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   258篇
  免费   21篇
电工技术   1篇
化学工业   98篇
金属工艺   5篇
机械仪表   4篇
建筑科学   10篇
矿业工程   1篇
能源动力   11篇
轻工业   67篇
水利工程   1篇
无线电   15篇
一般工业技术   23篇
冶金工业   8篇
原子能技术   2篇
自动化技术   33篇
  2024年   2篇
  2023年   6篇
  2022年   11篇
  2021年   10篇
  2020年   4篇
  2019年   9篇
  2018年   16篇
  2017年   5篇
  2016年   6篇
  2015年   12篇
  2014年   14篇
  2013年   23篇
  2012年   19篇
  2011年   23篇
  2010年   25篇
  2009年   16篇
  2008年   12篇
  2007年   12篇
  2006年   7篇
  2005年   8篇
  2004年   6篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  1999年   1篇
  1998年   4篇
  1997年   1篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1991年   1篇
  1989年   1篇
  1985年   2篇
  1981年   1篇
  1980年   1篇
  1976年   1篇
  1975年   2篇
排序方式: 共有279条查询结果,搜索用时 15 毫秒
271.
Antiphospholipid antibodies (aPL) comprise a group of autoantibodies that reflect prothrombotic risk in antiphospholipid syndrome (APS) but may also be present in a small proportion of healthy individuals. They are often transiently elevated in infections, including SARS-CoV-2, and may also be associated with vaccine-induced autoimmunity. Therefore, we aimed to investigate the dynamics of aPL in COVID-19 patients and in individuals (healthcare professionals—HCPs) after receiving BNT162b2 vaccine and to compare aPL levels and positivity with those found in APS patients. We measured solid-phase identifiable aPL, including anticardiolipin (aCL), anti-β2 glycoprotein I (anti-β2GPI), and anti-prothrombin/phosphatidylserine (aPS/PT) antibodies in 58 HCPs before and after vaccination (at 3 weeks, 3, 6, and 9 months after the second dose, and 3 weeks after the third booster dose), in 45 COVID-19 patients hospitalized in the ICU, in 89 COVID-19 patients hospitalized in the non-ICU (at admission, at hospital discharge, and at follow-up), and in 52 patients with APS. The most frequently induced aPL in COVID-19 patients (hospitalized in non-ICU) were aCL (50.6% of patients had positive levels at at least one time point), followed by anti-β2GPI (21.3% of patients had positive levels at at least one time point). In 9/89 COVID-19 patients, positive aPL levels persisted for three months. One HCP developed aCL IgG after vaccination but the persistence could not be confirmed, and two HCPs developed persistent anti-β2GPI IgG after vaccination with no increase during a 1-year follow-up period. Solid-phase aPL were detected in 84.6% of APS patients, in 49.4% of COVID-19 patients hospitalized in the non-ICU, in 33.3% of COVID-19 patients hospitalized in the ICU, and in only 17.2% of vaccinated HCPs. aPL levels and multiple positivity were significantly lower in both infected groups and in vaccinated individuals compared with APS patients. In conclusion, BNT162b2 mRNA vaccine may have induced aPL in a few individuals, whereas SARS-CoV-2 infection itself results in a higher percentage of aPL induction, but the levels, persistence, and multiple positivity of aPL do not follow the pattern observed in APS.  相似文献   
272.
Precise genetic diagnosis in RPE65-mediated retinitis pigmentosa (RP) is necessary to establish eligibility for genetic treatment with voretigene neparvovec: a recombinant adeno-associated viral vector providing a functional RPE65 gene. This case report aims to report a novel RP-related point mutation RPE65 c.353G>A, p.(Arg118Lys), a variant of uncertain significance associated with a severe clinical presentation and the striking phenotypic feature of complete macular atrophy. We report the case of a 40-year-old male with inherited retinal dystrophy, all features typical for the RPE65-associated RP, and marked macular atrophy. Genetic testing identified that the patient was a compound heterozygote in trans form with two heterozygous variants: RPE65 c.499G>T, p.(Asp167Tyr) and RPE65 c.353G>A, p.(Arg118Lys). Furthermore, short-wavelength and near-infrared autofluorescence patterns exhibited deficiencies specific to mutations in the visual cycle genes. To the best of our knowledge, RPE65 c.353G>A, p.(Arg118Lys) is the first described point mutation on this locus, among all other reported insertional mutations, currently classified as likely benign and of uncertain significance. We concluded that this variant contributed to the pathological phenotype, demonstrating its significance clearly to be reclassified as likely pathogenic. This being the case, patients with this specific variant in homozygous or compound heterozygous form would be likely candidates for genetic treatment with voretigene neparvovec.  相似文献   
273.
The corrosion behavior of cold isostatically pressed (CIP) high purity alumina ceramics in aqueous HCl and H2SO4 solutions with various concentrations has been studied simultaneously at room temperature (25 °C). Corrosion tests were also performed with 0.65 mol/l HCl and 0.37 mol/l H2SO4 solutions at 40, 55 and 70 °C for 48 h. Chemical stability was monitored by determining the amount of Al3+, Mg2+, Ca2+, Na+ Si4+ and Fe3+ ions eluted in different concentrations of HCl and H2SO4 solutions by means of atomic absorption spectrometry (AAS). By increasing the concentration from 0.37 to 6.5 mol/l, it was notified that the corrosion susceptibility in HCl and H2SO4 solutions for the CIP alumina specimens at room temperature decreases.  相似文献   
274.
