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61.
Reconfigurable mobile planetary rovers are versatile platforms that may safely traverse cluttered environments by morphing their physical geometry. Planning paths for these adaptive robots is challenging due to their many degrees of freedom, and the need to consider potentially continuous platform reconfiguration along the length of the path. We propose a novel hierarchical structure for asymptotically optimal (AO) sampling‐based planners and specifically apply it to the state‐of‐the‐art Fast Marching Tree (FMT*) AO planner. Our algorithm assumes a decomposition of the full configuration space into multiple subspaces, and begins by rapidly finding a set of paths through one such subspace. This set of solutions is used to generate a biased sampling distribution, which is then explored to find a solution in the full configuration space. This technique provides a novel way to incorporate prior knowledge of subspaces to efficiently bias search within existing AO sampling‐based planners. Importantly, probabilistic completeness and asymptotic optimality are preserved. Experimental results in simulation are provided that benchmark the algorithm against state‐of‐the‐art sampling‐based planners without the hierarchical variation. Additional experimental results performed with a physical wheel‐on‐leg platform demonstrate application to planetary rover mobility and showcase how constraints such as actuator failures and sensor pointing may be easily incorporated into the planning problem. In minimizing an energy objective that combines an approximation of the mechanical work required for platform locomotion with that required for reconfiguration, the planner produces intuitive behaviors where the robot dynamically adjusts its footprint, varies its height, and clambers over obstacles using legged locomotion. These results illustrate the generality of the planner in exploiting the platform's mechanical ability to fluidly transition between various physical geometric configurations, and wheeled/legged locomotion modes, without the need for predefined configurations. 相似文献
62.
In order to face new regulation directives regarding the environment and also for improving their customer relationship, enterprises
have to increasingly be more able to manage their product information during the entire lifecycle. One of the objectives among
others in this paper is to deal with product traceability along the product lifecycle. To meet this objective, the information
system has to be designed and, further built in such a way all information regarding products is recorded. The IEC 62264 standards
define generic logical models for exchanging product and process information between business and manufacturing levels of
enterprise applications. Thus, it can be a base for product information traceability. However, its complexity comes from the
fact it mixes conceptual and implementation details while no methodology exists that defines how to instantiate it. Product
traceability is then needed to increase its abstraction level in order to concentrate on its concepts and managing its application
by providing a methodology for its instantiation. In this paper, we propose to map the IEC 62264 standard models to a particular
view of Zachman framework in order to make the framework concrete as a guideline for applying the standard and for providing
the key players in information systems design with a methodology to use the standard for traceability purposes. 相似文献
63.
Salah S. Sedarous 《Ferroelectrics Letters Section》1998,23(5):107-119
The microscopic dynamics of phase transitions in ferroelectric crystals are studied using time-resolved fluorescence spectroscopy. Fluorescence decay times of the molecular probe tryptophan, embedded in the ferroelectric crystals potassium dihydrogen phosphate (KDP) and triglycine sulfate (TGS), are measured over a large temperature range. The dependence of the lifetime data on temperature were different between the two crystals. The magnitude of the fluorescence lifetime shows a rapid change around the phase transition temperature in KDP, while the changes in the lifetime data of the TGS crystal have been smooth. The data indicate that the order of the phase transition in solids (first or second) can be recovered using this technique. Since fluorescence lifetime is related to the dynamic interactions between the chromophore and the environment, insight into the emergence of macroscopic phase transition behavior from microscopic fluctuations near the phase transition region may be realized. 相似文献
64.
Shear Strength of Fiber-Reinforced Sands 总被引:3,自引:0,他引:3
Soil reinforcement using discrete randomly distributed fibers has been widely investigated over the last 30 years. Several models were suggested to estimate the improvement brought by fibers to the shear strength of soils. The objectives of this paper are to (1) supplement the data available in the literature on the behavior of fiber-reinforced sands; (2) study the effect of several parameters which are known to affect the shear strength of fiber-reinforced sands; and (3) investigate the effectiveness of current models in predicting the improvement in shear strength of fiber-reinforced sand. An extensive direct shear testing program was implemented using coarse and fine sands tested with three types of fibers. Results indicate the existence of a fiber-grain scale effect which is not catered for in current prediction models. A comparison between measured and predicted shear strengths indicates that the energy dissipation model is effective in predicting the shear strength of fiber-reinforced specimens in reference to the tests conducted in this study. On the other hand, the effectiveness of the predictions of the discrete model is affected by the parameters of the model, which may depend on the test setup and the procedure used for mixing the fibers. 相似文献
65.
