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排序方式: 共有242条查询结果,搜索用时 421 毫秒
61.
M. H. Abo-Shosha N. A. Ibrahim A. Hashem 《Polymer-Plastics Technology and Engineering》2013,52(6):931-943
Cellulose, melamine formaldehyde precondensate (MF), and methylamine hydrochloride (MA.HCl) were reacted in aqueous medium at different conditions, including time, temperature, MF/MA.HCl molar ratio, and liquor-to-cellulose ratio (LR). Reaction conditions were selected to prepare a cellulose/MF/MA anion exchanger having a total nitrogen and an amino nitrogen of 23.1% and 131 mEq/100 g, respectively. Potentiometric titration showed that the strength, pKb , of this resin was 7.2. The resin lost about 3% and 9% of its total and amino nitrogen, respectively, during the first five cycles of the durability test, after which it suffered no losses up to 25 cycles. The resin was utilized in the removal of three anionic dyestuffs (direct, acid, and reactive) as well as permanganate and dichromate anions from aqueous solutions at different pH values ranging from 3 to 12. Maximum extents of removal were manifested at a pH value of 3, at which they followed the descending order: (permanganate ~ acid dye) > (reactive dye ~ dichromate) » direct dye. 相似文献
62.
An analytical solution for the evaluation of scattering of waves by a circular cavity in infinite isotropic elastic porous media is presented. Two groups of complex functions for solid skeleton and pore fluid in a two-dimensional complex plane are introduced in order to solve the Biot equations. Stress, displacement, and pore pressure fields induced by incident and scattered waves in the medium and especially in the vicinity of the cavity are evaluated in this complex plane. The validation of the proposed solution is shown by various numerical examples. A parametric study including the effects of fluid compressibility changes, shear modulus, and permeability variations, several wave numbers, and wave types (fast, slow, and shear waves) is performed. 相似文献
63.
Shadows cast by trees and buildings can limit the solar access of rooftop solar-energy systems, including photovoltaic panels and thermal collectors. This study characterizes residential rooftop shading in Sacramento, San Jose, Los Angeles and San Diego, CA. Our analysis can be used to better estimate power production and/or thermal collection by rooftop solar-energy equipment. It can also be considered when designing programs to plant shade trees.High-resolution orthophotos and LiDAR (Light Detection And Ranging) measurements of surface height were used to create a digital elevation model of all trees and buildings in a well-treed 2.5–4 km2 residential neighborhood. On-hour shading of roofing planes (the flat elements of roofs) was computed geometrically from the digital elevation model. Values in future years were determined by repeating these calculations after simulating tree growth. Parcel boundaries were used to determine the extent to which roofing planes were shaded by trees and buildings in neighboring parcels.For the subset of S + SW + W-facing planes on which solar equipment is commonly installed for maximum solar access, absolute light loss in spring, summer and fall peaked about 2 to 4 h after sunrise and about 2 to 4 h before sunset. The fraction of annual insolation lost to shading increased from 0.07–0.08 in the year of surface-height measurement to 0.11–0.14 after 30 years of tree growth. Only about 10% of this loss resulted from shading by trees and buildings in neighboring parcels. 相似文献
64.
Ali Bahadur Shahid Iqbal Hashem O. Alsaab Nasser S. Awwad Hala A. Ibrahium 《Microscopy research and technique》2022,85(4):1494-1501
Organic polymers in the process of thermal degradation produce a lot of toxic fragments. In this work, we designed a new method of degradation of polymethylmethacrylate (PMMA) materials with aluminum triiodide nanoadditives (AlI3 NAs). In the present research work, a thermal degradation study of PMMA blends with AlI3 NAs was carried out by using a specially designed pyrolytic assembly. Different blends of PMMA with AlI3 (P0, P3, P6, P9, P12, and P15) were prepared by changing the concentration of AlI3 NAs from 0% to 15%. FTIR and TGA studies show the stability of polymers with AlI3 NAs. Scanning electron microscopy analysis shows All3 spread uniformly at nanoscale throughout the polymer matrix. Horizontal burning test (HBT) test confirms that polymer burning is retarded with AlI3 NAs. 相似文献
65.
66.
This paper considers the solution of nonlinear rationalexpectations models resulting from the optimality conditions of afinite-horizon intertemporal optimization problem satisfying Bellman'sprinciple of optimality (and possibly involving inequality constraints). Abackward recursive procedure is used to characterize and solve thetime-varying optimal decision rules generally associated with these models.At each stage of these backward recursions, either an analytical ornumerical solution of the optimality conditions is required. When ananalytical solution is not possible, a minimum weighted residual approach isused. The solution technique is illustrated using a life-cycle model ofconsumption under labor income and interest rate uncertainties (and possiblyinvolving liquidity constraints). Approximate numerical solutions areprovided and compared with certainty-equivalent solutions and, whenpossible, with exact solutions. 相似文献
67.
