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41.
The forced convective heat transfer characteristics for incompressible power-law fluids past a bundle of circular cylinders have been investigated numerically. The cylinder-to-cylinder hydrodynamic interactions have been approximated via a simple cell model. The momentum and energy equations have been solved using a finite difference based numerical method for a range of physical and kinematic conditions. The role of the two commonly used thermal boundary conditions, namely, constant temperature or constant heat flux, on heat transfer characteristics has also been studied. Extensive numerical results elucidating the effect of shear-thinning viscosity on the values of Nusselt number have been obtained for Peclet numbers ranging from 1 to 5000, Reynolds number in the range 1-500, flow behaviour index 1?n?0.5 and three values of voidages, namely, 0.4, 0.5 and 0.6, typical of tubular heat exchangers and tube banks. Under all conditions, varying levels of enhancement in Nusselt number are observed due to shear-thinning behaviour. The surface averaged Nusselt number shows strong dependence on the values of voidage, power-law index, Reynolds and Peclet numbers. The paper is concluded by presenting comparisons with the scant experimental results available in the literature. 相似文献
42.
J. Popplewell 《Chemical Engineering Communications》1988,67(1):243-257
Magnetic measurements on ferrofluids can be used to determine the magnetic concentration which may be as large as 15% by volume in a very viscous fluid. Additional information on the particle size distribution parameters and the mode of magnetisation can be obtained from an analysis of the magnetisation curve. Magnetic studies are also invaluable for a correct interpretation of the magnetic dichroism, birefringence and small angle neutron scattering (SANS) data. Measurements on a ferrofluid after freezing enables the shape anisotropy to be determined and the degree of particle elongation (∼15%) calculated. 相似文献
43.
The electrodiffusion technique was performed in order to investigate the shear rate on a scraped surface heat exchanger. Microelectrodes were placed inside: the walls of the outer cylinder; the inlet and outlet bowls; the rotor and the blades. Highly viscous Newtonian fluid (Emkarox HV45 solutions) and non-Newtonian model fluid (aqueous solutions of CMC) were used. The electrodiffusion method allowed us to measure wall shear rates. Maximum shear rate was observed at the scraping surface and caused by blades scraping, high shear rate was also measured on the leading edge of the blades. In the other parts of the exchanger, shear rate remained low but the development of Taylor vortices completely modified the scraped surface heat exchangers behaviour inside the surface of the bowls. A dimensionless representation of the friction factor was established for the inner and outer wall surface of the exchanger. 相似文献
44.
The ideal thermodynamic performances of a variety of non-CFC refrigerants and their mixtures were calculated by using the Patel-Teja equation of state. The results indicated that the preferable non-CFC refrigerant mixtures could be HCFC-I24 +HFC-152a, HFC-152a + HFC-134, dimethyl ether + HCFC-22, and dimethyl ether + HCFC-124 for air-conditioning systems, and binary mixtures of HCFC-22 + HFC-125, and HCFC-22 + HFC-143a for low-temperature applications. Those potential non-CFC mixtures were suggested for further investigations. 相似文献
45.
46.
The effects of the non-Newtonian properties on the effective deformation rate, mixing and circulation times and flow behaviour have been investigated in the transition flow regime of mixing systems. Based on the equivalent Couette flow, three models are proposed and are shown to predict similar and drastic increases of the effective deformation rate with the impeller rotational speed in the transition regime. The predictions are shown to fit very well data obtained for various non-Newtonian fluids mixed with helical ribbon agitators, and with literature data for anchor, blade turbine and flat disc agitators. The elasticity along with shear-thinning properties appear to have slight effects on the dimensionless mixing and circulation times in the transition regime, whereas their effects in the laminar regime are quite drastic, as reported by others. 相似文献
47.
Mixtures of tetrahydrofuran (THF) and carbon dioxide (CO2) were identified as new solvent systems for polysulfone. The miscibility and density of polysulfone in binary fluid mixtures of THF and CO2 were investigated from 300 to 425 K at pressures up to 70 MPa. The influence of the CO2 and polysulfone concentrations was studied, with the concentrations of the other two components kept constant. At a 4.5 wt % polymer concentration, the demixing pressures in a 10 wt % CO2 and 90 wt % THF mixture increased with temperature (310–425 K) from 15 to 40 MPa. With increasing CO2 concentration (from ca. 10 to 14 wt %), a significant increase (from 15 to 70 MPa at 310 K) was observed in the demixing pressures. Furthermore, with an increasing amount of CO2, the nature of the phase boundary shifted from lower critical solution temperature behavior to upper critical solution temperature behavior. The influence of the polymer concentration was studied in the 0–5 wt % range at two CO2 levels, with solvent compositions of 10 wt % CO2 and 90 wt % THF and 13 wt % CO2 and 87 wt % THF. The system with a higher level of CO2 (13 wt %) showed highly unusual phase behavior: on pressure–composition and temperature–composition diagrams, the system displayed two distinct regions of miscibility. In the system with 10 wt % CO2, the distinct regions of miscibility that were observed in the system with 13 wt % CO2 partially overlapped and led to a W‐shape phase boundary. The densities of the polymer solutions were measured from the one‐phase region through the demixing point into the two‐phase region at a constant temperature. No significant change in density was found around the phase boundary; this indicated that the coexisting phases had similar densities, as is often the case with liquid–liquid phase separation in polymer solutions under high pressure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2357–2362, 2002 相似文献
48.
S. Watanabe T. Fujita M. Sakamoto T. Kuramochi H. Kawahara 《Journal of the American Oil Chemists' Society》1993,70(9):927-929
A number of N,N′-diacylalkyldiamines were prepared from the reaction of acid chlorides with 1,8-diaminooctane and 1,12-diaminododecane
and screened for anti-rust properties and antimicrobial activity in spent coolants of water-based cutting fluids. Aqueous
solutions of N,N′-dihexanoyl-1,8-diaminooctane and N,N′-isobutyroyl-1,12-diaminododecane showed good anti-rust properties
for water-based cutting fluids. Aqueous emulsions of N,N′-dibutyroyl-, dipentanoyl-, dihexanoyl- and dioctanoyl-1,12-diaminododecane
showed good lubricities and antimicrobial activity for water-based cutting fluids. 相似文献
49.
50.
Yinling Wang Yuan Hu Xinglong Gong Wanquan Jiang Peiqiang Zhang Zuyao Chen 《应用聚合物科学杂志》2007,103(5):3143-3149
Magnetorheological (MR) elastomers, which are mainly composed of magnetic particles and elastic polymer, are a new kind of smart materials whose modulus can be controlled by changing the strength of magnetic fields. In this article, MR elastomers based on immiscible silicon rubber/polystyrene (SR/PS) blend matrix were fabricated successfully via cosolvent method and the MR effect, electric and mechanical properties, and the microstructures of the corresponding materials were studied. SEM studies showed that the dispersion of iron particles in blend matrix were different from that in single polymer, which could be further proved by the different electric conductivity. The MR effect of MR elastomers based on blend matrix varied with the different ratios of SR and PS, which was discussed in detail from the special dispersion of iron particles and of zero‐modulus of MR elastomers. In addition, the MR elastomers based on SR/PS blend matrix had enhanced mechanical properties, which made them more hopeful to be applied in practice. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3143–3149, 2007 相似文献