全文获取类型
收费全文 | 1484篇 |
免费 | 105篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 457篇 |
金属工艺 | 31篇 |
机械仪表 | 54篇 |
建筑科学 | 40篇 |
矿业工程 | 3篇 |
能源动力 | 78篇 |
轻工业 | 260篇 |
水利工程 | 19篇 |
石油天然气 | 17篇 |
无线电 | 71篇 |
一般工业技术 | 223篇 |
冶金工业 | 55篇 |
原子能技术 | 10篇 |
自动化技术 | 259篇 |
出版年
2024年 | 14篇 |
2023年 | 21篇 |
2022年 | 39篇 |
2021年 | 85篇 |
2020年 | 64篇 |
2019年 | 76篇 |
2018年 | 71篇 |
2017年 | 61篇 |
2016年 | 75篇 |
2015年 | 47篇 |
2014年 | 70篇 |
2013年 | 133篇 |
2012年 | 87篇 |
2011年 | 105篇 |
2010年 | 103篇 |
2009年 | 109篇 |
2008年 | 58篇 |
2007年 | 63篇 |
2006年 | 39篇 |
2005年 | 24篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1967年 | 2篇 |
1961年 | 1篇 |
1940年 | 1篇 |
1930年 | 1篇 |
1925年 | 2篇 |
1921年 | 1篇 |
排序方式: 共有1590条查询结果,搜索用时 15 毫秒
31.
32.
Wilson De Carvalho Jr. Mario Tosi Furtado Aryton André Bernussi Angelo Luiz Gobbi Mônica Alonso Cotta 《Journal of Electronic Materials》2000,29(1):62-68
We investigated the influence of the growth rate on the quality of zero-net-strained InGaAsP/InGaAsP/InP multiquantum well
structures for 1.55 μm emission grown by low pressure metalorganic vapor phase epitaxy. The samples consisted of fixed compressive
strained wells (ɛ=+1%) and tensile strained barriers (ɛ=−0.5%) grown with different quaternary bandgap wavelengths (λB=1.1–1.4 μm). Using higher growth rates, we obtained for the first time high quality zero net strained multi quantum well
structures, regardless having constant group V composition in the well and barriers. The samples were analyzed by x-ray diffraction,
photoluminescence and atomic force microscopy techniques. The amplitude of surface modulation roughness along [011] direction
decreased from 20 nm to 0.53 nm with increasing growth rate and/or quaternary compositions grown outside the miscibility gap.
A new deep PL broad emission band strongly correlated with the onset of wavy layer growth is also reported. Broad area and
ridge waveguide lasers with 10 wells exhibited low losses (34 cm−1) and low threshold current densities at infinite cavity length (1020 A·cm−2 and 1190 A·cm−2, respectively). 相似文献
33.
Antônio Alisson Alencar Freitas Fernando Lessa Tofoli Edilson Mineiro Sá Junior Sergio Daher Fernando Luiz Marcelo Antunes 《International Journal of Electronics》2016,103(5):898-912
A high voltage step-up nonisolated DC–DC converter based on coupled inductors suitable to photovoltaic (PV) systems applications is proposed in this paper. Considering that numerous approaches exist to extend the voltage conversion ratio of DC–DC converters that do not use transformers, a detailed comparison is also presented among the proposed converter and other popular topologies such as the conventional boost converter and the quadratic boost converter. The qualitative analysis of the coupled-inductor-based topology is developed so that a design procedure can be obtained, from which an experimental prototype is implemented to validate the theoretical assumptions. 相似文献
34.
Luiz A. Canalle Sander S. van Berkel Laurens T. de Haan Jan C. M. van Hest 《Advanced functional materials》2009,19(21):3464-3470
The copper‐catalyzed azide–alkyne 1,3‐dipolar cycloaddition (CuAAC) is extensively used for the functionalization of well‐defined polymeric materials. However, the necessity for copper, which is inherently toxic, limits the potential applications of these materials in the area of biology and biomedicine. Therefore, the first entirely copper‐free procedure for the synthesis of clickable coatings for the immobilization of functional molecules is reported. In the first step, azide‐functional coatings are prepared by thermal crosslinking of side‐chain azide‐functional polymers and dialkyne linkers. In a second step, three copper‐free click reactions (i.e., the Staudinger ligation, the dibenzocyclooctyne‐based strain‐promoted azide–alkyne [3+2] cycloaddition, and the methyl‐oxanorbornadiene‐based tandem cycloaddition?retro‐Diels?Alder (crDA) reaction) are used to functionalize the azide‐containing surfaces with fluorescent probes, allowing qualitative comparison with the traditional CuAAC. 相似文献
35.
