全文获取类型
收费全文 | 1219篇 |
免费 | 29篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 91篇 |
综合类 | 1篇 |
化学工业 | 391篇 |
金属工艺 | 32篇 |
机械仪表 | 31篇 |
建筑科学 | 21篇 |
能源动力 | 67篇 |
轻工业 | 90篇 |
水利工程 | 1篇 |
无线电 | 84篇 |
一般工业技术 | 221篇 |
冶金工业 | 121篇 |
原子能技术 | 41篇 |
自动化技术 | 59篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 22篇 |
2013年 | 49篇 |
2012年 | 49篇 |
2011年 | 81篇 |
2010年 | 52篇 |
2009年 | 42篇 |
2008年 | 44篇 |
2007年 | 49篇 |
2006年 | 43篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 24篇 |
2000年 | 30篇 |
1999年 | 27篇 |
1998年 | 73篇 |
1997年 | 41篇 |
1996年 | 43篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 20篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1974年 | 7篇 |
排序方式: 共有1251条查询结果,搜索用时 453 毫秒
51.
对一种新合成的两性界面活性剂N,N,N-三甲胺-N′-油酸酰亚胺在二维通道内的减阻特性进行了实验研究.为了能进行低温测试,以20%的甘醇不冻液为溶剂.溶液质量浓度范围为(5×10-5)~(1×10-3),测试温度为-5℃和25℃.用粒子成像测速仪对减阻流动的湍流特性进行了测量.实验表明,这种新型界面活性剂溶液呈现明显减阻特性,且减阻特性与浓度和温度均有很大的关系,最大减阻值可高达83%.该界面活性剂中加入NaNO2,在低温和低浓度条件下能有效改善减阻效果,而在常温和高浓度条件下反而降低减阻效果.添加界面活性剂抑制了湍流速度脉动和湍流涡脉动,使雷诺剪切应力完全消失. 相似文献
52.
Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers 总被引:1,自引:0,他引:1
Epoxy/vapor grown carbon nanofiber composites (VGCF) with different proportions of VGCF were fabricated by the in situ process.The VGCFs were well dispersed in both of the low and high viscosity epoxy matrices, although occasional small aggregates were observed in a high viscosity epoxy of 20 wt.%. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus and the glass transition temperature (Tg) of the polymer were increased by the incorporation of VGCFs.The electrical and mechanical properties of the epoxy-VGCFs nanocomposite sheets with different weight percentages of VGCFs were discussed. The results were that both had maximum tensile strength and Young’s modulus at 5 wt.% for both materials and reduced the fracture strain with increasing filler content. The electrical resistivity was decreased with the addition of filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites. 相似文献
53.
Hitoshi Suto Yasuo Hattori Hiromaru Hirakuchi Naoto Kihara Yasumasa Nakashiki 《Structure and Infrastructure Engineering》2017,13(10):1359-1371
Steel corrosion under atmospheric conditions is a critical issue in the maintenance of structures such as electric transmission towers and bridges during their long-term operation, which are generally located at many places over a wide area. Since a major factor causing corrosion is airborne salt particles coming from the sea, wide-area distributions of the long-term cumulative amount of sea salt deposited on surfaces are needed. Moreover, since the amount of airborne sea salt varies locally with the topography, it is also important to consider the effects of topography. In this paper, a method combining a computational fluid dynamics model and a statistical procedure is proposed to efficiently estimate wide-area distributions of the cumulative amount of airborne sea salt by considering the local topography. The predicted amount of airborne sea salt decreases with increasing distance from the coast and varies with the topography and the offshore wind. A comparison between predicted and observed amounts revealed that: (1) this method appropriately estimates topographical effects on sea-salt transport and enables the estimation of deposited sea salt on structure surfaces, and (2) consideration of the trapping efficiency of sea-salt particles on structure surfaces improves the prediction accuracy. 相似文献
54.
Manabu Gotoh 《Metals and Materials International》1998,4(4):628-639
Various types of behavior due to plastic instability under uniaxial tension and compression are numerically investigated regarding
sheet materials, plane strain blocks, and cylindrical bars and hollow cylinders. The code GOLDA for analysis of large elastic-plastic
deformation previously developed by the author is used, which is one of quasi-static explicit FEM programs. Both of diffuse
type and localized type of instability are concerned with. The role of vertex-hardening in plastic instability is payed attention,
by using the J2G (J2-Gotoh’s corner theory) as the plasticity constitutive equation, which was proposed previously by the
author and is a kind of vertex-hardening theory. Following results are mainly derived. 1) In plane strain tension, shear-type
strain localization is realized by the use of J2G, but not by the conventional J2F (J2-flow theory). In axisymmetric tension
of a cylindrical solid bar, however, such strain localization would never appear even by J2G, as expected by the experiment.
