全文获取类型
收费全文 | 2003篇 |
免费 | 160篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 32篇 |
化学工业 | 446篇 |
金属工艺 | 42篇 |
机械仪表 | 42篇 |
建筑科学 | 47篇 |
矿业工程 | 4篇 |
能源动力 | 72篇 |
轻工业 | 374篇 |
水利工程 | 11篇 |
石油天然气 | 13篇 |
无线电 | 183篇 |
一般工业技术 | 287篇 |
冶金工业 | 373篇 |
原子能技术 | 6篇 |
自动化技术 | 234篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 41篇 |
2021年 | 46篇 |
2020年 | 32篇 |
2019年 | 73篇 |
2018年 | 69篇 |
2017年 | 87篇 |
2016年 | 70篇 |
2015年 | 54篇 |
2014年 | 75篇 |
2013年 | 120篇 |
2012年 | 122篇 |
2011年 | 107篇 |
2010年 | 95篇 |
2009年 | 99篇 |
2008年 | 93篇 |
2007年 | 77篇 |
2006年 | 75篇 |
2005年 | 52篇 |
2004年 | 51篇 |
2003年 | 54篇 |
2002年 | 50篇 |
2001年 | 35篇 |
2000年 | 42篇 |
1999年 | 34篇 |
1998年 | 135篇 |
1997年 | 94篇 |
1996年 | 47篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 15篇 |
1975年 | 6篇 |
1970年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有2166条查询结果,搜索用时 15 毫秒
71.
We have recently shown that docosahexaenoic acid (DHA) is necessary for survival and differentiation of rat retinal photoreceptors
during development in vitro. In cultures lacking DHA, retinal neurons developed normally for 4 d; then photoreceptors selectively started an apoptotic
pathway leading to extensive degeneration of these cells by day 11. DHA protected photoreceptors by delaying the onset of
apoptosis; in addition, it advanced photoreceptor differentiation, promoting opsin expression and inducing apical differentiation
in these neurons. DHA was the only fatty acid having these effects. Mitochondrial damage accompanied photoreceptor apoptosis
and was markedly reduced upon DHA supplementation. This suggests that a possible mechanism of DHA-mediated photoreceptor protection
might be the preservation of mitochondrial activity; a critical amount of DHA in mitochondrial phospholipids might be required
for proper functioning of these organelles, which in turn might be essential to avoid cell death. Müller cells in culture
appeared to be involved in DHA processing: they took up DHA, incorporated in into glial phospholipids, and channeled it to
photoreceptors in coculture. Both Müller cells, when cocultured with neuronal cells, and the glial-derived neurotrophic factor
(GDNF) protected photoreceptors from cell death. These results suggest that glial cells may play a central role in regulating
photoreceptor survival during development through the provision of trophic factors. The multiple effects of DHA on photoreceptors
suggest that in addition to its structural role, DHA might be one of the trophic factors required by these cells. 相似文献
72.
María J. Aguirre Mauricio Isaacs Betty Matsuhiro Leonora Mendoza Leonardo S. Santos Simonet Torres 《Food chemistry》2011
Anthocyanins in aged Cabernet Sauvignon red wines were studied by HPLC–MS. The major anthocyanin in 6, 7, and 8 year old red wine extracts was the dimer vitisin A produced by condensation of malvidin-3-O-glucoside mediated by pyruvic acid. In aged wine, the content of malvidin-3-O-glucoside decreased with age with a concomitant increase of vitisin A. The latter is accompanied by several condensation products with molecular weight up to 1500 m/z. Differential pulse voltammetry indicated that aged wines have lower antioxidant capacity than young wine (400 mV), but higher than malvidin-3-O-glucoside (483 mV). Tafel’s plots showed that the electrochemical process occurring in aged wines is different from young wines. Six, seven and eight year old wines show similar behaviour with plots of 234, 177 and 188 mV/dec, respectively. These values are higher than the expected 120 mV/dec corresponding to a first electronic transfer but smaller compared to the 523 mV/dec corresponding to young wine. 相似文献
73.
