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排序方式: 共有470条查询结果,搜索用时 15 毫秒
431.
Ali Amiri 《Information Technology and Management》2003,4(1):113-127
This paper deals with the multi-hour bandwidth packing problem in telecommunication networks. The problem consists of selecting calls from a list of requests with time varying traffic conditions to be routed on an arc-capacitated network in order to maximize profit. Response time to users is considered by specifying an upper limit on the queueing delay in the network. The paper represents a significant improvement over previous research by presenting a unified model of the problem that considers all possible paths for each call, allows the traffic requirements of the calls to vary over the busy-hours of the day and integrates quality of service to users. A mathematical programming formulation for the problem is presented. A Lagrangean relaxation based heuristic solution procedure is developed. The results of extensive computational experiments over a wide range of problem structures indicate that the procedure is both efficient and effective. 相似文献
432.
Alireza Shamsi Ali Amiri Payam Heydari Hasan Hajghasem Mansour Mohtashamifar Mehrnaz Esfandiari 《Microsystem Technologies》2014,20(10-11):1925-1931
Polymer based microfabrication technologies are used extremely in Bio-MEMS, especially in Microfluidic devices in recent years. In this paper, a novel method for fabrication of microstructures on a polymeric material using hot embossing lithography process is presented. The proposed method involves usage of low cost materials and procedure with respect to previous methods and can be processed in a short time. The master is made from SU-8 on an inexpensive glass substrate which is patterned by standard lithography. The embossing pressure can be increased in our master as the glass substrate used in this paper is more robust than Silicon. Master robustness and SU-8 to glass adhesion is optimized by some substrate pretreatments and SU-8 baking time and temperatures. Microchannels are replicated on a Polymethylmetacrylate (PMMA) stamp which is a plexiglass sheet with thickness of 1 mm. Significant embossing parameters including temperature, pressure and time are discussed and optimum values are determined. Microchannels are imprinted by depth of 50 μm and minimum width of 15 μm and aspect ratio more than 3. The microchannels are sealed by a PMMA cap using thermal annealing bonding. 相似文献
433.
Stress‐Strength Reliability Analysis with Extreme Values based on q‐Exponential Distribution 下载免费PDF全文
Romero L. M. Sales Filho Enrique López Droguett Isis D. Lins Márcio C. Moura Mehdi Amiri Rafael Valença Azevedo 《Quality and Reliability Engineering International》2017,33(3):457-477
When dealing with practical problems of stress–strength reliability, one can work with fatigue life data and make use of the well‐known relation between stress and cycles until failure. For some materials, this kind of data can involve extremely large values. In this context, this paper discusses the problem of estimating the reliability index R = P(Y < X) for stress–strength reliability, where stress Y and strength X are independent q‐exponential random variables. This choice is based on the q‐exponential distribution's capability to model data with extremely large values. We develop the maximum likelihood estimator for the index R and analyze its behavior by means of simulated experiments. Moreover, confidence intervals are developed based on parametric and nonparametric bootstrap. The proposed approach is applied to two case studies involving experimental data: The first one is related to the analysis of high‐cycle fatigue of ductile cast iron, whereas the second one evaluates the specimen size effects on gigacycle fatigue properties of high‐strength steel. The adequacy of the q‐exponential distribution for both case studies and the point and interval estimates based on maximum likelihood estimator of the index R are provided. A comparison between the q‐exponential and both Weibull and exponential distributions shows that the q‐exponential distribution presents better results for fitting both stress and strength experimental data as well as for the estimated R index. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
434.
Boshra Amiri Hasan Ahmadvand Ali Farhadi Aazam Najmafshar 《Drug development and industrial pharmacy》2018,44(8):1371-1376
Vinblastine (VB), as a chemotherapeutic agent, is widely used in treatment of different types of cancer. However, its clinical application is limited due to its low water solubility, side effects, and multidrug resistance. The aim of this study was to increase the therapeutic efficacy of VB using drug delivery systems. For this purpose, a PEGylated niosomal formulation of vinblastine (Pn-VB) was prepared by thin film hydration method and physicochemically characterized. Drug release pattern was performed by dialysis diffusion method. The cytotoxicity of Pn-VB was investigated against murine lung cancer TC-1 cells using MTT assay and its tumor inhibitory effect was evaluated in lung tumor-bearing C57BL/6 mice. Mean particle size, zeta potential, entrapment, and loading efficiency of niosomes were obtained to be about 234.3?±?11.4?nm, -34.6?±?4.2?mV, 99.92?±?1.6%, and 2.673?±?0.30%, respectively. While, the mean particle size and zeta potential for non-PEGylated niosomes were obtained about 212.4?nm and -31.4?mV, respectively. The in vitro release pattern of drug from niosomes showed a sustained release behavior. Pn-VB indicated a significant increase in toxicity against TC-l cells as compared to free VB. In animal model, Pn-VB exhibited stronger tumor inhibitory effect and longer life time in comparison to free VB. In conclusion, Pn-VB showed appropriate stability, high-entrapment efficacy, lower releasing rate, and stronger cytotoxic activity against lung cancer TC-1 cells as compared to free drug. Thus, the Pn-VB could be a promising formulation for delivery of vinblastine to tumor cells with enhanced drug bioavailability and therapeutic efficacy. 相似文献
435.