2) In axisymmetric tension of a hollow cylinder under the condition of no contractlion of its bore (therefore, in almost plane
strain state with no circumferential strain), it is found that shear-type strain localization could occur. This is realized
again by the use of J2G, whereas J2F never allows such strain localization. 3) In compression under the embedded edges condition,
it is found that a sheet with initial aspect ratio of 2:1 (in height:breadth) yields double barreling, whereas a plane strain
block yields double barreling at the initial aspect ratio of 3:1, not at 2:1 though expected from the conventional slip-line
theory. As for a cylindrical solid bar, double barreling appears for the initial aspect ratio of 2:1 but only for higher n-vaiue
(the strain hardening exponent), say n=0.5. 4) As for barreling mode, when thick-walled axisymmetric tubes with the initial
ratio of thickness to inner diameter 1/5 to 1/3 are compressed axially, corresponding to the initial aspect ratios of 3:1,
2:1 and 1:1, triple barreling, double barreling and single barreling appear, respectively. 5) It is found that thin-walled
tubes buckle in a progressive periodic mode with almost stationary compressive load under axial compression. Thus it can be
used as a simplified model for buckling of more complex structures such as the honeycomb. 相似文献
55.
The dependence of the oxygen potentials on oxygen non-stoichiometry and temperature of Am0.5Pu0.5O2−x has been obtained by the electromotive force (EMF) method with the cell: (Pt) air |Zr(Ca)O2−x| Am0.5Pu0.5O2−x (Pt). The x value of Am0.5Pu0.5O2−x was changed at 1333 K over 0.02 < x ? 0.25 by the coulomb titration method. The temperature dependence of the oxygen potential was also measured over the range of 1173-1333 K. It was found that the oxygen potential decreased from −80 to −360 kJ mol−1 with increasing x from 0.021 to 0.22 at 1333 K and that it remained almost constant at −360 kJmol−1 around x = 0.23. It was concluded that Am0.5Pu0.5O2−x should be composed of the single fluorite-type phase over 0.02 < x ? 0.22 and the mixed phases of fluorite-type and (Am, Pu)9O16 at around x = 0.23. 相似文献
56.
Takeyuki Gotoh Fuyuki Abe Takenori Ishizu Masaki Yoshio 《Journal of power sources》1996,60(2):193-196
A study of the pyrolysis of an aqueous solution of manganese nitrate in the presence of silver compounds has been carried out. Thermal analysis showed that the MnO2 formation temperature and the transformation temperature from MnO2 to Mn2O3 shifted towards a lower temperature in the presence of silver acetate. A large particle-size and high crystallinity MnO2 was formed; this may be a useful method of making an excellent tantalum capacitor with high capacitance. 相似文献
57.
58.
Konosuke Nishida Yasuo Yanagibashi Masahiro Osako 《The International journal of environmental studies》2013,70(3):237-249
The adoption of the sensory odor test will prevail widely in many local self governments in Japan in order to evaluate and regulate the complex odor in fields. This is also done by the tri‐angle choice bag test. However, this procedure has several problems in the reliability and reproducibility of the results obtained. It is desired to solve these problems by the mechanization of the method. From this point of view, an experimental study on the flow rate of test odor has been carried out and the results obtained are described in this paper. It is confirmed that the optimum flow rate of test odor is about 41/min at the inlet of the mask in the dynamic sniffing method. 相似文献
59.
Pd(dibenzylideneacetone)2, when activated in situ with 1 equiv of [CPh3][B(C6F5)4] in the presence of 1 equiv of P(C6H11)3, efficiently catalyzed the addition polymerization and copolymerization of norbornene and its derivatives. Homopolymerization of 5-vinyl-2-norbornene took place regio-selectively with the endo-cyclic double bond to give high-molecular weight polymers, while the exocyclic double bond remained intact so that the resulting polymer had pendent vinyl groups along the polymer chain. In the polymerization of a mixture of the endo-/exo- isomers of 2-methoxycarbonyl-5-norbornene, the endo-isomer was consumed prior to consumption of the exo-isomer, contrary to the well-known tendency in Pd(II)-based catalyst systems. Another notable feature of the present catalytic system was the strong dependency of the molecular weight on the reaction temperature, which was studied in detail for the copolymerization of 2-methoxycarbonyl-5-norbornene with norbornene: we could control the molecular weight without the use of a chain transfer agent. The extracted oligomeric fraction of poly(norbornene) showed the presence of a terminal CC double bond as well as a C6F5 unit that was bound to the first norbornane unit in the polymer chain. 相似文献
60.
Yasuo Takagi Mitsuru Onoda Tamotsu Toriyama Katsunori Kawasaki Toshiyuki Hattori 《亚洲传热研究》2013,42(5):444-458
This study investigated the characteristics of cell performance degradation, decline of component performance, and changes in the properties of membrane electrode assembly materials caused by repeated cold starts under a subzero condition of ?30 °C. It was made clear that functional decay appeared mainly at the cathode due to increased proton conductive impedance and reduction of reactivity of the electrode catalyst. Among the cathode components, an increase in proton conductive impedance in the cathode electrolyte was dominant. Furthermore, the application of ion chromatography and a newly developed proton‐induced gamma‐ray emission method to measure fluorine in the off‐gas drain revealed that decomposition of the electrolyte was dominant in the cathode catalyst layer. A decrease in fluorine in the cathode electrolyte measured by fluorine‐19 nuclear magnetic resonance confirmed this decomposition. A hypothesis is also presented concerning the cause of the performance degradation. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20394 相似文献