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41.
Prashant Singh Pradeep Kumar Anju Katyal Rashmi Kalra Sujata K. Dass Satya Prakash Ramesh Chandra 《Catalysis Letters》2010,134(3-4):303-308
In this present work, we report that phosphotungstic acid provides a simple, efficient and environmentally benign route is a two-component one-pot domino Knoevenagel-type condensation/Michael reaction between 4-coumarin derivative and an aldehyde in water as a solvent in shorter duration with high yields. 相似文献
42.
Dipankar Saha Amretashis Sengupta Sitangshu Bhattacharya Santanu Mahapatra 《Journal of Computational Electronics》2014,13(4):862-871
We report the effect of topological as well as lattice vacancy defects on the electro-thermal transport properties of the metallic zigzag graphene nano ribbons at their ballistic limit. We employ the density function theory–Non equilibrium green’s function combination to calculate the transmission details. We then present an elaborated study considering the variation in the electrical current and the heat current transport with the change in temperature as well as the voltage gradient across the nano ribbons. The comparative analysis shows, that in the case of topological defects, such as the Stone-Wales defect, the electrical current transport is minimum. Besides, for the voltage gradient of 0.5 Volt and the temperature gradient of 300 K, the heat current transport reduces by \({\sim }62\,\%\) and \({\sim }50\,\%\) for the cases of Stones-Wales defect and lattice vacancy defect respectively, compared to that of the perfect one. 相似文献
43.
The present work deals with an ultrasonic type of wave propagation characteristics of monolayer graphene on silicon (Si) substrate. An atomistic model of a hybrid lattice involving a hexagonal lattice of graphene and surface atoms of diamond lattice of Si is developed to identify the carbon-silicon bond stiffness. Properties of this hybrid lattice model is then mapped into a nonlocal continuum framework. Equivalent force constant due to Si substrate is obtained by minimizing the total potential energy of the system. For this equilibrium configuration, the nonlocal governing equations are derived to analyze the ultrasonic wave dispersion based on spectral analysis. From the present analysis we show that the silicon substrate affects only the flexural wave mode. The frequency band gap of flexural mode is also significantly affected by this substrate. The results also show that, the silicon substrate adds cushioning effect to the graphene and it makes the graphene more stable. The analysis also show that the frequency bang gap relations of in-plane (longitudinal and lateral) and out-of-plane (flexural) wave modes depends not only on the y-direction wavenumber but also on nonlocal scaling parameter. In the nonlocal analysis, at higher values of the y-directional wavenumber, a decrease in the frequency band gap is observed for all the three fundamental wave modes in the graphene–silicon system. The atoms movement in the graphene due to the wave propagation are also captured for all the tree fundamental wave modes. The results presented in this work are qualitatively different from those obtained based on the local analysis and thus, are important for the development of graphene based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors and enhancer of surface image resolution that make use of the ultrasonic wave dispersion properties of graphene. 相似文献
44.
Anindita Bhadra Aniruddha Mitra Sujata A. Deshpande Kannepalli Chandrasekhar Dattatraya G. Naik Abraham Hefetz Raghavendra Gadagkar 《Journal of chemical ecology》2010,36(4):424-431
Queens and workers are not morphologically differentiated in the primitively eusocial wasp, Ropalidia marginata. Upon removal of the queen, one of the workers becomes extremely aggressive, but immediately drops her aggression if the
queen is returned. If the queen is not returned, this hyper-aggressive individual, the potential queen (PQ), will develop
her ovaries, lose her hyper-aggression, and become the next colony queen. Because of the non-aggressive nature of the queen,
and because the PQ loses her aggression by the time she starts laying eggs, we hypothesized that regulation of worker reproduction
in R. marginata is mediated by pheromones rather than by physical aggression. Based on the immediate loss of aggression by the PQ upon return
of the queen, we developed a bioassay to test whether the queen’s Dufour’s gland is, at least, one of the sources of the queen
pheromone. Macerates of the queen’s Dufour’s gland, but not that of the worker’s Dufour’s gland, mimic the queen in making
the PQ decrease her aggression. We also correctly distinguished queens and workers of R. marginata nests by a discriminant function analysis based on the chemical composition of their respective Dufour’s glands. 相似文献
45.
The Swedish legal restriction on construction of multi-storey timber buildings was imposed in 1888 and repealed in 1994. The subsequent emergence of such a timber building system in Sweden is analysed in the context of the existing concrete-based construction system. The characteristics of the construction industry and its path dependency over the past century hamper the development of a timber building system. However, government policies and funding, the wood industry's interest in an enhanced market for value-added wood products, and involvement of the wood research community has helped develop such a construction system. Investments in knowledge creation, incentives for the entry of new firms, and increased prefabrication may facilitate a transition from this formative phase to a growth phase in the diffusion of timber buildings. En Suède, les restrictions juridiques frappant la construction de bâtiments en bois de plusieurs étages ont été édictées en 1888 et annulées en 1994. L'auteur analyse l'arrivée résultante d'un tel système de construction en bois en Suède face à la construction en béton qui existe actuellement. Les caractéristiques de l'industrie du bâtiment et sa dépendance au chemin au cours du siècle dernier empêchent le développement d'un système de construction en bois. Toutefois, les politiques officielles et les financements ainsi que les intérêts de l'industrie du bois dans un marché amélioré pour des produits en bois à valeur ajoutée et l'engagement des chercheurs dans le domaine du bois ont aidé à développer un tel système de construction. Les investissements dans la création du savoir, les incitations à l'arrivée de nouvelles entreprises et l'augmentation de la préfabrication peuvent faciliter le passage de cette phase de formation à une phase de croissance à la diffusion des bâtiments en bois. Mots clés: système d'innovation, restriction, bâtiments de plusieurs étages, dépendance au chemin, systèmes technologiques, charpente en bois, bâtiments en bois, Suède 相似文献
46.
