全文获取类型
收费全文 | 14311篇 |
免费 | 971篇 |
国内免费 | 906篇 |
专业分类
电工技术 | 269篇 |
综合类 | 553篇 |
化学工业 | 3144篇 |
金属工艺 | 1963篇 |
机械仪表 | 417篇 |
建筑科学 | 164篇 |
矿业工程 | 130篇 |
能源动力 | 903篇 |
轻工业 | 181篇 |
水利工程 | 353篇 |
石油天然气 | 541篇 |
武器工业 | 55篇 |
无线电 | 2013篇 |
一般工业技术 | 4714篇 |
冶金工业 | 294篇 |
原子能技术 | 325篇 |
自动化技术 | 169篇 |
出版年
2024年 | 39篇 |
2023年 | 262篇 |
2022年 | 317篇 |
2021年 | 438篇 |
2020年 | 465篇 |
2019年 | 447篇 |
2018年 | 394篇 |
2017年 | 516篇 |
2016年 | 463篇 |
2015年 | 444篇 |
2014年 | 627篇 |
2013年 | 818篇 |
2012年 | 910篇 |
2011年 | 1208篇 |
2010年 | 942篇 |
2009年 | 953篇 |
2008年 | 835篇 |
2007年 | 904篇 |
2006年 | 888篇 |
2005年 | 670篇 |
2004年 | 608篇 |
2003年 | 570篇 |
2002年 | 429篇 |
2001年 | 307篇 |
2000年 | 286篇 |
1999年 | 213篇 |
1998年 | 233篇 |
1997年 | 175篇 |
1996年 | 172篇 |
1995年 | 172篇 |
1994年 | 110篇 |
1993年 | 70篇 |
1992年 | 61篇 |
1991年 | 56篇 |
1990年 | 46篇 |
1989年 | 33篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
铬酸酐副产物硫酸氢钠的利用 总被引:1,自引:0,他引:1
对生产铬酸酐时副产的含铬硫酸氢钠的利用作了评论,介绍了8种方法,即,化学沉淀法、磷酸沉淀法、铬酸铬法、电解氧化法、过硫酸钠氧化法、制商品硫酸氢钠、酸泥制碱式硫酸铬、硫酸氢钠制碱式硫酸铬,其中以化学沉淀法、磷酸沉淀法和铬酸铬法应用最广。 相似文献
83.
84.
Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140-160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H2 is largely suppressed. 相似文献
85.
A. Grüneis M.H. Rümmeli C. Kramberger A. Barreiro T. Pichler R. Pfeiffer H. Kuzmany T. Gemming B. Büchner 《Carbon》2006,44(15):3177-3182
We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube diameter distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10−5 mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented. 相似文献
86.
研究了玻璃颗粒在乙醇溶液中对Ca^2 的选择吸附,反转了玻璃颗粒在乙醇中的荷电性质,使玻璃颗粒能够在乙醇中与羟基磷灰石发生共沉积。讨论了不同离子浓度下电泳沉积的沉积量与沉积电流的变化情况,并以此对Ca^2 在电泳沉积中的作用进行了分析。实验结果证实:悬浮液中Ca^2 或吸附到玻璃颗粒上,改变其荷电性质;或留在溶液中,作为电泳沉积过程中电流的主要承载者。离子浓度对电泳沉积的效果有重要的影响,离子浓度太低或太高都易使涂层出现缺陷。分析了不同沉积条件下电泳沉积所得涂层的各种缺陷及其成因。 相似文献
87.
《Carbon》2004,42(1):187-190
Carbon nanotubes (CNTs) have been grown by chemical vapor deposition in a vacuum chamber equipped with in situ photoelectron spectroscopy technique that allows for precise characterization of the chemical state of substrate and catalyst before the CNTs growth. The CNTs were grown onto Si wafers covered with thin buffer layers of Al, Al2O3, TiN, and TiO2, using Fe as catalyst. Marked differences were observed both in growth rate and nanotube characteristics, as determined by SEM, TEM and micro-Raman spectroscopy, depending on the choice of buffer layer. 相似文献
88.
摘 要:为解决将数学模型运用于电站取水口长时段内的河床演变问题,从而引起计算效率与精度不足的缺陷。本文采用基于隐式与显式结合的算法,探索河道长时段的泥沙淤积特性,建立能模拟长时段河床演变的水沙数学模型,并将该模型应用于昭化电站取水河段泥沙冲淤模拟。通过物理模型与数学模型在不同频率洪水下取水口水位和流速的比较结果,表明此数学模型可以较好模拟取水口水流特性;通过预测昭化电站拉沙方案与不拉沙方案下取水河段运行多年后的河床演变,结果表明此数学模型模拟结果与实际工程结果相似,符合客观规律,能较好模拟河段的泥沙问题。 相似文献
89.
Jung Joon Lee Heeyeon Kim Jae Hyun Koh Ara Jo Sang Heup Moon 《Applied catalysis. B, Environmental》2005,61(3-4):274-280
The performance of a new type of CoMoS/Al2O3 catalyst, with added fluorine and prepared by sonochemical and chemical vapor deposition (CVD) methods, was investigated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The catalyst, which was designed to contain optimum amounts of fluorine and cobalt, exhibited a higher activity, ca. 4.6 times higher activity particularly in the HDS of 4,6-DMDBT, than a fluorine-free catalyst prepared by a conventional impregnation method. The enhanced activity of the new catalyst can be attributed to the cumulative effects of individual factors involved in the catalyst preparation. That is, the use of a sonochemical synthesis led to a high dispersion of small MoS2 crystallites on the alumina, and the addition of the Co species to the catalyst by CVD caused a close interaction between the Co species and the MoS2 crystallites to produce numerous CoMoS species, which are the catalytically active species for HDS. The addition of fluorine increased the amounts of acidic sites in the catalyst, which promoted hydrogenation (HYD) route to a greater extent than the direct desulfurization (DDS) route in DBT HDS and both HYD and DDS routes to similar extents in the case of 4,6-DMDBT HDS. Accordingly, the addition of fluorine led to a greater increase in catalytic activity for 4,6-DMDBT HDS than for DBT HDS. 相似文献
90.
A new catalyst (Ni/Mo/MgO) is reported, with which one can synthesize multi-walled carbon nanotube (MWNT) bundles with a yield of more than 45 times the amount of the pristine catalyst, using a methane-hydrogen mixture as precursor. Powder X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis show that the purity of the as-prepared MWNTs is over 97%. The diameter of the carbon nanotubes is 9-20 nm, measured by high-resolution electron microscopy on 421 individual MWNTs. The high purity of the as-prepared MWNTs allows us to omit the usual complex purification process required for carbon nanotubes synthesized by chemical vapor deposition. Because of its durable high activity, the Ni/Mo/MgO catalyst in its pristine state is ideal for mass production of high-quality MWNTs. The synergism of nickel and molybdenum is considered the main reason for the high yield of carbon nanotubes. 相似文献