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   1200篇
  免费   26篇
电工技术   4篇
化学工业   439篇
金属工艺   6篇
机械仪表   25篇
建筑科学   37篇
矿业工程   1篇
能源动力   40篇
轻工业   313篇
水利工程   4篇
石油天然气   4篇
无线电   65篇
一般工业技术   174篇
冶金工业   15篇
原子能技术   2篇
自动化技术   97篇
  2024年   17篇
  2023年   16篇
  2022年   89篇
  2021年   103篇
  2020年   39篇
  2019年   44篇
  2018年   38篇
  2017年   39篇
  2016年   49篇
  2015年   42篇
  2014年   51篇
  2013年   73篇
  2012年   73篇
  2011年   76篇
  2010年   78篇
  2009年   62篇
  2008年   55篇
  2007年   45篇
  2006年   38篇
  2005年   27篇
  2004年   25篇
  2003年   22篇
  2002年   28篇
  2001年   11篇
  2000年   5篇
  1999年   9篇
  1998年   16篇
  1997年   6篇
  1996年   9篇
  1995年   7篇
  1994年   6篇
  1993年   6篇
  1992年   5篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1979年   1篇
  1978年   2篇
  1961年   1篇
排序方式: 共有1226条查询结果,搜索用时 0 毫秒
71.
The aging of the population is giving rise to a large number of studies aimed at improving the quality of life, considering diet as a major contributing factor in this life stage. The objectives of the present study were to evaluate the nutritional status of a group of institutionalized elderly in Murcia, Spain, and to relate the diet to anthropometric and biochemical indices, paying special attention to total antioxidant status. The dietary evaluation showed excessive intakes of proteins and lipids, and deficiencies in those of carbohydrates, dietary fiber, zinc, iodine and vitamins A, E and D. The high proportion of overweight observed were not significantly correlated to the energy intakes. Although total plasma antioxidant status was low (0.62 mM eq Trolox and 0.98 mM eq Fe(II)) compared with reference values, estimated oxidative risk in this group of elderly was low according to plasma levels of vitamins C, A & E.  相似文献   
72.
A new method for decoding two-dimensional (2D) multicomponent separations based on the use of the 2D Autocovariance function (2D-ACVF) has been developed. Theoretical models of single component (SC) spot distributions in 2D separations, both random and structured, are developed as the basis for a nonlinear estimation of both sample and separation system parameters from experimental 2D separations. The number of SCs, the average spot size, the spot capacity, and the saturation factor can be evaluated in the case of random SC spot patterns. The procedure was validated by extensive numerical simulation under conditions close to those usually found in GC x GC or 2D-polyacrylamid gel electrophoresis of proteins. The worse precision degree was no greater than 10% in the case of maximum spot density. This imprecision was fully accounted for, and it seems acceptable owing to the intrinsic statistical character of the estimation method. Structured multicomponent 2D separations, where SCs are linked by linear relationships, give rise to specific structured patterns in 2D-ACVF plots from which the parameters (phase and frequency) of the structured SC sequences can be evaluated: the study of 2D-ACVF makes it possible to decode multicomponent 2D separation, that is, to determine the number, relative abundance, and structural similarities of the single components. Pertinent expressions of the theoretical 2D-ACVF were derived for simple cases, and a procedure for decoding cases of structured 2D separations was developed and applied. It was shown that 2D separations containing both random and structured patterns of SC spots give rise to 2D-EACVF, which is the superimposition of the two component parts. This feature allows one, in principle, to decode the two components. The relevance of these results for Giddings sample dimensionality and separation dimensionality and their effective experimental evaluation is discussed.  相似文献   
73.
As software development comes to be viewed more and more as an engineering discipline, Software Configuration Management is increasingly recognised as a key technology in the development of software. The Esprit VISCOUNT project1 aim is to implement an innovative Software Configuration Management (SCM) tool to use in a geographically distributed software development environment, a Virtual Software Corporation (VSC). The features implemented by the tool will be the following: ·Configurable process modelling ·Inter-working capabilities with COTS SCM tools ·Selective replication of archives ·Open to include plug-in applications (security mechanism, encryption, etc) This paper is based on the work undertaken as part of the VISCOUNT project, partially funded by European Union's Esprit Programme, and it describes the SIA (Societa' Italiana Avionica) requirements defined in the framework of VISCOUNT. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
74.
Reviews     
READING LANDSCAPE; COUNTRY-CITY-CAPITAL, Simon Pugh, ed., Manchester : Manchester University Press, 1990, pp. 245, £35.00 HB, £9.95 PB, ISBN 0-7190-2979-1, 0-7190-3189-3.

ENVISIONING INFORMATION

by Edward R. Tufte, Cheshire, Connecticut, The Graphics Press, 1990, £30.00.

THE MAKING OF THE AMERICAN LANDSCAPE, Michael P. Conzen, ed., Boston and London: Unwin Hyman, 1990. pp. xvi + 434. ISBN 0-04-917010-4. £14.95 PB.

THE EFFECTS OF THE GREAT STORM: REPORT OF A TECHNICAL COORDINATION COMMITTEE AND THE GOVERNMENT'S RESPONSE, London: HMSO, 1988, 43pp, £5.00, P.B., ISBN 011 752144 2.

