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   292篇
  免费   45篇
  国内免费   15篇
  2024年   2篇
  2023年   1篇
  2022年   6篇
  2021年   9篇
  2020年   21篇
  2019年   17篇
  2018年   22篇
  2017年   21篇
  2016年   18篇
  2015年   13篇
  2014年   10篇
  2013年   36篇
  2012年   16篇
  2011年   14篇
  2010年   10篇
  2009年   14篇
  2008年   17篇
  2007年   17篇
  2006年   17篇
  2005年   7篇
  2004年   13篇
  2003年   6篇
  2002年   4篇
  2001年   4篇
  2000年   4篇
  1999年   4篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1995年   2篇
  1994年   3篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1987年   1篇
  1986年   3篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1980年   2篇
排序方式: 共有352条查询结果,搜索用时 31 毫秒
71.
The bottle gourd (Lagenaria siceraria, Cucurbitaceae) is an important horticultural crop exhibiting tremendous diversity in fruit shape. The genetic architecture of fruit shape variation in this species remains unknown. We assembled a long-read-based, high-quality reference genome (ZAAS_Lsic_2.0) with a contig N50 value over 390-fold greater than the existing reference genomes. We then focused on dissection of fruit shape using a one-step geometric morphometrics-based functional mapping approach. We identified 11 quantitative trait loci (QTLs) responsible for fruit shape (fsQTLs), reconstructed their visible effects and revealed syntenic relationships of bottle gourd fsQTLs with 12 fsQTLs previously reported in cucumber, melon or watermelon. Homologs of several well-known and newly identified fruit shape genes, including SUN, OFP, AP2 and auxin transporters, were comapped with bottle gourd QTLs.  相似文献   
72.
Abstract.  1. The costs and benefits of behavioural care of offspring can often be easily quantified through observations and experiments. Other forms of parental investment, on the other hand, are usually less amenable to cost–benefit analysis.
2. Here, the costs and benefits are estimated for protective egg coating by a chrysomelid beetle, Cryptocephalus hypochaeridis , where the female spends a considerable amount of time adding extra structural components to each of the eggs after laying them.
3. Adding this protective coating was very costly, both in terms of material and energy used: the mass of the extrachorion is equivalent to half the mass of the egg, and water loss and energy expenditure while coating the egg is equivalent to half what would be lost while laying a further egg.
4. Choice tests with egg predators demonstrated that these high costs are offset by benefits in terms of protection against predation: whereas uncoated eggs are readily eaten by predators, coated eggs are always rejected.  相似文献   
73.
Long-persistent phosphorescent smart paints have the ability to continue glowing in the dark for a prolonged time period to function as energy-saving products. Herein, new epoxy/silica nanocomposite paints were prepared with different concentrations of lanthanide-doped aluminate nanoparticles (LAN; SrAl2O4:Eu2+,Dy3+). The LAN pigment was firstly coated with silicon dioxide (SiO2) utilizing the heterogeneous precipitation technique to provide LAN-encapsulated between SiO2 nanoparticles (LAN@SiO2). The epoxy/silica/lanthanide-doped aluminate nanoparticles (ESLAN) nanocomposite paints were coated on steel. The prepared ESLAN paints were studied by transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray fluorescence (XRF) analysis, and energy-dispersive X-ray spectroscopy (EDS). The transparency and coloration properties of the nanocomposite coated films were explored by CIE Lab parameters and photoluminescence spectra. The ultraviolet-induced luminescence properties of the transparent coated films demonstrated greenish phosphorescence at 518 nm upon excitation at 368 nm. Both hardness and hydrophobic activities were investigated. The anticorrosion activity of the nanocomposite films coated onto mild steel substrates immersed in aqueous sodium chloride (NaCl(aq)) (3.5%) was studied by electrochemical impedance spectroscopy (EIS). The silica-containing coatings were monitored to exhibit anticorrosion properties. Additionally, the nanocomposite films with LAN@SiO2 (25%) exhibited the optimized long-lasting luminescence properties in the dark for 90 min. The nanocomposite films showed highly reversible and durable long-lived phosphorescence.  相似文献   
74.
