全文获取类型
收费全文 | 15171篇 |
免费 | 1414篇 |
国内免费 | 595篇 |
专业分类
电工技术 | 1636篇 |
技术理论 | 1篇 |
综合类 | 1108篇 |
化学工业 | 3839篇 |
金属工艺 | 411篇 |
机械仪表 | 372篇 |
建筑科学 | 512篇 |
矿业工程 | 1171篇 |
能源动力 | 4267篇 |
轻工业 | 125篇 |
水利工程 | 54篇 |
石油天然气 | 552篇 |
武器工业 | 456篇 |
无线电 | 102篇 |
一般工业技术 | 670篇 |
冶金工业 | 1622篇 |
原子能技术 | 48篇 |
自动化技术 | 234篇 |
出版年
2024年 | 40篇 |
2023年 | 187篇 |
2022年 | 401篇 |
2021年 | 449篇 |
2020年 | 501篇 |
2019年 | 349篇 |
2018年 | 369篇 |
2017年 | 377篇 |
2016年 | 403篇 |
2015年 | 398篇 |
2014年 | 817篇 |
2013年 | 680篇 |
2012年 | 993篇 |
2011年 | 1201篇 |
2010年 | 889篇 |
2009年 | 994篇 |
2008年 | 808篇 |
2007年 | 1105篇 |
2006年 | 904篇 |
2005年 | 859篇 |
2004年 | 761篇 |
2003年 | 673篇 |
2002年 | 559篇 |
2001年 | 469篇 |
2000年 | 407篇 |
1999年 | 310篇 |
1998年 | 230篇 |
1997年 | 211篇 |
1996年 | 187篇 |
1995年 | 146篇 |
1994年 | 105篇 |
1993年 | 75篇 |
1992年 | 78篇 |
1991年 | 40篇 |
1990年 | 48篇 |
1989年 | 33篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 9篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
燃烧合成三元碳化合物Ti2AlC1-x 总被引:1,自引:0,他引:1
采用Ti,Al和C元素粉末为反应物原料,通过燃烧合成法首次成功地制备出了单相三元碳化合物Ti2AlC1-x。实验结果表明:若以“理想”晶体结构化学式Ti2AlC化学计量比为起始反应原料配比,燃烧产物主晶相为Ti2AlC2;以缺碳的非化学计量比(Ti2AlC1-x)为反应原料配比,即Ti:Al:C=3:1.5:1=2:1:0.7(摩尔比),得到单相的燃烧产物Ti2AlC1-x。从热力学原理的角度探讨了不同原料摩尔配比对燃烧产物相组成的影响机理。 相似文献
53.
为研究包覆方式对片状发射药燃烧性能的影响,建立了不同包覆方式下多层片状发射药的物理模型,并推导了形状函数和燃气生成猛度表达式,利用Matlab软件对不同的宽厚比、长厚比及多层结构的片状发射药进行了数值计算;制备了不同长厚比的片状变燃速发射药,并进行了密闭爆发器实验。结果表明,四面包覆和全包覆可以很好地消除临界宽厚比对片状发射药燃烧性能的影响;与两面包覆的片状发射药相比,四面包覆和全包覆的片状发射药能够延缓内层药减面燃烧的时间,其燃气生成猛度的阶跃程度分别提高了1.17%和1.23%,呈现出良好的燃烧渐增性。 相似文献
54.
