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981.
A diagnostic plot is suggested that can be used to judge wall bounded turbulence data of the mean and the rms of the streamwise velocity in terms of reliability both near the wall, around the maximum in the rms as well as in the outer region. The important feature of the diagnostic plot is that neither the wall position nor the friction velocity needs to be known, since it shows the rms value as a function of the streamwise mean velocity, both normalized with the free stream velocity. One must remember, however, that passing the test is a necessary, but not sufficient condition to prove good data quality. 相似文献
982.
The interaction between thyroxine hormone and 7 hydroxycoumarin (7HC) was investigated using fluorescence quenching method.
The experimental results showed that thyroxine could quench the fluorescence of 7HC by forming the 7HC–thyroxine complex with
static quenching. The apparent binding constants (K) between 7HC and thyroxine were determined to be 1.51 × 104 (297 K) and 9.06 × 103 (310 K). The binding sites (n) 0.98 ± 0.1. The thermodynamic parameters showed that the interaction between 7HC and thyroxine was driven mainly by hydrogen
bonding interactions and van der Waals force. Calibration for thyroxine, based on quenching titration data, was linear in
the concentration range 2.0 × 10−8 to 3.0 × 10−7 mol/l. The relative standard deviation was 2.58% for 2.0 × 10−7 mol/l thyroxine (n = 4) and the 3σ limit of detection was 3.42 × 10−8 mol/l in cationic surfactant CTAB medium. 相似文献
983.
Brian G. Brzek Raúl Bayoán Cal Gunnar Johansson Luciano Castillo 《Experiments in fluids》2008,44(1):115-124
Near-wall measurements are performed to study the effects of surface roughness and viscous shear stresses on the transitionally
rough regime (5 < k
+ < 70) of a zero pressure gradient turbulent boundary layer. The x-dependence is known from the eleven consecutive measurements in the streamwise direction, which allows for the computation
of the streamwise gradients in the boundary layer equations. Thus, the skin friction is computed from the integrated boundary
layer equation with errors of 3 and 5% for smooth and rough, respectively. It is found that roughness destroys the viscous
layer near the wall, thus, reducing the contribution of the viscous stress in the wall region. As a result, the contribution
in the wall shear stress due to form drag increases, while the viscous stress decreases. This yields Reynolds number invariance
in the skin friction as k
+ increases into the fully rough regime. Furthermore, the roughness at the wall reduces the high peak of the streamwise component
of the Reynolds stress in the near-wall region. However, for the Reynolds wall-normal and shear stress components, its contribution
is not significantly altered for sand grain roughness. 相似文献
984.
The stability problem of two-dimensional compressible flat-plate boundary layers is handled using the linear stability theory.
The stability equations obtained from three-dimensional compressible Navier–Stokes equations are solved simultaneously with
two-dimensional mean flow equations, using an efficient shoot-search technique for adiabatic wall condition. In the analysis,
a wide range of Mach numbers extending well into the hypersonic range are considered for the mean flow, whereas both two-
and three-dimensional disturbances are taken into account for the perturbation flow. All fluid properties, including the Prandtl
number, are taken as temperature-dependent. The results of the analysis ascertain the presence of the second mode of instability
(Mack mode), in addition to the first mode related to the Tollmien–Schlichting mode present in incompressible flows. The effect
of reference temperature on stability characteristics is also studied. The results of the analysis reveal that the stability
characteristics remain almost unchanged for the most unstable wave direction for Mach numbers above 4.0. The obtained results
are compared with existing numerical and experimental data in the literature, yielding encouraging agreement both qualitatively
and quantitatively.
相似文献
985.
Using translation formulas for Slater type orbitals (STO’s) the infinite series through the overlap integrals are derived
for the magnetic multipole moment integrals. By the use of the derived expressions the magnetic multipole moment integrals,
therefore, the magnetic properties of molecules can be evaluated most efficiently and accurately. The convergence of the series
is tested by calculating concrete cases. An accuracy of 10−5 for the computer results is obtained in the case 2
p
-pole magnetic moment integrals for 1 ≤ v ≤ 5, and for the arbitrary values of internuclear distances and screening constants of atomic orbitals. 相似文献
986.
Heinz Umhauer Stefan Berbner Gunnar Hemmer 《Particle & Particle Systems Characterization》2000,17(1):3-15
Based on previous experience, an optical particle counter has been designed which allows the direct measurement of the size and concentration of dust particles in gas flows at high temperatures. The instrument features a new optical measuring volume definition together with a signal control to avoid border‐zone error effects. The instrument has a free working distance of 200 mm. Hence it is possible to make true in situ measurements in pipe flows with a cross‐section of ca. 60 cm2 and additionally to protect the device against heat and dust precipitation on the optical windows. The instrument was initially used to examine the separation behaviour of cake‐forming rigid ceramic barrier filters at temperatures up to 1000 °C. In particular, the fractional efficiencies and the time‐related concentration changes on the clean gas side caused by a pulse jet cleaning event could be determined. The results obtained so far demonstrate that ceramic barrier filters show basically the same behaviour as conventional filters, but possess a substantially higher separation efficiency at a corresponding higher pressure drop (fractional penetration values between 10−5 and 10−9 depending on the type of filter material and the cake formation). 相似文献
987.
988.
Amir R. Ali Tindaro Ioppolo Volkan Ötügen Marc Christensen Duncan MacFarlane 《Journal of polymer science. Part A, Polymer chemistry》2014,52(3):276-279
The detection of electric field by monitoring the optical whispering gallery mode shifts of polymeric microspheres is demonstrated. Two types of spheres are considered; (i) a polydimethylsiloxane (PDMS) sphere with 60 parts base silicon elastomer-to-1 part polymer curing agent by volume and; (ii) a silica sphere coated with a PDMS (uncured) base. The optical mode shifts are caused by perturbations to the resonator morphology induced by electrostriction effect in the presence of an external electric field. Preliminary experiments show that the latter microsphere yields higher sensitivity (0.027 pm/V m−1) with a measurement precision of ∼1.8 V/m. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 276–279 相似文献
989.
990.
Rukiye Gümüşada Namık Özdemir Bekir Çetinkaya 《Journal of Coordination Chemistry》2016,69(9):1463-1472
Eight bicyclic amidinium precursors (3), prepared from R,S-tmcp (R,S-tmcp: (1R,3S)-diamino-1,2,2-trimethylcyclopentane) were described. Only five of the precursors (3a–e) could be converted to palladium complexes, (PdX2(6,7-NHC)PEPPSI) (4) by treatment with PdCl2, K2CO3, and pyridine (additional KBr was used for (PdBr2(6,7-NHC)PEPPSI)). The salts and complexes were fully characterized by spectroscopic methods and X-ray crystallography. 相似文献