Tyrocidines are a family of cyclic decapeptides produced by the soil bacterium, Brevibacillus parabrevis. These antibiotic peptides can be used to prevent infections in agriculture and food industry but also to prepare antimicrobial lozenges, creams, and dressings for medical applications. It has been observed that the tyrocidines interact with saccharides such as cellulose from their soil environment, as well as sugars in culture media and glycans in fungal cell walls. Here, we investigated the interactions of tyrocidines with glucose, sucrose, and cellotetraose (as cellulose model) in a quantitative fashion utilising CD and NMR spectroscopy. The CD and NMR spectra of tyrocidine A (TrcA) were analysed as a function of solvent composition, and the spectral properties agree with the formation of oligomeric structures that are governed by β‐sheet secondary structures once the acetonitrile content of the solvent is increased. Saccharides seem to also induce TrcA spectral changes reverting those induced by organic solvents. The CD spectral changes of TrcA in the presence of glucose agree with new ordered H‐bonding, possibly β‐sheet structures. The amides involved in intramolecular H‐bonding remained largely unaffected by the environmental changes. In contrast, amides exposed to the exterior and/or involved in TrcA intermolecular association show the largest 1H chemical shift changes. CD and NMR spectroscopic investigations correlated well with TrcA‐glucose interactions characterized by a dissociation constant around 200 μM. Interestingly, the association of cellotetraose corresponds closely to the additive effect from four glucose moieties, while a much higher dissociation constant was observed for sucrose. Similar trends to TrcA for binding to the three saccharides were observed for the analogous tyrocidines, tyrocidine B, and tyrocidine C. These results therefore indicate that the tyrocidine interactions with the glucose monosaccharide unit are fairly specific and reversible.  相似文献   
75.
Upgrading of the surface characteristics could enhance the bulk properties of naturally abundant fiber-forming materials for better performance or create new value-added products. Laccase can induce cross-linkage and covalent coupling of low molecular weight compounds onto lignocellulosic surfaces. For this purpose the 38-kDa laccase from Trametes hirsuta was purified and characterized. The best conditions for laccase-induced coating of flax fibers were determined. This evaluation was based on the obtained coloration and color depth. A screening was carried out with different phenols for their potential as monomers for enzyme-catalyzed polymerization resulting in a coating with antibacterial performance. While all the methoxyphenols showed different coloration with weak fastness properties, bacterial growth of Bacillus subtilis and Staphylococcus aureus was reduced significantly using ferulic acid and hydroquinone. Using laccase-induced coupling and polymerization, multi-functionality of the lignocellulosic surface, such as coloration and antimicrobial performance, was achieved, which depended on the nature of the applied phenolic monomer.  相似文献   
76.
77.
A wide range of proteins belonging to the SCP/TAPS “family” has been described for various eukaryotic organisms, including plants and animals (vertebrates and invertebrates, such as helminths). Although SCP/TAPS proteins have been proposed to play key roles in a number of fundamental biological processes, such as host–pathogen interactions and defence mechanisms, there is a paucity of information on their genetic relationships, structures and functions, and there is no standardised nomenclature for these proteins. A detailed analysis of the relationships of members of the SCP/TAPS family of proteins, based on key protein signatures, could provide a foundation for investigating these areas. In this article, we review the current state of knowledge of key SCP/TAPS proteins of eukaryotes, with an emphasis on those from parasitic helminths, and undertake a comprehensive, systematic phylogenetic analysis of currently available full-length protein sequence data (considering characteristic protein signatures or motifs) to infer relationships and provide a framework (based on statistical support) for the naming of these proteins. This framework is intended to guide genomic and molecular biological explorations of key SCP/TAPS molecules associated with infectious diseases of plants and animals. In particular, fundamental investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the control of parasitic diseases, with important biotechnological outcomes.  相似文献   
78.
