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   1924篇
  免费   110篇
  国内免费   12篇
电工技术   29篇
综合类   5篇
化学工业   493篇
金属工艺   26篇
机械仪表   75篇
建筑科学   49篇
矿业工程   2篇
能源动力   170篇
轻工业   184篇
水利工程   13篇
石油天然气   31篇
无线电   186篇
一般工业技术   397篇
冶金工业   48篇
原子能技术   17篇
自动化技术   321篇
  2024年   10篇
  2023年   73篇
  2022年   141篇
  2021年   155篇
  2020年   110篇
  2019年   116篇
  2018年   129篇
  2017年   99篇
  2016年   133篇
  2015年   74篇
  2014年   129篇
  2013年   174篇
  2012年   108篇
  2011年   102篇
  2010年   83篇
  2009年   75篇
  2008年   51篇
  2007年   42篇
  2006年   41篇
  2005年   23篇
  2004年   20篇
  2003年   15篇
  2002年   16篇
  2001年   15篇
  2000年   7篇
  1999年   12篇
  1998年   18篇
  1997年   6篇
  1996年   13篇
  1995年   5篇
  1994年   8篇
  1993年   6篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   4篇
  1985年   3篇
  1984年   3篇
  1983年   2篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1976年   1篇
排序方式: 共有2046条查询结果,搜索用时 15 毫秒
51.
52.
Kappa‐casein (κ‐CN) is the subtype of casein protein, an important constituent of bovine milk protein. The current study was undertaken to investigate the genetic polymorphism in κ‐CN gene of Nili‐ravi buffalo, Achai and Sahiwal cattle of Pakistan using polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) technique. The Nili‐ravi buffalo was found to be monomorphic (genotype BB only) for κ‐CN gene. Achai cattle were polymorphic for κ‐CN (having three genotypes AA, AB and BB) with a frequency of 0.70, 0.18 and 0.12, respectively, while in Sahiwal cattle, both the genotypes AA and AB were found with genotypic frequencies of 0.92 and 0.08, respectively. The presence of genotype BB in Achai cattle is surprising as it is absent in most of the cattle breeds worldwide.  相似文献   
53.
The objective of the present study was to analyze and compare the phenolic compounds and their antioxidant capacities of new lines of Dacus carota. The selected cultivars showed high variation in the contents of total phenolics (30.26–65.39 mg/100 g FW) and total ascorbic acid (41.12–58.36 mg/100 g FW). Analysis on RP-HPLC revealed that hydroxycinnamic acids and its derivatives were major phenolic compounds present in D. carota extracts, whereas 5-caffeolquinic acid was a major hydroxycinnamic acid (ranged from 30.26 to 65.39 mg/100 g FW). DCP cultivar showed high total antioxidant capacity (77.69 mg/100 g), 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity (52.36 mg/100 g), superoxide radical scavenging capacity (53.69 mg/100 g), and hydroxyl radical scavenging capacity (51.91 mg/100 g). A linear relationship was found between total phenolic acid contents and antioxidant capacity. Both phenolic compounds and antioxidant capacities varied significantly (ρ < 0.05) among cultivars. DCP cultivar was found to be a rich source of phenolics and ascorbic acid with high antioxidant activity.  相似文献   
54.
55.
Objective: To describe the characteristics of the Chinese subjects who utilised the first telephone smoking cessation service in Hong Kong, and to evaluate its effectiveness.

Methods: The Quitline provided Hong Kong residents with free telephone smoking cessation services which was publicised through a press conference, media reports, pamphlets, and posters at public and private hospitals and clinics. Callers who completed an initial interview from 13 December 2000 to 31 May 2002 were included. Smokers were interviewed using a structured record sheet and provided with stage matched counselling. A follow up interview was carried out after six months. Analysis was conducted by intention-to-treat.

Results: Of the 1120 callers who completed initial assessments, 1047 were current smokers and 872 consented to follow ups. Compared to the general smoking population, the Quitline attracted more of those who were female, younger, single, unemployed, higher educated, smoking more than 20 cigarettes per day, and those with quitting experience. At six months, 12% (95% confidence interval 10% to 15%) of the participants reported that they had not smoked a cigarette for the past seven days. A stepwise logistic regression model showed that the use of nicotine replacement therapy at the present attempt to quit, having made one or more serious attempts to quit in the past, perceiving less difficulties in quitting, and smoking the first cigarette at age 15 years or above were significant predictors of quitting.

Conclusion: This first Quitline in Asia appears to be acceptable to Chinese smokers, with quit rate comparable to those of better funded Quitlines in the West. A low cost Quitline is a promising model for smoking cessation services in the East.

