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81.
The main contribution of the present article consists of new 3D parallel and symmetric thinning schemes which have the following qualities: They are effective and sound, in the sense that they are guaranteed to preserve topology. This guarantee is obtained thanks to a theorem on critical kernels; They are powerful, in the sense that they remove more points, in one iteration, than any other symmetric parallel thinning scheme; They are versatile, as conditions for the preservation of geometrical features (e.g., curve extremities or surface borders) are independent of those accounting for topology preservation; They are efficient: we provide in this article a small set of masks, acting in the grid ?3, that is sufficient, in addition to the classical simple point test, to straightforwardly implement them. 相似文献
82.
In this paper, deformation and breakup under simple shear of single molten polymer drops in a polymer matrix were investigated. Flow visualization was carried out in a Couette‐Flow apparatus under relatively high shear rates and temperatures up to 230°C. Drop/Matrix combinations were composed of polystyrene drops of 0.5–0.6 mm in diameter in polyethylene matrix, and ethylene–propylene copolymer drops of approximately the same size in polypropylene matrix. The deformation and breakup processes were studied under steady state and time‐dependent shearing conditions. Either for steady state or time‐dependant shearing conditions, drop elasticity generated at relatively high shear rates helped the drops to align perpendicular to the flow direction, i.e., parallel to vorticity axis. Also, the most striking non‐Newtonian effects for the high viscosity ratio systems were the surface erosion and the drop splitting mechanisms. The particles eroded off the main droplet surface were very fine, in the range of 10–50 μm, and led to a significant reduction in main drop size before its final breakup. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2582–2591, 2006 相似文献
83.
NH3-NO/NO2 SCR for diesel exhausts after treatment: mechanism and modelling of a catalytic converter
Nova Isabella Ciardelli Cristian Tronconi Enrico Chatterjee Daniel Weibel Michel 《Topics in Catalysis》2007,42(1-4):43-46
We review herein the key mechanistic and kinetic features of the reactions involved in the NH3-NO/NO2 SCR system investigated by dynamic reactive experiments over a V-based commercial powdered catalyst, eventually leading to
the proposal of an original redox scheme which accounts for stoichiometry, selectivity and intrinsic kinetics of the global
SCR process. 相似文献
84.
L. Thimon F. Peyoux R. Maget-Dana G. Michel 《Journal of the American Oil Chemists' Society》1992,69(1):92-93
The interfacial behavior of antifungal lipopetides of the iturinic group was studied in comparison with that of surfactin,
an anionic lipopeptide. All these lipopeptides were isolated from various strains ofBacillus subtilis; each strain produced surfactin and one antifungal compound. The iturinic compounds differ from surfactin by their lower
surfactant properties. The critical micelle concentration (CMC) values were dependent on the nature of the peptide moiety
in the iturinic compounds. The highest values were observed for anionic antibiotics. The arrangement of lipopeptides at the
air-water interface was largely dependent on the size of the lipid moiety; surfactin, which has a C14 or C15 β-hydroxy fatty acid, iturins A, C, and bacillomycins D, L, which have a C14 or C15 β-amino fatty acid, occupied a smaller area than mycosubtilin and bacillomycin F, which have a C16 or C17 β-amino fatty acid. These data can be related to bioactivity of these lipopeptides. 相似文献
85.
Michel Keddam Christiane Rakotomavo Hisasi Takenouti 《Journal of Applied Electrochemistry》1984,14(4):437-448
When the impedance is measured on a battery, an inductive impedance is often observed in a high frequency range. This inductance is frequently related to the cell geometry and electrical leads. However, certain authors claimed that this inductance is due to the concentration distribution of reacting species through the pores of battery electrodes. Their argument is based on a paper in which a fundamental error was committed. Hence, the impedance is re-calculated on the basis of the same principle. The model shows that though the diffusion process plays an outstanding role, the overall reaction rate is never completely limited by this process. The faradaic impedance due to the concentration distribution is capacitive. Therefore, the inductive impedance observed on battery systems cannot be, by any means, attributed to the concentration distribution inside the pores. Little frequency distribution is found and the impedance is close to a semi-circle. Therefore depressed impedance diagrams in porous electrodes without forced convection cannot be ascribed to either a Warburg nor a Warburg-de Levie behaviour.Nomenclature
A
D¦C¦ (mole cm s–1)
-
B
j+K¦C¦ (mole cm s–1)
-
b
Tafel coefficient (V–1)
-
C(x)
Concentration ofS in a pore at depthx (mole cm–3)
-
C
0
Concentration ofS in the solution bulk (mole cm–3)
- C C(x)
change under a voltage perturbation (mole cm–3)
- ¦C¦
Amplitude of C (mole cm–3)
-
D
Diffusion coefficient (cm2 s–1)
-
E
Electrode potential (V)
- E
Small perturbation inE namely a sine-wave signal (V)
- ¦E¦
Amplitude of E(V)
-
F
Faraday constant (96500 A s mol–1)
-
F(x)
Space separate variable forC
-
f
Frequency in Hz (s–1)
-
g(x)
KC(x)¦E¦(mole cm s–1)
-
I
Apparent current density (A cm–2)
-
I
st
Steady-state current per unit surface of pore aperture (A cm–2)
- j
Imaginary unit [(–1)1/2]
-
K
Pseudo-homogeneous rate constant (s–1)
-
K
Potential derivative ofK, dK/dE (s–1 V–1)
-
K
*
Heterogeneous reaction rate constant (cm s–1)
-
L
Pore depth (cm)
-
n
Reaction order
- P
Reaction product
-
p
Parameter forF(x), see Equation 13
-
q
Parameter forF(x), see Equation 13
-
R
e
Electrolyte resistance (ohm cm)
-
R
p
Polarization resistance per unit surface of pore aperture (ohm cm2)
-
R
t
Charge transfer resistance per unit surface of pore aperture (ohm cm2)
- S
Reacting species
-
S
a
Total surface of pore apertures (cm2)
-
S
0
Geometrical surface area
-
S
p
Developed surface area of porous electrode per unit volume (cm2 cm–3)
-
s
Concentration gradient (mole cm–3 cm–1)
-
t
Time
-
U
Ohmic drop
-
x
Distance from pore aperture (cm)
-
Z
Faradaic impedance per unit surface of pore aperture (ohm cm2)
-
Z
x
Local impedance per unit pore length (ohm cm3)
-
z
Charge transfer number
-
Porosity
-
Thickness of Nernst diffusion layer
-
Penetration depth of reacting species (cm)
-
Penetration depth of a.c. signal determined by the potential distribution (cm)
-
Electrolyte (solution) resistivity (ohm cm)
-
0
Flow of S at the pore aperture (mole cm2 s–1)
-
Angular freqeuncy of a.c. signal, 2f(s–1)
-
Integration constant 相似文献
86.
