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981.
Espedito Vassallo Anna Cremona Fabio Dell’Era Francesco Ghezzi Giovanni Grosso Laura Laguardia 《Fusion Engineering and Design》2011,86(9-11):1639-1641
Erosion of materials by physical sputtering is the most fundamental of plasma–surface interactions in tokamaks. Carbon and tungsten materials planned to be used in ITER divertor are subjected to erosion, which produces local redeposition of mixed layers. Tritium retention in mixed materials is the major concern due to the limits imposed for safety reason by nuclear licensing. No technique has yet been proven capable of remove trapped tritium in ITER operating environment. In-situ oxidative cleaning techniques have been developed to remove co-deposits. Since oxygen can be incompatible with Be first wall (getter effect), a plasma cleaning using hydrogen–argon gas mixture has been proposed in this work. C–W mixed materials were produced for this purpose by capacitively coupled RF plasma sputtering. The process has been investigated by optical emission spectroscopy and Langmuir probe. 相似文献
982.
A neural pulse waveform analyzer, which uses an Intel 8080A Microprocessor to help separate pulse data received from sensory organ nerves, has been developed. The analyzer sorts data pulses according to their rise amplitudes, rise times, fall amplitudes, and fall times, all of which are measured relative to the maxima and minima points of the input waveform. The display is in the form of four histograms on an oscilloscope operated in the X-Y-Z mode. Each histogram shows the distribution of each parameter measured. With the aid of movable cursors (two on each histogram), discrimination windows may be set about peaks of interest to locate and isolate the four related parameters of a single pulse type. Simultaneous discrimination with respect to all four parameters can be accomplished using this apparatus in conjunction with a suitable nerve pulse discriminator. 相似文献
983.
Nikolaus Muellner Marco Cherubini Wolfgang Kromp Francesco DAuria Gianni Petrangeli 《Nuclear Engineering and Design》2007,237(22):2151-2156
The analysis of beyond design basis accidents (BDBA) is an essential component of the safety concept of nuclear power plants (NPP). Goal of the analysis is to achieve a set of actions aimed to prevent the escalation into a severe accident, to mitigate consequences of a severe accident, and to achieve a long term controllable state of the NPP. This paper presents an analytical procedure to optimize the timing of operator interventions. The procedure is demonstrated based on four sets of parameters, first, parameters which define the operator actions are chosen. Second, parameters which define the system availability are chosen. Third, parameters which define in a continuous way the status of the plant are chosen. Finally, one looks for a functional dependency of the accident management (AM)-parameters and the parameters describing the plant status. Once a function could be found, this function is “optimized” in the sense that the AM-parameters are varied to find a optimal overall condition for the plant. In the first part, the paper presents the analytical procedure in a general way, in the second part, an initiating event is chosen. The procedure is applied to a station black out (SBO) transient, and as operator action secondary side bleed and feed, followed by primary side bleed and feed, is foreseen. As result, the optimal timing to initiate both actions is achieved. 相似文献
984.
The neutronic properties of U-ZrH1.6 fuelled PWR cores are investigated and compared against those of the currently used UO2 fuelled cores. In the first part of this work a parametric study is performed to quantify the neutronically achievable burnup for both hydride and oxide fuels at a number of enrichment levels and for a large number of geometries covering a wide design space of fuel rod outer diameter, D, and lattice pitch, P. The fuel temperature and coolant temperature reactivity coefficients as well as the small and large void reactivity coefficients are calculated for hydride fuel with 5% and 12.5% enriched uranium. For this purpose a simplified procedure was developed that can, using single unit cell or assembly calculations, (1) account for non-linear burnup dependent k∞ and thus to adequately predict the discharge burnup; (2) estimate the burnup dependent soluble boron concentration and; (3) estimate the reactivity coefficients; all of the above for a multi-batch core. In the second part of this work a detailed neutronic analysis is carried out for the six most economical geometries of both oxide and hydride fuels, with the purpose of designing the U-ZrH1.6 fueled PWR cores to have negative reactivity coefficients. The preferred design found is replacement of 25 v/o of the ZrH1.6 by thorium hydride, along with addition of some IFBA burnable poison. It is also found that the conversion from oxide to hydride fueled PWR cores could be done without modifications in the control system. 相似文献
985.
The European Energy Efficiency Building Directive 2002/91/CE, as well as other acts and funding programs, strongly promotes the adoption of passive strategies for buildings, in order to achieve indoor thermal comfort conditions above all in summer, so reducing or avoiding the use of air conditioning systems.In this paper, the energy performances achievable using an earth-to-air heat exchanger for an air-conditioned building have been evaluated for both winter and summer. By means of dynamic building energy performance simulation codes, the energy requirements of the systems have been analysed for different Italian climates, as a function of the main boundary conditions (such as the typology of soil, tube material, tube length and depth, velocity of the air crossing the tube, ventilation airflow rates, control modes). The earth-to-air heat exchanger has shown the highest efficiency for cold climates both in winter and summer.The possible coupling of this technology with other passive strategies has been also examined. Then, a technical-economic analysis has been carried out: this technology is economically acceptable (simple payback of 5–9 years) only in the cases of easy and cheap moving earth works; moreover, metallic tubes are not suitable.Finally, considering in summer a not fully air-conditioned building, only provided with diurnal ventilation coupled to an earth-to-air heat exchanger plus night-time ventilation, the possible indoor thermal comfort conditions have been evaluated. 相似文献
986.
