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   136篇
  免费   37篇
  国内免费   5篇
  2024年   2篇
  2023年   10篇
  2022年   7篇
  2021年   7篇
  2020年   11篇
  2019年   10篇
  2018年   17篇
  2017年   11篇
  2016年   13篇
  2015年   8篇
  2014年   10篇
  2013年   16篇
  2012年   7篇
  2011年   6篇
  2010年   3篇
  2009年   12篇
  2008年   8篇
  2007年   4篇
  2006年   4篇
  2005年   3篇
  2004年   1篇
  2003年   1篇
  2002年   2篇
  2001年   1篇
  1999年   1篇
  1998年   2篇
  1992年   1篇
排序方式: 共有178条查询结果,搜索用时 78 毫秒
91.
Forgery and low-quality products pose a danger to society. Therefore, there are increasing demands for the production of easy-to-recognize and difficult-to-copy anticounterfeiting materials. Products with smart photochromic and fluorescence properties can change colour and emission spectra responding to a light source. In this context, we devised a straightforward preparation of a luminescent polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) nanocomposite to function as a transparent labelling film. The lanthanide-doped aluminate (LdA) was prepared in the nanoparticle form to indicate diameters of 35–115 nm. Different ratios of the LdA were physically dispersed in the PVA/CMC nanocomposite label film to provide photochromic, ultraviolet protection, antimicrobial activity, and hydrophobic properties. Fluorescence peaks were detected at 365 and 519 nm to indicate a colour change to green. As a result of increasing the phosphor ratio, improved superhydrophobic activity was achieved as the contact angle was increased from 126.1° to 146.0° without affecting the film's original physical and mechanical properties. Both ultraviolet (UV) light protection and antibacterial activity were also investigated. The films showed a quick and reversible photochromic response without fatigue. The current strategy reported the development of a photochromic smart label that is transparent, cost effective, and flexible. As a result, numerous anticounterfeiting products can benefit from the current label for a better market. LdA-loaded PVA/CMC films demonstrated antibacterial activity between poor, good, very good, and outstanding as the percentage of LdA in the film matrix increased. The current film can be applied as a transparent photochromic security barcode for anticounterfeiting applications and smart packaging.  相似文献   
92.
Affinity‐triggered assemblies rely on affinity interactions as the driving force to assemble physically crosslinked networks. WW domains are small hydrophobic proteins binding to proline‐rich peptides that are typically produced in the insoluble form. Previous works attempted the biological production of the full WW domain in tandem to generate multivalent components for affinity‐triggered hydrogels. In this work, an alternative approach is followed by engineering a 13‐mer minimal version of the WW domain that retains the ability to bind to target proline‐rich peptides. Both ligand and target peptides are produced chemically and conjugated to multivalent polyethylene glycol, yielding two components. Upon mixing together, they form soft biocompatible affinity‐triggered assemblies, stable in stem cell culture media, and display mechanical properties in the same order of magnitude as for those hydrogels formed with the full WW protein in tandem.  相似文献   
93.
Osteoarthritis (OA), due to cartilage degeneration, is one of the leading causes of disability worldwide. Currently, there are not efficacious therapies to reverse cartilage degeneration. In this study we evaluated the potential of hybrid hydrogels, composed of a biodegradable and thermosensitive triblock copolymer cross-linked via Michael addition to thiolated hyaluronic acid, in contrasting inflammatory processes underlying OA. Hydrogels composed of different w/w % concentrations of hyaluronan were investigated for their degradation behavior and capacity to release the polysaccharide in a sustained fashion. It was found that hyaluronic acid was controllably released during network degradation with a zero-order release kinetics, and the release rate depended on cross-link density and degradation kinetics of the hydrogels. When locally administered in vivo in an OA mouse model, the hydrogels demonstrated the ability to restore, to some extent, bone remineralization, proteoglycan production, levels of Sox-9 and Runx-2. Furthermore, the downregulation of proinflammatory mediators, such as TNF-α, NFkB, and RANKL and proinflammatory cytokines was observed. In summary, the investigated hydrogel technology represents an ideal candidate for the potential encapsulation and release of drugs relevant in the field of OA. In this context, the hydrogel matrix could act in synergy with the drug, in reversing phenomena of inflammation, cartilage disruption, and bone demineralization associated with OA.  相似文献   
94.
