全文获取类型
收费全文 | 4091篇 |
免费 | 257篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 43篇 |
综合类 | 6篇 |
化学工业 | 1181篇 |
金属工艺 | 66篇 |
机械仪表 | 110篇 |
建筑科学 | 194篇 |
矿业工程 | 8篇 |
能源动力 | 149篇 |
轻工业 | 510篇 |
水利工程 | 24篇 |
石油天然气 | 13篇 |
无线电 | 275篇 |
一般工业技术 | 700篇 |
冶金工业 | 130篇 |
原子能技术 | 45篇 |
自动化技术 | 898篇 |
出版年
2024年 | 8篇 |
2023年 | 40篇 |
2022年 | 187篇 |
2021年 | 214篇 |
2020年 | 99篇 |
2019年 | 114篇 |
2018年 | 151篇 |
2017年 | 140篇 |
2016年 | 189篇 |
2015年 | 113篇 |
2014年 | 171篇 |
2013年 | 300篇 |
2012年 | 275篇 |
2011年 | 335篇 |
2010年 | 219篇 |
2009年 | 244篇 |
2008年 | 227篇 |
2007年 | 182篇 |
2006年 | 190篇 |
2005年 | 150篇 |
2004年 | 106篇 |
2003年 | 95篇 |
2002年 | 76篇 |
2001年 | 59篇 |
2000年 | 57篇 |
1999年 | 54篇 |
1998年 | 41篇 |
1997年 | 33篇 |
1996年 | 36篇 |
1995年 | 40篇 |
1994年 | 22篇 |
1993年 | 23篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有4352条查询结果,搜索用时 15 毫秒
151.
Katia Rodríguez Kong Ah‐Hen Antonio Vega‐Gálvez Jessica López Issis Quispe‐Fuentes Roberto Lemus‐Mondaca Lena Gálvez‐Ranilla 《International Journal of Food Science & Technology》2014,49(4):990-1000
Murta (Ugni molinae T.) berries were air‐dried at five temperatures (40, 50, 60, 70 and 80 °C), and the changes in β‐carotene, phenolic acids, total phenolic and flavonoid contents and antioxidant capacities (DPPH and ORAC) were investigated. The berries showed a high content of β‐carotene, which decreased during drying temperature between 40 °C and 80 °C. Free and bound phenolic acids were also determined, showing gallic acid to be the prevalent phenolic acid. Total phenolic and flavonoid contents in the dried berries showed a higher decrease at lower temperature due to longer drying time. The radical‐scavenging activity also showed higher antioxidant activity at higher drying temperatures (70–80 °C) than at lower drying temperatures (40–50 °C). Total phenolic content (TPC) and flavonoids showed good correlation with antioxidant capacity. Murta berries proved to be an excellent source of antioxidants and bioactive compounds and are therefore a potential ingredient for new functional food products. 相似文献
152.
Gabriella Carrozza Roberto Pietrantuono Stefano Russo 《International Journal on Software Tools for Technology Transfer (STTT)》2014,16(5):593-607
Testing accounts for a relevant part of the production cost of complex or critical software systems. Nevertheless, time and resources budgeted to testing are often underestimated with respect to the target quality goals. Test managers need engineering methods to perform appropriate choices in spending testing resources, so as to maximize the outcome. We present a method to dynamically allocate testing resources to software components minimizing the estimated number of residual defects and/or the estimated residual defect density. We discuss the application to a real-world critical system in the homeland security domain. We describe a support tool aimed at easing industrial technology transfer by hiding to practitioners the mathematical details of the method application. 相似文献
153.