66.
Although the wind farms based on squirrel cage induction generators (SCIG) is cheaper than the wind farms based on doubly fed induction generators (DFIG), it is always in desperate need for reactive power compensation. Nevertheless, the wind farms based on DFIG are expensive compared with the SCIG wind farm, it features by its ability to control the active power independent of reactive power. However, combined wind farm (CWF) has been developed to collect the benefits of SCIG and DFIG wind turbines in the same wind farm. In this article, artificial neural network (ANN) is used to evaluate gain parameters of static synchronous compensator (STATCOM) in order to improve the stability performance of CWF. The impact of tuned STATCOM on the performance of CWF during gust wind speed and during three-phase fault is comprehensively investigated. The performance of CWF with STATCOM tuned by ANN is compared with its performance when the STATCOM tuned by the multiobjective genetic algorithm (MOGA) and whale optimization algorithm (WOA). The results show that the performance of CWF can be enhanced using STATCOM tuned by ANN more than MOGA and WOA. 相似文献
67.
Khadhraoui Imen Ben Salah Taha Aguili Taoufik 《Journal of Computational Electronics》2022,21(3):713-723
Journal of Computational Electronics - One of the challenges in antenna analysis is achieving concordance between the results of a purely theoretical numerical method application and commercial... 相似文献
68.
Linear polyethyleneimine (L-PEI)-based nanoparticles were synthesized via hydrolysis of poly-2-methyl-2-oxazoline (PMeOx), which was prepared by cationic ring-opening polymerization of the oxazoline five-membered ring. Herein, a kinetic study of the ring-opening polymerization reaction is discussed. The nuclear magnetic resonance spectrum of PMeOx verified the presence of repeating units and terminal groups in the polymer's structure. Molar ratios of PEI and PMeOx were characterized using size exclusion chromatography with low-polydispersity polymer chains as the controlled polymerization reaction. PEI and PMeOx exhibited narrow particle size distribution with hydrodynamic radii of 89 and 67 nm, respectively, as determined via dynamic light scattering analysis. In addition, atomic forces and scanning electron microscopy were used to investigate the topography of the PEI thin films. Poly(glycidyl methacrylate) P(GMA) was grafted onto a PEI chain in the presence of trimethylolpropane triacrylate (TMPTA) as the crosslinking agent to synthesize the P(GMA–PEI–TMPTA) tripolymer via free radical polymerization using gamma irradiation. The thermal characterization of the P(GMA–PEI–TMPTA) tripolymer was conducted using thermogravimetric analysis and differential scanning calorimeter. Generally, the thermal stability of the P(GMA–PEI–TMPTA) tripolymer was improved at low-glycidyl methacrylate concentrations. The prepared tripolymer could be used as effective packaging materials for electronics industries. 相似文献
69.
70.
Research into integrated design and manufacturing based on STEP 总被引:1,自引:1,他引:0
Yaoyao F. Zhao Salah Habeeb Xun Xu 《The International Journal of Advanced Manufacturing Technology》2009,44(5-6):606-624
This paper discusses a typical STEP-compliant manufacturing environment, which effectively integrates two systems. The first generates native data that retain the information needed to machine a part on a particular machine tool, whereas the second carries out optimization for machining parameters using the dispatched information from the first system. The related research work is divided into four areas, feature generation, macro process planning, micro process planning, and machining execution. The main part of the paper is devoted to reviewing the most recent research publications. The publications have been organized into the four areas as mentioned above. The discussion section that follows looks at the STEP-compliant research from the perspectives of industrial adoption, feature recognition for process planning, challenges in STEP-enabled inspection and STEP-NC controllers. 相似文献