全文获取类型
收费全文 | 35282篇 |
免费 | 3679篇 |
国内免费 | 2137篇 |
专业分类
电工技术 | 1663篇 |
技术理论 | 3篇 |
综合类 | 3331篇 |
化学工业 | 6322篇 |
金属工艺 | 4782篇 |
机械仪表 | 1530篇 |
建筑科学 | 2383篇 |
矿业工程 | 2404篇 |
能源动力 | 676篇 |
轻工业 | 1923篇 |
水利工程 | 556篇 |
石油天然气 | 1497篇 |
武器工业 | 318篇 |
无线电 | 1817篇 |
一般工业技术 | 3301篇 |
冶金工业 | 5138篇 |
原子能技术 | 242篇 |
自动化技术 | 3212篇 |
出版年
2024年 | 138篇 |
2023年 | 428篇 |
2022年 | 1017篇 |
2021年 | 1089篇 |
2020年 | 1041篇 |
2019年 | 896篇 |
2018年 | 824篇 |
2017年 | 1040篇 |
2016年 | 1270篇 |
2015年 | 1272篇 |
2014年 | 2114篇 |
2013年 | 2206篇 |
2012年 | 2621篇 |
2011年 | 2695篇 |
2010年 | 2022篇 |
2009年 | 1932篇 |
2008年 | 1638篇 |
2007年 | 2225篇 |
2006年 | 2119篇 |
2005年 | 1798篇 |
2004年 | 1564篇 |
2003年 | 1462篇 |
2002年 | 1289篇 |
2001年 | 1116篇 |
2000年 | 933篇 |
1999年 | 737篇 |
1998年 | 621篇 |
1997年 | 566篇 |
1996年 | 454篇 |
1995年 | 419篇 |
1994年 | 342篇 |
1993年 | 227篇 |
1992年 | 236篇 |
1991年 | 156篇 |
1990年 | 155篇 |
1989年 | 115篇 |
1988年 | 80篇 |
1987年 | 50篇 |
1986年 | 33篇 |
1985年 | 23篇 |
1984年 | 35篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1966年 | 3篇 |
1961年 | 5篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
252.
A novel iron phosphate templated with ethylenediammonium cation, [H3N(CH2)2NH3]2 Fe4 O(PO4)4H2O, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, thermo-gravimetric analysis, magnetic susceptibility and Mossbauer spectroscopy. The compound crystallizes in the mono-clinic space group C2 with a= 30.3801(5),b= 10.1204(5),c= 10.0977(5) Å, = 107.712(1)°, V = 2957.5(4) Å3 and Z = 6. The structure contains 5 and 6-coordinated Fe atoms bridged by 4-oxygen and PO4 groups to form two types of mixed-valence Fe4P4 cubane-like clusters, which are connected via Fe- O- P bonds to give rise to intersecting channels that house the ethylenediammonium cations and water molecules. Room-temperature Mossbauer data confirm the presence of FeII and FeIII. 相似文献
253.
Yinzhong Guo Vijay M. Mannari Pulin Patel John L. Massingill 《Journal of Coatings Technology and Research》2006,3(4):327-331
A series of soybean oil phosphate ester polyols (SOPEP) was prepared by reaction of fully epoxidized soybean oil with phosphoric
acid and simultanoeous hydrolysis in the presence of a polar solvent. The polyols were characterized by determination of acid
value, oxirane number, hydroxyl value, molecular weight (GPC), and FTIR spectra. These polyols with varying amounts of acid
phosphate groups could be self-emulsified to form aqueous dispersions after neutralization with organic base. These aqueous
dispersion showed varying degrees of stability and their appearance ranged from opaque dispersions to translucent to clear
solutions. Waterborne coating compositions were prepared using these aqueous dispersions as principal components and their
thermally cured film properties were studied. it was found that by careful selection and formulation, SOPEPs can be successfully
used for low-VOC waterborne coating formulations. SOPEPs with 3.5% phosphate ester content showed visibly superior corrosion
resistance properties. 相似文献
254.
磷酸铁锂锂离子电池正极材料的研究 总被引:1,自引:0,他引:1
锂离子电池是绿色高能可充电池,具有工作电压高、比能量大、自放电小、循环寿命长、无记忆效应、无环境污染等突出优点。本文从磷酸铁锂的结构与性能、材料的制备方法、改性、粒径控制等几方面综述了近年来对橄榄石型磷酸铁锂(LiFePO4)锂离子电池正极材料的研究进展。材料的粒度大小及其分布、离子和电子的传导能力对产品的电化学性能影响很大。在制备时,采用惰性气氛、掺杂导电材料和控制晶粒生长制备粉体是获得性能优良的LiFePO4的有效方法。 相似文献
255.
