裂纹扩展中扩展期由3个阶段组成,每一阶段的能量和分形维数都不同。A-B段的能量最小,归一化值为0-0.0156,A-B段的分形维数居中,在工工方向均值为2.2796,标准差为0.0277,在LH方向均值为2.4516,标准差为0.0592。D-E段能量远大于A-B段,归一化值为0.8754~0.9652,但分形维数最小,LL方向均值为2.2214,标准差为0.0131,LH方向均值为2.3477,标准差为0.0550。F-H(或G-H)段能量最大,归一化值达到1,同时分形维数也达到最大,LL方向均值为2.3414,标准差为0.0704,LH方向均值为2.5398,标准差为0.0263。虽后,根据二次电子成像原理以及锆-4合金低周疲劳断口的形貌特征对此现象进行了初步分析。 相似文献
957.
Lü Cheng ZH ANG Li-wen .State Key Laboratory for Materials Modification by Later Ion Electron Beams Dalian University of Technology Dalian China .School of Materials Science Engineering Dalian University of Technology Dalian China 《中国有色金属学会会刊》2006,16(6):1386-1390
1Introduction The TC4alloy mounting part is an important part of aeronautic engine.Currently,these mounting parts are mainly manufactured by metal cutting,which is expensive and requires a lot of manufacturing time.Furthermore,in this way the forging flow… 相似文献
958.
Five ternary additions, Cr, Ti, Mn, V, and Al were studied at equi-atomicpercent levels (17 a/o) for their effect on the sulfidation behavior of Ni-19a/o Mo (28–30 w/o) over the range of 600–800°C in 0.01 atm S2. Al was by far the most effective addition. A linear decrease in log kp vs. Al content was observed up to 7.5w/o Al, beyond which no further change was observed. All alloys followed the parabolic rate law. Arrhenius plots gave activation energies of 36.9–41.2 Kcal/mol for alloys containing Ti, Cr, Mn, and V, whereas the activation energies for Al-containing alloys were 47.2 Kcal/mol, indicating that a different diffusion process was involved. Complex scales were formed on all alloys, consisting of an outer layer of Nis1+x and complex inner layers which depended upon alloy composition. Two alloys, those with Cr and Mn, formed intermediate layers of Cr2S3 and MnS, respectively, but these layers had little effect on the kinetics. MoS2 was a constituent of the inner scales except for the alloys with Al. A ternary sulfide, Al0.55Mo2S4 and Al2S3 were observed. The presence of the mixed sulfide was always associated with the low sulfidation rates. The formation of MoS2 on alloys results in a different, less-protective behavior than for MoS2 formed on pure Mo. This effect is due to the intercalation of Ni into MoS2 in octahedral positions between the weakly bonded layers of covalently bonded sheets of trigonal prisms. The size of Al+3 is too small to be intercalated, and thus MoS2 is destabilized by Al. 相似文献
959.
将Ti与C同时加入Al熔体可制备出Ti与C摩尔比分别大于、等于、小于4的3种含不同物相的Al—TiC合金:Al—TiAl3-TiC、Al—TiC、Al-Al4C3-TiC。对纯铝的细化实验表明:不含过量Ti的后两种合金的细化效果相近,Al4C3在Al—TiC合金中的大量出现不会进一步降低合金的细化能力;含TiAl3的第一种合金的细化效率远高于后两者的;TiC物相在基体中以离散颗粒或聚集团形式在Al基体中分布;Al4C3相极脆,易与空气中的水蒸汽反应而分解。分析表明Ti与C在Al熔体中反应生成TiC是通过两条途径同时进行的:熔体中的固体C颗粒与溶解态的Ti直接反应;固体C颗粒和Al反应生成的A4C3与溶解态的Ti发生反应。 相似文献
960.
High-energy NdFeB magnets and their applications 总被引:3,自引:0,他引:3
In sintered NdFeB magnets, additive elements for increasing coercivity decrease residual magnetization. Also, fine magnetic
powder oxidization prevents identification of the stoichiometry composition (Nd
2Fei14B).To improve the magnetic properties of a sintered NdFeB magnet, the authors have developed a method involving two alloys. Magnetic
Nd
2Fei14Balloy and a rare- earth- rich alloy (including richer dysprosium content) are melted individually and mixed together after
coarse pulverization. After the sintering process, dysprosium in the sintered body is enriched in each grain region near the
grain boundary. The two- alloy method minimizes the liquid phase necessary to keep the coercive force at a useful level, and
thus results in compositions closer to stoichiometry. The energy product of magnets having an inhomogeneous dysprosium distribution
is typically 360 kj - m
- 3
(45 MG.Oe) at production level. The corrosion characteristics of cobalt- substituted NdFeB magnets also were investigated.
These magnets are now used in voice coil motors for hard disk drives and contribute to shortening access time and hard- drive
downsizing. 相似文献