全文获取类型
收费全文 | 8873篇 |
免费 | 594篇 |
国内免费 | 243篇 |
专业分类
电工技术 | 124篇 |
综合类 | 349篇 |
化学工业 | 3209篇 |
金属工艺 | 223篇 |
机械仪表 | 108篇 |
建筑科学 | 122篇 |
矿业工程 | 116篇 |
能源动力 | 301篇 |
轻工业 | 2262篇 |
水利工程 | 10篇 |
石油天然气 | 810篇 |
武器工业 | 24篇 |
无线电 | 318篇 |
一般工业技术 | 1459篇 |
冶金工业 | 102篇 |
原子能技术 | 76篇 |
自动化技术 | 97篇 |
出版年
2024年 | 54篇 |
2023年 | 160篇 |
2022年 | 206篇 |
2021年 | 232篇 |
2020年 | 267篇 |
2019年 | 291篇 |
2018年 | 299篇 |
2017年 | 306篇 |
2016年 | 357篇 |
2015年 | 286篇 |
2014年 | 514篇 |
2013年 | 591篇 |
2012年 | 586篇 |
2011年 | 610篇 |
2010年 | 408篇 |
2009年 | 492篇 |
2008年 | 472篇 |
2007年 | 470篇 |
2006年 | 469篇 |
2005年 | 344篇 |
2004年 | 301篇 |
2003年 | 326篇 |
2002年 | 310篇 |
2001年 | 267篇 |
2000年 | 203篇 |
1999年 | 178篇 |
1998年 | 132篇 |
1997年 | 117篇 |
1996年 | 69篇 |
1995年 | 63篇 |
1994年 | 49篇 |
1993年 | 45篇 |
1992年 | 39篇 |
1991年 | 39篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 1篇 |
1980年 | 10篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1959年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有9710条查询结果,搜索用时 0 毫秒
81.
Preparation, characterisation and applications of thin films for gas sensors prepared by cheap chemical method 总被引:1,自引:0,他引:1
The physical properties of pure and doped (Ni, Os, Pd and Pt) SnO2 thin films, prepared by using a chloride-based inorganic sol–gel route, have been reported. These properties were investigated by using differential scanning calorimetry and thermogravimetric (DSC/TG), FTIR, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. Microsensors for gas detection were also fabricated and tested in various atmospheres (nitrogen oxide, carbon monoxide, ethanol, methanol and methane). The dopants affected the coating properties depending on the formation of nanoparticles. Furthermore the gas-sensing properties towards reducing and oxidising gases were found to be dependent on the nature of doping element. An array consisting of the manufactured sensors has been arranged and examples of applications for “electronic nose” are given. 相似文献
82.
应用聚丙烯酰胺凝胶电泳法研究了北京鸭的血清前白蛋多态性,在2个位点观察到多态,Pam位点为单态,在Pas位点发现有5种表现型,它们的频率是:Pas2-2O 26.67%,Pas1-2为12%,Pas2-1为45.33%,Pas1-1为2.67%,Pas2-0为13.33%,在Paf位点发现有4种表现型,它们的频率是:PafF为29.33%,PafS为41.33%,PafFS为10.67%,Paf0为18.67%,并计算了它们的基因频率,群体平均杂合度和遗传距离,遗传分析表明,樱桃谷鸭和奥白星鸭遗传结构相似,而与B系北京鸭遗传结构有明显差异。 相似文献
83.
改良BBs法用光电法测发泡高度-时间曲线,用机械手完成投掷钢球动作,过程用微机控制。本文对此法测得的三乙胺、四甲基乙二胺、二甲基乙醇胺、双(二甲基氨基乙基)醚、三乙烯二胺等催化剂在聚氨酯软质泡沫塑料形成过程中的胶化-发泡曲线进行了讨论,并评价了它们的催化特性。改良BBs法与手工BBs法相比,具有检测精度高,样本采集点多的优点。 相似文献
84.
《国际计算机数学杂志》2012,89(9):2010-2020
The problem of covering a convex 3D polytope by the minimal number of congruent spheres is reduced to a sequence of problems of minimising sphere radius when fixing the number of the spheres. We form a mathematical model of the problem using the Voronoi polytopes. Characteristics of the model are investigated. Extrema are attained at the vertices of the Voronoi polytopes constructed for sphere centres. To search for local minima, a modification of the Zoutendijk feasible directions method in a combination with random search is developed. Some numerical results for a cube and a non-regular octahedron are obtained. 相似文献
85.
