全文获取类型
收费全文 | 39844篇 |
免费 | 3695篇 |
国内免费 | 2193篇 |
专业分类
电工技术 | 996篇 |
综合类 | 2207篇 |
化学工业 | 13224篇 |
金属工艺 | 7192篇 |
机械仪表 | 1039篇 |
建筑科学 | 1362篇 |
矿业工程 | 732篇 |
能源动力 | 1903篇 |
轻工业 | 4017篇 |
水利工程 | 240篇 |
石油天然气 | 1605篇 |
武器工业 | 272篇 |
无线电 | 1998篇 |
一般工业技术 | 4617篇 |
冶金工业 | 2323篇 |
原子能技术 | 1594篇 |
自动化技术 | 411篇 |
出版年
2024年 | 122篇 |
2023年 | 844篇 |
2022年 | 1166篇 |
2021年 | 1456篇 |
2020年 | 1461篇 |
2019年 | 1422篇 |
2018年 | 1316篇 |
2017年 | 1442篇 |
2016年 | 1305篇 |
2015年 | 1251篇 |
2014年 | 1930篇 |
2013年 | 2344篇 |
2012年 | 2376篇 |
2011年 | 2795篇 |
2010年 | 2040篇 |
2009年 | 2337篇 |
2008年 | 2059篇 |
2007年 | 2608篇 |
2006年 | 2336篇 |
2005年 | 1966篇 |
2004年 | 1747篇 |
2003年 | 1470篇 |
2002年 | 1184篇 |
2001年 | 1081篇 |
2000年 | 959篇 |
1999年 | 689篇 |
1998年 | 606篇 |
1997年 | 524篇 |
1996年 | 509篇 |
1995年 | 335篇 |
1994年 | 312篇 |
1993年 | 305篇 |
1992年 | 264篇 |
1991年 | 217篇 |
1990年 | 180篇 |
1989年 | 124篇 |
1988年 | 79篇 |
1987年 | 70篇 |
1986年 | 60篇 |
1985年 | 62篇 |
1984年 | 56篇 |
1983年 | 25篇 |
1982年 | 73篇 |
1981年 | 56篇 |
1980年 | 32篇 |
1979年 | 24篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The oxidation behavior of Ti5Si3+y (y=0 or 0.2) and Ti5Si3Zx (Z=C, N or O, x=0.25 or 0.5) was studied at 1000°C in air or argon–oxygen mixtures for up to 500 h. Ti5Si3 has poor oxidation resistance in air because of the formation of an oxide scale rich in rutile and subscale formation of TiN, TiSi, TiSi2 and Si. In contrast, Ti5Si3.2 has excellent oxidation resistance because of the formation of a silica scale. Samples with interstitial oxygen or nitrogen show only slight improvements in the early stages of oxidation, compared to Ti5Si3, which is in stark contrast to previous research. However, samples with interstitial carbon displayed excellent oxidation resistance at 1000°C, consistent with previous research. 相似文献
992.
(Ti,Al)N涂层的微观组织和性能 总被引:3,自引:1,他引:3
采用EPMA、XRD、SEM、TEM、HR-TEM、EDX、纳米压痕、氧化实验和切削实验研究了磁控溅射在硬质合金基体上沉积TiN涂层和(Ti,Al)N涂层的微观组织结构和性能。结果表明:TiN涂层晶粒为喇叭口柱状晶,(Ti,Al)N涂层为面心立方平直柱状晶,由于固溶了Al元素,(Ti,A l)N涂层呈(200)面择优生长;(Ti,Al)N涂层在硬质合金基体上无外延生长;(Ti,Al)N涂层在800℃氧化后形成Al2O3/TiO2/(Ti,Al)N的分层结构;(Ti,Al)N涂层具有更高的硬度和更好的切削性能。 相似文献
993.
In this work, nanopowders of perovskite cathode materials (La0.8Sr0.2MnO3−δ, La0.8Sr0.2FeO3−δ, and La0.8Sr0.2CoO3−δ), for use in solid oxide fuel cells (SOFC), were successfully synthesized, using induction plasma techniques. Their compositions,
structures, morphology, particle size distributions, and BET specific surface areas were determined for comparison with their
counterparts prepared by the Pechini method and by the glycine-nitrate combustion (GNC) technique. The particle sizes of the
plasma-synthesized powders are mostly around 63 nm. These plasma-synthesized powders are generally globular, their BET specific
surface areas being about 26 m2g−1, approximately twice those of powders prepared by the GNC and Pechini methods. These plasma-synthesized powders are readily
reproducible and are not agglomerated. Their individual particle sizes and distributions are very independent of their composition. 相似文献
994.