Cool roofs—roofs that stay cool in the sun by minimizing solar absorption and maximizing thermal emission—lessen the flow
of heat from the roof into the building, reducing the need for space cooling energy in conditioned buildings. Cool roofs may
also increase the need for heating energy in cold climates. For a commercial building, the decrease in annual cooling load
is typically much greater than the increase in annual heating load. This study combines building energy simulations, local
energy prices, local electricity emission factors, and local estimates of building density to characterize local, state average,
and national average cooling energy savings, heating energy penalties, energy cost savings, and emission reductions per unit
conditioned roof area. The annual heating and cooling energy uses of four commercial building prototypes—new office (1980+),
old office (pre-1980), new retail (1980+), and old retail (pre-1980)—were simulated in 236 US cities. Substituting a weathered
cool white roof (solar reflectance 0.55) for a weathered conventional gray roof (solar reflectance 0.20) yielded annually
a cooling energy saving per unit conditioned roof area ranging from 3.30 kWh/m2 in Alaska to 7.69 kWh/m2 in Arizona (5.02 kWh/m2 nationwide); a heating energy penalty ranging from 0.003 therm/m2 in Hawaii to 0.14 therm/m2 in Wyoming (0.065 therm/m2 nationwide); and an energy cost saving ranging from 0.126/m < sup > 2 < /sup > in West Virginia to0.126/m2 in West Virginia to 1.14/m2 in Arizona ($0.356/m2 nationwide). It also offered annually a CO2 reduction ranging from 1.07 kg/m2 in Alaska to 4.97 kg/m2 in Hawaii (3.02 kg/m2 nationwide); an NOx reduction ranging from 1.70 g/m2 in New York to 11.7 g/m2 in Hawaii (4.81 g/m2 nationwide); an SO2 reduction ranging from 1.79 g/m2 in California to 26.1 g/m2 in Alabama (12.4 g/m2 nationwide); and an Hg reduction ranging from 1.08 μg/m2 in Alaska to 105 μg/m2 in Alabama (61.2 μg/m2 nationwide). Retrofitting 80% of the 2.58 billion square meters of commercial building conditioned roof area in the USA would
yield an annual cooling energy saving of 10.4 TWh; an annual heating energy penalty of 133 million therms; and an annual energy
cost saving of $0.356/m2 nationwide). It also offered annually a CO2 reduction ranging from 1.07 kg/m2 in Alaska to 4.97 kg/m2 in Hawaii (3.02 kg/m2 nationwide); an NOx reduction ranging from 1.70 g/m2 in New York to 11.7 g/m2 in Hawaii (4.81 g/m2 nationwide); an SO2 reduction ranging from 1.79 g/m2 in California to 26.1 g/m2 in Alabama (12.4 g/m2 nationwide); and an Hg reduction ranging from 1.08 μg/m2 in Alaska to 105 μg/m2 in Alabama (61.2 μg/m2 nationwide). Retrofitting 80% of the 2.58 billion square meters of commercial building conditioned roof area in the USA would
yield an annual cooling energy saving of 10.4 TWh; an annual heating energy penalty of 133 million therms; and an annual energy
cost saving of 735 million. It would also offer an annual CO2 reduction of 6.23 Mt, offsetting the annual CO2 emissions of 1.20 million typical cars or 25.4 typical peak power plants; an annual NOx reduction of 9.93 kt, offsetting the annual NOx emissions of 0.57 million cars or 65.7 peak power plants; an annual SO2 reduction of 25.6 kt, offsetting the annual SO2 emissions of 815 peak power plants; and an annual Hg reduction of 126 kg. 相似文献
68.
Effect of chitosan coatings enriched with cinnamon oil on the quality of refrigerated rainbow trout 总被引:7,自引:0,他引:7
Seyed Mahdi Ojagh Masoud Rezaei Seyed Hadi Razavi Seyed Mohamad Hashem Hosseini 《Food chemistry》2010
The effects of a chitosan (Ch) coating enriched with cinnamon oil (Ch + C) on quality of rainbow trout (Oncorhynchus mykiss) during refrigerated storage (4 ± 1 °C) were examined over a period of 16 days. A solution of Ch (2%, w/v) and Ch + C (2%, w/v Ch + 1.5%, v/v C) was used for the coating. The control and the coated fish samples were analysed periodically for microbiological (total viable count, psychrotrophic count), chemical (TVB-N, PV, TBA), and sensory (raw and cooked fish) characteristics. The results indicated that the effect of the Ch + C coating on the fish samples was to enable the good quality characteristics to be retained longer and to extend the shelf life during the refrigerated storage. 相似文献
69.
70.
Masood Ghasemi Garrett Clayton Hashem Ashrafiuon 《International journal of control》2013,86(12):2615-2633
In this paper, we develop a new integrated coordinated control and obstacle avoidance approach for a general class of underactuated agents. We use graph-theoretic notions to characterise communication topology in the network of underactuated agents as determined by the information flow directions and captured by the graph Laplacian matrix. Obstacle avoidance is achieved by surrounding the stationary as well as moving obstacles by elliptical or other convex shapes that serve as stable periodic solutions to planar systems of ordinary differential equations and using transient trajectories of those systems to navigate the agents around the obstacles. Decentralised controllers for individual agents are designed using sliding mode control approach and are only based on data communicated from the neighbouring agents. We demonstrate the efficacy of our theoretical approach using an example of a system of wheeled mobile robots that reach and maintain a desired formation. Finally, we validate our results experimentally. 相似文献