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   4297篇
  免费   404篇
  国内免费   31篇
电工技术   1篇
综合类   154篇
化学工业   405篇
金属工艺   7篇
机械仪表   55篇
建筑科学   28篇
矿业工程   3篇
能源动力   7篇
轻工业   3844篇
水利工程   1篇
石油天然气   14篇
无线电   18篇
一般工业技术   152篇
冶金工业   6篇
原子能技术   7篇
自动化技术   30篇
  2024年   55篇
  2023年   152篇
  2022年   218篇
  2021年   267篇
  2020年   249篇
  2019年   248篇
  2018年   210篇
  2017年   227篇
  2016年   177篇
  2015年   216篇
  2014年   263篇
  2013年   241篇
  2012年   380篇
  2011年   326篇
  2010年   181篇
  2009年   153篇
  2008年   132篇
  2007年   187篇
  2006年   155篇
  2005年   118篇
  2004年   100篇
  2003年   87篇
  2002年   67篇
  2001年   68篇
  2000年   58篇
  1999年   39篇
  1998年   34篇
  1997年   22篇
  1996年   15篇
  1995年   14篇
  1994年   12篇
  1993年   6篇
  1992年   7篇
  1991年   5篇
  1990年   10篇
  1989年   4篇
  1988年   7篇
  1987年   4篇
  1986年   6篇
  1985年   2篇
  1984年   1篇
  1982年   1篇
  1980年   7篇
  1978年   1篇
排序方式: 共有4732条查询结果,搜索用时 31 毫秒
1.
2.
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.  相似文献   
3.
4.
5.
Theabrownins (TB) are polymeric phenolic compounds associated with the multiple bioactivities of Pu-erh tea, a post-fermented Chinese dark tea. High-TB instant Pu-erh tea was produced via a novel submerged fermentation (SF) using Aspergillus tubingensis and compared with samples produced commercially via the conventional solid-state fermentation (SSF). Viable microorganisms and microbial toxins, especially aflatoxins B1, G1, B2, G2, cyclopiazonic acid, fumonisins B1, B2, B3 and ochratoxin A, were below the detection limit in all samples. Fewer microbial metabolites were found in SF instant tea compared with the SSF teas. Based on an adult consuming 1 g of instant Pu-erh tea daily, the dietary intake of investigated elements was below the safe limits recommended by various authorities. Tasters viewed the instant tea infusions as very mild, smooth, mellow and full. This suggested that submerged fermentation using A. tubingensis offers a speedy and safe alternative to commercial production of instant Pu-erh tea.  相似文献   
6.
The Jian kiln, located in present-day Jianyang county of Fujian province, mainly produced black-glazed tea bowls. Jian tea bowl was used as a utensil for tea tasting and was greatly appreciated by emperor Huizong of the Northern Song dynasty. The black glaze of Jian bowl was sometimes marked with streaks or spots, usually called “hare's fur” or “oil spot”, which are the crystalline markings of iron oxide precipitated during firing in the dragon kiln. In this study, black-glazed Jian bowl sherds excavated from the late Northern Song strata of Luhuaping and Daluhoumen Jian kiln sites were adopted as test samples. Based on the physico-chemical foundation for the formation of glaze microstructure, the correlation among composition, microstructure, and visual appearance has been investigated by means of energy-dispersive X-ray fluorescence, X-ray diffraction, and field emission electron microscopy. For the first time, the study provides realizing proofs for two kinds of microstructural forming mechanics.  相似文献   
7.
对新鲜茶树叶中六六六和滴滴涕共八种异构体的残留量进行测定,与同地点成品茶叶农药残留量相比较基本无差异。本法检测限为>1.8ng/g,回收率为78.2%-99.0%,相对标准偏差<10.0%。  相似文献   
8.
本文介绍了以各种中药材为主要原料 ,配以茶叶为辅料 ,运用先进的处理方法制备降脂减肥果茶的生产工艺、质量标准 ,并对确定生产工艺的几个主要问题进行了探讨  相似文献   
9.
The influence of drinking tea on copper bioavailability is unclear, particularly when tea is consumed with food. A breakfast meal containing white bread, margarine, strawberry jam, cheese and tea, with or without milk, was digested in; vitro and the dialysis of copper investigated. Reference breakfasts were prepared with water and water with milk. Copper dialysability (percentage of copper dialysed) was markedly increased by tea. The influence of adding milk to tea was not significant. A second study was carried out in rats using the breakfasts containing tea and water. They were spiked with 64Cu and given orally to the animals in a single dose. Whole-body 64Cu retention was measured over a 4-day period after administration. In order to determine the true absorption of 64Cu a control group of rats received the dose intraperitioneally. The results in vivo indicate a tendency to higher absorption and retention of 64Cu with tea. Liver 64Cu retention was significantly elevated by tea. Therefore, the presence of tea in a breakfast meal favours the formation of soluble low-molecular-weight ligands which can be absorbed and retained by rats. The concomitant increase in liver copper retetition may be associated with higher bioavailability and/or lower copper mobilisation.  相似文献   
10.
Artificial domestication and improvement of the majority of crops began approximately 10,000 years ago, in different parts of the world, to achieve high productivity, good quality, and widespread adaptability. It was initiated from a phenotype-based selection by local farmers and developed to current biotechnology-based breeding to feed over 7 billion people. For most cereal crops, yield relates to grain production, which could be enhanced by increasing grain number and weight. Grain number is typically determined during inflorescence development. Many mutants and genes for inflorescence development have already been characterized in cereal crops. Therefore, optimization of such genes could fine-tune yield-related traits, such as grain number. With the rapidly advancing genome-editing technologies and understanding of yield-related traits, knowledge-driven breeding by design is becoming a reality. This review introduces knowledge about inflorescence yield-related traits in cereal crops, focusing on rice, maize, and wheat. Next, emerging genome-editing technologies and recent studies that apply this technology to engineer crop yield improvement by targeting inflorescence development are reviewed. These approaches promise to usher in a new era of breeding practice.  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