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   2741篇
  免费   189篇
  国内免费   9篇
电工技术   57篇
综合类   1篇
化学工业   842篇
金属工艺   34篇
机械仪表   66篇
建筑科学   74篇
矿业工程   3篇
能源动力   105篇
轻工业   317篇
水利工程   10篇
石油天然气   1篇
无线电   204篇
一般工业技术   442篇
冶金工业   41篇
原子能技术   33篇
自动化技术   709篇
  2024年   4篇
  2023年   44篇
  2022年   191篇
  2021年   205篇
  2020年   80篇
  2019年   98篇
  2018年   117篇
  2017年   90篇
  2016年   137篇
  2015年   114篇
  2014年   152篇
  2013年   225篇
  2012年   172篇
  2011年   199篇
  2010年   139篇
  2009年   167篇
  2008年   138篇
  2007年   99篇
  2006年   97篇
  2005年   89篇
  2004年   65篇
  2003年   49篇
  2002年   42篇
  2001年   30篇
  2000年   25篇
  1999年   16篇
  1998年   27篇
  1997年   16篇
  1996年   23篇
  1995年   14篇
  1994年   5篇
  1993年   8篇
  1992年   6篇
  1991年   7篇
  1990年   3篇
  1989年   5篇
  1988年   2篇
  1987年   5篇
  1985年   2篇
  1984年   4篇
  1983年   4篇
  1982年   4篇
  1980年   4篇
  1979年   2篇
  1978年   2篇
  1977年   4篇
  1976年   2篇
  1975年   3篇
  1974年   1篇
  1973年   1篇
排序方式: 共有2939条查询结果,搜索用时 15 毫秒
71.
The purpose of the paper is to contribute to understanding the role and effectiveness of different quality clues in the creation of value for the main wines of the Lazio region. The study presents a hedonic price model. An ordinary least squares and a quantile regression models were estimated. The latter is able to detect additional patterns related to the effects of the covariates. Prices are regressed on wine color, sub-regional area of origin, the type of certification of origin, and on experts' evaluation. The analysis is based on data released by three major Italian wine guides: Gambero Rosso, l'Espresso, and AIS (Italian Sommelier Association). Results show that: (i) white and red wines follow two different price patterns; (ii) prices are correlated with experts' evaluation; (iii) the impact of the latter is higher when other quality clues, such as geographical indications, are less effective; (iv) the role of different quality clues varies at different price levels and it is different for red and white wines; overall, wines from the Lazio region are associated with poor to mediocre quality levels. This may explain the decline in reputation and in market share that these wines are experiencing after centuries of popularity.  相似文献   
72.
Preventive maintenance is a group of maintenance policies based on preventive actions in order to predate the failure of a component or a system. Usually, these policies are designed using a series of data related to the studied units. All policies do not consider the effect of the environment where the components or systems operate. In this article, one of the most used policies, the age replacement policy, is also discussed taking into consideration the environmental effects using an innovative concept, introduced by Pham, called systemability. Several numerical examples are carried out in order to illustrate the aim of this work. The importance of environmental factors is also demonstrated thanks to the application to a real case.  相似文献   
73.
Modern construction makes frequent use of composite steel-concrete beams for bridge and building applications. This paper describes a three-dimensional finite element model in which all components forming the composite member are modelled by means of solid elements. The proposed approach is developed using the commercial software Abaqus and is able to model the composite response without requiring information from push-out tests commonly performed to define the constitutive relationship for the shear connectors. All materials are assumed to behave in a nonlinear fashion. Contact between the elements is simulated using surface-to-surface and embedment techniques. The adequacy and accuracy of the proposed modelling approach are validated against experimental results available in the literature on simply-supported and continuous beam tests with both solid and composite slabs.  相似文献   
74.
In this paper we investigate some analysis and control problems for discrete-time hybrid systems in the piece-wise affine form. By using arguments from the dissipativity theory for non-linear systems, we show that H X analysis and synthesis problems can be formulated and solved via linear matrix inequalities by taking into account the switching structure of the considered system. In this paper we address the generalized problem of controlling hybrid systems whose switching structure does not depend only on the state but also on the control input.  相似文献   
75.
Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical properties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants.The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the microstructural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests.Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues microstructural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues.  相似文献   
76.
In this work, the influence of packaging mass transport properties on quality loss of fresh‐cut cauliflower mixtures was addressed. The study was organised in two subsequent experimental steps; first, the selection of micro‐perforated packaging films was carried out by monitoring the package headspace gas concentrations of fresh‐cut white, green cauliflower and roman cabbage. Then, the effects of the barrier properties of the selected micro‐perforated film on shelf life of two different fresh‐cut cauliflower mixtures, stored at 4 ± 1 °C, were addressed. Results suggested that, among the investigated films, the micro‐perforated polymeric matrix with the lowest oxygen transmission rate value showed the best performance as it created the optimum headspace gas composition for each cauliflower variety, as well as, for the product mixtures. The appearance of visible moulds was the factor limiting product shelf life that accounted for about 18 days for both the investigated cauliflower mixtures.  相似文献   
77.
78.
Two novel process variations aware, necessary and sufficient conditions suitable for implementation in CAD optimizers are proposed to check amplifiers stability. Case studies are presented, showing that the new criteria allow robust amplifier design, under variation of active device immittance parameters in pre‐specified rectangular regions, due to manufacturing tolerances. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 619–626, 2013.  相似文献   
79.
In the paper, one presents the theoretical set-up of an original formulation aimed at accounting for the contribution of the fill to the structural strength of masonry vaults and arches and at providing an evaluation about its skill of cooperating to stress absorption with the main vaulted resisting structure. Usually the action of components ordinarily regarded as non-structural members is often neglected in static analyses. Actually, it is a common practice to assume a number of elements of vaulted or arched constructions, such as the fill and the buttress, as completely unable to exert any structural action, rather than trying to evaluate their contribution; therefore, those are usually assumed to be a dead weight, unable to contribute to the bearing capacity of the vault. Starting from the consideration that the fill is somehow subject to some pre-compression because of the permanent load, an approach is proposed where the fill is considered to be able to provide a partial absorption of the variable loads with a reduced load transmission onto the main structural members. The procedure leads to more realistic evaluations about the safety assessment of vaulted structures, which are in major agreement with their real behaviour.  相似文献   
80.
The Cherenkov Telescope Array (CTA) is currently building the next generation, ground-based, very high-energy gamma-ray instrumentation. CTA is expected to collect very large datasets (in the order of petabytes) which will have to be stored, managed and processed. This paper presents a graphical user interface built inside a science gateway aiming at providing CTA-users with a common working framework. The gateway is WS-PGRADE/gUSE workflow-oriented and is equipped with a flexible SSO (based on SAML) to control user access for authentication and authorization. An interactive desktop environment is provided, called Astronomical & Physics Cloud Interactive Desktop (ACID). Users are able to exploit the graphical interface as provided natively by the tools included in ACID. A cloud data service shares and synchronizes data files and output results between the user desktop and the science gateway. Our solution is a first attempt towards an ecosystem of new technologies with a high level of flexibility to suit present and future requirements of the CTA community.  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