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   2166篇
  免费   135篇
电工技术   13篇
综合类   1篇
化学工业   681篇
金属工艺   17篇
机械仪表   51篇
建筑科学   80篇
矿业工程   5篇
能源动力   54篇
轻工业   621篇
水利工程   16篇
石油天然气   15篇
无线电   84篇
一般工业技术   275篇
冶金工业   244篇
原子能技术   1篇
自动化技术   143篇
  2024年   5篇
  2023年   28篇
  2022年   137篇
  2021年   139篇
  2020年   73篇
  2019年   90篇
  2018年   83篇
  2017年   96篇
  2016年   80篇
  2015年   57篇
  2014年   123篇
  2013年   169篇
  2012年   151篇
  2011年   162篇
  2010年   106篇
  2009年   102篇
  2008年   97篇
  2007年   103篇
  2006年   72篇
  2005年   44篇
  2004年   50篇
  2003年   32篇
  2002年   29篇
  2001年   14篇
  2000年   27篇
  1999年   16篇
  1998年   25篇
  1997年   17篇
  1996年   23篇
  1995年   14篇
  1994年   19篇
  1993年   12篇
  1992年   12篇
  1991年   4篇
  1990年   8篇
  1989年   6篇
  1988年   8篇
  1987年   10篇
  1986年   13篇
  1985年   8篇
  1984年   4篇
  1983年   7篇
  1982年   7篇
  1981年   4篇
  1980年   3篇
  1979年   2篇
  1977年   3篇
  1970年   1篇
  1940年   1篇
  1928年   1篇
排序方式: 共有2301条查询结果,搜索用时 0 毫秒
991.
Superoxide dismutase enzymes (SODs) are an essential part of the first line of cellular defense system against free radicals species. They catalyze the dismutation of superoxide radicals into oxygen and hydrogen peroxide. Although several studies have examined the attachment of superoxide dismutases to nanoparticles and nanostructures, never has been used a member of the Fe/MnSOD family. In this study, the behavior of plant origin FeSOD enzyme on three different nanopatterned surfaces was investigated as a function of covalent and electrostatic binding. Fluorescence microscopy was used to demonstrate that the protein is attached only to the gold layer. We also examined the activity of SOD by a colorimetric assay, and we have shown that the enzyme remains active after attachment to the three different surfaces under both kind of binding (electrostatic and covalent). This methodology could be useful for those who want to functionalize nanostructures with a SOD enzyme and test the activity. This process could be of great interest for the development of peroxynitrite and superoxide biosensors.  相似文献   
992.
993.
Despite widespread consumption of soil among animals, the role of geophagy in health maintenance remains an enigma. It has been hypothesized that animals consume soil for supplementation of minerals and protection against toxins. Most studies determine only the total elemental composition of soil, which may not reflect the amount of minerals available to the consumer. Our aim was to test these hypotheses by evaluating the bioavailability of iron in soil consumed by chacma baboons, using a technique that simulates digestion and adsorption. Our results indicate that, despite variation in absolute iron concentration of soil samples, actual iron bioavailability was low while clay content was quite high. This suggests that iron supplementation is unlikely to be the primary motivation for geophagy in this population, and that detoxification is a plausible explanation. This study demonstrates that more research on bioavailability and clay composition is needed to determine the role geophagy plays in health maintenance.  相似文献   
994.
A new approach for the detection and visualization of nano-scaled film defects, such as fissures and holes is described. The procedure is based on a selective electrochemical deposition of bismuth onto uncovered parts of stainless steel substrates due to film cracking after deformation. Cyclic voltammetry experiments enabled the identification of the bismuth redox signals, necessary for the subsequent potentiostatic electrodeposition. A combination of XPS and ToF-SIMS analyses demonstrated that deposition with commonly used acidified electrolytes led to a significant film degradation, by defluorination and chain scission. When an identical procedure was performed in neutral conditions, which was realized by the addition of a bismuth chelating agent, no influence onto the integrity of the fluorocarbon coatings was observed. By SEM, XPS and ToF-SIMS analyses, the deposition of bismuth on the film defects was clearly demonstrated and the failures were evidenced. The identification of nano-scaled coating failures, which was extremely difficult before using common characterization tools, was now realized. This work makes part of a strategy to cover stent materials with a protective fluorocarbon layer and to examine the influence of stent expansion onto the film cohesive properties.  相似文献   
995.