Brain stiffness changes in response to injury or disease. As a secondary consequence, glutamate is released from neurons and astroglia. Two types of glutamate receptors, N‐methyl‐d ‐aspartate (NMDA) and α‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors, sense mechanotransduction, leading to downstream signaling in neurons. Recently, our group reported that these two receptors affect dendrite morphology in hippocampal neurons grown on compliant substrates. Blocking receptor activity has distinct effects on dendrites, depending on whether neurons are grown on soft or stiff gels. In the current study, we examine whether exposure to glutamate itself alters stiffness‐mediated changes to dendrites in hippocampal neurons. We find that glutamate augments changes seen when neurons are grown on soft gels of 300 or 600 Pa, but in contrast, glutamate attenuates changes seen when neurons are grown on stiff gels of 3,000 Pa. These results suggest that there is interplay between mechanosensing and glutamate receptor activation in determining dendrite morphology in neurons. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:1128–1132, 2015  相似文献   
95.
Methods for culturing mammalian cells ex vivo are increasingly needed to study cell and tissue physiology and to grow replacement tissue for regenerative medicine. Two‐dimensional culture has been the paradigm for typical in vitro cell culture; however, it has been demonstrated that cells behave more natively when cultured in three‐dimensional environments. Permissive, synthetic hydrogels and promoting, natural hydrogels have become popular as three‐dimensional cell culture platforms; yet, both of these systems possess limitations. In this perspective, we discuss the use of both synthetic and natural hydrogels as scaffolds for three‐dimensional cell culture as well as synthetic hydrogels that incorporate sophisticated biochemical and mechanical cues as mimics of the native extracellular matrix. Ultimately, advances in synthetic–biologic hydrogel hybrids are needed to provide robust platforms for investigating cell physiology and fabricating tissue outside of the organism. Biotechnol. Bioeng. 2009;103: 655–663. © 2009 Wiley Periodicals, Inc.  相似文献   
96.
An electrochemical glucose sensor has been integrated, together with a pH sensor, on a flexible polyimide substrate for in vivo applications. The glucose sensor is based on the measurement of H2O2 produced by the membrane-entrapped enzyme glucose oxidase (GOD). To minimize electrochemical interference, an electrode configuration was designed to perform differential measurements. The solid-state pH sensor employs a PVC-based neutral carrier membrane. The enzymes GOD and catalase were immobilized into two layers of photolithographically patterned hydrogels. The intended use of this device is the short-term monitoring of glucose and pH in intensive care units and operating theatres, especially for neurosurgical applications. The developed immobilization technique can also be used to create integrated multi-sensor chips for clinical analysers. The glucose and pH sensor exhibited excellent performance during tests in buffer solutions, serum and whole blood.  相似文献   
97.
Sap salinity effects on xylem conductivity in two mangrove species   总被引:5,自引:0,他引:5  
Xylem sap salinity and conductivity were examined in two mangrove ecosystem tree species . For Avicennia germinans , extracted xylem sap osmotic potentials ranged from −0.24 to −1.36 MPa versus −0.14 to −0.56 MPa for Conocarpus erectus. Xylem sap of Conocarpus did not vary in osmotic potential between sites nor between predawn and midday. In Avicennia , values were more negative at midday than predawn, and also more negative at hypersaline than hyposaline sites. After removing embolisms, specific conductivity ( K s) was measured as a function of salinity of the artificial xylem sap perfusion. For both species the lowest K s values, about 70% of the maximum K s, were obtained when stems were perfused with deionized water (0 m m ; 0.0 MPa) or with a 557-m m saline solution (−2.4 MPa). Higher K s values were obtained in the range from −0.3 to −1.2 MPa, with a peak at −0.82 ± 0.08 MPa for Avicennia and −0.75 ± 0.08 MPa for Conocarpus . The variations in K s values with minima both at very low and very high salt concentrations were consistent with published results for swelling and shrinking of synthetic hydrogels, suggesting native hydrogels in pit membranes of vessels could help regulate conductivity.  相似文献   
98.