在Li NbO3(LN)中掺摩尔分数为1%的In和掺质量分数为0.03%的Fe,用提拉法技术生长具有不同n(Li)/n(Nb)[n(Li)/n(Nb)=0.94,1.05,1.20,1.38]的In∶Fe∶LN晶体。测试不同n(Li)/n(Nb)的In∶Fe∶LN晶体的吸收光谱、抗光致散射能力和指数增益系数,并计算晶体的有效载流子浓度。结果表明晶体样品随着n(Li)/n(Nb)增加,吸收光谱的吸收边发生紫移,抗光致散射能力增加,指数增益系数和有效载流子浓度增大。采用n(Li)/n(Nb)=1.38的In∶Fe∶LN晶体作记录介质,n(Li)/n(Nb)=1.05的In∶Fe∶LN晶体作位相共轭镜进行全息关联存储实验。实验表明存储系统具有实时处理,成像质量好,信噪比高和能反复使用等优点。 相似文献
256.
The effect of Mo loading, calcination temperature, reaction temperature and space velocity on the catalytic performance of methane dehydrogenation and aromatization without using oxidants over Mo/HZSM-5 has been studied. The XRD and BET measurements show that Mo species are highly dispersed in the channels of the HZSM-5 zeolite, resulting from the interaction between the Mo species and the zeolite, which also leads to a decrease in its crystallinity. The Brønsted acidity, the channel structure and the state and location of Mo species in the zeolite seem to be crucial factors for its catalytic performance. It was found that 2% Mo/HZSM-5 calcined at 773 K showed the best aromatization activity among the tested catalysts, the methane conversion being 9% at 1013 K with the selectivity to aromatics higher than 90%. The experimental results obtained from the variation of space velocity gave evidence that ethylene is an initial product. On the basis of these results a possible mechanism for methane dehydrogenation and aromatization has been proposed in which both the heterolytic splitting of methane in a solid acid environment and a molybdenum carbene-like complex as an intermediate are of significance. 相似文献
257.
258.
Electrochemical ferrate generation for waste water treatment using cast irons with high silicon contents 总被引:5,自引:0,他引:5
This paper deals with the electrochemical preparation of ferrate in 15 M NaOH media, with a view to treatment of waste waters. Grey cast irons with high silicon contents were shown to allow current yields in the range 20–40% depending on the applied current density, up to 34 mA cm–2. Ferrate solutions with contents up to 0.08 M could be produced in a divided cell of simple design, and provided with flat or packed-bed electrodes. Deactivation of the anode surface was shown to be of moderate significance for hour-long runs. The ferrate produced was tested for treatment of industrial liquid wastes: coagulation efficiency of the suspended matter was comparable with that of an electrocoagulation process with sacrificial Al anodes. The potential of waste water treatment by addition of ferrate is discussed. 相似文献
259.
The crosslinked poly[3‐(methacryloylamino)propyl]dimethyl(3‐sulfopropyl)ammonium hydroxide], P(MAPDSA), and poly[3‐(methacryloylamino)propyl]dimethyl(3‐sulfopropyl)ammonium hydroxide‐co‐acrylic acid], P(MAPDSA‐co‐AA), were synthesized by radical polymerization. The resins were completely insoluble in water. Due to the lower metal ion retention of P(MAPDSA), the metal ions investigated under competitive and noncompetitive conditions for Cu(II), Cd(II), Hg(II), Zn(II), Pb(II), and Cr(III) ions by batch and column equilibrium procedures were carried out only for P(MAPDA‐co‐AA), particularly for Hg(II). The resin–Hg(II) ion equilibrium was achieved before 15 min. The resin showed a maximum retention capacity value for Hg(II) at pH 2 of 1.89 meq/g. The resin showed a high selectivity to Hg(II) ions. The recovery of the resin was investigated at 25°C with different concentrations of HNO3 and HClO4. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 525–530, 2005 相似文献
260.
日本在水处理混凝剂研发、生产、管理和应用方面都具有国际先进水平。介绍了日本水处理主宴混凝剂——聚氯化铝(PAC)和硫酸铝(AS)的产业现状,新混凝剂聚硅氯化铁的研发推广工作,水处理药剂标准的制定和管理,以及混凝剂的生产应用效果。文中有详尽的统计资料,可供中国水处理行业参考。 相似文献