全文获取类型
收费全文 | 1137篇 |
免费 | 72篇 |
专业分类
电工技术 | 18篇 |
化学工业 | 279篇 |
金属工艺 | 7篇 |
机械仪表 | 17篇 |
建筑科学 | 45篇 |
能源动力 | 41篇 |
轻工业 | 139篇 |
水利工程 | 18篇 |
无线电 | 113篇 |
一般工业技术 | 184篇 |
冶金工业 | 180篇 |
原子能技术 | 16篇 |
自动化技术 | 152篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 36篇 |
2021年 | 62篇 |
2020年 | 30篇 |
2019年 | 26篇 |
2018年 | 36篇 |
2017年 | 31篇 |
2016年 | 32篇 |
2015年 | 35篇 |
2014年 | 58篇 |
2013年 | 69篇 |
2012年 | 65篇 |
2011年 | 52篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 52篇 |
2007年 | 35篇 |
2006年 | 37篇 |
2005年 | 29篇 |
2004年 | 33篇 |
2003年 | 33篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 10篇 |
1999年 | 28篇 |
1998年 | 57篇 |
1997年 | 36篇 |
1996年 | 31篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 8篇 |
1974年 | 2篇 |
排序方式: 共有1209条查询结果,搜索用时 31 毫秒
61.
We consider a continuous time linear multi-inventory system with unknown demands bounded within ellipsoids and controls bounded within ellipsoids or polytopes. We address the problem of ε-stabilising the inventory since this implies some reduction of the inventory costs. The main results are certain conditions under which ε-stabilisability is possible through a saturated linear state feedback control. All the results are based on a linear matrix inequalities approach and on some recent techniques for the modelling and analysis of polytopic systems with saturations. Numerical simulations are provided. 相似文献
62.
63.
Valeriano Lanese Danilo Spasiano Raffaele Marotta Ilaria Di Somma Luciana Lisi Stefano Cimino Roberto Andreozzi 《International Journal of Hydrogen Energy》2013
A new photocatalytic system consisting of two subsystems – Cu0/Cl−/H+/UVssr and CuII/H+/TiO2/formic acid/UVssr – is proposed as a tool to produce hydrogen by reforming an organic species. Formic acid is used as hole scavenger during the experimental runs. An experimental campaign is carried out to demonstrate that the systems can generate hydrogen and to assess how the generation rate depends upon experimental conditions such as copper and TiO2 loads, chloride and proton ions, and formic acid concentrations. A strong dependence of the Cu0/Cl−/H+/UVssr subsystem reactivity upon copper load, chloride concentration and pH is observed. The investigation on the complete system, starting from zero-valent copper, indicates that the addition of TiO2 and formic acid to the Cu0/Cl−/H+/UVssr subsystem does not result into any gain in terms of hydrogen produced and, renders the system totally unreactive under some conditions. On the other hand, when a complete system, starting from cupric ions, is adopted, hydrogen production is observed also for prolonged reaction times with a surplus of hydrogen production with respect to that generated by the Cu0/Cl−/H+/UVssr subsystem with the same Cu0 starting load and in absence of TiO2 and sacrificial agent. 相似文献
64.
65.
Oehlschlager AC Gonzalez L Gomez M Rodriguez C Andrade R 《Journal of chemical ecology》2002,28(8):1653-1664
Attraction of Metamasius hemipterus (Oliver) to gallon and bamboo traps baited with insecticide-treated sugarcane, the male-produced pheromone, 4-methyl-5-nonanol, and 2-methyl-4-heptanol is more efficient if ethyl acetate is added. The optimal traps are ground-level gallon traps baited with insecticide-laced sugarcane, pheromone, and ethyl acetate. Capture rates of ground-level gallon traps are doubled by placing an insecticide-laced pad under the trap, but significantly decreased by placing the trap on a stick above ground. The efficiency of ground-level gallon traps is the same as ground level ramp traps. Mass-trapping M. hemipterus in newly planted sugarcane using ground level bamboo traps baited with insecticide-laced sugarcane and pheromone over six months revealed populations were low for the first two months, became maximum at five months, and declined thereafter. Capture rates of traps bordering newly planted and mature sugarcane were not significantly different from capture rates of traps in the interior of the plots. Capture rates of bamboo traps containing only insecticide-laced sugarcane and deployed at 30 traps/ha averaged 6 weevils/trap/week compared with 66 weevils/trap/week for traps additionally containing pheromone lures and deployed at 5 traps/ha. Capture rates for bamboo traps baited with insecticide-laced sugarcane and pheromone and deployed at 10 and 15 traps/ha were 43 and 38 weevils/trap/week, respectively. Total captures were higher in those plots with a higher density of insecticide-laden sugarcane and pheromone baited traps, and the differences were approximately proportional to trap density in the range of 5–15 traps/ha. Capture rates of traps containing insecticide-laced sugarcane and pheromone were always higher than of traps containing only insecticide-laced sugarcane, but in the first two months after planting the differences were much greater than in months 3–6 after planting. 相似文献
66.