Thanit Tangcharoen Jiraroj T-Thienprasert Chanapa Kongmark 《International Journal of Applied Ceramic Technology》2021,18(4):1125-1143
Using the sol–gel auto combustion method with diethanolamine (DEA) as fuel, a sequence of iron-substituted zinc aluminates, ZnFexAl2-xO4 powders, including variable Fe3+ ion concentrations (0 ≤ x ≤ 2) were effectively prepared. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer–Emmett–Teller (BET) method, UV–visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM) were employed to examine the structures, chemical bonds, morphologies, composition, surface area, and optical properties as well as the magnetic behavior of the obtained samples. A single-phase spinel structure was obtained for the calcined aluminate powders with different interplanar spacing and crystallite sizes, as revealed by the classification results. The bandgap energy (Eg) of adapted aluminates was in the range of 2.04-3.14 eV, identified as being much lower compared to the pure sample (5.60 eV). Thus, Fe3+-substituted ZnAl2O4 samples could be successfully photoexcited using both ultraviolet and visible light, as suggested by the results. Examination of how the four main pollutant types decay when irradiated by sunlight was carried out to assess the samples and establish photocatalytic activity. These contaminants included rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). The performance of photocatalytic degradation reached 98% after 150 min for all optimal samples of organic dyes. Besides, each of the altered photocatalysts could be recycled and displayed high stability. The S-shaped curve of ferrimagnetism can result in those samples as found by the magnetic measurements, though pure ZnAl2O4 displays diamagnetic characteristics. The adapted samples show intense improvement in the remanent magnetization (Mr) when compared to pure ZnAl2O4, signifying that magnetic photocatalyst recovery by applying an external magnetic field is easy. Thus, these results offer a convincing sign that ZnAl2O4 powders replaced by Fe3+ could provide the ability to aid in the ecologically friendly collection of solar energy. 相似文献
55.
铁基载氧体是一种具有工业应用前景的载氧体,但存在氧利用率低、在高温下易烧结等问题。虽可通过制备双金属复合载氧体或添加惰性组分改进其性能,但均存在一定缺陷。若将活性组分和惰性材料融入到一个晶体结构制备尖晶石结构载氧体,则可实现利用双金属协同作用提高载氧体活性的同时,利用Al3+提高载氧体的稳定性。采用共沉淀法和溶胶凝胶法制备了具有尖晶石结构的NiFeAlO4载氧体,考察了制备方法、载氧体与煤质量比对NiFeAlO4载氧体化学链燃烧特性和循环稳定性的影响,并分析了载氧体对煤转化过程的作用。结果表明,溶胶凝胶法制备的NiFeAlO4载氧体具有更好的反应性,载氧体与煤质量比为20∶1时,碳转化率为86.7%,远高于煤单独热解时的碳转化率(34%),此时CO2体积分数为93.6%。对反应前后NiFeAlO4载氧体晶相结构和形貌进行分析,表明循环过程中经“还原-氧化”后生成的NiO和载氧体颗粒团聚是导致载氧体活性下降的主要原因。相较于载热作用,NiFeAlO4载氧体在煤化学链燃烧中主要起供氧作用,其不仅会促进挥发分向煤气的转化,且NiFeAlO4载氧体与焦炭之间也存在固-固反应,利于更多CO2的生成。 相似文献
56.
The formation of a phase pure silicon ingot from SiO2+Al+KClO3 and Na2SiO3+Al+KClO3 systems was investigated thermodynamically and experimentally under combustion mode, known also as self-propagating high-temperature
synthesis (SHS). The regularities of combustion and phase formation versus KClO3 concentration by a thermocouple technique were obtained. The morphology, chemical and phase composition of the silicon ingot
were analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and ICP-analysis. The method reported
here proved effective in producing silicon ingots with a purity of 98%. 相似文献
57.
58.
Iron nitrate, nickel nitrate and cobalt nitrate were used as catalyst precursors to study their effects on carbon nanowires synthesized by ethanol catalytic combustion (ECC) process. The as-grown carbon nanowires were characterized by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results show that relatively uniform nanowires will be formed when the catalyst precursor is iron nitrate; while helical structure or disordered structure will be formed when the catalyst precursor is nickel nitrate or cobalt nitrate. precursor 相似文献
59.
60.
Mercury transformation across particulate control devices in six power plants of China: The co-effect of chlorine and ash composition 总被引:2,自引:0,他引:2
This paper presents the results of field measurements on mercury speciation in six power plants of China by applying the Ontario hydro method. During the tests, flue gas was sampled simultaneously before and after particulate control devices (electrostatic precipitator and fabric filter baghouse) along with the pulverized coal, bottom ash and fly ash sampling. The amount of oxidized mercury in gas phase before and after ESP/FF suggests that mercury oxidation after combustion is a kinetically controlled process. The comparison of mercury speciation in different power plant indicates a clear relationship with coal type, especially the chlorine concentration and the basic ash compositions in coal. Both of the factors are analyzed quantitatively in this study. A new parameter C (ratio of chlorine in coal to base/acid ratio) has been introduced to evaluate the co-effect of the two factors above on mercury speciation. 相似文献