全文获取类型
收费全文 | 528篇 |
免费 | 52篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 161篇 |
金属工艺 | 4篇 |
机械仪表 | 8篇 |
建筑科学 | 26篇 |
能源动力 | 10篇 |
轻工业 | 132篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 35篇 |
一般工业技术 | 97篇 |
冶金工业 | 44篇 |
自动化技术 | 50篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 36篇 |
2020年 | 20篇 |
2019年 | 26篇 |
2018年 | 32篇 |
2017年 | 21篇 |
2016年 | 26篇 |
2015年 | 25篇 |
2014年 | 12篇 |
2013年 | 26篇 |
2012年 | 25篇 |
2011年 | 45篇 |
2010年 | 29篇 |
2009年 | 15篇 |
2008年 | 30篇 |
2007年 | 25篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有581条查询结果,搜索用时 31 毫秒
61.
Hanna-Liisa Kangas Jussi Lintunen Johanna Pohjola Lauri Hetemäki Jussi Uusivuori 《Energy Economics》2011,33(6):1165-1176
Increasing scarcity of oil reserves and the high CO2 emissions from using oil have contributed to the development of renewable biofuels. Pulp and paper mill integrated forest biorefineries offer one important means to increase biofuel production. This study analyzes the effects of policies to support biofuel production in the pulp and paper sector. We study the relative effectiveness of three biofuel supporting policy instruments, namely production subsidy, input subsidy and investment subsidy. We present a partial equilibrium pulp and paper market model with a biorefinery investment option. A numerical model is used to evaluate the impacts of policy instruments on wood prices, as well as input choices and investment strategies of pulp and paper industries. The data represent the Finnish pulp and paper sector. We evaluate the values and direct costs of the policy instruments in a situation of exogenous biofuel production targets. The direct costs of input and investment subsidies are higher than those of a production subsidy. With all the policy instruments, Finnish pulp and paper mills would invest in wood-gasifying technology, instead of black liquor based one. The number of biorefinery units is dependent on the subsidy type — investment and input subsidies are likely to result in more numerous but smaller biofuel production units than a production subsidy. With all the policy instruments the demand for wood increases in Finland leading to higher wood prices. This, in turn, could reflect negatively on the profitability of the pulp and paper industries. To a significant degree, the model and the results can be generalized to other countries and markets where integrated pulp and paper mills are operating. 相似文献
62.
Johanna Ivy Levene Margaret K. Mann Robert M. Margolis Anelia Milbrandt 《Solar Energy》2007,81(6):773-780
Three aspects of producing hydrogen via renewable electricity sources are analyzed to determine the potential for solar and wind hydrogen production pathways: a renewable hydrogen resource assessment, a cost analysis of hydrogen production via electrolysis, and the annual energy requirements of producing hydrogen for refueling. The results indicate that ample resources exist to produce transportation fuel from wind and solar power. However, hydrogen prices are highly dependent on electricity prices. For renewables to produce hydrogen at $2 kg−1, using electrolyzers available in 2004, electricity prices would have to be less than $0.01 kWh−1. Additionally, energy requirements for hydrogen refueling stations are in excess of 20 GWh/year. It may be challenging for dedicated renewable systems at the filling station to meet such requirements. Therefore, while plentiful resources exist to provide clean electricity for the production of hydrogen for transportation fuel, challenges remain to identify optimum economic and technical configurations to provide renewable energy to distributed hydrogen refueling stations. 相似文献
63.
Anna-Maria Spehar-Deleze Johanna Suomi Nico de Rooij Sakari Kulmala 《Electrochimica acta》2006,51(25):5438-5444
This paper describes a heterogeneous oligonucleotide-hybridization assay based on hot electron-induced electrochemiluminescence (HECL) of a rhodamine label. Thin oxide-film coated aluminum and silicon electrodes were modified with an aminosilane layer and derivatized with short, 15-mer oligonucleotides via diisothiocyanate coupling. Target oligonucleotides were conjugated with tetramethylrhodamine (TAMRA) dye at their amino modified 5′ end and hybridization was detected using HECL of TAMRA. Preliminary results indicate sensitivity down to picomolar level and low nonspecific adsorption. The sensitivity was better on oxide-coated silicon compared to oxide-coated aluminum electrodes and two-base pair mismatched hybrids were successfully discriminated. The experimental results presented here might be useful for the design of disposable electrochemiluminescent DNA biosensors. 相似文献
64.
65.
Johanna M. Tan & Miang H. Lim 《International Journal of Food Science & Technology》2008,43(9):1699-1704
The effects of gelatine concentration, bloom strength, and origin on the quality and shelf-life stability of marshmallows were studied. All six sample treatments were carried out under accelerated storage conditions of 25 °C and 75% relative humidity (RH) for 25 weeks. Gelatine A 150 bloom had the highest viscosity because of its highest concentration (2.54%), lowest density and greatest amount of moisture loss producing the hardest marshmallows. Hardness and water activity measurements correlate for all sample treatments indicating that moisture loss is the main mechanism for hardening. With the exception of Gelatine B 2.2%, sugar crystallisation may have occurred in all sample treatments at week 20 which would have an impact on hardness as well. Gel network formation may be contributing towards hardness in Gelatine B 2.2% as there was an increase in hardness but no changes were perceived in water activity. 相似文献
66.