Marco Roberto Cavallari Vinicius Ramos Zanchin Mariana Pojar Antonio Carlos Seabra Marcelo de Assumpção Pereira-da-Silva Fernando Josepetti Fonseca Adnei Melges de Andrade 《Journal of Electronic Materials》2014,43(5):1317-1325
A low-cost patterning of electrodes was investigated looking forward to replacing conventional photolithography for the processing of low-operating voltage polymeric thin-film transistors. Hard silicon, etched by sulfur hexafluoride and oxygen gas mixture, and flexible polydimethylsiloxane imprinting molds were studied through atomic force microscopy (AFM) and field emission gun scanning electron microscopy. The higher the concentration of oxygen in reactive ion etching, the lower the etch rate, sidewall angle, and surface roughness. A concentration around 30 % at 100 mTorr, 65 W and 70 sccm was demonstrated as adequate for submicrometric channels, presenting a reduced etch rate of 176 nm/min. Imprinting with positive photoresist AZ1518 was compared to negative SU-8 2002 by optical microscopy and AFM. Conformal results were obtained only with the last resist by hot embossing at 120 °C and 1 kgf/cm2 for 2 min, followed by a 10 min post-baking at 100 °C. The patterning procedure was applied to define gold source and drain electrodes on oxide-covered substrates to produce bottom-gate bottom-contact transistors. Poly(3-hexylthiophene) (P3HT) devices were processed on high-κ titanium oxynitride (TiO x N y ) deposited by radiofrequency magnetron sputtering over indium tin oxide-covered glass to achieve low-voltage operation. Hole mobility on micrometric imprinted channels may approach amorphous silicon (~0.01 cm2/V s) and, since these devices operated at less than 5 V, they are not only suitable for electronic applications but also as sensors in aqueous media. 相似文献
154.
André Medeiros De Andrade Roberto Ferreira Machado Michel Ulisses Franz Bremer Carlos Ernesto Gonçalves Reynaud Schaefer Jefferson Cardia Simões 《International journal of remote sensing》2018,39(8):2238-2254
The aim of this work is to produce a simplified vegetation map of ice-free areas of the Fildes Peninsula (FP) and Ardley Island (AI) thought object-oriented classification using a QuickBird satellite image and to evaluate the influence of the global solar radiation (GSR) over the vegetation distribution. The vegetation data were generated from multiresolution segmentation using the panchromatic and infrared layers, and for the classification we calculated the normalized vegetative difference index (NVDI) and the green NVDI. Two classes were created – Lichen and Moss Cushion SubFormation and Moss Subformation – with 48 vegetation samples collected on surveys during the austral summers of 2008 and 2009. We used a kappa index to evaluate the classification efficiency using 100 sampled points obtained in austral summer of 2013. The GSR was estimated, and in order to evaluate the effect of meteorological phenomena and cloudless, we measured the GSR using a net radiometer model CNR4 installed in FP between 2014 and 2016. The estimate of GSR was done for seasons of 2015, in order to estimate the light compensation point and the saturation point for the plant communities in FP and AI. The kappa index was 0.73 and the global accuracy was 0.78, showing consistency between the classification and ground truth. The area was covered by vegetation in FP was 16.7% and in AI is 59.1%. The vegetation cover is distributed differently at FP and AI, and our results suggest GSR plays an important role in vegetation distribution and these tendencies could be related to greater GSR demand by mosses when compared to lichens. 相似文献
155.
156.
The nanostructure of stretched and nonstretched PVDF samples was studied by small-angle X-ray scattering (SAXS). The crystallinity of the samples was determined by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), and crystalline phases by Fourier transform infrared spectroscopy (FTIR). The nanostructure can be described by a lamellar stacking of crystalline and amorphous layers, with a fairly well defined long period D and a diffuse-boundary in the interface between the crystalline and amorphous phases. The crystallinity of the stretched sample was found to be greater than that of the nonstretched sample. The long period D and the thicknesses of the crystalline lamellae Tc were found to be greater in the stretched sample than those in the nonstretched sample. The thickness of the diffuse-boundary was evaluated as being ∼ 1.4 nm in the nonstretched sample and 1.1 nm in the stretched sample. It was concluded that the growth of the thickness of the crystalline layer induced by the stretching process (stretch-induced crystallization) occurs partially at expense of the diffuse boundary and also by the coarsening of the structure with the stretching process, because of the diminution in the surface area to volume ratio observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
157.
