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   2526篇
  免费   166篇
  国内免费   1篇
电工技术   8篇
化学工业   966篇
金属工艺   24篇
机械仪表   48篇
建筑科学   114篇
矿业工程   1篇
能源动力   79篇
轻工业   542篇
水利工程   12篇
石油天然气   15篇
无线电   101篇
一般工业技术   278篇
冶金工业   245篇
原子能技术   3篇
自动化技术   257篇
  2024年   6篇
  2023年   24篇
  2022年   186篇
  2021年   160篇
  2020年   81篇
  2019年   89篇
  2018年   98篇
  2017年   91篇
  2016年   99篇
  2015年   82篇
  2014年   113篇
  2013年   167篇
  2012年   179篇
  2011年   169篇
  2010年   133篇
  2009年   130篇
  2008年   127篇
  2007年   101篇
  2006年   96篇
  2005年   71篇
  2004年   59篇
  2003年   38篇
  2002年   40篇
  2001年   37篇
  2000年   18篇
  1999年   18篇
  1998年   44篇
  1997年   35篇
  1996年   31篇
  1995年   26篇
  1994年   19篇
  1993年   12篇
  1992年   6篇
  1991年   6篇
  1990年   12篇
  1989年   10篇
  1988年   7篇
  1987年   5篇
  1986年   4篇
  1985年   3篇
  1984年   7篇
  1983年   6篇
  1980年   4篇
  1979年   6篇
  1978年   4篇
  1976年   8篇
  1975年   4篇
  1974年   4篇
  1972年   3篇
  1966年   3篇
排序方式: 共有2693条查询结果,搜索用时 15 毫秒
991.
The problem of the ageing infrastructure of urban water distribution networks and the loss of water associated with this has been one of the greatest infrastructure problems in urban areas. When a leakage is detected in the water supply network, problems arise when seeking to rehabilitate the network. Therefore, the decision problem is to choose which components to add or to improve and to maximize the benefits, which will result from the changes implemented. In addition, it is important to minimize costs, since water supply companies have limited budgets. Moreover, there are often several leakage points in the same water supply network and in the same period of analysis. Therefore, this paper puts forward a model for rehabilitating the greatest number of leakage points in a water network; it respects the constraints which a water company may have. Promethee V is used to assist the decision maker (DM) in selecting a set of feasible alternatives for rehabilitating the network from the criteria and the constraints set by the DM on the problem. For demonstration purposes, the proposed model was tested in a simulated network.  相似文献   
992.
Bacteria-hemocyte interactions and phagocytosis in marine bivalves   总被引:7,自引:0,他引:7  
Marine bivalves (such as mussels, oysters, and clams) are widespread mollusks in coastal waters at different latitudes; due to their filter-feeding habits, they accumulate large numbers of bacteria from the harvesting waters and may act as passive carriers of human pathogens. To cope with this challenge, bivalves possess both humoral and cellular defense mechanisms with remarkably effective capabilities. The circulating cells, or hemocytes, are primarily responsible for defense against parasites and pathogens; microbial killing results from the combined action of the phagocytic process with humoral defense factors such as agglutinins (e.g., lectins), lysosomal enzymes (e.g., acid phosphatase, lysozyme), toxic oxygen intermediates, and various antimicrobial peptides. In this work, current knowledge of the mechanisms underlying the interactions between bacteria and the hemolymph components of marine bivalves is summarized. Bacterial susceptibility to hemolymph killing in different bivalve species may be a consequence of the different ability of bacterial products to attract phagocytes, the presence or absence of specific opsonizing molecules, the hemocyte capability to bind and engulf different bacteria, and the different bacterial sensitivity to intracellular killing. The role of soluble (e.g., agglutinins and opsonins) and surface-bound factors in bacterial phagocytosis by hemocytes of the most common marine bivalve species is described and the possibility that environmental temperatures and other seasonal factors may influence this process is considered. Moreover, the potential strategies used by bacteria to evade phagocytic killing by hemocytes are discussed. From the available data it is clear that several questions need further investigation; the elucidation of the factors influencing phagocytosis in bivalves and the fundamental strategies used by bacteria to escape hemolymph killing are important not only to understand bivalve immune defenses but also to explain the persistence of pathogenic bacteria in bivalve tissues and to predict the consequent impact on human health.  相似文献   
993.
