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991.
Kent E. Wardle Todd R. Allen Mark H. Anderson Ross E. Swaney 《American Institute of Chemical Engineers》2009,55(9):2244-2259
The annular centrifugal contactor is a compact mixer/centrifuge developed for solvent extraction processes for recycling used nuclear fuel. This research effort couples computational fluid dynamics (CFD) modeling with a variety of experimental observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the volume-of-fluid method combined with large eddy simulation of turbulence was found to have very good agreement with the experimental measurements. A detailed comparative analysis of the flow and mixing with different housing vane geometries (four straight vanes, eight straight vanes, and curved vanes) was performed. Two additional variations on the eight straight vane geometry were also simulated. This analysis determined that at the simulated moderate flow rate the four straight mixing vane geometry has greater mixing and fluid residence time as compared to the other mixing vane configurations. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
992.
Transient flow behaviors in a novel circulating‐turbulent fluidized bed (C‐TFB) were investigated by a multifunctional optical fiber probe, that is capable of simultaneously measuring instantaneous local solids‐volume concentration, velocity and flux in gas‐solid two‐phase suspensions. Microflow behavior distinctions between the gas‐solid suspensions in a turbulent fluidized bed (TFB), conventional circulating fluidized bed (CFB), the bottom region of high‐density circulating fluidized bed (HDCFB), and the newly designed C‐TFB were also intensively studied. The experimental results show that particle‐particle interactions (collisions) dominate the motion of particles in the C‐TFB and TFB, totally different from the interaction mechanism between the gas and solid phases in the conventional CFB and the HDCFB, where the movements of particles are mainly controlled by the gas‐particle interactions (drag forces). In addition, turbulence intensity and frequency in the C‐TFB are significantly greater than those in the TFB at the same superficial gas velocity. As a result, the circulating‐turbulent fluidization is identified as a new flow regime, independent of turbulent fluidization, fast fluidization and dense suspension upflow. The gas‐solid flow in the C‐TFB has its inherent hydrodynamic characteristics, different from those in TFB, CFB and HDCFB reactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
993.
A. A. Burluka J. F. Griffiths K. Liu M. Ormsby 《Combustion, Explosion, and Shock Waves》2009,45(4):383-391
Flames of di-t-butyl-peroxide (DTBP) decomposition in a 0.376DTBP + 1.0N2 mixture are studied in laminar and turbulent media. The observed values of unstretched laminar burning velocity are in reasonable
agreement with the value obtained from the Zel’dovich-Semenov-Frank-Kamenetsky theory. Turbulent explosions in this particular
mixture are characterized by a number of features that are believed to be common for all developing turbulent flames and have
relevance to spark-ignition engine combustion of lean mixtures. Flame propagation is unsteady and is characterized by a mass
burning rate that increases in time. The rate of the flame acceleration varies from one explosion to another. If the burning
rate is related to the average flame radius, however, it exhibits much smaller variations. This phenomenon bears a striking
resemblance to cycle-to-cycle variations in a spark-ignition engine. Comparisons of the present results with mixtures of significantly
different composition, chemical kinetics, and exothermicity, but with similar laminar flame speed and Lewis number show that
the data obtained in closed-volume explosions are in good agreement if the unsteady character of the flame is taken into account.
The differences in details of the kinetic mechanisms and thermochemistry appear to be responsible for the flame behaviour
only near the limit of extinction by turbulence.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 43–52, July–August, 2009. 相似文献
994.
995.
本文以多个国内地下工程的岩爆资料为基础,对岩爆彤成的力学机理进行了详细的分析,时多处工程实例进行研究,总结了目前岩爆过程发生的条件。最后。就国内外的常用和新型监测预报、防治方法予以阐述和归纳。 相似文献
996.
997.