Paula C. Rodrigues Bruno D. Fontes Bruno B. M. Torres Washington S. Sousa Gregório C. Faria Debora T. Balogh Roberto M. Faria Leni Akcelrud 《应用聚合物科学杂志》2015,132(38)
Synthesis of a polyfluorene/poly(p‐phenylene vinylene) derivative, the Poly [(9,9′‐di‐hexylfluorenediylvinylene‐alt‐1,4‐phenylenevinylene)‐co‐((9,9′‐(3‐t‐butylpropanoate) fluorene‐1,4‐phenylene)] (LaPPS 42) was performed following Wittig and Suzuki routes. Polyfluorenes and derivatives have been used in electroluminescent devices, and the synthesis described here has the advantage in pave the way to get distinct structures having different emission spectra. An extensive study of its electrochemical, thermomechanical, optical, and structural properties was carried out, as well as its application in electroluminescent devices. Polymer light‐emitting diodes (PLEDs) and polymer light‐emitting electrochemical cells (PLECs) were built using LaPPS 42 as active layer, and their electric and optical characterizations confirm they have a potential as active element in electroluminescent devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42579. 相似文献
74.
Oxidative Stability and Changes in Chemical Composition of Extra Virgin Olive Oils After Short‐Term Deep‐Frying of French Fries
下载免费PDF全文
![点击此处可从《Journal of the American Oil Chemists](/ch/ext_images/free.gif)
Emília Akil Vanessa Naciuk Castelo‐Branco André Mesquita Magalhães Costa Ana Lúcia do Amaral Vendramini Verônica Calado Alexandre Guedes Torres 《Journal of the American Oil Chemists' Society》2015,92(3):409-421
We aimed at investigating oxidative stability and changes in fatty acid and tocopherol composition of extra virgin olive oil (EVOO) in comparison with refined seed oils during short‐term deep‐frying of French fries, and changes in the composition of the French fries deep‐fried in EVOO. EVOO samples from Spain, Brazil, and Portugal, and refined seed oils of soybean and sunflower were studied. Oil samples were used for deep‐frying of French fries at 180 °C, for up to 75 min of successive frying. Tocopherol and fatty acid composition were determined in fresh and spent vegetable oils. Tocopherol, fatty acid, and volatile composition (by SPME–GC–MS) were also determined in French fries deep‐fried in EVOO. Oil oxidation was monitored by peroxide, acid, and p‐anisidine values, and by Rancimat after deep‐frying. Differential scanning calorimetry (DSC) analysis was used as a proxy of the quality of the spent oils. EVOOs presented the lowest degree of oleic and linoleic acids losses, low formation of free fatty acids and carbonyl compounds, and were highly stable after deep‐frying. In addition, oleic acid, tocopherols, and flavor compounds were transferred from EVOO into the French fries. In conclusion, EVOOs were more stable than refined seed oils during short‐term deep‐frying of French fries and also contributed to enhance the nutritional value, and possibly improve the flavor, of the fries prepared in EVOO. 相似文献
75.
76.
