全文获取类型
收费全文 | 22036篇 |
免费 | 1007篇 |
国内免费 | 314篇 |
专业分类
电工技术 | 472篇 |
综合类 | 543篇 |
化学工业 | 3960篇 |
金属工艺 | 542篇 |
机械仪表 | 770篇 |
建筑科学 | 930篇 |
矿业工程 | 180篇 |
能源动力 | 645篇 |
轻工业 | 2240篇 |
水利工程 | 252篇 |
石油天然气 | 188篇 |
武器工业 | 27篇 |
无线电 | 2486篇 |
一般工业技术 | 3058篇 |
冶金工业 | 3742篇 |
原子能技术 | 178篇 |
自动化技术 | 3144篇 |
出版年
2023年 | 103篇 |
2022年 | 126篇 |
2021年 | 552篇 |
2020年 | 311篇 |
2019年 | 385篇 |
2018年 | 439篇 |
2017年 | 427篇 |
2016年 | 465篇 |
2015年 | 404篇 |
2014年 | 602篇 |
2013年 | 1135篇 |
2012年 | 876篇 |
2011年 | 1123篇 |
2010年 | 827篇 |
2009年 | 903篇 |
2008年 | 894篇 |
2007年 | 900篇 |
2006年 | 770篇 |
2005年 | 652篇 |
2004年 | 732篇 |
2003年 | 952篇 |
2002年 | 1233篇 |
2001年 | 1039篇 |
2000年 | 617篇 |
1999年 | 558篇 |
1998年 | 1348篇 |
1997年 | 870篇 |
1996年 | 650篇 |
1995年 | 431篇 |
1994年 | 309篇 |
1993年 | 348篇 |
1992年 | 202篇 |
1991年 | 156篇 |
1990年 | 149篇 |
1989年 | 138篇 |
1988年 | 129篇 |
1987年 | 110篇 |
1986年 | 115篇 |
1985年 | 156篇 |
1984年 | 93篇 |
1983年 | 93篇 |
1982年 | 86篇 |
1981年 | 107篇 |
1980年 | 100篇 |
1979年 | 65篇 |
1978年 | 51篇 |
1977年 | 99篇 |
1976年 | 192篇 |
1975年 | 51篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 219 毫秒
991.
Alemayehu Gebremedhin Jarle De Oliveira Granheim 《Renewable & Sustainable Energy Reviews》2012,16(3):1611-1615
This paper presents the results of a Norwegian power system analysis. An energy system analysis model based on linear programming is used for modelling and optimisation. The analyses cover a number of scenarios where the studied system is subjected to changes by introducing other renewable energy sources, energy conservation measures and measures to promote renewable energy. The study shows that due to a combination of cheap hydropower and high investment costs, it is quite difficult for new generation units to be profitable. This is also true during periods of low precipitation where the system tends to survive on imported power instead of investing in new generation units. However, this does not apply to energy conservation measures that easily enter the system. On the other hand, biomass based CHP, wind power and wave power could be viable if measures are introduced to promote their use. Most of the scenarios show a high potential for reducing global emissions. 相似文献
992.
Taejin Song Jaihyun Kwak B. C. De Cooman 《Metallurgical and Materials Transactions A》2012,43(1):245-262
Whereas low-carbon (<0.2 mass pct) martensitic grades can be produced easily in continuous annealing processing lines equipped
with the required cooling capacity, the thermal cycles in continuous galvanizing lines make it difficult to produce hot-dip
Zn or Zn-alloy coated high-strength martensitic grades. This is because of the tempering processes occurring during dipping
of the strip in the liquid Zn bath and, in the case of galvannealed sheet steel, the short thermal treatment required to achieve
the alloying between the Zn and the steel. These short additional thermal treatments last less than 30 seconds but severely
degrade the mechanical properties. Using a combination of internal friction, X-ray diffraction, and transmission electron
microscopy, it is shown that the ultrafine-grained lath microstructure allows for a rapid dislocation recovery and carbide
formation during the galvanizing processes. In addition, the effective dislocation pinning occurring during the galvannealing
process results in strain localization and the suppression of strain hardening. 相似文献
993.
994.
Polyacrylonitrile (PAN), is an important base polymer to cast porous membranes. In this work, a detailed study of the effects of molecular weight of PAN homopolymer and its concentration on the cast membrane has been undertaken. The effects of molecular weight of additive polyethylene glycol (PEG) and its concentration have also been investigated. The membranes are cast using dimethyl formamide as solvent using phase inversion technique. They are characterized in terms of porosity, water permeability, molecular weight cut off, average pore diameter, contact angle, and tensile strength at breaking point. Fourier transform infrared spectroscopy and scanning electron microscopy are used to characterize the chemical and morphological changes of the membrane surface. Further studies have been considered to evaluate the antifouling property of various membranes using filtration of bovine serum albumin solution. Membrane modified by PEG 400 membrane shows an improved separation performance and antifouling characteristics. POLYM. ENG. SCI., 54:2375–2391, 2014. © 2013 Society of Plastics Engineers 相似文献
995.
