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   708篇
  免费   51篇
  国内免费   3篇
电工技术   6篇
综合类   1篇
化学工业   151篇
金属工艺   22篇
机械仪表   32篇
建筑科学   35篇
能源动力   70篇
轻工业   52篇
水利工程   4篇
石油天然气   2篇
无线电   72篇
一般工业技术   145篇
冶金工业   44篇
原子能技术   8篇
自动化技术   118篇
  2024年   4篇
  2023年   13篇
  2022年   20篇
  2021年   37篇
  2020年   33篇
  2019年   31篇
  2018年   47篇
  2017年   33篇
  2016年   42篇
  2015年   24篇
  2014年   47篇
  2013年   76篇
  2012年   37篇
  2011年   68篇
  2010年   47篇
  2009年   40篇
  2008年   35篇
  2007年   23篇
  2006年   26篇
  2005年   19篇
  2004年   7篇
  2003年   10篇
  2002年   5篇
  2000年   3篇
  1999年   1篇
  1998年   4篇
  1997年   3篇
  1996年   6篇
  1995年   3篇
  1994年   3篇
  1992年   2篇
  1990年   1篇
  1989年   1篇
  1985年   2篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1975年   1篇
排序方式: 共有762条查询结果,搜索用时 187 毫秒
51.
Proximate composition and fatty acid (FA) profile of three commercial sea cucumbers; Holothuria tubulosa, Holothuria polii and Holothuria mammata caught from Aegean Sea of Turkey were analysed. The effects of regional variation and drying process on FA composition were also investigated. Moisture, protein, fat and ash contents of the species ranged between 81.24% and 85.24%, 7.88% and 8.82%, 0.09% and 0.18%, and 5.13% and 7.85%, respectively, with a significant changes among species (P < 0.05) with some exceptions. Although FA values varied significantly (P < 0.05) among species and regions, the changes for most FA types representing the same region for different species were not significantly different. Total polyunsaturated fatty acids (PUFA) were found to be higher than total saturated (SFA) and monosaturated FAs (MUFA) accounting for 53.0–62.12% for ∑PUFA, 13.28–16.41% for ∑MUFA and 13.99–19.21% for ∑SFA. While some individual SFAs and PUFAs decreased after drying process, various individual FAs of MUFA increased in their amounts (P < 0.05). Among PUFAs, the highest mean value of eicosapentaenoic acid and docosahexaenoic acid for all regions were determined for H. polii as 7.25% and H. tubulosa as 12.37% in fresh samples, respectively. This study represents new information relating to FA contents and drying effect on FA profile for these species.  相似文献   
52.
In the present study, we investigate influence of HCl-etching on magnetic parameters of B2O3-doped M-type barium ferrites. Our studies have shown that magnetization parameters; the remanence magnetization M r and the specific magnetization M s at 1.5?T, increase significantly with HCl-etching. The best magnetic parameters were observed in the sample of 0.1?wt% B2O3-doped and HCl-washed one after calcination at 1000?°C (M r =34.9?emu/g, M s =0.63.3?emu/g). Increments up to 50% in magnitudes could be achieved with HCl washing. Exchange interactions between particles were also examined by Wohlfarth model. It was observed that magnetizing-like interactions between particles become stronger but ,on the other hand, demagnetizing-like interactions becomes weaker with HCl-etching.  相似文献   
53.
<正>一座建筑的性能应当如何来衡量?除了通过统治当代建筑舆论的美学、技术以及经济价值来进行描述之外,我们还能够如何来阐释一座建筑,尤其是一座致力于庇护那些渴望展现自己的艺术家的建筑?有人会问成功的表演是如何实现的,表演者是如何进行伪装的、又是如何展现自己的?根据海德格尔的理论,当我们看不到钉子的时候,铁锤的表现才是成功的;钉子本身的出现通常表明出现了问题。  相似文献   
54.
55.
Leadership in Energy and Environmental Design (LEED) is a certification program developed by the U.S. Green Building Council for designing, constructing, and certifying green buildings. This paper presents a LEED implementation guide for construction practitioners to assist them in the certification process. The guide was formulated primarily through input, suggestions, and recommendations received from LEED accredited professionals including architects, engineers, commissioning authorities, general contractors, construction managers, and facility managers. Data were collected through four questionnaire surveys where two of which were used for guide development and the other two for modification and validation. General contractors, construction managers, and engineers can use the LEED implementation guide as a reference for managing their LEED certification process. The proposed guide can also assist owners interested in building a LEED certified facility.  相似文献   
56.