Rayssa Ferreira Zanatta Tatiane Josefa da Silva Maria Filomena Rocha Lima Huhtala Alessandra Bühler Borges Carlos Rocha Gomes Torres 《Journal of Adhesion Science and Technology》2016,30(23):2557-2564
Purpose: The aim of this study was to evaluate the influence of previous application of an adhesive system on bond strength of resinous liner materials to dentin. Methods: Ninety bovine incisors crowns had a 6 × 6 mm area of dentin exposed, with minimum of 2 mm thickness. They were embedded in acrylic resin, and the dentin was polished with P600 SiC sandpaper for 30 s to standardize the smear layer. The specimens were divided into 6 groups (n = 15) according to the application or not of a self-etching system (Futurabond U – Voco) and the type of resinous liner used: A+Ionoseal (adhesive and Ionoseal – Voco); Ionoseal (Ionoseal only); A+Vitrebond (adhesive and Vitrebond – 3M/ESPE); Vitrebond (Vitrebond only); A+Ionosit (adhesive and Ionosit – DMG) and Ionosit (Ionosit only). Adhesives were used following manufacturer’s instructions, and the liner materials were applied inside a 2-mm-depth matrix and light-cured for 20 s. The bond strength was measured by microtensile test, using a universal testing machine with a cross-speed of 1 mm/min. Data were analyzed using one-way ANOVA and Tukey’s test (p < 0.05). Results: The adhesive system application increased bond strength of all liners tested. Ionoseal presented the highest bond strength when the adhesive system was used and exhibited similar performance to Vitrebond without adhesive. Ionosit without adhesive showed the smallest bond strength compared with the other liners tested. Conclusion: The application of an adhesive system prior to the use of the resinous liners improved the bond strength to dentin and should be preconized. 相似文献
77.
Tiago F. A. Santos Edwar A. Torres Tahiana F. C. Hermengildo Antonio J. Ramirez 《Welding International》2016,30(5):338-347
Usually, a workpiece is deformed during friction stir welding due to high applied loads. Consequently, fully and consolidated friction stir-welded joints as well as tool life time can be affected promoting unscheduled manufacturing stops, which favour decreasing the welding productivity. Furthermore, the workforce is dislocated to not predicted maintenance steps. This work proposes the development of a special ceramic backing to joining and processing material using FSW technologies. Four ceramic deposits were tested over a steel plate, which allowed selecting those with less porosity and, thus, better strength. This backing allowed us to obtain full penetration welds for duplex stainless steels, to high forces during engagement for high-strength low-alloy steels and to obtain consolidated aluminium–steel dissimilar joints. For the last one, there was not adherence of the soft material in the workpiece. In addition, the ceramic backing allowed us to confine the heat and plasticized metal, as well as develop established welding parameters. 相似文献
78.
Carlos A. H. Laurindo Carlos M. Lepienski Fred L. Amorim Ricardo D. Torres 《摩擦学汇刊》2018,61(4):733-741
Plasma electrolytic oxidation (PEO) is a technique that produces a hard oxide layer on the titanium surface where its properties can be tailored by changing the process parameters or by a posterior heat treatment (HT). In this work, a TiO2 layer with different crystallinity was produced by PEO with different applied voltages (250 to 400 V) and post-HT at 600°C. Our aim was to evaluate the influence of the PEO voltage and HT on the mechanical and tribological properties of anodized Ti. There is an increase in pore size, oxide thickness, and Ca/P ratio for the oxide layer with the applied voltage during the PEO process. X-ray diffraction (XRD) results indicated an increase in the crystalline rutile phase in the oxide layer with voltage and HT. Nanoindentation shows an increase in the oxide hardness and elastic modulus with increased voltage and HT, leading to an improvement in the wear resistance. 相似文献
79.
80.
Advanced Monte Carlo simulations of the adsorption of chiral alcohols in a homochiral metal‐organic framework
下载免费PDF全文
![点击此处可从《American Institute of Chemical Engineers》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zhiwei Qiao Ariana Torres‐Knoop David Dubbeldam David Fairen‐Jimenez Jian Zhou Randall Q. Snurr 《American Institute of Chemical Engineers》2014,60(6):2324-2334
Grand canonical Monte Carlo (GCMC) simulations with configurational biasing were used to study the enantioselective adsorption of four alkanols in a homochiral metal‐organic framework, known as hybrid organic‐inorganic zeolite analogue HOIZA‐1. Conventional GCMC simulations are not able to converge satisfactorily for this system due to the tight fit of the chiral alcohols in the narrow pores. However, parallel tempering and parallel mole‐fraction GCMC simulations overcome this problem. The simulations show that the enantioselective adsorption of the different (R,S)‐alkanols is due to the specific geometry of the chiral molecules relative to the pore size and shape. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2324–2334, 2014 相似文献