The microactivity test (MAT) for cracking catalyst test works with an approximately plug flow isothermal reactor. The yields at the outlet of such a reactor is numerically computed in the case of lumped kinetic with large molecular expansion and rapid catalyst deactivation expressed versus poison concentration. The poison (coke in cracking reaction) is considered as a product formed by several reaction routes. The results are applied to catalytic cracking kinetic with a four lump model (feedstock, gasoline, gas, coke). The comparison between experimental and computed yields, permits the adjustment of kinetic constants with a set of experimental results obtained from a laboratory scale reactor derived from the MAT. The simulation of concentration profile in the reactor permits a better understanding of the reaction courses. 相似文献
87.
Sara Cavaliere-Jaricot Arnaud Etcheberry Michel Herlem Henri Perez 《Electrochimica acta》2007,52(6):2285-2293
Platinum nanoparticles (n-Pt), over-grafted with 2-thiophenecarbonyl chloride are assembled on gold electrodes, by the Langmuir Blodgett (LB) technique using behenic acid (BHA) as promoting agent. These layers are electrochemically active without any preliminary activation. The [Fe(CN)6]3−/4− redox couple was used as electrochemical probe. This paper reports on the influence of the number of deposited LB layers, and the n-Pt density on the electrochemical response. n-Pt density was modified by the change of the “BHA/n-Pt” ratio. Cyclic voltammograms of “[Fe(CN)6]3−/4−” were observed whatever the coating conditions. As soon as the first layer was deposited the electrochemical response was associated to the n-Pt coverage, its response slightly increased up to a steady state for five or seven layers. As expected, the increase of the Pt density favored the increase of the current density. XPS analysis performed before and after electrochemical cycling showed that 4-mercaptoaniline capped platinum nanoparticles, and their over grafting were chemically and electrochemically stable. Analysis of influence of the number or the n-Pt density of the layers showed that the electrochemically active part of LB electrodes was provided by the last layer plus a part of the underlying one. 相似文献
88.
The resistance to chemical attack of low water to binder ratio pastes containing silica fume was studied by soaking small paste disks in three different pH controlled solutions, with or without sodium chloride, for periods of up to three months. The pastes were made using water to binder ratios of 0,25 and 0,38. The three solutions in which the paste disks were soaked were the following: 3% NaCl (by weight) at a pH level of 8,5,0% NaCl at 8,5, and 0% NaCl at 4,5. After three months of exposure, the results show that the pH level of the aggressive solution is the most important factor controlling the durability of cement pastes subjected to chemical attack. The total porosity and the depth of decalcification was found to increase with the decrease of the pH level. It was also found that the3water to binder ratio does not significantly affect the deterioration processes, but only influences the kinetics of these processes. The decrease of the water to binder ratio reduces significantly the rate of deterioration. Chloroaluminate crystals were observed only in the cement pastes having a water to binder ratio of 0,38. 相似文献
89.
The axial and radial distributions of solid and gas holdups were investigated in an air‐water‐glass bead circulating fluidized bed (GLSCFB) using a new ultrasonic technique, with a new method based on signal fluctuations. The cross‐sectional averaged gas and solid holdups measured at two axial positions appear to be similar at all studied operating conditions. The radial non‐uniformity decreases with increasing liquid velocity but does not change with an increasing solid circulating rate. The radial distribution of gas holdup was more uniform for 1.3 mm beads than for 433 µm glass beads. 相似文献
90.
Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates 总被引:7,自引:0,他引:7
Daoud Naoufal Jean-Marc Millet Edouard Garbowski Yes Brullé Michel Primet 《Catalysis Letters》1998,54(3):141-148
A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the -alumina structure was obtained. Formation of the mixed BaFexAl12-xO19 phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe3+ ions substituting Al3+ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe3+ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe3+ ions in some specific sites. 相似文献