全文获取类型
收费全文 | 1026篇 |
免费 | 62篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 35篇 |
综合类 | 1篇 |
化学工业 | 357篇 |
金属工艺 | 27篇 |
机械仪表 | 37篇 |
建筑科学 | 13篇 |
矿业工程 | 1篇 |
能源动力 | 53篇 |
轻工业 | 128篇 |
水利工程 | 2篇 |
石油天然气 | 1篇 |
无线电 | 50篇 |
一般工业技术 | 175篇 |
冶金工业 | 49篇 |
原子能技术 | 52篇 |
自动化技术 | 109篇 |
出版年
2023年 | 27篇 |
2022年 | 52篇 |
2021年 | 70篇 |
2020年 | 37篇 |
2019年 | 39篇 |
2018年 | 58篇 |
2017年 | 40篇 |
2016年 | 53篇 |
2015年 | 45篇 |
2014年 | 38篇 |
2013年 | 81篇 |
2012年 | 70篇 |
2011年 | 83篇 |
2010年 | 51篇 |
2009年 | 46篇 |
2008年 | 57篇 |
2007年 | 47篇 |
2006年 | 24篇 |
2005年 | 28篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 22篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1090条查询结果,搜索用时 0 毫秒
71.
We study population dynamics of a trapped spin-1 Bose gas above the Bose-Einstein transition temperature. Starting from the semiclassical kinetic equation for a spin-1 gas, we derive coupled rate equations for the populations of internal states. Solving the rate equations, we study the dynamical evolution of spin populations. We also estimate the characteristic timescale in which the system reaches equilibrium. Finally, we briefly discuss the extension of the theory to Bose-condensed phase below the Bose-Einstein transition temperature, and discuss the static equilibrium condition for the spin-1 system. 相似文献
72.
A mechanistic aspect of the susceptibility to the delayed fracture is studied with an emphasis on the critical behaviour of the subsurface growth of Quasi-Cleavage (QC) and Inter-Granular (IG) cracks. The materials employed are 0.35%C plain carbon steel and boron added bolt steel which were quenched and tempered to have various levels of yield strength ranging from 500 to 1400 MPa. Fractographic analysis shows us that QC + IG cracking process can be an essential mode in the delayed fracture of steels. A low susceptibility to delayed fracture can be explained by the crack growth behavior when the crucial blunting occurs at the crack tip. 相似文献
73.
Izumi Kita Tomohiro Shibata Yuki Kamiya Daishi Kato Kazuo Kunieda Keiji Yamada Kazushi Ikeda 《Artificial Life and Robotics》2009,14(3):375-378
To increase the productivity of knowledge workers, it is necessary to manage their organization so that they are motivated
to collaborate with each other for their synergy. However, it is difficult for managers to grasp the explicit interactions
of workers in the organization all the time. Owing to advanced communications technology, and the reduced size and improved
capabilities of computers, we are able to record group behaviors as logging data in the office. The aim of this study is to
extract features of group behavior from long-range office-logging data. We apply principal component analysis to the data
matrix whose element is the mean travel velocity calculated from an individual’s trajectory per day. The results demonstrate
the feasibility of our approach, since nontrivial informative group features can be extracted. 相似文献
74.
Abrupt changes in the cross-polarization discrimination (XPD) and cross-polar phase were observed in cross-polarization measurements at 4, 6, and 11 GHz on propagation paths with low elevation angles. These abrupt changes were always observed during thunder, though exact time-to-time correspondence with lightning strokes was not clear in the measurement. In most cases, these sudden changes occurred in the direction in which the distortion of polarization ellipse increases, and the rate of change in XPD was much faster than rain-induced depolarizations by an order of magnitude. Based on the simultaneous measurement of circular and linear polarizations at 11 GHz, it was also found that the differential phase shift component suddenly increased to as large as20deg to40deg upon occurrence of these XPD changes, which confirms that this phenomenon is attributed to the effect of ice particles. 相似文献
75.
Sho Kataoka Takuji Yamamoto Yuki Inagi Akira Endo Masaru Nakaiwa Takao Ohmori 《Carbon》2008,46(10):1358-1360
Mesoporous carbon thin films with ordered structures were prepared by using resorcinol-surfactant self-assembly. A mixture of resorcinol, surfactant, and ethanol coated on silicon substrates was exposed to formaldehyde vapor as a cross-linking agent to form structured resorcinol/formaldehyde resin films. The films were then carbonized at 800 °C in an inert atmosphere to remove the surfactant and to obtain structured carbon materials. With this vapor infiltration method, thin films with several structures were obtained from the same precursor solution by employing different vapor infiltration temperatures. The results were interpreted from the transformation of the self-assembly during the vapor infiltration process. 相似文献
76.
Dr. Naoki Umezawa Yuhei Horai Dr. Yuki Imamura Makoto Kawakubo Mariko Nakahira Dr. Nobuki Kato Akira Muramatsu Prof. Dr. Yuko Yoshikawa Prof. Dr. Kenichi Yoshikawa Prof. Dr. Tsunehiko Higuchi 《Chembiochem : a European journal of chemical biology》2015,16(12):1811-1819
A versatile solid‐phase approach based on peptide chemistry was used to construct four classes of structurally diverse polyamines with modified backbones: linear, partially constrained, branched, and cyclic. Their effects on DNA duplex stability and structure were examined. The polyamines showed distinct activities, thus highlighting the importance of polyamine backbone structure. Interestingly, the rank order of polyamine ability for DNA compaction was different to that for their effects on circular dichroism and melting temperature, thus indicating that these polyamines have distinct effects on secondary and higher‐order structures of DNA. 相似文献
77.