TaC涂层的氧化特征与氧化机制 总被引:1,自引:0,他引:1
用在空气中氧化、氧炔焰超高温烧蚀等方法对TaC涂层在不同温度的氧化特征与氧化机制进行研究。研究结果表明:TaC在508℃以上开始氧化,在508~690℃时氧化产物为六角Ta2O3固溶体,690~900℃时氧化产物转化为斜方Ta2O5晶体,900~1500℃时氧化产物为斜方Ta2O5,其形态为龟裂或多孔烧结态,未能形成对TaC的隔离保护膜;1500℃氧化时出现部分Ta2O5液相与Ta2O5斜方相共存的现象;在氧炔焰超高温2300℃烧蚀时形成大量的Ta2O5熔体液膜,熔体与TaC的润湿性很好。TaC涂层由低温无熔体情况下界面反应控制机制变为氧通过熔体溶解与扩散的控制机制。 相似文献
995.
Ni-Cr-Al纳米晶合金在1000℃的高温氧化行为 总被引:5,自引:0,他引:5
研究了纳米晶Ni-Cr-Al合金的高温氧化行为,发现与
铸态合金不同,随成分不同纳米晶合金在1000℃氧化时,氧化物可分为四个区:A单一Al2O3区;B复杂氧化膜含一连续Al2O3内层区; C复杂氧化膜含内氧化物区;D Al2O3和NiAl2O4共生区.纳米晶化明显扩展了Al2O3生成区的成份范围. 相似文献
996.
997.
M. O. H. Cioffi H. J. C. Voorwald V. Ambrogi T. Monetta F. Bellucci L. Nicolais 《Journal of Materials Engineering and Performance》2003,12(3):279-287
As a followup to previous work, experiments with argon and oxygen Radio Frequency plasma treated polyethylene terepthalate
(PET) exposed to 100 °C after cold plasma treatment were performed. Tensile tests results in monofilaments treated in oxygen
and argon plasma for 5 s, 20 s, 30 s, and 100 s showed a decrease in the average tensile strength compared with the untreated
fibers. It was also observed that the reduction in mechanical strength is more significant for argon plasma and very sensitive
to the treatment time for oxygen plasma. Experimental data obtained from tensile tests in samples thermal exposed to 100 °C
after plasma treatments indicate the same influence of treatment times on mechanical strength, as observed for cold plasma
treated fibers. Furthermore, an increase in tensile strength when compared with the samples unexposed to 100 °C was observed.
Scanning electron microscopy, used to analyze effects of cold plasma treatment on fibers surfaces, indicates differences in
roughness profiles depending on the type of treatment. The distance of roughness interval, Dri, was a parameter introduced to relate the fibers surface condition and average tensile strength. Statistical analysis of
experimental data was performed to explain influences of treatment time, and environmental and temperature effects on mechanical
properties. 相似文献
998.
测定了IC-6高温合金在900℃-1100℃的氧化动力学曲线。结果表明:900℃,IC-6合金的氧化膜主要由α-Al2O3、NiAl2O4和NiO构成并含有少量的NiMoO4和MOo2.1050℃和1100℃氧化时,IC-6合金表面生成了挥发性很强的MoO3,发生了氧化失重,IC-6合金上沉积NiCoCrAlY涂层后,900℃,涂层的氧化膜主要为α-Al2o3;1050℃时,氧化膜主要为α-Al2O3和Cr2O3,大大改善了合金的抗氧化性;1100℃时,氧化膜主要由α-Al2o3、NiAl2O4和NiO构成,涂层虽然有一定的保护性,但效果不如900℃和1050℃时显著,形成以α-Al2O3和Cr2O3为主的氧化膜是使合金沉积NiCoCrAlY涂层后抗氧化能力大大提高的直接原因。 相似文献
999.
1000.
On the induction plasma deposition of tungsten metal 总被引:1,自引:0,他引:1
X. L. Jiang R. Tiwari F. Gitzhofer M. I. Boulos 《Journal of Thermal Spray Technology》1993,2(3):265-270
The central particle injection and long residence time characteristics of induction plasma have given rise to the complete
melting of tungsten particles injected into an Ar- H2 plasma under soft vacuum conditions. The influences of process variables such as power level, chamber pressure, and spray
distance on splat morphology, apparent density, and deposition efficiency have been studied. Dense tungsten deposits with
no oxidation have been obtained. Scanning electron microscopy (SEM) micrographs reveal a well-flattened lamellar structure
in deposits. Radiative cooling is observed to play a significant role in the plasma spraying of this refractory metal. 相似文献