Photopolymerizable hydrogels offer great potential in cartilage tissue engineering due to their ability to conform to irregular defect shapes and be applied in a potentially minimally invasive manner. An important process requirement in the use of photopolymerizable hydrogels is the ability of the suspended cells to withstand low intensity ultraviolet light (UV) exposure (4–5 mW/cm2) and photoinitiator concentrations. For cartilage integration with underlying subchondral bone tissue, robust localized osteoblast activity is necessary. Yet, while it is known that osteoblasts do not respond well to UV light, limited work has been conducted to improve their survivability. In this study, we evaluated the cellular cytotoxicity of five different human cell sources at different UV exposure times, with and without a commercially used photoinitiator. We were able to confirm that human osteoblasts were the least tolerant to varying UV exposure times in comparison to bone marrow stem cell, periodontal ligament cell, smooth muscle and endothelial cell lineages. Moreover osteoblasts cultured at 39 °C did not deteriorate in terms of alkaline phosphatase expression or calcium deposition within the extracellular matrix (ECM), but did reduce cell proliferation. We believe however that the lower proliferation diminished osteoblast sensitivity to UV and the photoinitiator. In fact, the relative survivability of osteoblasts was found to be augmented by the combination of a biochemical factor and an elevated incubation temperature; specifically, the use of 50 mg/l of the anti-oxidant, ascorbic acid significantly (P < 0.05) increased the survivability of osteoblasts when cultured at 39 °C. We conclude that ascorbic acid at an incubation temperature of 39 °C can be included in in vitro protocols used to assess cartilage integration with bone ECM. Such inclusion will enhance conditions of the engineered tissue model system in recapitulating in vivo osteoblast activity.  相似文献   
99.
Transforming growth factor (TGF)-β1 is a multifunctional cytokine that plays important roles in health and disease. Previous studies have revealed that TGFβ1 activation, signaling, and downstream cell responses including epithelial-mesenchymal transition (EMT) and apoptosis are regulated by the elasticity or stiffness of the extracellular matrix. However, tissues within the body are not purely elastic, rather they are viscoelastic. How matrix viscoelasticity impacts cell fate decisions downstream of TGFβ1 remains unknown. Here, we synthesized polyacrylamide hydrogels that mimic the viscoelastic properties of breast tumor tissue. We found that increasing matrix viscous dissipation reduces TGFβ1-induced cell spreading, F-actin stress fiber formation, and EMT-associated gene expression changes, and promotes TGFβ1-induced apoptosis in mammary epithelial cells. Furthermore, TGFβ1-induced expression of integrin linked kinase (ILK) and colocalization of ILK with vinculin at cell adhesions is attenuated in mammary epithelial cells cultured on viscoelastic substrata in comparison to cells cultured on nearly elastic substrata. Overexpression of ILK promotes TGFβ1-induced EMT and reduces apoptosis in cells cultured on viscoelastic substrata, suggesting that ILK plays an important role in regulating cell fate downstream of TGFβ1 in response to matrix viscoelasticity.  相似文献   
100.
Advanced thermoelectric technologies can drastically improve energy efficiencies of industrial infrastructures, solar cells, automobiles, aircrafts, etc. When a thermoelectric device is used as a solid‐state heat pump and/or as a power generator, its efficiency depends pivotally on three fundamental transport properties of materials, namely, the thermal conductivity, electrical conductivity, and thermopower. The development of advanced thermoelectric materials is very challenging because these transport properties are interrelated. This paper reviews the physical mechanisms that have led to recent material advances. Progresses in both inorganic and organic materials are summarized. While the majority of the contemporary effort has been focused on lowering the lattice thermal conductivity, the latest development in nanocomposites suggests that properly engineered interfaces are crucial for realizing the energy filtering effect and improving the power factor. We expect that the nanocomposite approach could be the focus of future materials breakthroughs.  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