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991.
Secret sharing schemes are multi-party protocols related to key establishment. They also facilitate distributed trust or shared
control for critical activities (e.g., signing corporate cheques and opening bank vaults), by gating the critical action on
cooperation from t(t ∈ Z
+) of n(n ∈ Z
+) users. A (t, n) threshold scheme (t < n) is a method by which a trusted party computes secret shares Γ
i
(1 ⩽ i ⩽ n) from an initial secret Γ
0 and securely distributes Γ
i
to user. Any t or more users who pool their shares may easily recover Γ
0, but any group knowing only t−1 or fewer shares may not. By the ElGamal public key cryptophytes and the Schnorr’s signature scheme, this paper proposes
a new (t, n) threshold signature scheme with (k,m) (k,m ∈ Z
+) threshold verification based on the multivariate linear polynomial. 相似文献
992.
In an identity based proxy signature (IBPS) scheme, a designated proxy signer can generate the signature on behalf of an original
signer. Traditional IBPS schemes normally rely on the assumption that private keys are kept perfectly secure. However, due
to viruses, worms or other break-ins allowed by operating-system holes, key exposure seems inevitable. To minimize the damage
caused by key exposure in IBPS, we propose an identity-based key-insulated proxy signature (IBKIPS) scheme in the standard
model, i.e. without random oracles. 相似文献
993.
Giles Thomas Stefan Winkler Michael Davis Damien Holloway Shinsuke Matsubara Jason Lavroff Ben French 《Journal of Marine Science and Technology》2011,16(1):8-21
Slam events experienced by high-speed catamarans in irregular waves were characterised through experiments using a hydroelastic
segmented model. The model was designed to represent the dynamic behaviour of the full-scale Incat 112 m vessel and to allow
the measurement of the slam load on the centrebow and wet deck. It was tested in irregular head seas at two speeds relating
to Froude numbers of 0.32 and 0.60. Nearly 300 slams were identified in the test data and analysed with respect to kinematic
parameters. Slams were found to have a large range of magnitudes, with the largest equivalent to 1785 tonnes full scale (approximately
70% of vessel displacement); however, the majority of events were of relatively low severity. Differences in slam characteristics
were found for the two model speeds tested; slams at the slower speed generally occurred further forward on the hull, prior
to the wave crest and with a bow down pitch angle. Immersion of the centrebow to the two-dimensional filling height of the
cross-section between the centrebow and demihulls is shown to be a better indicator of slam occurrence than immersion to the
top of the archway. 相似文献
994.
Sloshing waves in moving tanks is an important engineering problem, and most studies of this phenomenon have focused on tanks
that are excited by forcing motion in a limited number of directions and with fixed excitation frequencies throughout the
forcing. In practice, the excitation comprises multiple degree of freedom motion that potentially couples surge, sway, heave,
pitch, roll, and yaw motions. In the present study, a time-independent finite difference method is used to simulate fluid
sloshing in three-dimensional tanks filled to an arbitrary depth for various excitation frequencies and multiple degree of
freedom motion. The numerical scheme developed here was verified by rigorous benchmark tests. The coupled motions of surge
and sway are simulated for various excitation angles, frequencies and water depths. Five kinds of sloshing waves found under
coupled surge–sway motions: diagonal, single-directional, square-like, swirling, and irregular waves. The effect of excitation
angle on the frequency responses of different sloshing waves is analyzed and discussed in the present study. Further, the
components of horizontal force of various sloshing waves are also presented. The coupled effect of surge, sway and heave motions
is also discussed, and the results show that unstable sloshing occurs when the excitation frequency of the heave motion is
twice the fundamental natural frequency. Moreover, the effects of heave motion on the different types of sloshing waves are
explored. It is found that heave motion causes all of the sloshing waves to change type. 相似文献
995.