A major source of inaccuracy in CNC machines is unwanted vibrations induced by the frequency spectra of reference motion trajectory. This paper presents a novel approach where instead of filtering techniques, axis motion commands are generated with optimal frequency spectra in the first place. Tangential feedrate profile is defined as parametric spline, and its frequency spectrum is optimized with respect to structural dynamics of the machine. The optimization problem is solved efficiently using Quadratic Programming. Experimental results confirm that proposed technique can greatly improve surface finish during machining spline tool-paths without sacrificing from cycle time and contouring performance. 相似文献
78.
Dong‐Won Kang Yuki Takiguchi Porponth Sichanugrist Makoto Konagai 《Progress in Photovoltaics: Research and Applications》2016,24(7):1016-1023
In this work, we practically demonstrated spectrum‐splitting approach for advances in efficiency of photovoltaic cells. Firstly, a‐Si:H//c‐Si 2‐junction configuration was designed, which exhibited 24.4% efficiency with the spectrum splitting at 620 nm. Then, we improved the top cell property by employing InGaP cells instead of the a‐Si:H, resulting in an achievement of efficiency about 28.8%. In addition, we constructed 3‐junction spectrum‐splitting system with two optical splitters, and GaAs solar cells as middle cell. This InGaP//GaAs//c‐Si architecture was found to deliver 30.9% conversion efficiency. Our splitting system includes convex lenses for light concentration about 10 suns, which provided concentrated efficiency exceeding 33.0%. These results suggest that our demonstration of 3‐junction spectrum‐splitting approach can be a promising candidate for highly efficient photovoltaic technologies. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
79.
Antioxidant Effects of Herbal Tea Leaves from Yacon (Smallanthus sonchifolius) on Multiple Free Radical and Reducing Power Assays,Especially on Different Superoxide Anion Radical Generation Systems 下载免费PDF全文
Shintaro Sugahara Yuto Ueda Kumiko Fukuhara Yuki Kamamuta Yasushi Matsuda Tatsuro Murata Yasuhiro Kuroda Kiyotaka Kabata Masateru Ono Keiji Igoshi Shin Yasuda 《Journal of food science》2015,80(11):C2420-C2429
Yacon (Smallanthus sonchifolius), a native Andean plant, has been cultivated as a crop and locally used as a traditional folk medicine for the people suffering from diabetes and digestive/renal disorders. However, the medicinal properties of this plant and its processed foods have not been completely established. This study investigates the potent antioxidative effects of herbal tea leaves from yacon in different free radical models and a ferric reducing model. A hot‐water extract exhibited the highest yield of total polyphenol and scavenging effect on 1,1‐diphenyl‐2‐picryl hydrazyl (DPPH) radical among four extracts prepared with hot water, methanol, ethanol, and ethylacetate. In addition, a higher reducing power of the hot‐water extract was similarly demonstrated among these extracts. Varying concentrations of the hot‐water extract resulted in different scavenging activities in four synthetic free radical models: DPPH radical (EC50 28.1 μg/mL), 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) cation radical (EC50 23.7 μg/mL), galvinoxyl radical (EC50 3.06 μg/mL), and chlorpromazine cation radical (EC50 475 μg/mL). The yacon tea‐leaf extract further demonstrated superoxide anion (O2?) radical scavenging effects in the phenazine methosulfate‐NADH‐nitroblue tetrazolium (EC50 64.5 μg/mL) and xanthine oxidase assay systems (EC50 20.7 μg/mL). Subsequently, incubating human neutrophilic cells in the presence of the tea‐leaf extract could suppress the cellular O2? radical generation (IC50 65.7 μg/mL) in a phorbol 12‐myristate 13‐acetate‐activated cell model. These results support yacon tea leaves may be a good source of natural antioxidants for preventing O2? radical‐mediated disorders. 相似文献
80.
Kiyonobu Ida Masanori TomonariYasuyuki Sugiyama Yuki ChujyoTomoharu Tokunaga Tetsu YonezawaKotaro Kuroda Katsuhiro Sasaki 《Thin solid films》2012,520(7):2789-2793
Cu nanoparticle ink was prepared from Cu nanoparticles that were coated with a gelatin layer at an average diameter of 46 nm. The Cu nanoparticle ink was applied on the polyimide substrate. Conductive films were fabricated using the Cu nanoparticle ink with a two-step annealing process consisting of oxidative pre-heating at 200 °C under 10 ppm O2-N2 mixed gas flow and reductive calcination at 250 °C under 3 vol.% H2-N2 mixed gas flow showed a low resistivity of 5 μΩ cm. The hydrolysis of the remaining gelatin layer by H2O vapor, which was formed during the reduction of the Cu oxide by 3 vol.% H2-N2 mixed gas, was suggested. The results suggest the possibility of the removal of the gelatin layer without oxidative pre-heating and simultaneous sintering of Cu nanoparticles in reductive calcination. 相似文献