全文获取类型
收费全文 | 33331篇 |
免费 | 2840篇 |
国内免费 | 2286篇 |
专业分类
电工技术 | 1054篇 |
技术理论 | 1篇 |
综合类 | 2108篇 |
化学工业 | 8541篇 |
金属工艺 | 7134篇 |
机械仪表 | 1620篇 |
建筑科学 | 1700篇 |
矿业工程 | 654篇 |
能源动力 | 789篇 |
轻工业 | 2887篇 |
水利工程 | 457篇 |
石油天然气 | 1025篇 |
武器工业 | 344篇 |
无线电 | 1420篇 |
一般工业技术 | 4834篇 |
冶金工业 | 1343篇 |
原子能技术 | 199篇 |
自动化技术 | 2347篇 |
出版年
2024年 | 183篇 |
2023年 | 624篇 |
2022年 | 1009篇 |
2021年 | 1098篇 |
2020年 | 1085篇 |
2019年 | 1019篇 |
2018年 | 1033篇 |
2017年 | 1241篇 |
2016年 | 1181篇 |
2015年 | 1204篇 |
2014年 | 1783篇 |
2013年 | 1881篇 |
2012年 | 2372篇 |
2011年 | 2590篇 |
2010年 | 2037篇 |
2009年 | 1953篇 |
2008年 | 1655篇 |
2007年 | 2089篇 |
2006年 | 2011篇 |
2005年 | 1692篇 |
2004年 | 1487篇 |
2003年 | 1205篇 |
2002年 | 1043篇 |
2001年 | 896篇 |
2000年 | 787篇 |
1999年 | 619篇 |
1998年 | 539篇 |
1997年 | 406篇 |
1996年 | 354篇 |
1995年 | 300篇 |
1994年 | 243篇 |
1993年 | 215篇 |
1992年 | 171篇 |
1991年 | 116篇 |
1990年 | 80篇 |
1989年 | 68篇 |
1988年 | 38篇 |
1987年 | 18篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1976年 | 4篇 |
1964年 | 2篇 |
1959年 | 2篇 |
1955年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Although Mg alloy possesses high specific strength, low density, and good biocompatibility, poor corrosion resistance hinders its further applications. In the present study, an innovative protective layer against corrosion was prepared on the AZ31 Mg alloy via alkali pretreatment followed by vanillic acid treatment. The alkali pretreatment supplied –OH for the AZ31 Mg alloy surface to react with vanillic acid. The vanillic acid treatment played a crucial role in enhancing the corrosion resistance due to the excellent ability to act as a barrier and retard aqueous solution penetration, which effectively isolated the underlying Mg alloy from the corrosive environment. The corrosion current density of alkali and vanillic acid-treated Mg alloy (AZ31V) almost showed two orders of magnitude lower values in comparison with that of the AZ31 Mg alloy, and the corrosion potential of AZ31V Mg alloy increased from −1.41 to −1.25 V. The immersion tests proved that there was no occurrence of severe corrosion. Hence, the alkali pretreatment and vanillic acid treatment may represent a promising method to improve the corrosion resistance of Mg alloy. 相似文献
23.
Rahul Sasidharan Pillai Matteo Frasnelli Vincenzo M. Sglavo 《Ceramics International》2018,44(2):1328-1333
The present work focuses on the fabrication of βTCP (β-tricalcium phosphate) and HA/βTCP (hydroxyapatite/β-tricalcium phosphate) composite coatings by plasma spraying. The starting powders were produced via solid-state method using 2 wt% MgO to stabilize βTCP phase. The synthesized powders were preliminarily granulated to be used by the plasma spray process. Coatings obtained on titanium substrates are uniform and well adherent but due to the high temperature and cooling rate typical for plasma spraying process, βTCP phase is almost totally transformed into the α allotrope. Thermal treatment at 800 °C allows the reconversion of the phase αTCP→ βTCP. It is therefore possible to produce coatings with tuneable dissolution properties by selecting the proper initial powder mixture and the specific thermal treatment. 相似文献
24.
Galin Ivanov Ertugrul Bilgucu Ivelina Ivanova Milena Dimitrova 《International Journal of Dairy Technology》2020,73(3):563-569
The present study aimed to investigate the effect of somatic cell count (SCC) of raw cow's milk on the volatile organic compound (VOC) profiles of yoghurt. Test yoghurt samples were produced from three batches of cow's milk with low, medium and high SCC, respectively. The VOCs were determined by gas chromatography–mass spectrometry (GC–MS) analysis. A lower diacetyl and acetoin content and a higher content of 2‐heptanone, and butanoic and hexanoic acids were established in the yoghurt samples from batches with high SCC of above 1 000 000 cells/cm3. The increased SCC of cow's milk had a negative effect on the volatile organic compound profiles of yoghurt. 相似文献
25.
高浓度聚合物驱提高采收率方法实验研究 总被引:3,自引:0,他引:3
为探索一种新的提高原油采收率的方法,在外形尺寸为4.5 cm×4.5 cm×30 cm、气测渗透率0.9~1.0μm2、变异系数为0.72的二维纵向非均质人造岩心上,模拟大庆油田油藏流体性质及温度条件,研究了高浓度聚合物(HPAM)驱注入时机、聚合物相对分子质量、聚合物段塞体积及段塞组合对驱油效果的影响。通过注入大分子量、高浓度聚合物,结合合理的注入方式,在化学剂成本与三元复合驱相当的情况下,采收率比水驱提高20个百分点以上,接近或超过三元复合驱的水平。实验表明,采用高浓度聚合物驱油是一种较好的提高原油采收率的方法。 相似文献
26.
Zk线性码的对称形式的MacWilliams恒等式 总被引:8,自引:2,他引:6
该文定义了Zk线性码的码字的对称重量计数公式,利用离散的Hadamard变换,建立了线性码与其对偶码之间的对称形式的MacWilliams恒等式. 相似文献
27.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
28.
29.
The oxidation behavior of Hastelloy-XR alloy was investigated to obtain the optimum surface condition for corrosion-resistant glass-coatings. The surface morphology of oxide scales changed significantly with variation of temperatureand oxygen partial pressure (po2 ). The oxidation kinetics was mainly parabolic independent of oxidation conditions.The oxide scales were consisted of inner Cr2O3 and outer spinel layers. The phase component of spinel layers wereMn1.5Cr1.5O4 and (Mn,Ni)(Cr,Fe)2O4 for the oxygen partial pressures po2<10 kPa and po2>10 kPa, respectively.The optimum oxidation condition to obtain an oxide scale for well-adhered glass-coating to the substrate was 1248 Kand po2 =0.01 kPa for the oxidation time of 43 ks. 相似文献
30.