全文获取类型
收费全文 | 2123篇 |
免费 | 76篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 41篇 |
化学工业 | 510篇 |
金属工艺 | 35篇 |
机械仪表 | 60篇 |
建筑科学 | 54篇 |
矿业工程 | 2篇 |
能源动力 | 172篇 |
轻工业 | 108篇 |
水利工程 | 14篇 |
石油天然气 | 9篇 |
无线电 | 238篇 |
一般工业技术 | 540篇 |
冶金工业 | 174篇 |
原子能技术 | 13篇 |
自动化技术 | 241篇 |
出版年
2024年 | 6篇 |
2023年 | 29篇 |
2022年 | 85篇 |
2021年 | 80篇 |
2020年 | 79篇 |
2019年 | 57篇 |
2018年 | 98篇 |
2017年 | 72篇 |
2016年 | 55篇 |
2015年 | 43篇 |
2014年 | 94篇 |
2013年 | 180篇 |
2012年 | 91篇 |
2011年 | 122篇 |
2010年 | 85篇 |
2009年 | 95篇 |
2008年 | 96篇 |
2007年 | 85篇 |
2006年 | 58篇 |
2005年 | 61篇 |
2004年 | 46篇 |
2003年 | 27篇 |
2002年 | 40篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 47篇 |
1997年 | 44篇 |
1996年 | 29篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 22篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有2211条查询结果,搜索用时 15 毫秒
41.
A novel ether connected epoxy star like polymer was synthesized by selective reaction of water soluble polyhydroxy fullerene (fullerenol) with a commercial grade cycloaliphatic epoxy resin (CY-230, Ciba Geigy) in heterogeneous medium at ambient alkaline condition using tetrabutylammonium hydroxide as phase transfer catalyst. The reaction went well in such conditions and the hydroxy groups of fullerenol underwent selective nucleophilic addition reaction with polar carbonyl groups of the epoxy resin with the formation of a hemiketal. The progress of the reaction was monitored by FTIR analysis of the product formed. The disappearance of characteristic FTIR bands of fullerenol (at 1593.2, 1381.2, and 1068 cm−1) and the typical carbonyl peak (at 1725 cm−1) of parent epoxy resin and also changes of broad hydroxy peak (at 3431 cm−1) of fullerenol into a sharp peak (at 3396.6 cm−1, indicating reduced hydrophilicity) in the reaction product clearly demonstrated the chemical attachment of the epoxy units to the fullerene core. Multiple epoxy units (about 8-10) were attached to fullerene core. Non-reactivity of fullerenol towards DGEBA epoxy resin (LY 556 Ciba Geigy) in similar conditions further supports our result. The thermal properties of the product were influenced by the presence of fullerenol and exhibits higher thermal stability compared to parent epoxy. A probable reaction mechanism for the reaction has also been discussed. 相似文献
42.
Crystallization kinetics of the Se80–x
Sb
x
Te20 (0x9) alloys have been studied using differential scanning calorimetry. The activation energies for the glass transition and that for crystallization have been determined from the heating rate dependence of the glass transition temperature and the peak crystallization temperature. The results have been analysed using the modified Kissinger's and Matusita's equations for the non-isothermal crystallization of materials. The variation of glass transition temperature with composition suggests that a small amount of Sb ( 4 at %) leads to an increase in the chain length of Se-Te, whereas further increase in Sb atomic per cent increases the number of Se-Te chains in the alloys. 相似文献
43.
Soubhik De Abhinav Omprakash Fulmali Krishna Chaitanya Nuli Rajesh Kumar Prusty B. Gangadhara Prusty Bankim Chandra Ray 《应用聚合物科学杂志》2021,138(15):50208
In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites. 相似文献
44.
Soubhik De P.N. Shivangi Saswat Choudhury Abhinav Omprakash Fulmali Bankim Chandra Ray Rajesh Kumar Prusty 《应用聚合物科学杂志》2021,138(42):51231
Carbon fiber reinforced epoxy (CE) composite is ideal for a cryogenic fuel storage tank in space applications due to its unmatched specific strength and modulus. In this article, inter-laminar shear strength (ILSS) of carbon fiber/epoxy (CE) composite is shown to be considerably improved by engineering the interface with carboxyl functionalized multi-walled carbon nanotube (FCNT) using electrophoretic deposition technique. FCNT deposited fibers from different bath concentrations (0.3, 0.5, and 1.0 g/L) were used to fabricate the laminates, which were then tested at room (30°C) and in-situ liquid nitrogen (LN) (−196°C) temperature as well as conditioning for different time durations (0.25, 0.5, 1, 6, and 12 h) followed by immediate RT testing to study the applicability of these engineered materials at the cryogenic environment. A maximum increment in ILSS was noticed at bath concentration of 0.5 g/L, which was ~21% and ~ 17% higher than neat composite at 30°C and − 196°C, respectively. Short-term LN conditioning was found to be detrimental due to developed cryogenic shock, which was further found to be compensated by cryogenic interfacial clamping upon long-term exposure. 相似文献
45.
