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61.
62.
A new optical instrument has been developed for direct measurement of instantaneous velocity gradients at the bounding wall. Light emerging from two tiny optical slits in the surface is used to form a fan of fringes in the region very near the wall. Doppler frequency of the light scattered by the seed particles is directly proportional to the velocity gradient. The system has been used to measure the statistics of the streamwise and spanwise velocity gradients in a turbulent boundary layer. The streamwise and spanwise rms fluctuations were found to be 38% and 11% of the mean streamwise value respectively. The latter result is subject to a large uncertainty.List of symbols
a
slit width
-
B
transfer function of the instrument
-
B
*
normalized transfer function
-
path-averaged value of the normalized transfer function
-
c
constant in logarithmic velocity profile
-
C
f
skin friction coefficient
-
d
f
fringe spacing
-
f
1,f2
frequencies at the downstream and upstream slits resp.
-
f
d
heterodyne Doppler frequency of the signal
-
g(t)
instantaneous wall velocity gradient
-
G
Clauser shape factor
-
mean wall velocity gradient
-
g
rms value of the wall velocity gradient
-
H
boundary layer shape factor
-
i, j, k
unit vectors along x, y, z axes
-
wavenumber of laser light
-
L
major axis of the elliptic cross-section of the laser sheet at the slit
-
l
length of each slit
-
N
number of cycles in a signal
-
N
0
number of cycles without frequency-shifting
-
n
difference of the unit vectors u
1and u
2
-
P
power transmitted through a slit
-
P
o
power incident on a slit
-
Re
1
Reynolds number based on displacement thickness and free-stream velocity
-
Re
2
Reynolds number based on momentum thickness and free-stream velocity
-
S
spacing between the slits
-
S
*
normalized spacing between the slits
-
u
streamwise velocity
-
u
1,u2
unit vectors along the local directions of propagation of the two cylindrical waves
-
u
l
linear term in the streamwise velocity profile
-
u
nl
nonlinear terms in the streamwise velocity
-
u
nl
*
normalized value of nonlinear streamwise velocity
-
u
nl
*
mean streamwise velocity
-
u
friction velocity
- u+
mean velocity normalized with friction velocity
-
v
velocity component normal to the wall
-
v
*
normal velocity normalized with streamwise velocity
-
V
velocity vector
-
w
spanwise component of velocity
-
W
minor axis of the elliptic cross-section of the laser sheet at the slit
-
x
streamwise distance
- ± x
m
limiting values of streamwise distance for a signal
-
x
*
normalized streamwise distance
-
x
*
normalized value of x
m
-
y
normal distance
-
y
+
normal distance normalized with friction length scale
-
z
spanwise distance
-
z
+
spanwise distance normalized with friction length scale
-
half-spreading angle of the cylindrical waves
-
boundary layer thickness in Coles' profile
-
1
displacement thickness of the boundary layer
-
2
momentum thickness of the boundary layer
-
3
energy thickness of the boundary layer
-
constant in logarithmic velocity profile
-
wavelength of laser light
-
kinematic viscosity
-
coefficient of wake function in Coles' profile
Currently at LSTM, Universitat Erlangen-Nürnberg, Cauerstraße 4, W-8520 Erlangen, BRD 相似文献
63.
J.W.H. Smith P. Westreich A.J. Smith H. Fortier L.M. Croll J.H. Reynolds J.R. Dahn 《Journal of colloid and interface science》2010,341(1):162-170
Copper oxide impregnated activated carbon was prepared by three methods and studied as a respirator carbon. Using techniques such as dynamic flow testing, X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), copper oxide impregnants, derived from different sources such as basic copper carbonate (Cu2CO3(OH)2), copper nitrate (Cu(NO3)2) and copper chloride (CuCl2) reacted with sodium hydroxide (NaOH), have been studied. Dynamic flow tests performed using sulfur dioxide (SO2), ammonia (NH3) and hydrogen cyanide (HCN) challenge gases allow the determination of the stoichiometric ratio of reaction (SRR) between challenge gas and impregnant. Thermal gravimetric analysis experiments showed that an inert heating environment was required when thermally decomposing the Cu(NO3)2 impregnant to CuO to avoid damaging the activated carbon substrate. SEM has been used to investigate dispersal and particle size of the impregnant on the activated carbon. XRD permits the identification of crystalline and amorphous phases as well as the grain size of the impregnant. XRD analysis of samples before and after exposure to SO2 has allowed the active impregnant in SO2 adsorption to be identified. The relationship between SRR, impregnant loading and grain size is discussed. Methods to improve impregnant distribution are presented and their impact discussed. 相似文献
64.