THE 1987 STORM: IMPACTS AND RESPONSES, A. J. Grayson (ed.), London: HMSO, 1989, 46pp, £4.00, P.B., ISBN 011 752144 2.

VIEWS OF AMERICAN LANDSCAPES, edited by Mick Gidley and Robert Lawson-Peebles, Cambridge: Cambridge University Press, 1989, £27.50; $39.50, H.B., 228pp.

TAMING THE FLOOD: A HISTORY AND NATURAL HISTORY OF RIVERS AND WETLANDS by Jeremy Purseglove, Oxford: Oxford University Press in association with Channel 4, 1989, 291pp, ISBN 0 19 286091 7, £9.95, P.B.

THE ITALIAN RENAISSANCE GARDEN FROM THE CONVENTIONS OF PLANTING, DESIGN, AND ORNAMENT TO THE GRAND GARDENS OF SIXTEENTH-CENTURY CENTRAL ITALY, Claudia Lazzaro with photographs by Ralph Lieberman, New Haven and London, Yale University Press, 1990, pp. i-ix + 342, £45.00, $65.00, ISBN 0-300-4765-7.

LANDSCAPE OR LAND?, poems for Devon, Mark Beeson and Christopher Southgate, Wheal Press, Devon, ISBN 0-9511588-1-3.  相似文献   
75.
Four experiments investigated the influence of a sudden social request on the kinematics of a preplanned action. In Experiment 1, participants were requested to grasp an object and then locate it within a container (unperturbed trials). On 20% of trials, a human agent seated nearby the participant unexpectedly stretched out her arm and unfolded her hand as if to ask for the object (perturbed trials). In the remaining 3 experiments, similar procedures were adopted except that (a) the human was replaced by a robotic agent, (b) the gesture performed by the human agent did not imply a social request, and (c) the gaze of the human agent was not available. Only when the perturbation was characterized by a social request involving a human agent were there kinematic changes to the action directed toward the target. Conversely, no effects on kinematics were evident when the perturbation was caused by the robotic agent or by a human agent performing a nonsocial gesture. These findings are discussed in the light of current theories proposed to explain the effects of social context on the control of action. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
76.
Contact effects in organic thin-film transistors (OTFTs) sensors are here investigated specifically respect to the gate field-induced sensitivity enhancement of more than three orders of magnitude seen in a DHα6T OTFT sensor exposed to 1-butanol vapors. This study shows that such a sensitivity enhancement effect is largely ascribable to changes occurring to the transistor channel resistance. Effects, such as the changes in contact resistance, are seen to influence the low gate voltage regime where the sensitivity is much lower.  相似文献   
77.
In this paper the contrasting effects of transmission impairments and capture on both the network and single user performance of a slotted Aloha system are investigated in a mobile radio environment, accounting for frequency non-selective random propagation phenomena, and employing the packet error probability in order to define packet losses and capture. With this study we demonstrate that it is possible to generalize in a real propagation context a method previously proposed in literature for evaluating the network behavior in terms of steady-state throughput, backlog and stability in conventional transmission conditions, i.e., when all the transmission channels were error-free and the collisions caused the loss of all the packets involved. Moreover, we indicate under which specific constraints on the terminal mobility we can apply this method to analytically predict the single user performance, which we show being an important design parameter. Through the numerical results reported we quantitatively point out that in the absence of coding capture increases system stability and moderately improves the overall system throughput and backlog. We also outline the trade-off between an increased capture gain obtained by means of coding and the corresponding system cost in terms of complexity and bandwidth occupancy. Furthermore, we demonstrate the unfairness which affects the single user performance and the consequent need for countermeasures in order not to discriminate among users differently located within the network; yet, this last solution is detrimental as regards the positive capture effects.This work was supported by M.U.R.S.T. and C.N.R. (Italy).  相似文献   
78.
Erva-mate (Ilex paraguariensis St. Hil.) is a native species from temperate regions of South America, such as Brazil, Paraguay, and Argentina, that is consumed as a beverage known as mate. The objective of this research was to determine the content of caffeic acid, catechin, chlorogenic acid, caffeine, and gallic acid in mate to explain their influence in beverage taste and sensory differences between native and reforested plants, as well as between beverages from plants of different regions of Brazil (Santa Catarina and Rio Grande do Sul states). Compounds were determined by HPLC and results were related to a sensory evaluation performed by trained tasters. Tasters considered the beverage from reforested plants to be more bitter than the beverage from native plants. Beverages from reforested plants had significantly higher caffeic acid and lower catechin, chlorogenic acid, caffeine, and gallic acid content than native plants. Beverages from plants of Santa Catarina state had significantly higher catechin, caffeine, and gallic acid content than plants from Rio Grande do Sul state.  相似文献   
79.
The essential oils, isolated by hydrodistillation and distillation-extraction, from the aerial parts of different populations of Pterospartum tridentatum collected during the flowering phase, at different locations in Portugal, were analysed by GC and GC–MS. All the P. tridentatum populations studied afforded a yellowish oil in a yield <0.05% (v/w). cis-Theaspirane (2–14%), trans-theaspirane (2–17%) and octen-3-ol (2–37%) were, in variable amounts, the dominant components of the oils. Cluster analysis of the essential oil compositions from the nine populations studied, confirmed a major chemical variability.  相似文献   
80.
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