N. Mahapatra G. C. Dash S. Panda M. Acharya 《Journal of Engineering Physics and Thermophysics》2010,83(1):130-140
The effect of a chemical reaction on a free convection flow through a porous medium bounded by a vertical infinite surface
has been studied. Velocity, temperature, and concentration profiles have been obtained for different values of parameters
like the Grashof number, Prandtl number, and the chemical reaction parameter in the presence of homogeneous chemical reaction
of first order. It is observed that the velocity and concentration increase during a generative reaction and decrease in a
destructive reaction. The same is true for the behavior of the fluid temperature. The presence of the porous media diminishes
the temperature. 相似文献
47.
Batch type production strategies need adoption of cellular manufacturing (CM) in order to improve operational effectiveness by reducing manufacturing lead time and costs related to inventory and material handling. CM necessitates that parts are to be grouped into part families based on their similarities in manufacturing and design attributes. Then, machines are allocated into machine cells to produce the identified part families so that productivity and flexibility of the system can be improved. Zero-one part-machine incidence matrix (PMIM) generated from route sheet information is commonly presented as input for clustering of parts and machines. An entry of ‘1’ in PMIM indicates that the part is visiting the machine and zero otherwise. The output is generated in the form of block diagonal structure where each block represents a machine cell having more than one machines and a part family. The major limitations of this approach lies in the fact that important production factors like operation time, sequence of operations, and lot size of the parts are not accounted for. In this paper, an attempt has been made to propose a clustering methodology based on adaptive resonance theory (ART) for addressing these issues. Initially, a methodology considering only the operation sequence of the parts has been proposed. Then, the methodology is suitably modified to deal with combination of operation sequence and operation time of the parts to address generalized cell formation (CF) problem. A new performance measure is proposed to quantify the performance of the proposed methodology. The performance of the proposed algorithm is tested with benchmark problems from open literature and the results are compared with the existing methods. The results clearly indicate that the proposed methodology outperforms the existing methods in most cases. 相似文献
48.
M.M. Mahapatra G.L. Datta B. Pradhan N.R. Mandal 《International Journal of Pressure Vessels and Piping》2006
Achieving adequate top and bottom reinforcement is important to minimize angular distortions in single-pass submerged arc welded (SAW) butt joints. This is achieved in the present work by using a reusable flux-filled backing strip and proper SAW process parameters without resorting to costly distortion mitigation techniques. The butt joints were made without edge (square butts) preparation. The process was also modeled by using three-dimensional finite element analysis by incorporating the top and bottom reinforcements into the modeling. Filler material deposition was also simulated. Temperature distributions and angular distortions obtained from the modeling closely matched with the experimental values. Thus, the cost effective experimental methodology established in the present work can be utilized for minimizing angular distortions in SAW square butts. The modeling methodology adopted can be used for predicting the angular distortions in SAW square butts with top and bottom reinforcements. 相似文献
49.
R. B. Mahapatra J. K. Brimacombe I. V. Samarasekera 《Metallurgical and Materials Transactions B》1991,22(6):875-888
Axial heat-flux profiles have been determined quantitatively from temperature measurements conducted on a slab mold under
routine operating conditions. As in earlier studies, the heat flux was observed to have a maximum value at the meniscus and
to decline with increasing distance down the mold. The mold heat flux increased with increasing casting speed and was greater
with a mold powder having lower viscosity and melting point being applied as lubricant. The heat extraction was largest while
casting 0.29 pet carbon steel and least for a 0.09 pet carbon grade; reducing the depth of the submerged entry nozzle increased
the heat flux slightly in the upper region of the mold. Most significant was the higher heat flux observed at the meniscus
of the outside-radius face, attributable to the locally greater copper plate thickness compared to that of the opposite broad
face. All of the measurements can be explained straightforwardly by heat flow in the vicinity of the meniscus and the resulting
behavior of the so-called slag rim adjacent to the mold wall. It is postulated that the difference in copper plate thickness
between the two broad faces at the meniscus causes the slag rim to be smaller on the outside-radius face which gives rise
to shallower oscillation marks, as observed, higher heat transfer, and a slightly thicker solid shell. The dissimilar behavior
has implications for quality because the inside-radius shell, experiencing reduced heat extraction, cools and shrinks less
than the outside-radius shell. Thus, for a given end-plate taper, the narrow face of the slab adjacent to the inside radius
can push against the end plate, accelerating copper wear, and, owing to squeezing of the broad face, cause an off-corner depression
and subsurface crack toward the mold exit. If this is correct, maintenance of the same copper plate thickness at the meniscus
is fundamental to preventing such an occurrence. Moreover, adjustment of the heat extraction at the meniscus should be achievable
by changing copper plate thickness, mold coating thickness/conductivity, cooling water velocity, cooling channel configuration,
and mold flux composition for a given steel grade.
Formerly Graduate Student, Centre for Metallurgical Process Engineering, The University of British Columbia, 相似文献
50.
The spectral photoresponse and the current-voltage (I–V) characteristics of the illuminated n-CdS electrode in 1 M Na2S, 1 M S and 1 M KOH electrolyte were measured. Both pressure-sintered and electro-deposited polycrystalline CdS electrodes were used in the study of their photoelectrochemical behaviour. The results indicate that the addition of a small amount of CdSe into the CdS electrode enhances the performance of the photoelectrochemical (PEC) cell. 相似文献