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排序方式: 共有64条查询结果,搜索用时 15 毫秒
1.
This paper tackles the design of scalable and fault-tolerant evolutionary algorithms computed on volunteer platforms. These platforms aggregate computational resources from contributors all around the world. Given that resources may join the system only for a limited period of time, the challenge of a volunteer-based evolutionary algorithm is to take advantage of a large amount of computational power that in turn is volatile. The paper analyzes first the speed of convergence of massively parallel evolutionary algorithms. Then, it provides some guidance about how to design efficient policies to overcome the algorithmic loss of quality when the system undergoes high rates of transient failures, i.e. computers fail only for a limited period of time and then become available again. In order to provide empirical evidence, experiments were conducted for two well-known problems which require large population sizes to be solved, the first based on a genetic algorithm and the second on genetic programming. Results show that, in general, evolutionary algorithms undergo a graceful degradation under the stress of losing computing nodes. Additionally, new available nodes can also contribute to improving the search process. Despite losing up to 90 % of the initial computing resources, volunteer-based evolutionary algorithms can find the same solutions in a failure-prone as in a failure-free run.  相似文献   
2.
基于弯矩和轴力随机相关特性的RC偏压构件可靠度分析   总被引:4,自引:0,他引:4  
我国现行规范在分析混凝土偏心受压构件可靠度时,未考虑轴力和弯矩的随机相关特性。基于此,首先推导了弯矩和轴力间相关系数与对应荷载效应比值的函数表达式,得到了相关系数随荷载效应比值变化的规律。在此基础上定性分析了弯矩和轴力的随机相关特性对大偏压和小偏压两类构件失效概率的不同影响规律。采用Monte Carlo方法计算了当水...  相似文献   
3.
8279芯片是专用数码显示器接口芯片,能对显示器自动扫描,并大大减轻CPU的负担。因此,在单片机应用系统中,获得了广泛的应用。主要阐述了8279芯片的主要结构、原理以及在铝电解智能槽控机的硬件组成、应用软件上的初始化、软件构成。  相似文献   
4.
The silicone elastomer latex formulated with polyethylene glycol and colloidal silica produced a controlled release film coating on potassium chloride tablets. The release rate of potassium chloride was controlled by the total amount of polyethylene glycol and the weight fraction of polyethylene glycol 8000 and 1450 incorporated in the coating. A mathematical model was developed to quantitate the effect of coating components on the drug release rate using the statistical extreme vertices design. The predictive capability of this functional relationship was tested and validated experimentally.  相似文献   
5.
《Food chemistry》2005,93(3):497-501
Bay leaf belongs to the family Lauraceae, and it is one of the most popular culinary spices in all Western countries. Bay leaf has been used as herbal medicine and has pharmacological activity which includes anti-bacterial, anti-fungal, anti-diabetes and anti-inflammatory effects. The goal of this study was to identify compounds from Bay leaf (Laurus nobilis), which are responsible for inducing apoptosis using bioassay-directed isolation. The isolation of active compounds was carried out in three steps: multiple extractions, fractionation using column chromatography and purification using semi-preparative HPLC. The structure of separated compounds was determined on the basis of 1H, 13C nuclear magnetic resonance data, atmospheric pressure chemical ionization mass spectrometry data, and electron ionization mass spectrometry. Six compounds were identified; all of them are sesquiterpene lactones.  相似文献   
6.
A method for constructing an approximation of the critical excitation that drives an elastoplastic system from rest to a target threshold at a specified time instant, referred to as the “suboptimal excitation,” is presented in this paper. It is based on the observations gained from study of the critical excitations in the companion paper. Essentially, for the usual case of interest where the failure time is not small compared to the natural period, the duration of the positive and negative pulses of the critical excitation are roughly equal to half of the natural period. This consideration allows for a simple intuitive approximation of the critical excitation. The amplitudes of the positive and negative pulses are obtained in closed forms using energy balance. Numerical investigations show that the critical excitations are well approximated by the suboptimal excitations.  相似文献   
7.
The rate of wear and hardness of tablets of Emcompress and sodium chloride compressed at various applied pressures in a lubricated and an unlubricated die are compared. The effect of applied pressure and concentration of magnesium stearate blended with several direct compression excipients on the wear rate constant, hardness and tensile strength of a tablet is reported. The data allow a comparison of the methods used to express the mechanical strength of tablets.  相似文献   
8.
The relation of concentration of starch and povidone in tablets of Emcompress and Fast-Flo lactose and the relation of pressure applied to the tablets to wear rate constant, hardness and tensile strength are reported. The extent to which these parameters are changed by concentration and applied pressure is compared. The influence of shape on the wearability of flat face, flat face bevel edge bisect and standard convex tablets with and without a lubricant was studied.  相似文献   
9.
In a nuclear power plant, a loose part monitoring system (LPMS) provides information on the location and the mass of a loosened or detached metal impacted onto the inner surface of the primary pressure boundary. Typically, accelerometers are mounted on the surface of a reactor vessel to localize the impact location caused by the impact of metallic substances on the reactor system. However, in some cases, the number of accelerometers is not sufficient to estimate the impact location precisely. In such a case, one of useful methods is to utilize other types of sensor that can measure the vibration of the reactor structure. For example, acoustic emission (AE) sensors are installed on the reactor structure to detect leakage or cracks on the primary pressure boundary. However, accelerometers and AE sensors have a different frequency range. The frequency of interest of AE sensors is higher than that of accelerometers. In this paper, we propose a method of impact source localization by using both accelerometer signals and AE signals, simultaneously. The main concept of impact location estimation is based on the arrival time difference of the impact stress wave between different sensor locations. However, it is difficult to find the arrival time difference between sensors, because the primary frequency ranges of accelerometers and AE sensors are different. To overcome the problem, we used phase delays of an envelope of impact signals. This is because the impact signals from the accelerometer and the AE sensor are similar in the whole shape (envelope). To verify the proposed method, we have performed experiments for a reactor mock-up model and a real nuclear power plant. The experimental results demonstrate that we can enhance the reliability and precision of the impact source localization. Therefore, if the proposed method is applied to a nuclear power plant, we can obtain the effect of additional installed sensors.  相似文献   
10.
《Materials Letters》2007,61(4-5):964-967
Finite-deformation elastoplastic analysis of a crack subjected to mode I cyclic loading under small scale yielding was performed. The influence of the load range, load ratio and overload on the crack tip deformations is presented. Cyclic crack tip opening displacements agreed with predictions of simpler models, where available. Crack closure was not detected. Plastic crack advance was evidenced. Its rate per cycle reproduced common trends of the fatigue cracking dependence on loading range and overload.  相似文献   
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