Giacomo Valerio Iungo Vignesh Santhanagopalan Umberto Ciri Francesco Viola Lu Zhan Mario A. Rotea Stefano Leonardi 《风能》2018,21(3):184-197
A numerical framework for simulations of wake interactions associated with a wind turbine column is presented. A Reynolds‐averaged Navier‐Stokes (RANS) solver is developed for axisymmetric wake flows using parabolic and boundary‐layer approximations to reduce computational cost while capturing the essential wake physics. Turbulence effects on downstream evolution of the time‐averaged wake velocity field are taken into account through Boussinesq hypothesis and a mixing length model, which is only a function of the streamwise location. The calibration of the turbulence closure model is performed through wake turbulence statistics obtained from large‐eddy simulations of wind turbine wakes. This strategy ensures capturing the proper wake mixing level for a given incoming turbulence and turbine operating condition and, thus, accurately estimating the wake velocity field. The power capture from turbines is mimicked as a forcing in the RANS equations through the actuator disk model with rotation. The RANS simulations of the wake velocity field associated with an isolated 5‐MW NREL wind turbine operating with different tip speed ratios and turbulence intensity of the incoming wind agree well with the analogous velocity data obtained through high‐fidelity large‐eddy simulations. Furthermore, different cases of columns of wind turbines operating with different tip speed ratios and downstream spacing are also simulated with great accuracy. Therefore, the proposed RANS solver is a powerful tool for simulations of wind turbine wakes tailored for optimization problems, where a good trade‐off between accuracy and low‐computational cost is desirable. 相似文献
987.
The photovoltaic-thermal (PVT) systems allow the enhancement of the energy performance of photovoltaics, by removing thermal energy and subsequently decreasing the operating temperature of the cells. The possibility of the utilization of heat for climatization makes them attractive for the building integration. In order to diffuse this kind of solar systems it is necessary to translate the basic concepts into efficient and functional technological components and associated performance should be evaluated in a reliable manner. This paper presents the experimental and theoretical results of a research and development program carried out at the Politecnico di Milano on the design, development and performance monitoring of a hybrid PVT air collector. One of the main products of the research consists of a simulation model for performance prediction of the system. This R&D program led to the development of the TIS (tetto integrale solarizzato, i.e. integrated solar roof), an innovative technological system for building integration of hybrid PVT air collectors. The successful commercial application of the TIS in a research center building is also shown as a case study. 相似文献
988.
The present work considers the possibility of using Petri Nets (PN) as a systematic model to analyze delays in digital circuits. It has been found that PN's exhibit some interesting features in representing digital circuits at gate, element, unit or system level, whichever is needed. Furthermore, the logic verification can be achieved as a special case of the design verification because of the direct implementation of the thruth table of the circuit in the PN. In particular, a set of basic PN functions and a method of converting the circuit into the final PN, composed of the basic functions, are proposed. Moreover, an algorithm has been developed for the analysis of combinational circuits including also reconvergent fanouts and some examples are reported in the text. The algorithm may be employed to obtain the pdf of the overall circuit delay and to detect static hazards as well. The complexity of the model is directly related to that of the physical circuit to be analyzed, while the complexity of simulation does not increase with the timing precision required. 相似文献
989.
Marco Cherubini Nikolaus Muellner Francesco Dauria Gianni Petrangeli 《Nuclear Engineering and Design》2008,238(1):74-80
The University of Pisa was involved in investigations of an Accident Management (AM) procedure based on passive feed water injection. Some experiments were performed to validate this possibility (e.g. in LOBI and Bethsy facilities) and fully analyzed by thermal hydraulic system codes. Recent activities in which the University of Pisa is engaged (also as leader) are focused on VVER-1000 safety analyses. The idea is now to use the acquired knowledge to explore if a procedure based on passive feed water injection is applicable and can provide any benefits to the Russian design pressurised plant.The postulated accident is a station blackout, in such a way only passive systems are available. The proposed AM is based on secondary and primary side depressurisation in sequence. The secondary side depressurisation performed by the BRU-A valves has the scope to feed passively the SGs with the water left in the feed water lines and in the deaerators. The primary side depressurisation, via the PORV, is foreseen to keep the plant at the lowest pressure (to reduce the energy of the system) and to maximize the “grace time” of the plant. Three cases are here considered: no operator action, application of the optimized AM sequence, application of the AM procedure at the last time when it is effective.The intention of this paper is to show that in case of an unlikely event such a SBO the implementation of a strategy based on systems not designed for specific safety application can have a large impact on the “grace time” of the plant. 相似文献
990.
Francesco Saverio Marra Francesco Miccio Roberto Solimene Riccardo Chirone Massimo Urciuolo Michele Miccio 《国际能源研究杂志》2020,44(15):12572-12582
The paper deals with the integration between a kinematic Stirling engine and a fluidized bed combustor for micro-scale cogeneration of renewable energy. A pilot-scale facility integrating a 40 kWt combustor and a γ-type Stirling engine (0.5 kWe) was set up and tested to demonstrate the feasibility of this solution. The Stirling engine was installed at a lateral wall of the combustor in direct contact with the fluidized bed region. An experimental campaign was executed to assess the performance of the innovative integrated system. The experimental results can be summarized in: (a) very high combustion efficiency with biomass feeding, (b) elevated heat transfer rate to the engine, (c) a relatively small share (about 2 kWt) transferred to the engine from the thermal power generated by the combustor (around 13 kWt), (d) conversion to electric power close to the upper limit of the engine, (e) limited impact of the Stirling engine on the fluidized bed behavior, for example, temperature. From the analysis of measured variables, the dynamics is dominated by the fast response of the Stirling engine, which rapidly reacts to the slow changes of the fluidized bed combustor regime: the dynamic response of the tested facility as a thermal system was slow, the time constant being of the order of 10 minutes. 相似文献