Igor M. Moraes Rafael P. Laufer Daniel de O. Cunha Otto Carlos M. B. Duarte 《Photonic Network Communications》2009,18(1):65-76
This article proposes the load-level-based admission control (LLAC) mechanism in order to provide service differentiation
for optical burst-switched networks. The LLAC mechanism admits bursts of a given service class according to the network load
and a class-associated parameter. Based on this parameter, called load level, the proposed mechanism differentiates the burst blocking probability experienced by each service class. We develop an analytical
model for the proposed mechanism and evaluate its performance for different configurations through mathematical analysis.
The results show that the load-level-based mechanism reduces the blocking probability of high-priority bursts by two orders
of magnitude or more depending on the analyzed scenario. In addition, compared to other similar mechanisms, the load-level-based
mechanism effectively differentiates the services in all analyzed configurations, requires less states in optical burst switching
(OBS) nodes, and does not suffer from priority inversion.
相似文献
Otto Carlos M. B. DuarteEmail: |
998.
Optical burst switching (OBS) is regarded as one of the most promising switching technologies for next generation optical
networks. Contention resolution of data bursts is a critical mission to implement practical OBS. The use of fiber delay line
(FDL) buffers has received a lot of attention as a fundamental but effective solution to resolve burst contention. Several
studies have investigated the way to achieve the optimal performance of FDL buffers at a single-node level. However, this
article studies how to achieve the best performance of OBS networks with FDL buffers under varying traffic condition at a
network level. For this purpose, we propose an adaptive load-aware burst assembly (ALBA) scheme, which adaptively adjusts
the size threshold of burst assembler optimized to the current network traffic load. A piggybacking method used to deliver
the traffic-load information from core nodes to ingress edge nodes accelerates the adaptiveness of the proposed scheme by
reducing the update time of the size threshold. The effectiveness of the ALBA scheme is proved by comparing with No-FDL case
and fixed size-threshold cases under changing traffic-load environment from extensive simulation tests.
相似文献
JungYul ChoiEmail: |
999.
Reinaldo Vallejos Alejandra Zapata-Beghelli Víctor Albornoz Marco Tarifeño 《Photonic Network Communications》2009,17(3):266-276
Existing methods for handling routing and dimensioning in dynamic WDM networks solve the two problems separately. The main drawback of this approach is that a global minimum cost solution cannot be guaranteed. Given that wavelengths are costly resources, determining the minimum network cost is of fundamental importance. We propose an approach which jointly solves the routing and dimensioning problems in optical burst switching (OBS) networks, guaranteeing a target blocking per connection. The method finds the set of routes and the number of wavelengths per network link that minimise the total network cost. To accomplish this, an integer linear programming problem is solved. The proposed method was applied to ring networks, where the optimal solution achieves a reduction in the network cost of 10–40% (for traffic loads <0.4, compared to solving both problems separately). In the case of mesh topologies, to reduce the computational complexity of the method, we applied a variation of it which achieves a local minimum. Even so, a reduction of 5–20% (for traffic loads <0.4) in the network cost was obtained. This ability to lower network cost could make the proposed method the best choice to date for dynamic network operators. 相似文献
1000.
Sheng Huang Keping Long Xiaolong Yang Qianbin Chen Yun Li 《Photonic Network Communications》2009,18(1):49-54
Optical burst switching (OBS) is a promising switching paradigm for building the next generation optical internet. The proportional
differentiation model is very convenient for network operators to quantitatively adjust the quality differentiation among
service classes. To provide proportional differentiated services for OBS networks, a proportional differentiation scheme based
on batch scheduling is proposed in this article. The scheme adopts the batch scheduling idea to reserve data channel resources
for a batch of data bursts. It helps to decrease burst dropping probability. When some data bursts are unsuccessfully scheduled,
a preemption method is used to keep a proportional burst dropping probability among service classes according to the expected
burst dropping probability equations given by the proportional differentiation model. The scheme has low computational complexity.
Simulation results show that the scheme can provide proportional differentiated services and efficiently decrease the burst
dropping probability.
相似文献
Keping LongEmail: |