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   3357篇
  免费   417篇
  国内免费   74篇
电工技术   14篇
综合类   50篇
化学工业   1277篇
金属工艺   51篇
机械仪表   51篇
建筑科学   62篇
矿业工程   9篇
能源动力   27篇
轻工业   2036篇
水利工程   22篇
石油天然气   8篇
武器工业   1篇
无线电   54篇
一般工业技术   89篇
冶金工业   23篇
原子能技术   30篇
自动化技术   44篇
  2025年   56篇
  2024年   161篇
  2023年   167篇
  2022年   466篇
  2021年   476篇
  2020年   233篇
  2019年   193篇
  2018年   152篇
  2017年   146篇
  2016年   142篇
  2015年   150篇
  2014年   151篇
  2013年   182篇
  2012年   127篇
  2011年   99篇
  2010年   97篇
  2009年   95篇
  2008年   85篇
  2007年   93篇
  2006年   82篇
  2005年   66篇
  2004年   61篇
  2003年   45篇
  2002年   56篇
  2001年   30篇
  2000年   25篇
  1999年   25篇
  1998年   18篇
  1997年   15篇
  1996年   17篇
  1995年   16篇
  1994年   12篇
  1993年   9篇
  1992年   11篇
  1991年   6篇
  1990年   6篇
  1989年   5篇
  1988年   8篇
  1987年   10篇
  1986年   8篇
  1985年   12篇
  1984年   8篇
  1983年   3篇
  1981年   3篇
  1980年   4篇
  1978年   5篇
  1977年   2篇
  1975年   4篇
  1973年   1篇
  1951年   1篇
排序方式: 共有3848条查询结果,搜索用时 0 毫秒
41.
The objective was to determine the effects of linoleic acid and different isomers of conjugated linoleic acid (CLA) at different concentrations on hepatic lipid and glucose metabolism in the bovine. Monolayer cultures of hepatocytes obtained from 7- to 10-d-old Holstein bull calves were exposed to treatments from 16 to 64 h after plating. The treatments included 1.0 mM palmitic acid plus either 0.1 or 1.0 mM of cis-9, cis-12 linoleic acid, cis-9, trans-11 CLA, or trans-10, cis-12 CLA. Metabolism of palmitic acid to cellular triacylglycerol (TAG) was decreased when media contained cis-9, trans-11 compared with trans-10, cis-12 CLA. Total cellular TAG content was increased for the CLA isomers compared to cis-9, cis-12 linoleic acid. Both CLA isomers increased palmitic acid incorporation into phospholipids, cholesterol, and media triacylglycerol compared with cis-9, cis-12 linoleic acid at a concentration of 1.0 mM. Increasing the concentration of treatment fatty acids from 0.1 to 1.0 mM decreased oxidation of palmitic acid to acid-soluble products, but no effects of fatty acids were observed. There was no treatment effect on rates of gluconeogenesis from propionic acid. Overall, CLA isomers elicited changes in palmitic acid metabolism to cellular and media triacylglycerol, and cellular phospholipids and cholesterol, but had little or no effect on other measured pathways of lipid metabolism or gluconeogenesis in bovine hepatocytes.  相似文献   
42.
L-肉碱对肉鸡腹脂沉积的影响及作用机理探讨   总被引:2,自引:0,他引:2  
选用 4 80羽 1日龄Avain肉鸡 ,随机分成 4个处理组 ,分别饲喂添加 0、2 5、5 0、75 (mg/kg)L -肉碱的试验饲粮 4 9d ,研究L -肉碱对肉鸡腹脂沉积的影响及其作用机理。结果表明 :不同水平L -肉碱对肝重比率和肝脂含量均无明显影响 (P >0 .0 5 ) ,但添加 5 0mg/kg和 75mg/kgL -肉碱均显著地降低了肉鸡腹脂重比率(P <0 .0 5 )。添加 5 0mg/kg和 75mg/kgL -肉碱使腹脂中激素敏感脂酶的总活力增强 (P <0 .0 3) ,苹果酸脱氢酶的总活力降低 (P <0 .0 5 ) ;使胸肌中总肉碱含量 (P <0 .0 5 )、酸不溶肉碱含量 (P <0 .0 1)及其与游离肉碱含量的比值 (P <0 .0 3)增高 ;使血清中总肉碱 (P <0 .0 1)、游离脂肪酸 (P <0 .0 1)和肌酸酐浓度 (P <0 .0 3)提高 ,甘油三酯浓度降低 (P <0 .0 5 )。上述结果提示 :L -肉碱通过改变鸡体内脂肪代谢相关酶的活力 ,促进脂肪酸的氧化利用 ,而产生降低腹脂沉积的效果  相似文献   
43.
刘芳 《酿酒科技》2004,(2):28-30
对乳酸菌在葡萄酒苹果酸-乳酸发酵过程中的有关物质代谢,包括苹果酸代谢、柠檬酸与糖的共代谢、含N化合物的代谢、细菌素的产生等进行了概述。  相似文献   
44.
Abstract

Background: Multiple micronutrient supplementation has been suggested to have a role on health outcomes in patients with heart failure (HF), but the evidence is inconclusive. Objective: To elucidate the role of multiple micronutrient supplementation in heart failure we performed a comprehensive review of the literature. Methods and results: The search in databases included PUBMED (until June 2018) to detect randomized controlled trials (RCTs) and meta-analyzes that investigated the impact of micronutrient supplementation in HF. Results: With more than 2357 titles and abstracts reviewed, we included only the studies suitable for the final review. Whether alone or in combination, micronutrients have been found to improve the health outcomes of patients with HF by improving symptoms, work capacity and left ventricular ejection fraction (LVEF), thus increasing the quality of life in these patients. Conclusion: Future studies are needed to document the effects of multiple micronutrient associations in order to include them in nutritional guidelines to increase survival and to improve quality of life in patients with heart failure.  相似文献   
45.