BACKGROUND: Recent studies indicate that microalgal cultivation using organic carbon sources has the potential to provide high yields. Haematococcus pluvialis and Chlorella zofingiensis, two important carotenoid producers, were selected for co‐culture cultivations to utilize the unique advantages of both organisms. A co‐culture production process was investigated in terms of the effects of organic carbon source, co‐cultivation method, and light intensity on carotenoid production. RESULTS: The addition of 5 g L?1 glucose resulted in a growth rate of 0.60 day?1 for H. pluvialis and 0.59 day?1 for C. zofingiensis, which were higher than those for other carbon sources tested and the control group. Incremental increase of light intensity instead of direct increase to 170 µE m?2s? prevented cell loss in both cultures. Co‐cultivation based on cell numbers (60% H. pluvialis and 40% C. zofingiensis) prevented population domination of one microalgae over the other. The biomass production rate of the co‐culture was higher (0.61 g L?1 day?1) in glucose‐enriched medium. The total carotenoid content of the co‐culture in the control culture was higher (0.83 mg total carotenoids g?1 cell) than that obtained in glucose‐enriched medium (0.54 mg total carotenoids g?1 cell) but not as high as the amounts reached in mono‐cultures. CONCLUSION: Total carotenoid content of the mono‐cultures gave higher yields in standard bold basal medium (BBM). Preliminary high performance liquid chromatography (HPLC) studies indicated a variation in the amounts of astaxanthin isomers produced. Further studies are in progress to determine the effects of carbon‐enriched media and co‐cultivation on the type of isomers and caretenoids produced. Copyright © 2010 Society of Chemical Industry  相似文献   
57.
Team-oriented approaches are widely being used in modern real life assembly systems, as are other modern systems. In this paper, first the literature of single and mixed model assembly line balancing, which plays an important role for the design of assembly systems, is reviewed. The associated literature matrixes reveal that team-oriented approaches do not have an intensive research area. Second, a team-oriented mathematical programming model for creating assembly teams (physical stations) in mixed model assembly lines is devised. Owing to the fact that this model is NP hard, a scheduling based heuristic algorithm is developed. The mixed model assembly line design methodology, which includes a team-oriented algorithm as a step, is proposed. Both model sequencing and worker transfer systems are included in the methodology. The algorithms for each step of the methodology are also coded by using MATLAB and MS Excel is used as the user interface. Furthermore, the presented methodology was applied in a chosen segment of a real life mixed model tractor assembly system.  相似文献   
58.
We describe a new replicatedobject protocol designed for use in mobile and weaklyconnected environments. The protocol differs from previous protocols in combining epidemic information propagation with voting, and in using fixed perobject currencies for voting. The advantage of epidemic protocols is that data movement only requires pairwise communication. Hence, there is no need for a majority quorum to be available and simultaneously connected at any single time. The protocols increase availability by using voting, rather than primarycopy or primarycommit schemes. Finally, the use of perobject currencies allows voting to take place in an entirely decentralized fashion, without any server having complete knowledge of group membership. We show that currency allocation can be used to implement diverse policies. For example, uniform currency distributions emulate traditional voting schemes, while allocating all currency to a single server emulates a primarycopy scheme. We present simulation results showing both schemes, as well as the performance advantages of using currency proxies to temporarily reallocate currency during planned disconnections. Furthermore, we discuss an initial design of the underlying replicatedobject system and present a basic API.  相似文献   
59.
There are a lot of technologically interesting characteristics of glass–ceramics, which are hard, wear resistant, oxidation and corrosion resistant ceramic materials. In the present study, the production of the basalt-based glass–ceramic coating by atmospheric plasma spray technique and their structural characterization were reported. Basalt-based glass coating was performed on AISI 1040 steel substrate which was pre-coated with Ni–5 wt% Al by using plasma spray gun. Basalt coatings of the glass form were crystallized at 800, 900 and 1000 °C for 1–4 h in orders to transform to the glass–ceramic structure. The presence of augite [(CaFeMg)SiO3], diopside [Ca(Mg0.15Fe0.85)(SiO3)2] and aluminian diopside [Ca(Mg,Al)(Si,Al)2O6] crystalline phases formed in the basalt-based glass–ceramic coating layer was detected by X-ray diffraction analysis. Optical microscopy with micrometer was used for metallographic examinations. Differential scanning calorimeter was used for determining the crystallization temperature of glass form basalt-based coatings. Microhardness measurements were carried out on the basalt-based glass–ceramic coating layer with Vickers indenter. The hardness of coating layers is changing between 1009 and 1295 HV0.05 depending on crystallization temperature and process times. It was found that, the higher the crystallization temperature, the more the crystalline phases were resulted. In addition, the lower the crystallization temperature and the longer the treatment time, the harder the coating layer became.  相似文献   
60.
Aurora: a new model and architecture for data stream management   总被引:43,自引:0,他引:43  
This paper describes the basic processing model and architecture of Aurora, a new system to manage data streams for monitoring applications. Monitoring applications differ substantially from conventional business data processing. The fact that a software system must process and react to continual inputs from many sources (e.g., sensors) rather than from human operators requires one to rethink the fundamental architecture of a DBMS for this application area. In this paper, we present Aurora, a new DBMS currently under construction at Brandeis University, Brown University, and M.I.T. We first provide an overview of the basic Aurora model and architecture and then describe in detail a stream-oriented set of operators.Received: 12 September 2002, Accepted: 26 March 2003, Published online: 21 July 2003Edited by Y. Ioannidis  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