全文获取类型
收费全文 | 19946篇 |
免费 | 582篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 231篇 |
综合类 | 18篇 |
化学工业 | 3002篇 |
金属工艺 | 241篇 |
机械仪表 | 357篇 |
建筑科学 | 944篇 |
矿业工程 | 42篇 |
能源动力 | 467篇 |
轻工业 | 2100篇 |
水利工程 | 273篇 |
石油天然气 | 29篇 |
无线电 | 1764篇 |
一般工业技术 | 2581篇 |
冶金工业 | 5596篇 |
原子能技术 | 143篇 |
自动化技术 | 2757篇 |
出版年
2023年 | 84篇 |
2022年 | 217篇 |
2021年 | 353篇 |
2020年 | 178篇 |
2019年 | 244篇 |
2018年 | 300篇 |
2017年 | 287篇 |
2016年 | 307篇 |
2015年 | 301篇 |
2014年 | 423篇 |
2013年 | 724篇 |
2012年 | 756篇 |
2011年 | 1012篇 |
2010年 | 704篇 |
2009年 | 728篇 |
2008年 | 774篇 |
2007年 | 740篇 |
2006年 | 620篇 |
2005年 | 585篇 |
2004年 | 542篇 |
2003年 | 501篇 |
2002年 | 454篇 |
2001年 | 366篇 |
2000年 | 336篇 |
1999年 | 450篇 |
1998年 | 1957篇 |
1997年 | 1189篇 |
1996年 | 803篇 |
1995年 | 485篇 |
1994年 | 466篇 |
1993年 | 463篇 |
1992年 | 202篇 |
1991年 | 203篇 |
1990年 | 193篇 |
1989年 | 194篇 |
1988年 | 202篇 |
1987年 | 130篇 |
1986年 | 131篇 |
1985年 | 187篇 |
1984年 | 140篇 |
1983年 | 101篇 |
1982年 | 108篇 |
1981年 | 113篇 |
1980年 | 84篇 |
1979年 | 93篇 |
1978年 | 79篇 |
1977年 | 133篇 |
1976年 | 150篇 |
1975年 | 78篇 |
1974年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Nicole Jacqueline Jensen Helena Zander Wodschow Malin Nilsson Jrgen Rungby 《International journal of molecular sciences》2020,21(22)
Under normal physiological conditions the brain primarily utilizes glucose for ATP generation. However, in situations where glucose is sparse, e.g., during prolonged fasting, ketone bodies become an important energy source for the brain. The brain’s utilization of ketones seems to depend mainly on the concentration in the blood, thus many dietary approaches such as ketogenic diets, ingestion of ketogenic medium-chain fatty acids or exogenous ketones, facilitate significant changes in the brain’s metabolism. Therefore, these approaches may ameliorate the energy crisis in neurodegenerative diseases, which are characterized by a deterioration of the brain’s glucose metabolism, providing a therapeutic advantage in these diseases. Most clinical studies examining the neuroprotective role of ketone bodies have been conducted in patients with Alzheimer’s disease, where brain imaging studies support the notion of enhancing brain energy metabolism with ketones. Likewise, a few studies show modest functional improvements in patients with Parkinson’s disease and cognitive benefits in patients with—or at risk of—Alzheimer’s disease after ketogenic interventions. Here, we summarize current knowledge on how ketogenic interventions support brain metabolism and discuss the therapeutic role of ketones in neurodegenerative disease, emphasizing clinical data. 相似文献
3.
Production planning and control (PPC) systems that employ aspects from both make-to-order (MTO) and make-to-stock (MTS) production control are known as hybrid MTS/MTO systems. While both MTO and MTS separately have been studied extensively, their combined use has received less attention. However, the literature on this topic is growing and this paper shows that the review performed in this paper is an important addition to the field. We categorise relevant literature according to a novel taxonomy and show that hybrid MTS/MTO production control can be used in different contexts. In addition, an overview of the modelling techniques and methods used in these papers is provided. Based on the reviewed literature, relevant research questions and directions for future research are identified. Finally, it is shown that hybrid MTS/MTO production control is prevalent in practice by discussing research with industrial applications. The paper contains an overview of research on hybrid MTS/MTO production control to be used as reference for researchers active in the field, and provides managerial insights and directions for future research on this topic. 相似文献
4.
5.
6.
7.
Iris Bakker Theo van der Voordt Peter Vink Jan de Boon Conne Bazley 《Color research and application》2015,40(1):62-71
Studies on color preferences are dependent on the topic and the relationships with personal characteristics, particularly personality, but these are seldom studied in one population. Therefore a questionnaire was collected from 1095 Dutch people asking for color preferences about different topics and relating them to personal characteristics. Color preferences regarding different topics show different patterns and significant differences were found between gender, age, education and personality such as being technical, being emotional or being a team player. Also, different colors were mentioned when asked for colors that stimulate to be quiet, energetic, and able to focus or creative. Probably, due to unconsciousness of contexts, many people had no color preference, a result that in the literature seldom is mentioned. Blue was the overall favorite color; however, most males chose for blue (25%) while most females had no color preference (18%). Black was the overall favorite color for clothing, mainly chosen by females (40%), while males primarily chose blue (27%). For building interiors subjects preferred white. For moods, subjects preferred white for being quiet or being able to focus, red for being energetic and had no color preference for being creative. It is concluded that color preferences are dependent upon the topic, and personal characteristics. The findings are important for architects, interior designers, fashion designers and product designers to have a basic idea of preferred colors for different objects by different types of people. © 2013 Wiley Periodicals, Inc. Col Res Appl, 40, 62–71, 2015 相似文献
8.
9.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
10.
Zhao M. Shea J. D. Hagness S. C. van der Weide D. W. 《Microwave and Wireless Components Letters, IEEE》2006,16(12):675-677
We present a 3-12 GHz compact mixer-based reflectometer (CMR) and horn antenna system, and demonstrate its use in detecting backscatter signals with a free space calibration procedure. We evaluate the frequency-domain performance of the CMR-antenna system for measuring the complex reflection coefficient of a dielectric slab and compare it with that of a commercial vector network analyzer (VNA)-antenna setup. Time-domain responses are also investigated, and show the effectiveness of this calibration method. This low-cost, compact system eliminates the need for traditional mechanical standards and a VNA, is effective in reducing reflection artifacts, and allows for flexibility in the placement of reference planes; thus it is well suited for array-based imaging applications 相似文献