Pumpkin seed oil has become a recognized source of phenolic compounds. The main aim of this paper was to evaluate the concentration of phenolic compounds and their extraction from pumpkin seed oil. The total phenolics content (TPC) measured in the pumpkin seed oil samples ranged from 24.71 to 50.93 mg GAE/kg of oil. The individual phenolics were tyrosol, vanillic acid, vanillin, luteolin and sinapic acid. Hexane and acetone were the best solvents for the washing step, and methanol for the elution of the phenolics in the solid‐phase extraction (diol‐SPE), whereas bleaching caused a significant increase in the TPC obtained (24.5–30.7%). Additionally, some other oil characteristics were evaluated. The mean oxidative stability of the oils (OSI) was around 4 h, with 5.43 h for the most stable oil. The maximum antioxidant capacity measured by the reduction of the DPPH radical was 62%, which was comparable to 0.16 mM Trolox equivalent. The color of the oil was expressed by L*a*b* coefficients and its hue and saturation. Whereas all samples had similar lightness, their rates of green, red, yellow and blue color were different. Moreover, TPC correlated negatively with lightness, b* and saturation (–0.49, –0.48, and –0.43), and positively with a* and hue (0.58 and 0.52).  相似文献   
275.
Novel pH‐sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were prepared in two steps. Chitosan was first ionically crosslinked with itaconic acid, after which a free radical polymerization and crosslinking of the chitosan/itaconic acid network was performed by adding methacrylic acid and a crosslinker in order to achieve better mechanical properties and tunable swelling. The samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, X‐ray diffraction, dynamic mechanical analysis and the swelling ratios of the hydrogels at various pH values (2.0–8.0). The hydrogel composition is found to have a great impact on the hydrogel structure, mechanical and thermal properties, morphology and swelling kinetics. The highly porous morphology of the gels is probably connected with the bulky chitosan/itaconic acid network which reduces the degree of crosslinking in the second step of the synthesis due to steric hindrances. The gels demonstrate substantial change in buffer absorbency with change of pH, low for acid buffers and the higher for pH values above 6 where the swelling is considerably slow, thus suggesting their strong candidature for use as oral drug‐delivery systems in the lower parts of the gastrointestinal tract and for drugs that require longer release times. Copyright © 2010 Society of Chemical Industry  相似文献   
276.
Sequential centrifugal partition chromatography (sCPC) is a novel cyclic liquid–liquid chromatographic process. Each cycle comprises two steps, which differ by the liquid phase used as a mobile phase (upper or lower phase) and its flow direction. The feed is continuously separated into two product streams, which are collected alternately. The process includes six (four flow rates and two‐step durations) interconnected operating parameters. In this work, by imposing a complete separation of a binary feed mixture and using the assumption of instantaneous solutes partition equilibrium, a set of constraints on the sCPC unit operating parameters is derived. Using these constraints, a region of complete separation, composed of a set of combinations of the two‐step times, can be defined for a preselected feed and mobile phase flow rates. The approach is validated by simulation of a binary mixture separation in a sCPC using the cell model. © 2012 American Institute of Chemical Engineers AIChE J, 59: 241–249, 2013  相似文献   
277.
New semi-interpenetrating networks (semi-IPNHs) (P(HEMA/IA)/PVP) were prepared by free radical crosslinking copolymerization of 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA, 5 mol%), in the presence of poly(vinyl pyrrolidone) (PVP, 2, 5, and 10 mol%), as an interpenetrating agent. The structure of the semi-IPNHs was confirmed by Fourier transform infrared spectroscopy, and morphology study was performed by scanning electron microscopy, which revealed the characteristic porous morphology. The results obtained by dynamic mechanical analysis showed the improvement of mechanical properties with increasing PVP content in semi-IPNs. The maximum swelling was observed for all studied systems at a slightly acidic media (around pH 6), so it can be said that the content of PVP has no influence on the swelling behavior, in the PVP range investigated. Along with the pH sensitivity, which was expected due to the presence of IA, semi-IPNHs showed temperature-sensitive swelling properties, with the lower critical solution temperature value around 41 °C, which is in the physiologically interesting interval. The antimicrobial activity of the samples was tested using E. coli, S. aureus, and C. albicans pathogens. It was noticed that the antimicrobial potential depends on type of microbes, time of exposure, and PVP content in the samples. Due to their good antimicrobial and mechanical properties these stimuli-sensitive semi-IPNHs have potential to be used as biomaterials for the applications in medicine and pharmacy.  相似文献   
278.
To provide new insight into the field of urea-formaldehyde (UF) adhesives science, in this work, for the first time, UF resin was modified with hydrochar of spent mushroom substrate (HCUF) and chitosan (CHUF) to investigate the effect of these bio-fillers on the hydrolytic and thermal stability of in situ prepared UF resins. The characterization of the modified UF biocomposites was performed using X-ray diffraction analysis (XRD), Fourier transforms infrared spectroscopy (FTIR), non-isothermal thermogravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA). Scanning electron micrographs (SEM) of the CHUF and HCUF biocomposites show a spherical structure that differs from each other because the surface of the CHUF biocomposite has pronounced pores that form a network structure. With its hydroxyl and amino groups, chitosan bonding to UF resin through hydrogen bonds, which is confirmed by FTIR analysis. The content of free FA in CHUF biocomposite is 0.06%, while that of HCUF is higher and amounts to 0.48%. The content of released FA in both modified UF biocomposites was similar (2.5% and 2.8% for CHUF and HCUF, respectively). The hydrolytic stability of CHUF is slightly higher compared to the HCUF biocomposite. Thermal analysis shows that the CHUF is thermally more stable because it starts to decompose at a slightly higher temperature than the HCUF biocomposite.  相似文献   
279.
Information Systems and e-Business Management - The subject of this article is to analyze the users’ attitude towards new, 5G-enabled smart living services before their commercial launch. The...  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