The dynamic response of planing vessels in regular head seas is investigated numerically. Nonlinear time domain simulations
were performed using a 2D + t theory (two-dimensional plus time dependent theory). A prismatic hull form was assumed. We employed a two-dimensional (2D)
boundary element method to solve the initial boundary value problems in 2D cross planes, in which nonlinear free-surface conditions
and exact body boundary conditions were satisfied. At each time step, the total force and moment on the hull could be obtained
by using the sectional forces calculated in those 2D planes. Heave and pitch motions were then acquired by solving the equations
for those motions. The calculated heave and pitch responses were compared with the experiments by Fridsma (A systematic study
of the rough-water performance of planing boats. Davidson Laboratory Report R-1275, 1969) for two different Froude numbers. Three-dimensional (3D) corrections at the transom stern were applied to show the influence
of the 3D effect at the stern on the numerical results. Ship motions were affected by the 3D corrections, especially near
the resonance frequency, while the phase angles were slightly affected and the acceleration peaks at the bow near the resonance
frequency were sensitive to the 3D corrections. Other error sources in the theoretical results are also mentioned. 相似文献
996.
Manivannan Kandasamy Daniele Peri Seng Keat Ooi Pablo Carrica Frederick Stern Emilio F. Campana Philip Osborne Jessica Cote Neil Macdonald Nic de Waal 《Journal of Marine Science and Technology》2011,16(2):143-156
The wakes of high-speed passenger-only ferries that operated through Rich Passage, on the Seattle-Bremerton ferry route, caused
beach erosion and damage to habitat. A task was initiated to design a low-wake high-speed vessel using multi-fidelity CFD
based design optimization by using low-fidelity potential flow solvers for initial global design optimization and by using
URANS solvers for high-fidelity tuning of the optimized design. This simulation based design process involved a close collaboration
between ship designers, and hydrodynamics and CFD specialists, whose collective expertise guided the evolution of the design
based on both hydrodynamic and structural aspects. The initial hull shape optimization using potential flow code was carried
out by blending three different initial concepts provided by the designers. Subsequently, URANS was used to evaluate the potential
flow optimized hull and to further optimize the hull configuration parameters, namely, the centre-of-gravity, demihull spacing,
foil location, foil angle and slenderness ratio at different displacement conditions. The URANS based configuration optimization
also took into account the far field wakes’ energy spectrum with an objective of reducing the energetic, low frequency far
field wakes which are associated with beach flattening on the mixed sand and gravel beaches. Calculation of the far field
wake using URANS would require an unfeasibly large domain size; therefore, a Havelock code with a source distribution matching
the URANS calculated near field wave elevation was used to propagate the wakes into the far field. The end result of the optimization
was a design with significantly reduced far field wake, which is currently being built for experimental testing. 相似文献
997.
DongYoung Lee GyungNam Jo YunHo Kim Hang S. Choi Odd M. Faltinsen 《Journal of Marine Science and Technology》2011,16(3):323-330
In this paper, we investigated the effect of sloshing on the sway motions of two-dimensional rectangular cylinders in regular
waves, bearing in mind possible applications for LNG-FPSO and LNG-FSRU. First, we carried out experiments for two models with
different drafts, or the same draft but different filling ratios, in which the models were firmly connected to each other.
The sway motion was measured with a noncontact video camera. This is an extension of Rognebakke and Faltinsen’s work for a
single model (J Ship Res 47(3):208–221, 2003). It was found that the sway motion became small when the incident wave frequency was close to the lowest natural frequency
of each model. The sway motion greatly increased when the wave frequency was higher than this frequency. The measured data
were compared with numerical results obtained by a single-dominant multi-modal method; relatively good agreement was noted.
However, the numerical results deviated from the experimental results near the lowest natural frequency of the smaller model,
which was believed to be due to overturning waves, as observed during the experiment. Since this is out of the valid range
for the single-dominant multi-modal method, other, more appropriate, methods such as the multi-dominant modal method must
be applied instead. 相似文献
998.