共轭亚油酸的功能性质及安全性评价   总被引:1,自引:0,他引:1  
介绍了共轭亚油酸及其对健康的益处,综述了共轭亚油酸对动物和人体机体组成影响的研究进展,并讨论了共轭亚油酸添加物的安全性问题。研究认为,共轭亚油酸对健康和机体组成等均具有较好的作用,但人体服用共轭亚油酸的安全性问题有待进一步的研究。  相似文献   
46.
Effects of fumigation with 15 μl l−1 of nitric oxide gas (NO), intermittent warming (IW) and a combination of NO and IW (NO + IW) in preventing chilling injury of ‘Feicheng’ peaches were investigated. Chilling injury index, firmness, ethylene production, cell wall fractions and cell wall metabolism-associated enzymes were evaluated. These results indicated that three treatments significantly prevented the mealiness of ‘Feicheng’ peaches. Further, NO fumigation could counteract the side effect of IW. Trans-1,2-diaminocyclohexane – N,N,N′,N′-tetraacetic acid (CDTA)-soluble fractions in control peaches significantly increased, but maintained lower contents in the three treatments. IW obviously increased the activity of polygalacturonase (PG) and endo-1,4-glucanase. NO fumigation preserved lower PG activity in early 20 days of storage, and endo-PG activity was significantly higher than that of control peaches during the later storage time. Exo-PG and endo-PG activity of the fruits treated with NO + IW was midway between those single treatments with NO and IW.  相似文献   
47.
微生物中的碳水化合物活性酶(carbohydrate active enzymes,CAZymes)具有降解植物组织的作用,相对于真菌,目前对于乳杆菌的CAZymes研究还比较少.该研究从广西酸菜中筛选获得了3株产CAZymes的乳杆菌,并通过二代测序技术比较其编码基因.16S rRNA测序结果表明3株乳杆菌分别是La...  相似文献   
48.
探讨棕榈油酸(POA)对高脂血症小鼠的影响。将25只小鼠随机分成空白对照组、高脂血症模型组、棕榈油酸高、中、低剂量组5个小组,每组5只。采用高脂饲料建立小鼠高脂血症模型,连续给药30 d后,测体重;取血测定各剂量组高脂血症小鼠血清中总胆固醇(TC)、三酰甘油(TG)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)含量。结果表明,棕榈油酸能够有效抑制高脂血症小鼠体重的增长,降低血清中TC、TG、LDL-C水平,增加HDL-C水平。灌胃适量棕榈油酸可以达到控制体重增长,降低高脂血症的目的。  相似文献   
49.
选用健康的1日龄的樱桃谷鸭128只,在基础日粮预饲一周后,分别饲喂在基础日粮中添加不同水平葛根素的日粮,于21日龄屠宰对血清及骨骼里的钙、磷及相关指标进行检测.结果表明:低水平的葛根素(5 mg/kg)对骨的形成有利,可以有效阻止骨的吸收,促进骨的形成;高水平的葛根素对骨的形成不利,其主要作用机理是雌激素样作用.  相似文献   
50.
Eight multiparous Holstein cows (676 ± 57 kg of body weight; 121 ± 17 d-in-milk) were used in a replicated 4 × 4 Latin square design to determine the effects of 4 sources of carbohydrate on milk yield and composition, ruminal fermentation, and microbial N flow to the duodenum. Four cows in one of the Latin squares were fitted with permanent ruminal cannulae. Diets contained (DM basis) 50% forage in combinations of alfalfa hay and barley silage, and 50% concentrate. The concentrate portion of the diets contained barley, corn, wheat, or oats grain as the primary source of carbohydrate. Intake of DM ranged from 24.0 to 26.2 kg/d, and it tended to be lower in cows fed the wheat-based diet compared with those fed the barley-based diet; consequently, milk yield tended to be lower in cows fed the wheat-based diet compared with those fed the barley-based diet. Cows fed the barley- or wheat-based diets had a lower milk fat content compared with those fed the corn-based diet. Ruminal fermentation characteristics were largely unaffected by the source of dietary carbohydrate, with similar ruminal pH and volatile fatty acid and ammonia concentrations for the first 6 h after the morning feeding. Dietary treatment did not affect total tract apparent digestibility of DM, organic matter, and neutral detergent fiber; however, total tract apparent digestibility of starch in cows fed the oats-based diet was higher compared with those fed the corn-and wheat-based diets. Nitrogen that was used for productive purposes (i.e., N secreted in milk + N apparently retained by the cow) tended to be lower in cows fed the wheat-based diet compared with cows fed the barley-, corn-, or oats-based diets. Urinary purine derivative (PD) excretion was similar in cows fed the barley-, corn-, and wheat-based diets; however, purine derivative excretion was higher in cows fed the barley-based diet compared with those fed the oats-based diet. Consequently, estimated microbial N flow to the duodenum was 49 g/d higher in cows fed the barley-based diet compared with those fed the oats-based diet. Improved production performance with corn and barley diets appeared to be due to greater nutrient absorption than in cows fed oats and wheat diets, rather than improved nutrient utilization efficiency.  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