全文获取类型
收费全文 | 3587篇 |
免费 | 78篇 |
专业分类
公路运输 | 638篇 |
综合类 | 1100篇 |
水路运输 | 1193篇 |
铁路运输 | 310篇 |
综合运输 | 424篇 |
出版年
2024年 | 6篇 |
2023年 | 10篇 |
2022年 | 45篇 |
2021年 | 78篇 |
2020年 | 59篇 |
2019年 | 23篇 |
2018年 | 358篇 |
2017年 | 304篇 |
2016年 | 273篇 |
2015年 | 45篇 |
2014年 | 77篇 |
2013年 | 102篇 |
2012年 | 166篇 |
2011年 | 321篇 |
2010年 | 375篇 |
2009年 | 196篇 |
2008年 | 296篇 |
2007年 | 280篇 |
2006年 | 155篇 |
2005年 | 162篇 |
2004年 | 70篇 |
2003年 | 76篇 |
2002年 | 40篇 |
2001年 | 63篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有3665条查询结果,搜索用时 0 毫秒
981.
The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined.
This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution
around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed
from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage
defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and
can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular
cartilages. When the defect size was smaller than 1.00 cm2, the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution
were detected due to the large defect sizes (⩾1.00 cm2). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA
in the human knee joint. 相似文献
982.
The simulation of injection molding process requires a stable algorithm to model the molten polymer with non-isothermal non-Newtonian
property. In this paper, a staggered and iterative scheme is particularly designed to solve the velocity-pressure-temperature
variables. In consideration of the polymer characteristic of high viscosity and low thermal conductivity, the non-Newtonian
momentum-mass conservation equations are solved by the Crank-Nicolson method based split (CNBS) scheme, and the energy conservation
equation with convective character is discretized by the characteristic Galerkin (CG) method. In addition, an arbitrary Lagrangian
Eulerian (ALE) free surface tracking and mesh generation method is introduced to catch the front of the fluid flow. The efficiency
of the proposed scheme is demonstrated by numerical experiments including a lid-driven cavity flow problem and an injection
molding problem. 相似文献
983.
Rolling force and temperature field are important parameters in the hot rolling process of plate steel. Most researchers use
ANSYS/LS-DYNA and MSC.Marc to simulate the hot rolling process, however, software DEFORM-3D is not used widely in this field.
Therefore, in this study, the commercially available finite element analysis software DEFORM-3D is used to simulate the distribution
of rolling force, stress-effective, strain-effective and temperature field during the hot rolling process of plate steel with
the size of 0.220m×2.070m×1.904m. Both the simulated rolling force and temperature of the multi-pass are compared with the
measured results. It is shown that the simulated values by the finite element method are approximate to the measured values
in the hot rolling of plate steel. So the simulation can provide an important reference and optimization to make rolling process
and parameters in steel factory. 相似文献
984.
The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during
the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling
and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0
software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated
at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of
the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases
with increasing melting rate and a direct proportional relationship exists. 相似文献
985.
HAVAL is a hash function proposed by Zheng et al. in 1992, including 3-, 4- and 5-pass versions. We improve pseudo-preimage
and preimage attacks on 3-pass HAVAL at the complexity of 2172 and 2209.6, respectively, as compared to the previous best known results: 2192 and 2225 by Sasaki et al. in 2008. We extend the skip interval for partial-patching and apply the initial structure technique to find
the better message chunks, and combine the indirect-partial-matching, partial-fixing and multi-neutral-word partial-fixing
techniques to improve the attacks based on the meet-in-the-middle method. These are the best pseudo-preimage and preimage
attacks on 3-pass HAVAL. 相似文献
986.
Problems related to fault detection of networked control systems (NCSs) with both uncertain timevarying delay and quantization
error are studied in this paper. A novel model with the form of polytopic uncertainty is given to represent the influences
of both the time-varying delay and the quantization error, and then the reference model based method is used to design the
residual generator that is robust to both unknown network-induced delay and unknown inputs. A numerical example is also given
to illustrate the merits of the presented method. The proposed method can be regarded as an extension of the authors’ former
work, which can only deal with time-varying delay. 相似文献
987.
To give concurrent consideration both the efficiency and the security (intensity of intractable problem) in the standard model,
a chosen ciphertext secure identity-based broadcast encryption is proposed. Against the chosen ciphertext security model,
by using identity (ID) sequence and adding additional information in ciphertext, the self-adaptive chosen identity security
(the full security) and the chosen ciphertext security are gained simultaneously. The reduction of scheme’s security is the
decisional bilinear Diffie-Hellman (BDH) intractable assumption, and the proof of security shows that the proposed scheme
is indistinguishable against adaptive chosen ciphertext attacks in the standard model under the decisional BDH intractable
assumption. So the security level is improved, and it is suitable for higher security environment. 相似文献
988.
The optical rays that form the image of an object and propagate a supersonic flow over a vehicle are refracted by the density
variations. A numerical analysis of the aero-optical characteristics of supersonic flow over blunt wedge with a cavity window
is carried out. A hybrid method of Reynold averaged Navier-Stokes and direct simulation Monte Carlo (RANS/DSMC) is employed
to simulate the flowfield. Refraction factor is introduced to evaluate the flowfield’s aero-optical characteristic. The results
show that mean flow’s aero-optical effects are mainly caused by the shock wave, the expansion wave and the turbulent boundary
layer. Fluctuation flow’s aero-optical effects are mainly caused by the turbulent boundary layer and the shock wave induced
by the cavity window. The aero-optical effects at the leading side of window are caused by the mean density variations, while
the effects at the trailing side are caused by the density fluctuations. Different draft angles of the cavity window are investigated.
The airborne optical devices of supersonic vehicle should be mounted in the middle of the cavity window with a large draft
angle. 相似文献
989.
入口匝道控制是缓解高速公路交通拥挤的主要控制方式之一。在分析高速公路交通流运行特性的前提下,选择交通流平均速度、入口匝道排队长度作为模糊控制的输入量,入口匝道调节率作为模糊控制的输出量;然后,借鉴入口匝道控制的原理和模糊控制系统的设计步骤,运用MATLAB仿真软件确定了相应的隶属函数、模糊控制规则、模糊推理以及反模糊化的方法;最后,从交通流平均速度、入口匝道排队长度以及入口匝道调节率这三者之间的输入/输出特性曲面,可以明显地看出该模糊控制系统更符合匝道控制的实际情况,并且在行程时间和总服务流量上均优于定时控制。 相似文献
990.
Giorgio Contento Guido Lupieri Marco Venturi Tiziana Ciuffardi 《Journal of Marine Science and Technology》2011,16(2):181-201
The present study is aimed at determining the confidence limits of design wave parameters derived from numerical modeling—for
both extremes and operational conditions—over the Central and Western Mediterranean Sea. The paper presents the methodology
and results of an extensive validation activity conducted on a chain of medium-resolution third-generation wave models used
for hindcast purposes. The stringent requirements of state-of-the-art coastal and offshore engineering applications over this
area make the adoption of medium- or high-resolution hindcast wave and wind models almost mandatory because of the complex
coastal geometry, bathymetry, and orography that in turn lead to large variations of the design wave parameters even within
small regions. The chains of nested meteorological and wave models used in this hindcast study belong to the ETA and WaveWatch III
families, respectively. In this study the wind and wave numerical models have been run over the past 20 years, with increasing
resolutions of the wave models from 0.2° up to 0.04°. The results presented herein have 0.1° resolution for both wind and
wave models. The wave data obtained are compared with available measurements from 14 wave buoys in coastal zones in the Central
and Western Mediterranean Sea. 相似文献