首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13335篇
  免费   1182篇
  国内免费   10篇
电工技术   83篇
综合类   11篇
化学工业   5472篇
金属工艺   133篇
机械仪表   309篇
建筑科学   478篇
矿业工程   17篇
能源动力   345篇
轻工业   3261篇
水利工程   113篇
石油天然气   70篇
无线电   535篇
一般工业技术   1824篇
冶金工业   564篇
原子能技术   36篇
自动化技术   1276篇
  2024年   43篇
  2023年   195篇
  2022年   1015篇
  2021年   1138篇
  2020年   445篇
  2019年   450篇
  2018年   508篇
  2017年   518篇
  2016年   587篇
  2015年   469篇
  2014年   620篇
  2013年   927篇
  2012年   871篇
  2011年   1004篇
  2010年   752篇
  2009年   696篇
  2008年   635篇
  2007年   598篇
  2006年   464篇
  2005年   354篇
  2004年   293篇
  2003年   258篇
  2002年   242篇
  2001年   147篇
  2000年   97篇
  1999年   132篇
  1998年   113篇
  1997年   112篇
  1996年   108篇
  1995年   74篇
  1994年   61篇
  1993年   59篇
  1992年   65篇
  1991年   49篇
  1990年   41篇
  1989年   36篇
  1988年   35篇
  1987年   31篇
  1986年   42篇
  1985年   38篇
  1984年   26篇
  1983年   23篇
  1982年   15篇
  1981年   17篇
  1980年   19篇
  1979年   19篇
  1978年   20篇
  1977年   13篇
  1976年   8篇
  1975年   11篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Excessive energy intake may evoke complex biochemical processes characterized by inflammation, oxidative stress, and impairment of mitochondrial function that represent the main factors underlying noncommunicable diseases. Because cow milk is widely used for human nutrition and in food industry processing, the nutritional quality of milk is of special interest with respect to human health. In our study, we analyzed milk produced by dairy cows fed a diet characterized by a high forage:concentrate ratio (high forage milk, HFM). In view of the low n-6:n-3 ratio and high content of conjugated linoleic acid of HFM, we studied the effects of this milk on lipid metabolism, inflammation, mitochondrial function, and oxidative stress in a rat model. To this end, we supplemented for 4 wk the diet of male Wistar rats with HFM and with an isocaloric amount (82 kJ, 22 mL/d) of milk obtained from cows fed a diet with low forage:concentrate ratio, and analyzed the metabolic parameters of the animals. Our results indicate that HFM may positively affect lipid metabolism, leptin:adiponectin ratio, inflammation, mitochondrial function, and oxidative stress, providing the first evidence of the beneficial effects of HFM on rat metabolism.  相似文献   
32.
33.
34.
35.
The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu2?xNixNdyFe28?yO46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd3+) as compared to (Fe3+), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å3). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd3+ ions at octahedral site impedes the valence alternation of Fe3+; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc).  相似文献   
36.
The usage of cling wraps is emerging as an easy and cost-effective approach to protect fresh-cut fruits and vegetables from dust, whilst improving visual appeal on retail counters. This study focused on developing an alternate, protein-based packaging material as a food grade cling wrap for food packaging applications. Zein-based cling wraps were produced, and their physical and mechanical characteristics were evaluated and compared with conventionally used chitosan biopolymer films and commercial synthetic polymer films. Antioxidant potential of the prepared films was studied, and the effectiveness of the developed films as anti-browning cling wraps was evaluated using studies conducted on fresh-cut apple slices at ambient conditions. Anti-browning effects were in par with polymeric counterparts; however, zein cling wraps could better prevent weight loss in apple slices. Zein-based films can be adopted as biodegradable food grade cling wraps as an alternative to chitosan and synthetic polymeric materials.  相似文献   
37.
38.
39.
40.
The authenticity and traceability of meat products are issues of primary importance to ensure food safety. Unfortunately, food adulteration (e.g. the addition of inexpensive cuts to minced meat products) and mislabelling (e.g. the inclusion of meat from species other than those declared) happens frequently worldwide. The aim of this study was to apply a droplet digital PCR assay for the detection and quantification (copies μL−1) of the beef, pork, horse, sheep, chicken and turkey in meat products. The analysis conducted on commercial meat showed the presence of traces of DNA from other animal species than those declared. We show that the method is highly sensitive, specific and accurate (accuracy = 100%). This method could be adopted by competent food safety authorities to verify compliance with the labelling of meat products and to ensure quality and safety throughout the meat supply chain, from primary production to consumption.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号