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11.
12.
Dr. Erik A. Toorman 《Rheologica Acta》1997,36(1):56-65
13.
14.
The analysis of the rotation of a ferromagnetic ellipsoid suspended in a Newtonian fluid and subjected to a uniform magnetic field is extended to include a long, slender cylindrical fiber which is magnetically saturated. Experimental observations of rotating nickel cylinders with aspect ratiosL/D ranging from 5 to 40 agree with the theoretical predictions that: (1) the proper magnetoviscous time constant for the motion is
MV =
s/µ
0
M
s
2
, (2) larger fiber aspect ratios result in considerably longer orientation times; and (3) the strength of the applied external field has only a slight effect on the overall fiber rotation, and has no effect on the maximum angular velocity achieved. Quantitative agreement of theory and experiments is obtained for fibers withL/D 20; for the shorter fibers, the theory tends to overpredict the fiber rotation rate by as much as 30%.
D
diameter of the cylinder
-
D
P
(r)
position-dependent demagnetization tensor, implicitly defined in eq. (2.5)
-
D
xx,D
yy,D
zz
volume-averaged demagnetizing factors for an ellipsoid equivalent to a uniformly magnetized cylinder, defined in eq. (2.6)
-
H
i
;H
i
magnetic field inside a ferromagnetic body; magnitude ofH
i
-
H
0;H
0
magnetic field applied by external sources; magnitude ofH
0
-
k
geometric parameter in the hydrodynamic resistance of a body rotating in a Newtonian fluid, eq. (2.2)
-
L
length of the cylinder
-
L
(h);L
z
(h)
hydrodynamic torque exerted on a rotating body; thez-component ofL
(h) on the cylinder
-
L
(m);L
z
(m)
magnetic torque exerted on a magnetic body in a magnetic field, eq. (2.4); thez-component ofL
(m) on the cylinder
-
M
the magnetization of a magnetic material
-
M
s
the saturation magnitude ofM, approached by all ferromagnetic materials asH
i becomes large
-
r
position vector of a point within a ferromagnetic body
-
V
volume of a magnetic particle
-
x, y, z
rectangular coordinate axes fixed in the cylinder according to figure 1
-
angle of inclination of the axis of the cylinder with respect toH
0
-
shear rate
-
small parameter of slender body theory,=1/ln (2L/D)
-
s
constant viscosity of the suspending fluid
-
µ
0
the magnetic permeability of free space,µ
0=4 · 10–7 H/m
-
MV
the magnetoviscous time constant, a characteristic time for a process involving a competition of viscous and magnetic stresses
-
1
the first normal-stress coefficient
-
;
z
angular velocity of a rotating body; angular velocity of a cylinder about thez-axis,
z =– d/dt 相似文献
15.
Linear and nonlinear viscoelastic properties were examined for aqueous suspensions of monodisperse poly(methyl methacrylate-co-styrene) (MS) particles having the radius a
0
=45 nm and the volume fractions φ=0.428−0.448. These particles had surface charges and the resulting electrostatic surface
layer (electric double layer) had a thickness of ts=5.7 nm. At low frequencies in the linear viscoelastic regime, the MS particles behaved approximately as the Brownian hard
particles having an effective radius a
eff=a
0 + ts, and the dependence of their zero-shear viscosity η0 on an effective volume fraction φeff (={a
eff/a
0}3φ) agreed with the φ dependence of η0 of ideal hard-core silica suspensions. In a range of φeff < 0.63, this φeff dependence was well described by the Brady theory. However, the φeff dependence of the high-frequency plateau modulus was weaker and the terminal relaxation mode distribution was narrower for
the MS suspensions than for the hard-core suspensions. This result suggested that the electrostatic surface layer of the MS
particles was soft and penetrable (at high frequencies). In fact, this “softness” was more clearly observed in the nonlinear
regime: the nonlinear damping against step strain was weaker and the thinning under steady shear was less significant for
the MS suspension than for the hard-core silica suspensions having the same φeff. These weaker nonlinearities of the concentrated MS particles with φeff∼ 0.63 (maximum volume fraction for random packing) suggested that the surface layers of those particles were mutually penetrating
to provide the particles with a rather large mobility.
Received: 10 July 2001 Accepted: 2 November 2001 相似文献
16.
Flow-induced fiber orientation and concentration distributions were measured in a concentrated fiber suspension (CFS) and a dilute one (DFS). The channel has a thin slit geometry containing a circular cylinder. In the previous work, many researchers have qualitatively studied fiber orientation and concentration distributions in injection-molded products of fiber-reinforced plastics. In the present work, however, they are quantitatively estimated by direct observation of fibers in the concentrated suspension flow. For the CFS, some fibers rotate in an expansion part between the channel wall and the circular cylinder, and the fiber orientation becomes almost random state. On the other hand, fibers are perfectly aligned along the flow direction owing to the elongational flow near the centerline downstream of the cylinder. The fiber concentration has a flat distribution except near the channel wall and the centerline. For the DFS a minimum in the fiber concentration distribution was clearly observed on the centerline, and two peaks beside the centerline and near the channel wall. This characteristic distribution is caused by the fiber-wall and fiber-cylinder interactions. It is found that the obstacle such as the circular cylinder in the channel significantly affects the fiber orientation downstream of the obstacle for the CFD, while it affects the fiber concentration distribution for the DFS. 相似文献
17.
