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431.
In this paper, a new N-way hybrid power combiner for improving the graceful degradation performance has been proposed. The proposed combiner has been configured with two dummy transmission lines per each section, where each dummy transmission line has a different characteristic impedance, of the standard combiner. Under this proposed configuration, a detailed theoretical analysis has been performed to show the general function of a power combiner. When any M amplifiers among N identical amplifiers are suffering the failure mode in a power combining circuit or system, the graceful degradation performance has been improved due to the separation of a transmission line and an internal resistor in every failed section from the proposed combiner by simultaneously operating two shorting devices. Simulation results for all the items which can be measured from the proposed combiner with an eight-way configuration have been presented. 相似文献
432.
This paper presents a model for throughput-improvement in stochastic networks. It synthesizes and extends the state-of-knowledge on determining the mean value, the lower bound (LB), and upper bound (UB) for the maximum-flow network-design problem. Through the use of an artificial-intelligence programming-language such as PROLOG, the LB was solved very efficiently the first time. The key lies in using `depth-first search' to generate the flow paths, which are then directly fed into a linear programming (LP) or mixed-integer mathematical programming (MIP) package. In all networks, the LB solution is a better approximation to the exact solution than the UB, which is consistent with theoretical findings. This finding is important in that the 7 acyclic networks represent a diversity of geometry and of survival probabilities. Another advantage of using the LB model and the path-enumeration solution-strategy has to do with an approximation of network reliability and vulnerability in that these approximate measures of performance are readily available from the solutions. Built upon the idea of most-probable states, reliability UB and vulnerability are related to the paths actually used. The paths used are but a small fraction of the paths generated, and the number of generated paths is again tiny compared to the 2n probability states. A minute fraction of the total number of failure states accounts for most of the state space-a fact that is further reinforced by the prevalence of a zero-throughput state in the flow distributions 相似文献
433.
W. H. Yim C. C. D. Kwan F. P. Coakley B. G. Evans 《International Journal of Satellite Communications and Networking》1988,6(3):243-251
A study of the digital transmultiplexor element of an on-board multi-carrier demodulator (MCD) results in design data for various architectures (FFT, tree etc.) which can be applied to a wide range of applications. A detailed design based on the latter for a 4 × 16 kb/s MCD for the U.K. T-SAT mobile OBP payload is presented. Implementation of the MCD using TMS320C25 signal processor technology has been performed and early test results are presented. 相似文献
434.
Jongsun Yoon Min Ryu Hyeongjeong Kim Gwang-Noh Ahn Se-Jun Yim Dong-Pyo Kim Hyomin Lee 《Advanced materials (Deerfield Beach, Fla.)》2020,32(34):2002710
Transparent substrates are widely used for optical applications from lenses for personal and sports eyewear to transparent displays and sensors. While these substrates require excellent optical properties, they often suffer from a variety of environmental challenges such as excessive fogging and surface contamination. In this work, it is demonstrated that a wet-style superhydrophobic coating, which simultaneously exhibits antifogging, antireflective, and self-cleaning properties, can be prepared by pattern transferring low-surface-energy microstructures onto a heterostructured nanoscale thin film comprising polymers and silica nanoparticles. The polymer–silica nanocomposite base layer serves as a hydrophilic reservoir, guiding the water molecules to preferentially condense into this underlying region and suppress reflection, while the low-surface-energy microstructure enables contaminants adsorbed on the surface to be easily removed by rinsing with water. 相似文献
435.
Modelling foot height and foot shape-related dimensions 总被引:1,自引:0,他引:1
The application of foot anthropometry to design good-fitting footwear has been difficult due to the lack of generalised models. This study seeks to model foot dimensions so that the characteristic shapes of feet, especially in the midfoot region, can be understood. Fifty Hong Kong Chinese adults (26 males and 24 females) participated in this study. Their foot lengths, foot widths, ball girths and foot heights were measured and then evaluated using mathematical models. The results showed that there were no significant allometry (p > 0.05) effects of foot length on ball girth and foot width. Foot height showed no direct relationship with foot length. However, a normalisation with respect to foot length and foot height resulted in a significant relationship for both males and females with R(2) greater than 0.97. Due to the lack of a direct relationship between foot height and foot length, the current practice of grading shoes with a constant increase in height or proportionate scaling in response to foot length is less than ideal. The results when validated with other populations can be a significant way forward in the design of footwear that has an improved fit in the height dimension. 相似文献
436.