Pirjo Koskela Merja Teirikangas Ari Alastalo Johanna Forsman Jari Juuti Unto Tapper Ari Auvinen Heikki Seppä Heli Jantunen Jorma Jokiniemi 《Advanced Powder Technology》2011,22(5):649-656
Metallic cobalt nanoparticles were synthesized by hydrogen reduction method. Particles were coated in situ with carbon by adding ethene to reaction flow. Particles were characterized by transmission electron microscopy, energy dispersive X-ray emission, X-ray diffraction, X-ray fluorescence and BET method. The observed cobalt particle size distributions in different cobalt batches produced with unvarying reaction parameters was reproducible: The mean diameter of primary cobalt particle varied only 5% from the mean value of 76 nm in different batches. Increased carbon precursor concentration decreased mean diameter of cobalt particles to 17 nm. The produced nanoparticles were used as filler material in 0–3 type metal–polymer composites. Composite samples with varying filler loading were fabricated with mixing extrusion and injection moulding techniques. The magnetic properties of the fabricated composites were measured up to 1 GHz. In order to analyse the particle distribution in composite matrix and its effect on magnetic properties the microstructure was studied. 相似文献
67.
68.
Lea Heikinheimo Arja Miettinen‐Oinonen Artur Cavaco‐Paulo Johanna Buchert 《应用聚合物科学杂志》2003,90(7):1917-1922
The mode of action of monocomponent purified Trichoderma reesei cellobiohydrolases (CBHI and CBHII) and endoglucanases (EGI and EGII) on cotton fabrics was studied by analyzing the weight loss of the fabric, the reducing sugars, the soluble oligosaccharides and the molecular weight of the cotton powder formed. The impact of mechanical action on these factors was also evaluated. EGI and EGII released the highest amounts of reducing sugars and soluble oligosaccharides in both treatments with or without additional mechanical action. After cellulase treatment without additional mechanical action, all of the cellulases were found to have reduced the molecular weight of cotton poplin powder. When mechanical action was combined with enzyme treatments, only EGII reduced the molecular weight. The weight loss of EG‐treated fabrics was clearly higher than the weight loss of CBH‐treated fabrics with both low and high mechanical action levels. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1917–1922, 2003 相似文献
69.
Looy Bart Van Zimmermann Edwin Veugelers Reinhilde Verbeek Arnold Mello Johanna Debackere Koenraad 《Scientometrics》2003,57(3):355-367
We investigate the relationship between the science intensity of technology domains and country's performance within these
domains. The number of references in patents to scientific articles is considered as an approximation of the science intensity
of a technology domain whereas a country's technological performance is measured in terms of its technological productivity
(i.e. number of patents per capita). We use USPTO patent-data for eight European countries in ten technological domains. A
variance analysis (ANOVA) is applied. Country as an independent variable does not explain a significant portion of the observed
variance in science intensity (p=0.25). Technology domain, however, explains a significant portion of the observed variance
(p<0.001). Moreover, in science intensive fields we find a positive relation between the science linkage intensity of these
fields and the technological productivity of the respective countries involved. These findings seem to suggest the relevancy
of designing innovation policies, aimed at fostering interaction between knowledge generating actors and technology producers,
in a field specific manner.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
70.
Johanna Dobereiner Segundo Urquiaga Robert M. Boddey 《Nutrient Cycling in Agroecosystems》1995,42(1-3):339-346
The development of sustainable agricultural systems for the tropics requires among other technologies, alternatives for nitrogen fertilizers which are often limited in availability for financial reasons and also represent a major source of groundwater and air pollution. There are many new alternatives for the development of agricultural systems which make use of biological processes in soil. Biological nitrogen fixation (BNF), that is, the biological conversion of atmospheric dinitrogen into mineral N, is the most important alternative among them. Examples are given of the impact of various technologies used in Brazil. Soybean, introduced into the country 30 years ago, is now the second most important export crop, reaching 24 million tons annually with no N fertilizer application. Consequently, Brazil today is the country in the world which uses the lowest amounts of nitrogen fertilizers in relation to phosphate. Alternatives for crop rotations and pastures are also discussed. Possibilities of expanding BNF to cereals and other non-legume crops are gaining new credibility due to the identification of endophytic associations with diazotropic bacteria. The definite proof of substantial BNF in sugar cane with N balance and15N methods in certain genotypes selected under low N fertilizer applications opens up new alternatives for sustainable agriculture and will be the key to viable bio-fuel programmes. 相似文献