K. Rózga-Wijas U. Mizerska W. Fortuniak J. Chojnowski R. Hałasa W. Werel 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(4):605-613
Three types of silica particles modified with vinyl groups were obtained: (i) xerogel formed by hydrolytic polycondensation
of the mixture of tetramethoxysilane (TMOS) and 1,1,1,7−tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyltetrasiloxane, (ii) mesoporous
silica obtained from the same precursors in the presence of the cetyltrimethylammonium bromide (CTAB), and (iii) commercial
Fluka silica gel 60A with a vinyltriethoxysilane-treated surface. Vinyl groups on these silica materials were transformed
into silyl chloride by hydrosilylation with HMe2SiCl. These groups were used to graft living polysiloxane that was synthesized by anionic ring-opening polymerization of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane
and initiated by BuLi. Chloropropyl groups on the grafted polymer were used to quaternize N,N-dimethyl-n-octylamine. Silica particles with grafted polysiloxane having quaternary ammonium salt (QAS) groups pendant to polymer chains
were obtained. Silica material with QAS groups directly attached to the surface were generated by the action of N,N-dimethyl-n-octylamine on particles obtained by the sol–gel process involving tetraethoxysilane (TEOS) with 3-chloropropyltriethoxysilane.
The bacteriocidal properties of all these materials were tested in water suspension against five representative strains for
Gram-positive and Gram-negative bacteria. Some of the silica–polysiloxane hybrid materials have good antibacterial properties
against Gram-positive strains, but not as good as the non-tethered QAS-substituted polysiloxane in water solution. The QAS
groups that are directly bonded to the silica material surface are inactive. 相似文献
86.
SiO2 surface film is insufficient to protect SiC from the oxidation at widely varying partial pressures of oxygen, in particular in the presence of water vapor (e.g. in gas turbines) and also in other environments, e.g. during brazing for hard “tipping” of turbine blades. This work demonstrates that sol–gel alumina, coated on 0.5 mm coarse SiC grit, may form an acceptable, up to 10 μm thick “environmental barrier coating” EBC for some of these applications. The sol–gel has advantages over other methods (such as CVD) is the simplicity and low cost. We have used NH4OH pre-treatment to hydroxylate surface of SiC prior to applying alumina coating. Such modified SiC/SiO2 surface helped to deposit the positively charged alumina sol, and thus allowed to build thick coatings on the SiC grit. There is some indication that these coatings partially convert to mullite through reaction at the interface with the native silica on SiC. Oxidation resistance tests at 1200 °C were performed to show effectiveness of such coated SiC grit. 相似文献
87.
Kee Bae Park Sang-Do Han Il Jin Kim Jin Suk Wang Young Sung Park 《Materials Science and Engineering: B》2006,130(1-3):158-162
Thick film H2 sensors were fabricated using SnO2 loaded with Ag2O and PdOx. The composition that gave highest sensitivity for H2 was in the wt.% ratio of SnO2:Ag2O:PdOx as 93:5:2. The nano-crystalline powders of SnO2–Ag2O–PdOx composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H2, CH4, C3H8, C2H5OH and SO2. The composite material was found sensitive against H2 at the working temperature 125 °C, with minor interference of other gases. H2 gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO2–Ag2O–PdOx nanocrystalline system exhibited high performance, high selectivity and very short response time to H2 at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H2. 相似文献
88.
Five cordierite-based powders were investigated regarding their thermal and crystallization behaviors. The powders were obtained from amorphous gels having nominal compositions of 2Mg : xAl : (4 − x)B : 5Si where x = 4 down to 0. Thermal gravimetry analysis of the dry gels showed some absorbed water and decomposition of organic ligands in addition to network condensation. Gradual substitution of B for Al in the dried gel powders showed a new band in their infrared spectra corresponding to triangular BO3, whereas the bands corresponding to Al vanished. This also showed a noticeable effect on the crystallization trends, type and stability of cordierite. Cordierite crystallized in samples of B/Al ratio up to 1 while protoenstatite predominated in samples of higher B/Al ratios. In addition, some silica minerals, with little amorphous phase, were formed. Incorporation of boron and increase in temperature enhanced the transformation of γ cordierite to its form. 相似文献
89.
采用溶胶-凝胶方法制备了Ti(1-x)CoxO2样品。研究了不同的热处理温度和掺杂浓度对样品晶型和颗粒尺寸的影响。样品400℃热处理呈锐钛矿相,600℃转变为全红石相并且晶粒尺寸明显增大。掺杂对晶型没有影响,但是随掺杂量的增大晶格常数减小。 相似文献
90.
Mingwei Zhu Guodong Qian Zhiyu Wang Minquan Wang 《Materials Chemistry and Physics》2006,100(2-3):333-336
A two-step silica deposition process, including prefunctionalization with poly(vinylpyrrolidone) and the following silica deposition, has been used to fabricate silica layer on the surface of nanoscaled silver shell. The influencing parameters of silica coating process were optimized to prevent the precoated silver nanoparticles from desquamating from silica spheres, finally to obtain mono-dispersed silica spheres with silver and silica multilayer films. The resulted silica layer was dense and uniform, its thickness was controllable in the range of 20–50 nm. Such coated silica layer can provide improved thermal stability of the SiO2-Ag core-shell structural spheres. 相似文献