The current state of research in polymer/carbon nanotubes (single wall and multiwall) composites has been reviewed in context to various types of pre-treatments presently employed. The fundamental aspects of carbon nanotubes are briefly discussed and various strategies designed to alter the dispersion stability and quality of nanotubes in the composites is highlighted. A complete survey of the published data is provided and both the opportunities and the limitations in the frame of covalent and non-covalent type of pre-treatments of carbon nanotubes are juxtaposed. In this context, diverse proposed mechanisms behind different molecular level interactions between nanotubes and the functional moieties are addressed. The effects of these pre-treatments on electrical and rheological percolation thresholds are assessed as they provide an alternative means to evaluate the state of dispersion of carbon nanotubes in the composites. In this regard, the influence of various pre-treatments on the nature of charge transfer mechanisms, system dimensions etc. deduced from different parameters of classical percolation theories are also discussed. These transport parameters offer a vital clue on the nature of the pre-treatment and the effects it has on the structure-property correlations.  相似文献   
996.
997.
998.
Among neurodegenerative disorders, Alzheimer's disease (AD) is the most common type of dementia, and there is an urgent need to discover new and efficacious forms of treatment for it. Pathological patterns of AD include cholinergic dysfunction, increased β-amyloid (Aβ) peptide concentration, the appearance of neurofibrillary tangles, among others, all of which are strongly associated with specific biological targets. Interactions observed between these targets and potential drug candidates in AD most often occur by competitive mechanisms driven by orthosteric ligands that sometimes result in the production of side effects. In this context, the allosteric mechanism represents a key strategy; this can be regarded as the selective modulation of such targets by allosteric modulators in an advantageous manner, as this may decrease the likelihood of side effects. The purpose of this review is to present an overview of compounds that act as allosteric modulators of the main biological targets related to AD.  相似文献   
999.
Magnetic biomaterials were prepared using magnetite and chitosan‐coated magnetite nanoparticles (CSNPs) dispersed in poly(vinyl alcohol) gels. Two different methods were developed to obtain ferrogels: in situ co‐precipitation of magnetite (Ferro‐IS) and by adding previously synthesized CSNPs to the neat matrix (Ferro‐CSNPs). In both cases, the crosslinking was carried out by freezing ? thawing (F‐T). The as‐prepared materials as well as precursor CSNPs were characterized by Fourier transform infrared spectroscopy, electronic microscopy (scanning and transmission), X‐ray diffraction, ζ potential, dynamic light scattering, thermogravimetric analysis, differential scanning calorimetry and magnetic properties. The performance of these gels as protein adsorbents was evaluated. Batch adsorption experiments were carried out using bovine serum albumin (BSA) as a model. Substantially different adsorption behaviour was found using Ferro‐IS and Ferro‐CSNPs. This was assigned to dissimilar bonding mechanisms of BSA to the ferrogel matrix. Hence, biomaterials potentially useful in drug delivery as well as in protein purification fields may be prepared by a relatively simple, non‐toxic and low cost method. © 2013 Society of Chemical Industry  相似文献   
1000.
In this work, functionalization of epoxy films with dansyl and naphthalimide fluorophores is described. The procedure involves UV‐photopolymerization of an epoxy formulation that includes bromomethyl reactive groups, and their post‐functionalization modification through a click strategy. Quantitative click reaction within the bulk of the film allows one to obtain films in which the fluorophore is uniformly and covalently linked throughout the epoxy network. Depending on the chromophore bounded, the films are sensitive to different stimuli. Evaluation of the fluorescence emission of the films shows a linear response towards changes in polarity but less sensitivity than that of the low‐molecular‐weight chromophore. © 2013 Society of Chemical Industry  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