The oxidation by H2O2 of 3,4-dihydroxybenzoic acid (3,4-DHB) in aqueous/goethite slurry at varying operating conditions (catalyst load, temperature, pH, substrate and hydrogen peroxide starting concentration) is investigated. At adopted catalyst loads the observed kinetic developments are consistent with a non-radicalic oxidation mechanism involving the interaction between hydrogen peroxide and 3,4-DHB acid both adsorbed on the active sites of the catalyst. The temperature dependence of rate parameters for the proposed model is also assessed. 相似文献
67.
De Angelis C Onori S Pacili M Cirrone GA Cuttone G Raffaele L Sabini MG 《Radiation protection dosimetry》2002,101(1-4):461-464
The present work reports preliminary measurements on the behaviour of a new p-type stereotactic silicon diode. Hi-pSi, produced by Scanditronix and dedicated to proton dosimetry. Diode response was investigated in low-energy proton beams (26.7 MeV and 12 MeV nominal energy), mainly with attention to stability, linearity, dose rate and energy dependence of the detector response. Three different Hi-pSi diodes of the same type were investigated. The diode response was linear with dose and the standard deviation of repeated readings was less than 2.5%. A marked dependence on dose rate was observed for one of the diodes (a response increase of 47% in the 0.7-11 Gy x min(-1) range). After the dose rate and water to silicon mass collision stopping power ratio correction of the diode response in the depth dose measurements, the difference, at the Bragg peak, with respect to the reference chamber was about 4%, ascribed to poor knowledge of the materials in front of the sensitive volume. The diode response was also nearly independent of linear energy transfer (LET) in the 9.6-21.5 MeV effective energy range. 相似文献
68.
In this paper, we consider multi-inventory systems in the presence of uncertain demand. We assume that (i) demand is unknown but bounded in an assigned compact set and (ii) the control inputs (controlled flows) are subject to assigned constraints. Given a long-term average demand, we select a nominal flow that feeds such a demand. In this context, we are interested in a control strategy that meets at each time all possible current demands and achieves the nominal flow in the average. We provide necessary and sufficient conditions for such a strategy to exist and we characterize the set of achievable flows. Such conditions are based on linear programming and thus they are constructive. In the special case of a static flow (i.e. a system with 0-capacity buffers) we show that the strategy must be affine. The dynamic problem can be solved by a linear-saturated control strategy (inspired by the previous one). We provide numerical analysis and illustrative examples. 相似文献
69.
Raffaele Di Gregorio 《野外机器人技术杂志》2002,19(12):595-603
Translational parallel manipulators are parallel manipulators wherein the end‐effector performs only spatial translations. This paper presents a new family of translational parallel manipulators. The manipulators of this family are independent constraint manipulators. They have three limbs that are topologically identical and have no rotation singularity. The limbs of these manipulators feature five one‐degree‐of‐freedom kinematic pairs in series. Four joints are revolute pairs and the remaining one, called T‐pair, is a kinematic pair that can be manufactured in different ways. In each limb, three adjacent revolute pairs have parallel axes and the remaining revolute pair has an axis that is not parallel to the axes of the other revolute pairs. The mobility analysis of the manipulators of this new family is addressed by taking into account two different choices for the actuated pairs. One of the results of this analysis is that the geometry of a translational parallel manipulator free from singularities can be defined for a particular choice of the actuated pairs. © 2002 Wiley Periodicals, Inc. 相似文献
70.
Romano AJ Bucaro JA Ehnan RL Shirron JJ 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2000,47(6):1575-1581
The performance of an inversion algorithm is investigated when applied to measured displacement data for a determination of the material parameters /sup /spl lambda/+2/spl mu////sub /spl rho// (longitudinal wave velocity squared) and /sup /spl mu////sub /spl rho// (shear wave velocity squared) throughout an inhomogeneous test phantom. The vector displacement components throughout a test phantom subject to monochromatic shear excitation measured in time using magnetic resonance imaging (MRI) were temporally Fourier transformed to extract the component of monochromatic excitation, and the data was delivered to the inversion algorithm. A series of inversions is presented demonstrating the effects of subsequent wavenumber filtering, polarization selection, and variation in the size of the incremental volume elements. The resulting performance is assessed, and recommendations for future efforts are discussed. 相似文献