36.
37.
Marta C. Picardo José Luiz de Medeiros Juliana Garcia M. Monteiro Ricardo Moreira Chaloub Mario Giordano Ofélia de Queiroz Fernandes Araújo 《Clean Technologies and Environmental Policy》2013,15(2):275-291
The increasing interest for biotechnological use of microalgae demands a methodology for selection of species suitable to support the development of technologies based on the use of such non-conventional renewable raw material, i.e., green industrial applications. The vast and expanding collection of experimental data on both cell growth and biomass composition available in the literature can be used to reduce the cost of the experimental investigations required to support process engineering and optimization. Selecting the appropriate organism requires extracting useful information from such data, a cumbersome task since various multidisciplinary factors must be considered. This paper presents a computer-aided methodology for selecting appropriate algal species given an energy or green chemical process application employing microalgae as a renewable raw material. The approach is “system oriented”, based on biomass composition and chemical processing of the biomass downstream of the CO2 biofixation and harvesting operations. Quantitative performance results are supported by professional process simulation. Besides comparison of a set of species performances, the proposed methodology also allows the discrimination among distinct algal compositions resulting from different growth conditions for a given species. Furthermore, three categories of screening metrics are proposed to be maximized by the decision making procedure in order to elicit the relevant information. To demonstrate the potential of the proposed methodology, a databank of both biochemical and elemental compositions of microalgal biomass was used in three green applications: Assessment of biomass heating value; production of syngas by gasification of the biomass; and production of Bio-H2. Within the accuracy of the databank employed to illustrate the procedure, the methodology selected Botryococcus braunii and Isochrysis galbana as potential promising candidates, for the three examined applications. 相似文献
38.
Maria Helena Santos Rafael M. Silva Vitor C. Dumont Juliana S. Neves Herman S. Mansur Luiz Guilherme D. Heneine 《Materials science & engineering. C, Materials for biological applications》2013,33(2):790-800
Bovine pericardium is widely used as a raw material in bioengineering as a source of collagen, a fundamental structural molecule. The physical, chemical, and biocompatibility characteristics of these natural fibers enable their broad use in several areas of the health sciences. For these applications, it is important to obtain collagen of the highest possible purity. The lack of a method to produce these pure biocompatible materials using simple and economically feasible techniques presents a major challenge to their production on an industrial scale. This study aimed to extract, purify, and characterize the type I collagen protein originating from bovine pericardium, considered to be an abundant tissue resource. The pericardium tissue was collected from male animals at slaughter age. Pieces of bovine pericardium were enzymatically digested, followed by a novel protocol developed for protein purification using ion-exchange chromatography. The material was extensively characterized by electrophoresis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and infrared spectroscopy. The results showed a purified material with morphological properties and chemical functionalities compatible with type I collagen and similar to a highly purified commercial collagen. Thus, an innovative and relatively simple processing method was developed to extract and purify type I collagen from bovine tissue with potential applications as a biomaterial for regenerative tissue engineering. 相似文献
39.
Elisandra Rigo Jorge Luiz Ninow Siu Mui Tsai Ademir Durrer Lillian Liva Foltran Daniela Remonatto Melania Sychoski Renata Vardanega Débora de Oliveira Helen Treichel Marco Di Luccio 《Food and Bioprocess Technology》2012,5(5):1592-1600
Current studies about lipase production involve the use of agro-industrial residues and newly isolated microorganisms aimed at increasing economic attractiveness of the process. Based on these aspects, the main objective of this work is to perform the partial characterization of enzymatic extracts produced by a newly isolated Penicillium crustosum in solid-state fermentation. Lipase extract presented optimal temperature and pH of 37?°C and 9?C10, respectively. The concentrated enzymatic extract showed more stability at 25?°C and pH?7. The enzymes kept 100% of their enzymatic activity until 60?days of storage at 4 and ?10?°C. The stability under calcium salts indicated that the hydrolytic activity presented decay with the increase of calcium concentration. The specificity under several substrates indicated good enzyme activities in triglycerides from C4 to C18. 相似文献
40.
Luiz Antonio Joia Mariela Fontenelle Sily de Assis 《Information Systems Management》2019,36(3):228-242
ABSTRACTIn this paper, we use the Delphi method to identify the main motivations that have led IT professionals to intend to move to another area. We found that the pursuit of career growth and the quest for acquiring new experiences and abilities have a marked impact on the IT professional turnaway intention. Moreover, female IT professionals and IT professionals oriented by the career advancement paradigm have a higher propensity to abandon the IT area. 相似文献