We investigated the difference in fatigue behaviour between the aluminium alloys A5083-O and A5083-H321, which are used as structural components in ships and high speed craft. We obtained S–N curves for the base materials and the welded joints made of A5083-O. The relationships between the fatigue crack propagation rates and the stress intensity factor ranges ΔK, ΔK eff and ΔK RPG (Toyosada et al. in Int J Fatigue 26(9):983–992, 2004) were determined. Additionally, the evolution of fatigue crack growth for the base materials and the welded joints made of A5083-O was measured. We also carried out numerical simulations of fatigue crack growth for both base metals and their welded joints made of A5083-O. The difference in fatigue crack growth behaviour for each alloy and the validity of the numerical simulations of fatigue crack growth based on the RPG stress criterion (Toyosada et al. 2004) in the base materials and their welded joints was investigated. 相似文献
999.
Myeong-jo Son Sang Chul Lee Ki-chang Kwon Tae-wan Kim Rajiv Sharma 《Journal of Marine Science and Technology》2011,16(4):367-378
Ships are complex engineering structures that are designed and built on the basis of technical experience. A shipowner will
often be required to estimate the price of a new ship on the basis of the value of comparable ships identified in trade journals.
Similarly, shipbuilders are often interested in estimating approximate costs during the tendering phase in order to determine
whether a ship is likely to be competitive for a particular order. Thus, when designing a ship prior to having obtained a
contract, one of the most important processes is the estimation of approximate costs, including materials, associated labor,
and overhead. During this preliminary design phase, the design is temporary and subject to change based on variations in the
shipowner’s requirements. Hence, quick and flexible responses are key during this period and an integral aspect of the competitive
powers of the shipbuilder. Given this environment, we propose a “configuration estimation method.” Our method is based on
the configuration design method that is widely used in three-dimensional (3D) computer aided design (CAD) systems. We assume
that a product lifecycle management system is furnished and that the cost is then estimated via the configuration of the ship,
using an engineering bill of materials (E-BOM). In referring to the E-BOM, we utilize technical parametric costs derived from
similar ships built previously. Using the proposed method, it is possible to obtain an accurate list of materials from the
quotation, as well as a detailed work assessment for labor costs and overhead rates, so that reliable cost estimates can be
generated quickly and flexibly. To demonstrate the practical applicability and effectiveness of the proposed method, we implement
the prototype of a shipbuilding configuration estimation system by using a Microsoft Structured Query Language database and
an E-BOM from AVEVA Marine version 12.01, which is a representative CAD system for shipbuilding. 相似文献
1000.
Hyun Park Nam Hyun An Nicholas Hutchins Kwing-So Choi Ho Hwan Chun Inwon Lee 《Journal of Marine Science and Technology》2011,16(4):390-401
An experimental assessment has been made of the drag reducing efficiency of the outer-layer vertical blades, which were first
devised by Hutchins and Choi (Proceedings of ASME FEDSM’02 2002 ASME Fluids Engineering Division Summer Meeting, Montreal)
and Hutchins (An investigation of larger-scale coherent structures in fully developed turbulent boundary layers, Hutchins
N (2003), PhD thesis, University of Nottingham). The reported drag reduction efficiency, which was as much as 30%, was quantified
only in terms of the reduction in the local skin-friction coefficient. The assessment of the drag reducing efficiency did
not take the side effects of the inclusion of the blades into considerations. Those effects are the increase in the wetted
surface area and the flow disturbances due to the presence of the blades. In the present study, a series of drag force measurements
in towing tank has been performed toward the assessments of the total drag reduction efficiency of the outer-layer vertical
blades. It was found that for the case of h 4.0 × z 4.0 (h/δ = 1.04), the outer-layer vertical blades array achieved about 9.6% drag reduction without considering the increase in the
wetted surface area. A proper scaling method to give collapsed plot of drag reduction efficiency C
F/C
F0 was attempted, but the correlation remained limited. Of the two scaling methods, the outer scaling is found to be relevant
one. 相似文献