994.
A new concept for reusable eco‐friendly hydrogel electrolytes based on cellulose is introduced. The reported electrolytes are designed and engineered through a simple, fast, low‐cost, and eco‐friendly dissolution method of microcrystalline cellulose at low temperature using an aqueous LiOH/urea solvent system. The cellulose solution is combined with carboxymethyl cellulose, followed by the regeneration and simultaneous ion incorporation. The produced free standing cellulose‐based electrolyte films exhibit interesting properties for application in flexible electrochemical devices, such as biosensors or electrolyte‐gated transistors (EGTs), because of their high specific capacitances (4–5 µF cm?2), transparency, and flexibility. Indium–gallium–zinc‐oxide EGTs on glass with laminated cellulose‐based hydrogel electrolytes (CHEs) as the gate dielectric are produced presenting a low working voltage (<2 V), showing an on–off current ratio (I on/off) of 106, a subthreshold swing lower than 0.2 V dec?1, and saturation mobility (μSat) reaching 26 cm2 V?1 s?1. The flexible CHE‐gated transistors on paper are also demonstrated, which operate at switching frequencies up to 100 Hz. Combining the flexibility of the EGTs on paper with the reusability of the developed CHEs is a breakthrough toward biodegradable advanced functional materials allied with disposable/recyclable and low‐cost electronic devices.  相似文献   
995.
996.
The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO(2)-P25. Response surface methodology, based on a 3(2) full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO(2) (0.1-0.9 g/L) and H(2)O(2) (1-100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO(2)/L and 50 mmol H(2)O(2)/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min(-1). Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents.  相似文献   
997.
The antilisterial activity in biofilms developed in a small-scale model by two LAB (lactic acid bacteria) bacteriocin producers (Lactobacillus plantarum 35d, Enterococcus casseliflavus IM 416K1) and by two non-producers (L. plantarum 396/1, Enterococcus faecalis JH2-2) was evaluated against Listeria monocytogenes NCTC 10888. The LAB biofilms showed the capability to influence the survival and the multiplication of the pathogen with differences among the strains. L. plantarum 35d displayed the highest efficacy reducing L. monocytogenes by 5.4 log in the planktonic population and by 3.9 log in the adherent population at the end of the experiment (10 days). L. plantarum 396/1 reduced L. monocytogenes by 3.8 log in the adherent cells and by 4.9 log in the planktonic cells and this outcome could be attributed to the pH reduction.The E. casseliflavus IM 416K1 biofilm caused a L. monocytogenes reduction of 3.7 log in the adherent cells and of 4.8 log in the planktonic cells and the role of the bacteriocin production seemed to be predominant as the pH values did not significantly decrease. This hypothesis is confirmed by a slight capability to influence the L. monocytogenes survival by the non-bacteriocinogenic E. faecalis JH2-2. Studies performed with L. monocytogenes in co-culture with a Pseudomonas putida strain, revealed a reduction of the antilisterial activity only for the biofilms produced by lactobacilli.  相似文献   
998.
999.
1000.
Catalyst Tegoamin 33 has been used for the synthesis of rigid polyurethane (RPU) foams containing microencapsulated Rubitherm® RT27 and having a high mechanical resistance. These materials could be employed in buildings for thermal insulation and thermal energy storage (TES). The fillers content influence on the foaming process and also the foam properties was evaluated. It was observed that a foam containing up to a 18 wt% of microcapsules can be manufactured, improving the TES capacity while maintaining the mechanical properties of the neat foam. Besides, it was observed that the mechanical resistance of foams synthesized using catalyst Tegoamin 33 are higher than those obtained when catalyst Tegoamin BDE was employed, with the mechanical resistance of the foam containing 21 wt% being higher than those of foams synthesized with catalyst BDE containing only 11 wt% of fillers while maintaining the advantages of an improvement in TES capacity. A general model of reaction curve of n tank-in-series of a same time constant was used to fit the rising curves. This model allowed to predict the final volume of the synthesized foam. Finally, TES capacities and mechanical properties of the synthesized foams were in the range of those reported in literature. Moreover, foam densities satisfied the restriction established by the Spanish regulation for building applications.  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