Pavan Kumar Gangineni Satyaroop Patnaik Rajesh Kumar Prusty Bankim Chandra Ray 《应用聚合物科学杂志》2021,138(46):51365
The study aims at investigating the mechanical behavior of carbon fiber reinforced polymer (CFRP) composites modified with graphene carboxyl at elevated temperature (ET-110°C) and understanding the effect of electrophoretic deposition bath concentration (0.5 g/L, 1.0 g/L, and 1.5 g/L) on their mechanical behavior at ET. The 1.5 g/L composite has revealed a maximum improvement in energy absorbed before failure of 33.25% at RT and 22.54% at ET for flexural testing and ∼35% at RT for short beam shear testing, over neat CFRP composite. The modified composites have shown an improved flexural strain to failure at both RT and ET, with 1.5 g/L composite exhibiting maximum enhancement of 12.41% at RT and 26.52% at ET over neat composite. However, at ET, modified composites exhibited lower flexural strength and interlaminar shear strength values in comparison to that of neat. Viscoelastic behavior of all composites was studied to understand bath concentration's effect on thermal behavior via dynamic mechanical thermal analysis. Differential scanning calorimetry was employed for governing the glass transition temperature of composites. Fractography of tested samples (both ET and RT) was performed utilizing a scanning electron microscope to determine the prominent failure mode. 相似文献
46.
Galvannealed coating of high strength interstitial free (IF-HS) steel was characterised by Glow Discharge Optical Emission Spectroscopy (GDOES) and colour-etching techniques. Overalloyed galvannealed coatings with considerably high amount of Γ and Γ1 phases were detected in the first set of experiments. Necessary process modifications in galvannealing furnace were made to maximise the ä phase in the galvannealed coating, which was confirmed through GDOES and colour-etching techniques. As a result, an improvement in galvannealed product quality with a better powdering resistance property during forming has been achieved. 相似文献
47.
48.
This paper proposed the design of a broadband linear-to-circular reflecting polarizer for X-band applications. The polarizer is designed with three-arm dipole-shaped unit cells with a full ground plane to get wideband performance. The incident linear polarized wave is converted to a right-handed circularly polarized wave upon reflection from the polarizer. The footprint of the unit cell is 9 × 9 mm, which is printed on a FR-4 substrate. Fabricated prototype is measured for its performances like polarization conversion ratio (PCR), fractional bandwidth, and aperture efficiency. The PCR is about 97%, and the fractional bandwidth is 64% with the aperture efficiency of more than 80%. Polarizer performance is analyzed in transverse electric and transverse magnetic modes, and they are stable up to 40° of various incident angles. The polarizer exhibits the 3-dB axial ratio bandwidth from 8 to 12 GHz, which is suitable for satellite applications. 相似文献
49.
Pillai S. Vijayan Santhanakrishnan T. Kumar N. Suresh Rajesh R. 《Multidimensional Systems and Signal Processing》2022,33(3):879-898
Multidimensional Systems and Signal Processing - High-performance sonar systems mostly combine a large sensor array and an efficient beamformer for enhancing the overall detection capabilities and... 相似文献
50.
Adaptive relay co-ordination using a busbar splitting approach for a system integrity protection scheme
下载免费PDF全文
![点击此处可从《电力系统保护与控制》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Power system faults can often result in excessively high currents. If sustained for a long time, such high currents can damage system equipment. Thus, it is desirable to operate the relays in the minimum possible time. In this paper, a busbar splitting approach is used for adaptive relay setting and co-ordination purposes for a system integrity protection scheme (SIPS). Whenever a fault occurs, the busbar splitting scheme splits a bus to convert a loop into a radial structure. The splitting schemes are chosen such that the net fault current is also reduced. Busbar splitting eliminates the dependency upon minimum breakpoints set (MBPS) and reduces the relay operating time, thus making it adaptive. The proposed methodology is incorporated into the IEEE 14-bus and IEEE 30-bus systems with single and multiple fault conditions. The modeling and simulation carried out in ETAP, and the results of the proposed busbar splitting-based relay co-ordination are compared with the MBPS splitting-based relay co-ordination. 相似文献