An antimicrobial finishing for cotton fabric was prepared from commercial (iSys AG, Germany) silver chloride (Ag) dispersed at different concentrations in a reactive organic–inorganic binder (RB) (iSys MTX (CHT, Germany). Pad-dry-cure and exhaustion methods were used for the sols application, giving Ag-RB coating with Ag concentration from ca. 48 to ca. 290 ppm on the cotton fabric. The presence of silver on the cotton finishes was confirmed by measuring its concentration in the fabrics with the help of inductively coupled plasma mass spectroscopy (ICP-MS). The morphology of the finished fabrics was investigated by SEM, while their composition was established from EDXS measurements combined with the results of FT-IR spectral analysis. The antimicrobial activity of variously treated cotton fabrics was assessed before and after repetitive (up to 10×) washing by the application of standard tests: for the fungi Aspergillus niger (ATCC 6275) and Chaetomium globosum (ATCC 6205) by the modified DIN 53931 standard method, while the presence of Gram-negative bacterium Escherichia coli (ATCC 25922) was followed by using ISO 20645:2004 (E) and AATCC 100-1999 standard methods. Results revealed that the antimicrobial activity of the coatings strongly depended on the concentration of Ag in the corresponding Ag-RB dispersions, indirectly depending on the preparation method (pad-dry-cure vs. exhaustion) and that the Ag-RB coatings were more effective for bacteria than for fungi. The Ag concentrations on the cotton fabrics achieved by the pad-dry-cure method (48 and 52 ppm) were not sufficient to impart satisfactory antifungal activity to the cotton fabrics, though they assured excellent reduction of the bacterium E. coli (98–100%). A minimal inhibitory concentration of Ag in the coating providing a sufficient bacterial reduction of 60% was ca. 24 ppm. Effective antifungal activity was achieved only by applying the exhaustion method, enabling high initial Ag concentration in the Ag-RB coating (>100 ppm). The antibacterial activity depended on the washing treatment. No antifungal activity was noted for washed cotton fabric, even those with highly concentrated Ag (290 ppm) in the Ag-RB coating, but a 94% bacterial reduction was obtained for the corresponding cotton fabric, after 10 repetitive washings, corroborated by the Ag concentration on washed fabric of about 65 ppm.  相似文献   
79.
We previously developed a calcium phosphate (CaP) calcifying solution that allows to deposit a uniform layer of nanocrystalline apatite on metallic implants in a few hours. In this work we modified the composition of the CaP solution by addition of Sr2+, Mg2+, and Mn2+, in order to improve the biological performance of the implants. The results of the investigation performed on the coatings, as well as on the powders precipitated in the absence of the substrates, indicate that both Sr2+ and Mg2+ reduce the extent of precipitation, although they are quantitatively incorporated into the nanocrystalline apatitic phase. The inhibitory effect on deposition is much more evident for Mn2+, which completely hinders the precipitation of apatite and yields just a small amount of amorphous phosphate relatively rich in manganese content. Human osteoblast-like MG-63 cells cultured on the different materials show that the Mg2+ and Sr2+ apatitic coatings promote proliferation and expression of collagen type I, with respect to bare Ti and to the thin layer of amorphous phosphate obtained in the presence of Mn2+. However, the relatively high content of Mn2+ in the phosphate has a remarkable beneficial effect on osteocalcin production, which is even greater than that observed for Sr2+.  相似文献   
80.
临床中,内植物引起的相关感染是矫形外科以及创伤外科面临的重要问题。以聚乳酸(PDLLA)为载体,采用溶剂浇铸(solvent-casting)的方法,在钛合金植入物基体表面制备了载万古霉素(VCM)的PDLLA涂层,期望通过缓释万古霉素来抑制细菌感染。体外释药实验表明,涂层具有良好的缓释作用,在磷酸盐缓冲液(PBS)中持续释放VCM20天以上;涂层对引起感染的主要致病菌(金黄色葡萄球菌)具有超过15天的抑制作用。提示该涂层钛合金植入物有望在预防植入材料相关感染方面获得应用。  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