Laboratory experiments have been conducted in two separate boundary layer facilities to investigate steady spanwise variations
in mean velocity discovered during studies of developing flows over regular arrays of large roughness elements. Regular spanwise
variation was found with a steady wavelength, moderated by the growing boundary layer, which was an integer multiple of the
repeating unit of roughness. Amplitude variations greater than ±5% in the mean were found over the roughness and greater than
±10% in turbulence quantities. Due to the dominating nature of this phenomena throughout the layer, care should be taken in
undertaking local measurements aimed at identifying flow variations caused by roughness heterogeneity. 相似文献
65.
66.
67.
A sensitive and selective liquid chromatographic method to quantitate MDL 201,012 in human plasma was developed and validated. MDL 201,012 (I), diethyl-MDL 201,012 (internal standard, II) and desmethyldiol-MDL 201,012 (masking agent, III) were isolated from basified plasma (2 mL) by solid phase extraction using Bond-Elut C-18 cartridges. Endogenous components were selectively removed prior to eluting the analytes from the sorbent. Components were separated using on-line LC column switching with a cyanopropyl precolumn and a phenyl analytical column. The analytical column effluent was monitored electrochemically at a glassy carbon electrode at a potential of +1025 mV vs. Ag/AgCl. Peak-height ratios were proportional to the amount of MDL 201,012 added to plasma over the range 125-7500 pg/mL MDL 201,012. Absolute recovery of MDL 201,012 from human plasma was > 94% across the calibration range. The minimum quantitation limit was 125 pg/mL. Assay precision (%RSD) ranged from 5.2 to 13% based on the analysis of quality control standards containing 125, 250, 500, 1000, 2500, 5000 and 7500 pg/mL MDL 201,012. Corresponding assay accuracy (% relative error) was +/- 8.5%. The method has been successfully used to quantitate MDL 201,012 in samples from acute dose tolerance studies in human volunteers. 相似文献
68.
69.
Clustering Rules: A Comparison of Partitioning and Hierarchical Clustering Algorithms 总被引:1,自引:0,他引:1
A. P. Reynolds G. Richards B. de la Iglesia V. J. Rayward-Smith 《Journal of Mathematical Modelling and Algorithms》2006,5(4):475-504
Previous research has resulted in a number of different algorithms for rule discovery. Two approaches discussed here, the ‘all-rules’ algorithm and multi-objective metaheuristics, both result in the production of a large number of partial classification rules, or ‘nuggets’, for describing different subsets of the records in the class of interest. This paper describes the application of a number of different clustering algorithms to these rules, in order to identify similar rules and to better understand the data. 相似文献
70.
Ionization of aliphatic and aromatic aldehydes is improved by performing simultaneous chemical derivatization using 4-aminophenol to produce charged iminium ions during paper spray ionization. Accelerated reactions occur in the microdroplets generated during the paper spray ionization event for the tested aldehydes (formaldehyde, n-pentanaldehyde, n-nonanaldehyde, n-decanaldehyde, n-dodecanaldehyde, benzaldehyde, m-anisaldehyde, and p-hydroxybenzaldehyde). Tandem mass spectrometric analysis of the iminium ions using collision-induced dissociation demonstrated that straight chain aldehydes give a characteristic fragment at m/z 122 (shown to correspond to protonated 4-(methyleneamino)phenol), while the aromatic aldehyde iminium ions fragment to give a characteristic product ion at m/z 120. These features allow straightforward identification of linear and aromatic aldehydes. Quantitative analysis of n-nonaldehyde using a benchtop mass spectrometer demonstrated a linear response over 3 orders of magnitude from 2.5 ng to 5 μg of aldehyde loaded on the filter paper emitter. The limit of detection was determined to be 2.2 ng for this aldehyde. The method had a precision of 22%, relative standard deviation. The experiment was also implemented using a portable ion trap mass spectrometer. 相似文献