全文获取类型
收费全文 | 5170篇 |
免费 | 129篇 |
专业分类
公路运输 | 205篇 |
综合类 | 613篇 |
水路运输 | 4389篇 |
铁路运输 | 46篇 |
综合运输 | 46篇 |
出版年
2024年 | 33篇 |
2023年 | 59篇 |
2022年 | 100篇 |
2021年 | 155篇 |
2020年 | 201篇 |
2019年 | 103篇 |
2018年 | 65篇 |
2017年 | 156篇 |
2016年 | 144篇 |
2015年 | 179篇 |
2014年 | 302篇 |
2013年 | 238篇 |
2012年 | 354篇 |
2011年 | 435篇 |
2010年 | 338篇 |
2009年 | 369篇 |
2008年 | 319篇 |
2007年 | 521篇 |
2006年 | 457篇 |
2005年 | 271篇 |
2004年 | 129篇 |
2003年 | 106篇 |
2002年 | 53篇 |
2001年 | 45篇 |
2000年 | 26篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 4篇 |
排序方式: 共有5299条查询结果,搜索用时 359 毫秒
61.
单井型塔柱结构极大改善了水力式升船机竖井水位同步性问题,但随着提升高度增大,竖井内水深越大,侧壁位移、弯矩过大等问题更加突出。以150米级单井塔柱为例,提出了竖井内布置对拉钢索的设想和简化布置方案。基于钢索拉力权重分配系数的优化方法,取得了钢索等应力的密度分布最优解,并离散转化为等效的等荷载布置方案,可在实际工程中应用。经有限元模型结果对比分析,等荷载布置与简化方案相比,最大位移可减小47.44%,纵竖向弯矩极值差别不大。与无钢索方案比较,最大位移、纵向弯矩、竖向弯矩可分别减小93.5%、74.36%、75.84%。高强钢索预应力方案值得进一步研究。 相似文献
62.
63.
研究目的:曹妃甸吹填土含有大量细颗粒成分,且含盐量高,常规地基处理方法达不到强度和变形要求,化学固化方式处理该地区盐渍吹填土具有较大的优势。本文以10%矿粉作为固化剂主剂,硅酸钠、生石灰和石膏粉作为添加剂,分别进行单掺、双掺和三掺添加剂固化后的强度试验,分析盐渍吹填土在不同掺入材料、配比及不同期龄下的无侧限抗压强度变化规律。研究结论:(1)矿粉固化剂能大大提高曹妃甸盐渍吹填土的无侧限抗压强度,其中生石灰对矿粉固化盐渍吹填土的固化效果影响最大;(2)10%的矿粉+1.0%的生石灰+0.8%的硅酸钠+1.5%的石膏粉,是矿粉固化剂的最优配比方案,该配比固化土试样7 d无侧限抗压强度达到了2007 k Pa,28 d无侧限抗压强度增至3370 k Pa,完全能满足铁路地基强度要求;(3)该研究成果可为曹妃甸及其他滨海盐渍化吹填土地区铁路地基固化工程提供指导和理论依据。 相似文献
64.