  相似文献   
56.
The objectives of this study were to define the phenolic and fatty acid profiles, anticholinesterase, antioxidant, antimicrobial activities, and total phenolic-flavonoid contents of Lycopsis orientalis and Tragopogon latifolius var. angustifolius which have been used as food source and food supplement in Anatolia and have never been examined before. Rosmarinic and quinic acids (21.11 and 11.46 mg g–1 extract, respectively) were found to be the most abundant constituents in L. orientalis and T. latifolius var. angustifolius among the studied 27 compounds by liquid chromatography tandem mass spectrometry. In the fatty acid compositions of L. orientalis and T. latifolius var. angustifolius that were determined by gas chromatography mass spectrometry, oleic (29.1%) and palmitic (28.7%) acids were identified as the major components, respectively. The high antioxidant activity of the methanol extract of L. orientalis shows parallelism to its rosmarinic acid content. Besides, this extract showed medium anticholinesterase activity. The results of the present study proves that the L. orientalis might also be used as a food source due to its high phenolic acid content and strong antioxidant property.  相似文献   
57.
The objectives of this study were to examine varying extraction conditions of Thymus vulgaris L. as related to phenolic content and profiles of the extracts and their antioxidant, antihypertensive and antidiabetic properties. Phenolics were extracted under various conditions pertaining to free and bound phenolics, solvent type and combination of extraction time and temperature, and these extracts were evaluated in terms of their antioxidant activities and inhibitory activities of angiotensin‐converting enzyme (ACE), α‐glucosidase and α‐amylase. The acetone–water solvent mixture (1:1; v/v) produced the extract with the greatest phenolic content, antioxidant activity and inhibitory activities of ACE and α‐glucosidase. The optimal extraction temperature for maximum phenolic content and antioxidant activity associated with methanol extraction was 60 °C, whereas a lower temperature at 40 °C was required to maximise inhibitory activities for ACE, α‐glucosidase and α‐amylase. An inverse relationship was seen between antioxidant and glucosidase inhibitory activities vs. the ACE and α‐amylase inhibitory activities, which suggests the need for extractions to be directed to specific bioactivities of thyme extracts. Generally, the results indicate major differences in phenolic profiles among the tested extraction conditions with thymol as the predominant phenolic seen in most extractions, while gallic acid, rosmarinic acid or diosmin also predominated in other extracts. Extracts with the same predominant phenolic compound and similar phenolic content showed major disparities in their ACE, glucosidase and α‐amylase inhibitory activities, indicating that the major phenolic profiles of thyme extracts may not be necessarily related to the degree of inhibition of ACE, glucosidase and α‐amylase enzymes.  相似文献   
58.
High power ultrasonic energy at 20%, 40% and 60% amplitude was applied on whey protein suspension at concentrations of 100, 150 and 200 g kg?1 for 5, 15 and 25 min to improve its foaming quality. Ultrasound‐treated whey protein suspension at 200 g kg?1 showed improvement in terms of increased foaming capacity by 18%, foam stability by 35%, consistency index by 18%, storage modulus by 17%, loss modulus by 26% and viscosity by 21% compared with untreated whey protein. For maximally ultrasound‐treated samples of 60% amplitude treated for 25 min, the improved whey protein foams also had a 46% increase in the number of more evenly distributed fine bubbles which had a size smaller than 0.0025 mm3 as imaged using X‐ray microtomography.  相似文献   
59.
This study aims to determine phytochemicals and antibacterial activity of ethanolic extract and essential oil of Persicaria hydropiper, and their potential as antibacterial agents in polylactic acid (PLA) film. The yield of ethanolic extract and essential oil were 11.02 and 0.70%, respectively. Chlorogenic acid, ferulic acid, rutin, myricetin and quercetin were detected as major components in the P. hydropiper ethanolic extract, while dodecanal, caryophyllene, caryophyllene oxide, decanal, α‐caryophyllene, citronellol, heptadecanal, linalool and phytol were detected in the P. hydropiper essential oil. Based on the disc diffusion assay, both ethanolic extract and essential oil of P. hydropiper possessed antibacterial activity against bacteria Staphylococcus aureus only at different concentrations, with minimum inhibitory concentration values: 0.625 and 5 mg/ml, respectively; and minimum bactericidal concentration values: 5 and 40 mg/ml, respectively. However, they found to show antibacterial activity against three bacteria S. aureus, Escherichia coli and Salmonella Typhimurium at different concentrations and time using time‐kill kinetics assay. Incorporation of ethanolic extract and essential oil in PLA film also exhibited an antibacterial effect against S. aureus. Our findings confirmed the potential use of both P. hydropiper ethanolic extract and essential oil as antibacterial agents in biodegradable PLA film.  相似文献   
60.
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