996.
Jierong Yi Cristian De Gobba Leif H. Skibsted 《International Journal of Food Properties》2017,20(5):1129-1144
Grass carp skin pieces were homogenized in water and hydrolyzed by Alcalase®, collagenase, proteinase K, and/or trypsin at their optimum conditions. Samples were taken at various degrees of hydrolysis and were evaluated for antioxidant, antimicrobial, and angiotensin-converting enzyme inhibitory activities. Alcalase and collagenase completely hydrolyzed the skin with different rates, and released peptides with antioxidant and angiotensin-converting enzyme-inhibitory activity. These activities increased linearly with increasing degrees of hydrolysis. Subsequent incubation of the collagenase hydrolysates with trypsin slightly increased the antioxidant activity. Proteinase K, although only partially hydrolyzing the skin, also catalyzed the release of peptides with antioxidant and angiotensin-converting enzyme-inhibitory activities. These results show that skin by-products from grass carp can be a source of bioactive peptides produced by a one-step reaction. Such hydrolysates may be applied in food products to prolong shelf life and provide beneficial effects on blood pressure. 相似文献
997.
Melissa Fuster Ellen Messer Robert F. Houser Hedi Deman Patricia Palma De Fulladolsa Odilia I. Bermudez 《Food and Foodways: Explorations in the History and Culture of》2013,21(4):288-314
This study presents an assessment of local definitions and perceptions concerning healthy eating through a study in four resource-poor border communities in El Salvador. The study included focus groups, key-informant interviews, and observations of the food environment. Local definitions of healthy eating elicited through focus groups were compared to the national Salvadoran dietary guidelines recommendations. The comparison revealed several areas of overlap (including the importance of dietary variety, fruits, and vegetables, among others) and omissions (mention of limiting sweets/candy, salt, sugar, and alcohol). Focus group participants expressed concerns over the origin of their foods and whether food contained harmful chemicals. These conversations also revealed the contradictions between nutrition knowledge and preferences for foods classified as unhealthy. This article concludes with a discussion about barriers to healthy eating identified in the focus groups and through the food environment assessment. 相似文献
998.
999.
M.A. Heckman K. Sherry E. Gonzalez De Mejia 《Comprehensive Reviews in Food Science and Food Safety》2010,9(3):303-317
ABSTRACT: The consumption of energy drinks is rapidly increasing, as demonstrated by their large market growth. The targeted demographic group is teenagers, young adults, 18 to 34 y old; although expansion into nontraditional markets is also occurring. It is claimed that energy drinks can offer an increased energy boost related to their ingredient profile of caffeine, taurine, herbal extracts, and vitamins. Research suggests that energy drink formulations, in addition to increasing energy utilization, may also improve mood, enhance physical endurance, reduce mental fatigue, and increase reaction time. However, in most cases, the corresponding mechanisms of action are not clear. In addition, concerns have been raised over their safety and with a currently weak regulatory environment, efforts need to be made to ensure consumer safety. The objective of this article is to review the current U.S. energy drink market with emphasis on its market size, target demographic, active ingredients, potential benefits, safety, and regulations. 相似文献
1000.
De La Torre Jessica Elizabeth Fatma Gassara Anne Patricia Kouassi Khaled Belkacemi 《Critical reviews in food science and nutrition》2017,57(6):1078-1088
Spices are parts of plants that due to their properties are used as colorants, preservatives, or medicine. The uses of spices have been known since long time, and the interest in the potential of spices is remarkable due to the chemical compounds contained in spices, such as phenylpropanoids, terpenes, flavonoids, and anthocyanins. Spices, such as cumin (cuminaldehyde), clove (eugenol), and cinnamon (cinnamaldehyde) among others, are known and studied for their antimicrobial and antioxidant properties due to their main chemical compounds. These spices have the potential to be used as preservatives in many foods namely in processed meat to replace chemical preservatives. Main chemical compounds in spices also confer other properties providing a variety of applications to spices, such as insecticidal, medicines, colorants, and natural flavoring. Spices provide beneficial effects, such as antioxidant activity levels that are comparable to regular chemical antioxidants used so they can be used as a natural alternative to synthetic preservatives. In this review, the main characteristics of spices will be described as well as their chemical properties, different applications of these spices, and the advantages and disadvantages of their use. 相似文献