Suspension settings for optimal ride comfort of off-road vehicles travelling on roads with different roughness and speeds 总被引:2,自引:0,他引:2
This paper reports on an investigation to determine the spring and damper settings that will ensure optimal ride comfort of an off-road vehicle, on different road profiles and at different speeds. These settings are required for the design of a four stage semi-active hydro-pneumatic spring damper suspension system (4S4). Spring and damper settings in the 4S4 can be set either to the ride mode or the handling mode and therefore a compromise ride-handling suspension is avoided. The extent to which the ride comfort optimal suspension settings vary for roads of different roughness and varying speeds and the levels of ride comfort that can be achieved, are addressed. The issues of the best objective function to be used when optimising and if a single road profile and speed can be used as representative conditions for ride comfort optimisation of semi-active suspensions, are dealt with. Optimisation is performed with the Dynamic-Q algorithm on a Land Rover Defender 110 modelled in MSC.ADAMS software for speeds ranging from 10 to 50 km/h. It is found that optimising for a combined driver plus rear passenger seat weighted root mean square vertical acceleration rather than using driver or passenger values only, returns the best results. Results indicate that optimisation of suspension settings using one road and speed will improve ride comfort on the same road at different speeds. These settings will also improve ride comfort for other roads at the optimisation speed and other speeds, although not as much as when optimisation has been done for the particular road. For improved ride comfort damping generally has to be lower than the standard (compromised) setting, the rear spring as soft as possible and the front spring ranging from as soft as possible to stiffer depending on road and speed conditions. Ride comfort is most sensitive to a change in rear spring stiffness. 相似文献
18.
Railway wheelset experiences the problem of hunting above a critical speed, which is a kind of self-excited oscillation. At the critical speed, it is known that the system undergoes a subcritical Hopf bifurcation. Therefore, for clarifying the nonlinear characteristics of hunting it is very important to detect, for example, the nonlinear forces in the wheelset due to the creep forces acting between the wheels and rails, and the nonlinear component of the resorting forces by the suspensions. However, it is impossible to determine each force quantitatively. In the present paper, it is first shown, by using the center manifold theory and the method of normal form, that the nonlinear characteristics of the bifurcation in a wheelset model with two degrees of freedom are governed by a single parameter, hence each nonlinear force need not be detected when examining the nonlinear characteristics. Also, a method of determining the governing parameter from experimentally observed radiuses of the unstable limit cycle is proposed. Next, we experimentally investigate the variation of the parameter due to the presence of linear spring suspensions in the lateral direction and discuss the variation of the nonlinear characteristics of the hunting motion, which depends on the lateral stiffness. As a result, the improvement of the stability of the wheelset against the disturbance by the linear spring suspensions is clarified. 相似文献
19.
Rheological properties of suspensions of Na-kaolinite and colloidal quartz (Min-U-Sil) at constant overall volume concentration of 2% are determined with a Weissenberg Rheogoniometer using a combined Couette and cone-and-plate geometry. The results are interpreted in terms of the flocculation behaviour of the constituent particles in the presence of high salt concentrations (0.1–0.75m NaCl) at pH 6, 7 and 8. In these chemical environments these suspensions are pseudoplastic for much of the range of mixture compositions becoming Newtonian for suspensions containing only quartz. These properties reflect the dominant influence of interactions between kaolinite particles on the flocculation behaviour of the mixture.Nomenclature
a
1, a2
radii of spheres
-
A
Hamaker constant
-
b
radius of cylinder
-
C
volumetric solids concentration
-
e
0
electronic charge
-
H
0
shortest distance between surfaces
-
I
ionic strength
-
J
collision frequency per unit volume
-
k
Boltzmann constant
-
l
length of cylinder
-
m
number in eq. (2)
-
N
particle number concentration
-
S
(H
0 + b)/b in eq. (4)
-
T
absolute temperature
-
U
electrophoretic mobility
-
V
A
van der Waals attractive energy
-
V
R
coulombic energy
-
V
T
total energy of interaction
-
X
H
0/2a1 in eq. (5)
-
Y
a
2/a1 in eq. (5)
-
thickness of plate
-
shear rate
-
permittivity
-
zeta potential
-
k
Debye-Hückel parameter
-
µ
dynamic viscosity
-
µ
pl
plastic viscosity
-
v
valency of counter ion
-
shear stress
-
B
Bingham stress
-
1, 2
dimensionless potentials
-
1, 2
surface potentials 相似文献
20.
Summary The rheological properties of vinylon fiber suspensions in polymer solutions were studied in steady shear flow. Shear viscosity, first normal-stress difference, yield stress, relative viscosity, and other properties were discussed. Three kinds of flexible vinylon fibers of uniform length and three kinds of polymer solutions as mediums which exhibited remarkable non-Newtonian behaviors were employed. The shear viscosity and relative viscosity (
r
) increased with the fiber content and the aspect ratio, and depended upon the shear rate. Shear rate dependence of
r
was found only in the low shear rate region. This result was different from that of vinylon fiber suspensions in Newtonian fluids. The first normal-stress difference increased at first slightly with increasing fiber content but rather decreased and showed lower values for high content suspensions than that of the medium. A yield stress could be determined by using a modified equation of Casson type. The flow properties of the fiber suspensions depended on the viscosity of the medium in the suspensions under consideration.With 16 figures and 1 table 相似文献