K. J. Spyrou 《Journal of Marine Science and Technology》1995,1(1):24-36
The behavior of a ship encountering large regular waves from astern at low frequency is the object of investigation, with a parallel study of surf-riding and periodic motion paterns. First, the theoretical analysis of surf-riding is extended from purely following to quartering seas. Steady-state continuation is used to identify all possible surf-riding states for one wavelength. Examination of stability indicates the existence of stable and unstable states and predicts a new type of oscillatory surf-riding. Global analysis is also applied to determine the areas of state space which lead to surf-riding for a given ship and wave conditions. In the case of overtaking waves, the large rudder-yaw-surge oscillations of the vessel are examined, showing the mechanism and conditions responsible for loss of controllability at certain vessel headings.List of symbols
c
wave celerity (m/s)
-
C(p)
roll damping moment (Ntm)
-
g
acceleration of gravity (m/s2)
-
GM
metacentric height (m)
-
H
wave height (m)
-
I
x
,I
z
roll and yaw ship moments of inertia (kg m2)
-
k
wave number (m–1)
-
K
H
,K
W
,K
R
hull reaction, wave, rudder, and propeller
-
K
p
forces in the roll direction (Ntm)
-
m
ship mass (kg)
-
n
propeller rate of rotation (rpm)
-
N
H
,N
W
,N
R
hull reaction, wave, rudder, and propeller
-
N
P
moments in the yaw direction (Ntm)
-
p
roll angular velocity (rad/s)
-
r
rate-of-turn (rad/s)
-
R(,x)
restoring moment (Ntm)
-
Res(u)
ship resistance (Nt)
-
t
time (s)
-
u
surge velocity (m/s)
-
U
vessel speed (m/s)
-
v
sway velocity (m/s)
-
W
ship weight (Nt)
-
x
longitudinal position of the ship measured from the wave system (m)
-
x
G
,z
G
longitudinal and vertical center of gravity (m)
-
x
S
longitudinal position of a ship section (S), in the ship-fixed system (m)
-
X
H
,X
W
,X
R
hull reaction, wave, rudder, and propeller
-
X
P
forces in the surge direction (Nt)
-
y
transverse position of the ship, measured from the wave system (m)
-
Y
H
,Y
W
,Y
R
hull reaction, wave, rudder, and propeller
-
Y
p
forces in the sway direction (Nt)
-
z
Y
vertical position of the point of action of the lateral reaction force during turn (m)
-
z
W
vertical position of the point of action of the lateral wave force (m)
Greek symbols
angle of drift (rad)
-
rudder angle (rad)
-
wavelength (m)
-
position of the ship in the earth-fixed system (m)
-
water density (kg/m3)
-
angle of heel (rad)
-
heading angle (rad)
-
e
frequency of encounter (rad/s)
Hydrodynamic coefficients
K
roll added mass
-
N
v
,N
r
yaw acceleration coefficients
-
N
v
N
r
N
rr
N
rrv
,N
vvr
yaw velocity coefficients K. Spyrou: Ship behavior in quartering waves
-
X
u
surge acceleration coefficient
-
X
u
X
vr
surge velocity coefficients
-
Y
v
,Y
r
sway acceleration coefficients
-
Y
v
,Y
r
,Y
vv
,Y
rr
,Y
vr
sway velocity coefficients
European Union-nominated Fellow of the Science and Technology Agency of Japan, Visiting Researcher, National Research Institute of Fisheries Engineering of Japan 相似文献
65.
通过对各类改性沥青性能的分析 ,探讨了根据不同气候条件、不同荷载条件、现有加工能力以及成本分析进行选择改性剂的原则 相似文献
66.
67.
68.
阐述了静态爆破施工的作用机理和施工工艺,通过与常规爆破工艺相比较,论证了该工艺具有的造价低、无振动、无噪声、无粉尘、无飞石、无毒气污染等特点和其广泛的推广应用价值. 相似文献
69.
Transfer functions are often used together with a wave spectrum for analysis of wave–ship interactions, where one application addresses the prediction of wave-induced motions or other types of global responses. This paper presents a simple and practical method which can be used to tune the transfer function of such responses to facilitate improved prediction capability. The input to the method consists of a measured response, i.e. time series sequences from a given sensor, the 2D wave spectrum characterising the seaway in which the measurements are taken, and an initial estimate of the transfer function for the response in study. The paper presents results obtained using data from an in-service container ship. The 2D wave spectra are taken from the ERA5 database, while the transfer function is computed by a simple closed-form expression. The paper shows that the application of the tuned transfer function leads to predictions which are significantly improved compared to using the transfer function without tuning. 相似文献
70.
本文采用有限元软件ABAQUS建立了船舶撞击高桩码头群桩的空间有限元模型。通过计算评估了撞击力、桩体刚度、撞击位置和撞击角度下对群桩结构损伤位置的影响。基于人工神经网络(ANN)方法,对不同参数组合下的群桩结构损伤位置进行了预测,并对ANN方法的可行性进行了评估。 相似文献