Evaluations of apparent slip and polymer adsorption are reported for laminar capillary flow of dilute aqueous solutions of the three homologues WSR 301, Coagulant and FRA of Polyox. Measurements were carried out using glass tubes coated with a silane compound (dimethyldiethoxysilane) as well as for the untreated glass tubes. The results indicate that flow enhancement is dominant at the very low polymer concentrations and flow retardation is dominant at the higher concentrations comprising the polymer concentration range investigated. A transition from a positive to a negative effective velocity at the wall was observed with increasing polymer concentration. A new analysis was applied to separate the contributions of polymer adsorption and slip in the evaluation of the effective velocity at the wall. Effective hydrodynamic thicknesses of the adsorbed polymer layers are presented as a function of the polymer molar mass and concentration and the wall shear stress. The thickness of the adsorbed layer at zero shear was also evaluated from the capillary flow data. 相似文献
437.
Jong-Ki Jeon Heejin Lee Jin-Heong Yim Yong Seung Kim Seong Jun Lee Young-Kwon Park Jeong Kuk Shon Ji Man Kim 《Catalysis Letters》2007,119(1-2):179-184
A highly selective and active catalyst for the positional isomerisation of 2-butene into 1-butene has been developed by using
a mesoporous silica, MCM-41. The yields of 1-butene as well as total conversion decrease when aluminium or lanthanum was added
to the MCM-41 even though the amounts of acid sites increase. FT-IR spectra proved that the H site due to the silanol group
may act as an active site for the positional isomerisation of 2-butene to 1-butene. 相似文献
438.
Jin‐Heong Yim Yi‐Yeol Lyu Hyun‐Dam Jeong Sang Kook Mah Jingyu Hyeon‐Lee Jun‐Hee Hahn Gwang Seok Kim Seok Chang Jae‐Geun Park 《应用聚合物科学杂志》2003,90(3):626-634
Several kinds of homogeneous organic–inorganic hybrid polymer thin films were designed with improved mechanical properties and low dielectric constants (<3.0). Novel soluble siloxane–silsesquioxane hybrid polymers were synthesized with cyclic and/or cage silane monomers, which had triorganosiloxy (R3Si1/2), diorganosiloxane (R2SiO2/2), and organosilsesquioxane (RSiO3/2) moieties with ethylene bridges at the molecular level, by the hydrolysis and condensation of 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane (a cyclic monomer). The electrical properties of these films, including the dielectric constant (~2.51), leakage current (6.4 × 10?11 A/cm2 at 0.5 MV/cm), and breakdown voltage (~5.4 MV/cm) were fairly good. Moreover, the mechanical properties of the hybrid films, including the hardness (~7 GPa), modulus (~1.2 GPa), and crack‐free thickness (<2 μm), were excellent in comparison with those of previous spin‐on‐glass materials with low dielectric constants. The excellent mechanical properties were proposed to be due to the high contents of Si? OH groups (>30%) and the existence of ethylene bridge and siloxane moieties in the hybrid polymer precursors. In addition, the mechanical properties of the hybrid films were affected by the contents of the cagelike structures. The more cagelike structures a hybrid film contained, the worse its mechanical properties were. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 626–634, 2003 相似文献
439.
The planar 4H-SiC MESFETs were fabricated by employing an ion-implantation process instead of a recess gate etching process, which is commonly adapted in compound semiconductor MESFETs, to eliminate potential damage to the gate region during etching process. Excellent ohmic and Schottky contact properties were achieved by using the modified RCA cleaning of 4H-SiC surface and the sacrificial thermal oxide layer. The fabricated MESFETs was also free from drain current instability, which the most of SiC MESFETs have been reported to suffer for the charge trapping. The drain current recovery characteristics were also improved by passivating the surface with a thermal oxide layer and eliminating the charge trapping at the surface. The performance of fabricated MESFETs was characterized by analyzing the small-signal equivalent circuit parameters extracted from the measured parameters. 相似文献
440.
Three-feature based automatic lane detection algorithm (TFALDA) for autonomous driving 总被引:1,自引:0,他引:1
Young Uk Yim Se-Young Oh 《Intelligent Transportation Systems, IEEE Transactions on》2003,4(4):219-225
Three-feature based automatic lane detection algorithm (TFALDA) is a new lane detection algorithm which is simple, robust, and efficient, thus suitable for real-time processing in cluttered road environments without a priori knowledge on them. Three features of a lane boundary - starting position, direction (or orientation), and its gray-level intensity features comprising a lane vector are obtained via simple image processing. Out of the many possible lane boundary candidates, the best one is then chosen as the one at a minimum distance from the previous lane vector according to a weighted distance metric in which each feature is assigned a different weight. An evolutionary algorithm then finds the optimal weights for combination of the three features that minimize the rate of detection error. The proposed algorithm was successfully applied to a series of actual road following experiments using the PRV (POSTECH research vehicle) II both on campus roads and nearby highways. 相似文献