Silvia Gillermina Ceballos-Maga?a Jose Marcos Jurado Roberto Mu?iz-Valencia Angela Alcázar Fernado de Pablos María Jesus Martín 《Food Analytical Methods》2012,5(2):260-265
The elemental profile of tequila samples from the three main production areas of the State of Jalisco, namely Amatitlan, Guadalajara,
and Tequila, was used to carry out their geographical characterization. With this aim, the concentration of Al, Ba, Ca, Cu,
Fe, K, Mg, Mn, Na, S, Sr, and Zn was determined by inductively coupled plasma atomic emission spectroscopy. Principal component
analysis was addressed to visualize data trends. The number of input variables was reduced by means of backward stepwise linear
discriminant analysis and support vector machines were used to construct an adequate classification model. The best classification
performance was obtained by a linear support vector machine model with 100% of prediction ability. 相似文献
158.
Paola Riolo Roxana L. Minuz Gianfranco Anfora Marco V. Rossi Stacconi Silvia Carlin Nunzio Isidoro Roberto Romani 《Journal of chemical ecology》2012,38(8):1017-1030
The Palearctic planthopper Hyalesthes obsoletus is the natural vector of the grapevine yellow disease Bois noir. Grapevine is an occasional host plant of this polyphagous planthopper. To deepen our knowledge of the role of plant volatile organic compounds for H. obsoletus host plant searching, we carried out behavioral, morphological, and electrophysiological studies. We tested the attraction of H. obsoletus to nettle, field bindweed, hedge bindweed, chaste tree, and grapevine by using a Y-shaped olfactometer. The results showed a significant attraction of male H. obsoletus to chaste tree, and of the females to nettle. Male H. obsoletus were repelled by odor from hedge bindweed. Ultrastructural studies of the antennae showed at least two types of olfactory sensilla at the antennal pedicel: plaque organs and trichoid sensilla. Volatile organic compounds from nettle and chaste tree were collected, and the extracts were analyzed by coupling gas-chromatography to both mass-spectrometry and electroantennography. The volatile organic compounds that elicited electrophysiological responses in male and female antennae were identified. These findings are discussed with respect to behavior of H. obsoletus males and females in the field. 相似文献
159.
Fernando Valdés Roberto Iglesias Felipe Espinosa Miguel A. Rodríguez 《Applied Intelligence》2012,37(2):267-279
This paper describes an innovative routing strategy for intelligent transportation units willing to perform merging manoeuvres with a moving convoy. In particular, we consider a transportation unit located inside a city (pursuer unit), and which wishes to join a convoy that is constantly moving around the city. We first describe a solution that considers idealistic conditions, i.e., the traveling time along each street is constant. We then go on to improve our first approach to deal with the realistic random nature of the traveling times experienced by the pursuer and by the convoy leader. Our search strategy applies Dynamic Programming to achieve a meeting point that is optimal in two ways: on one hand, the optimal destination is the one closest to the current pursuer??s position; on the other hand, the optimal meeting point must minimize the time that elapses until the pursuer meets the convoy (considering that the pursuer must always arrive first). Calculating the optimal path to every possible destination is highly inefficient, error prone and time consuming. On the contrary, we propose an efficient search strategy that will achieve the meeting point and the path to it, both optimally and in a very short time. This enables the real-time application of our approach either for finding new solutions or for re-planning old ones owing to unexpected real-conditions. 相似文献
160.
In recent years, various proposals have been put forth to formalize the Grafcet graphical language. The objective of this paper is to propose an ontology-based approach to formalize this language. The authors have implemented a semi-coarse grain ontology written in Ontology Web Language and have tested it by including it in an existing educational tool for the teaching of Grafcet language for use in programmable logic controllers. 相似文献