全文获取类型
收费全文 | 471篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 6篇 |
综合类 | 1篇 |
化学工业 | 69篇 |
金属工艺 | 11篇 |
机械仪表 | 8篇 |
建筑科学 | 8篇 |
能源动力 | 13篇 |
轻工业 | 63篇 |
水利工程 | 5篇 |
石油天然气 | 11篇 |
无线电 | 59篇 |
一般工业技术 | 98篇 |
冶金工业 | 62篇 |
原子能技术 | 4篇 |
自动化技术 | 69篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 4篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 25篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 2篇 |
排序方式: 共有487条查询结果,搜索用时 0 毫秒
481.
The evolution in growth morphology and molecular orientation of n-type semiconducting alpha,omega-diperfluorohexyl-quaterthiophene (DFH-4T) on Au(111) is investigated by scanning tunneling microscopy and scanning tunneling spectroscopy as the film thickness is increased from one monolayer to multilayers. Monolayer-thick DFH-4T films are amorphous and morphologically featureless with a large pit density, whereas multilayer films exhibit drastically different terraced structures consisting of overlapping platelets. Large changes in DFH-4T molecular orientation are observed on transitioning from two to four monolayers. Parallel electrical characterization of top-versus-bottom contact configuration DFH-4T FETs with Au source/drain electrodes reveals greatly different mobilities (mu(TOP) = 1.1 +/- 0.2 10(-2) cm(2)V(-1)s(-1) versus mu(BOTTOM) = 2.3 +/- 0.5 10(-5) cm(2)V(-1)s(-1)) and contact resistances (R(C-TOP) = 4-12 MOmegacm vs R(C-BOTTOM) > 1 GOmegacm). This study provides important information on the organic semiconductor-source\drain electrode interfaces and explains why top-contact OFET devices typically have superior performance. By direct visualization, it demonstrates that the DFH-4T film growth transition from monolayer to multilayer on Au is accompanied by dramatic morphology and molecular orientation changes, starting from an amorphous, pitted, and disordered monolayer, to crystalline and smooth bi/tetralayers but with the molecules reoriented by 90 degrees . These chemisorption-derived inhomogenities at the contact-molecule interface and the large monolayer --> multilayer --> bulk microstructural changes are in accord with the large bottom-contact device resistance and poor OFET performance. 相似文献
482.
Coordinated preventive maintenance scheduling of GENCO and TRANSCO in restructured power systems 总被引:1,自引:0,他引:1
T. Geetha K. Shanti Swarup 《International Journal of Electrical Power & Energy Systems》2009,31(10):626-638
Preventive maintenance of generating units and lines, in a competitive electric energy environment is proposed. Inclusion of transmission constraints and forced outage rates, over a specified operational period is considered. For generator maintenance the objective of the ISO is to maintain adequate level of reliability throughout the operational period, for which Bender’s decomposition technique is used. The objective of the GENCO is to maximize profit or to minimize loss in profit, for which transmission constrained price based unit commitment (TCPBUC), based on Lagrangian relaxation method is used. Bender’s decomposition technique is used for line maintenance, with adequate level of reliability. A coordinating technique using penalty factors is incorporated to obtain convergence of the conflicting objectives. The transmission constraints are modeled using dc sensitivity factors. Detailed case studies of six-bus systems and IEEE RTS system are presented and discussed. 相似文献
483.
K. Hareesh C. Ranganathaiah P. Ramya R. Bhargavi Geetha G. Nair Sangappa Ganesh Sanjeev 《应用聚合物科学杂志》2013,127(3):2010-2018
The modifications in microstructural, optical, and photoluminescence properties of the Lexan polycarbonate (bisphenol‐A‐polycarbonate) films exposed to different electron doses have been studied using UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), positron annihilation lifetime spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The obtained UV–vis spectroscopy results showed decrease in optical energy gap, optical activation energy, and increase in number of carbon atoms per cluster with increase in electron dose. The chemical changes in electron irradiated polymers due to chain scission and reconstruction have been observed from FTIR spectroscopy. The correlation of positron lifetime study with optical measurement is obtained, and electron irradiation‐induced microstructural modifications within the polymer is understood. SEM result shows the degradation of Lexan polymer after electron irradiation. The mechanical properties and average molecular weight of Lexan decrease after irradiation, whereas average number of chain scissions per original polymer molecule increases. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
484.
A fibro‐porous wound dressing with antibacterial activity was fabricated from polycaprolactone (PCL) solution containing crude extract of biophytum sensitivum (BS) a potential antibacterial herbal drug. Scanning electron microscopy revealed the smooth fibrous morphology of the PCL membrane, whereas the drug‐loaded PCL formed fibers with more interconnective junctions with an average fiber diameter between 1 and 3 μm. Physical characterization of the membrane revealed that it has excellent mechanical stability, water vapor transmission rate and that it promotes water uptake. The release characteristics by total immersion method in phosphate buffer and acetate buffer displayed an increase in drug release with time. Finally, the antibacterial activity of the membrane was tested against standard strains of Staphylococcus aureus and Escherichia coli. PCL membranes loaded with the drug extracts were able to inhibit the growth of bacterial strains which indicated that this fibro‐porous membrane could act as a potential wound‐dressing material to treat various wounds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
485.
Thandavamoorthy Subbiah G. S. Bhat R. W. Tock S. Parameswaran S. S. Ramkumar 《应用聚合物科学杂志》2005,96(2):557-569
Nanotechnology is the study and development of materials at nano levels. It is one of the rapidly growing scientific disciplines due to its enormous potential in creating novel materials that have advanced applications. This technology has tremendously impacted many different science and engineering disciplines, such as electronics, materials science, and polymer engineering. Nanofibers, due to their high surface area and porosity, find applications as filter medium, adsorption layers in protective clothing, etc. Electrospinning has been found to be a viable technique to produce nanofibers. An in‐depth review of research activities on the development of nanofibers, fundamental understanding of the electrospinning process, and properties of nanostructured fibrous materials and their applications is provided in this article. A detailed account on the type of fibers that have been electrospun and their characteristics is also elaborated. It is hoped that the overview article will serve as a good reference tool for nanoscience researchers in fibers, textiles, and polymer fields. Furthermore, this article will help with the planning of future research activities and better understanding of nanofiber characteristics and their applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 557–569, 2005 相似文献
486.
T. R. Govindachari N. S. Narasimhan G. Suresh P. D. Partho Geetha Gopalakrishnan 《Journal of chemical ecology》1996,22(8):1453-1461
The antifeedant and insect growth-regulating activities of salannin, nimbin, and 6-deacetylnimbin, in comparison with azadirachtin-A, have been studied againstSpodoptera litura, Pericallia ricini, andOxya fuscovittata. Salannin deterred feeding, delayed molt by increasing larval duration, caused larval and pupal mortalities, and decreased pupal weights in the two lepidopterans. Salannin also caused molt delays and nymphal mortalities inOxya fuscovittata. The role of salannin and other compounds in conferring bioactivity, along with azadirachtin-A, to neem oil/neem seed extracts is emphasized. 相似文献
487.