Effect of processing method on migration of antioxidant from HDPE packaging into a fatty food simulant in terms of crystallinity 下载免费PDF全文
Migration of additives from plastic packaging into food products is generally considered to be affected by polymer crystallinity. In the present work, migration of Irganox 1010 from high density polyethylene into a fatty food simulant (ethanol 95%) was studied for samples prepared with different percent crystallinities. For this purpose, 2 different processing techniques, injection and compression molding, were used, and the preparation conditions were changed to obtain high density polyethylene samples with crystallinities in the range of 50 to 70%. Migration analysis was carried out at 121°C for 2 hours, and then at 40°C for 238 hours using high performance liquid chromatography. In general, the injection molded specimens had lower crystallinity and higher overall migration than the compression molded ones. A similar trend for both injection and compression molded samples was observed indicating that the overall migration was a function of crystallinity degree. However, the specific migration rates of Irganox 1010 especially before 50 hours were found to be different for the 2 processing methods because of dissimilar morphologies. Theoretical modeling based on Fickian diffusion was applied to give more insights into the involved processes during specific migration. The interaction of the food simulant with the polymer was taken into account considering the food sorption into the polymer. By fitting the model on experimental data, it was possible to obtain the model parameters such as partition coefficients (K) and the swelling constant (B) as a function of sample crystallinity. 相似文献
436.
M Amiri A Kahirdeh M Modarres 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(3):423-434
Evolution of the thermodynamic entropy generation during fatigue crack initiation life of notched specimens is studied. A set of experimental results of AA7075‐T651 is examined to determine applicability of the thermodynamic entropy generation as an index of fatigue crack initiation. Entropy accumulation is calculated from hysteresis energy and temperature rise. An increasing trend of entropy accumulation with the number of cycle to failure is observed on macroscale measurements. Results also determine that the entropy generations from the samples under the same operating conditions are similar as the crack grows. Scanning electron microscope analysis is performed on the fractured surfaces to observe the fatigue striations, and persistent slip bands are observed employing an optical microscope. A discussion is presented regarding the length scales on which crack initiation occurs and entropy calculation is made. 相似文献
437.
N. Amiri A. Ramirez-Serrano R. J. Davies 《Journal of Intelligent and Robotic Systems》2013,69(1-4):147-159
In this paper, a dynamic model of vertical take-off and landing (VTOL) aerial vehicles, having lateral and longitudinal rotor tilting mechanism, is first developed using a Newton–Euler formulation. Then an integral backstepping (IB) control technique is proposed to improve the pitch, yaw, and roll stability of the vehicle. Such control mechanisms enables the UAV to perform complex tasks that no other Unmanned Aerial Vehicles (UAVs) can execute such as hover pitched. This control tactic allows the vehicle under investigation, eVader, to use the full potential of its flying characteristics enabled by the novel dual-axis oblique active tilting (OAT) mechanism, which enables it to maneuver inside obstructed environments. The potential of the eVader as a small UAV and its model are verified and then used to for autonomous take-off and landing as well as stabilizing the vehicle’s attitude. Finally, diverse simulation scenarios on attitude and position control, stabilization and autonomous take off and landing are presented. 相似文献
438.
Interest in applying flying robots especially quadcopters for civil applications, in particular for delivering purposes, has dramatically grown in the recent years. In fact, since quadcopters are capable of vertical takeoff and landing, they can be widely employed for nearly any aerial task where a human presence is hazardous or response time is critical. In this regard, quadcopters come to be very beneficial in delivering packages; accordingly, generating an optimal flight trajectory plays a preponderant role for meeting this vision. This paper is concerned with generation of a time-optimal 3D path for a quadcopter under municipal restrictions in delivering tasks. To this end, the flying robot’s dynamics is first modeled through Newton–Euler method. Subsequently, the problem is formulated as a time-optimal control problem such that the urban constraints, which are safe-margins of high-rise buildings located throughout the course, are first modeled and then imposed to the trajectory optimization problem as inequality constraints. After discretizing the trajectory by means of Hermit–Simpson method, the optimal control problem is transformed into a nonlinear programming problem and finally is solved by the direct collocation technique. Extensive simulations demonstrate the efficacy of the proposed method and correspondingly verify the effectiveness of the suggested method in generation of optimum 3D routes while all constraints and mission requirements are satisfied. 相似文献
439.
Amirhossein Amiri Marzieh Mehrjoo Zbigniew J. Pasek 《The International Journal of Advanced Manufacturing Technology》2013,64(9-12):1323-1332
In profile monitoring, a relationship between a response variable and one or more explanatory variables is monitored. Different methods were developed for phase II monitoring of simple linear profiles. While some of the methods can be used to detect both increasing and decreasing shifts in the regression parameters, others need to be modified to enable detection of decreasing shifts in a process. In this paper, necessary modifications of the phase II methods for simple linear profile monitoring are proposed to improve their performance in detecting decreasing shifts. The paper also presents a performance comparison of several phase II methods. 相似文献
440.
Natural nickel electrodeposition on a copper substrate with a gold layer was studied with the aim of production of 64Cu radionuclide. The electrodeposition experiments were carried out in acid plating baths. The operating parameters such as
pH, temperature, and current density were optimized. The current efficiency was measured at different current densities. The
optimum conditions of the nickel electrodeposition are as follows: 5.7 g 1−1 nickel, pH 3–4, dc current density 85.54 mA cm−2, and 55°C, with 97% current efficiency. SEM photomicrographs demonstrated fine-grained structure of the deposit obtained
from the optimum bath. A 46-μm high-quality layer was deposited on a gold layer of the copper substrate. 相似文献