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61.
Identification of bio-aerosol particles may be enhanced by size sorting before applying analytical techniques. In this paper, the use of ultrasonic acoustic radiation pressure to continuously size fractionate particles in a moving air stream is described. Separate particle-laden and clean air streams are introduced into a channel and merged under laminar flow conditions. An ultrasonic transducer, mounted flush to one wall of the channel, excites a standing ultrasonic wave perpendicular to the flow of the combined air stream. Acoustic radiation forces on the particles cause them to move transverse to the flow direction. Since the radiation force is dependent upon the particle size, larger particles move a greater transverse distance as they pass through the standing wave. The outlet flow is then separated into streams, each containing a range of particle sizes. Experiments were performed with air streams containing glass microspheres with a size distribution from 2-22 μm, using a centerline air stream velocity of approximately 20 cm/s. An electrostatic transducer operating at a nominal frequency of 50 kHz was used to drive an ultrasonic standing wave of 150 dB in pressure amplitude. The microsphere size distributions measured at the outlet were compared with the predictions of a theoretical model. Experiments and theory show reasonable correspondence. The theoretical model also indicates an optimal partitioning of the particle-laden and clean air inlet streams. 相似文献
62.
Sequential pattern mining from sequence databases has been recognized as an important data mining problem with various applications. Items in a sequence database can be organized into a concept hierarchy according to taxonomy. Based on the hierarchy, sequential patterns can be found not only at the leaf nodes (individual items) of the hierarchy, but also at higher levels of the hierarchy; this is called multiple-level sequential pattern mining. In previous research, taxonomies based on crisp relationships between any two disjointed levels, however, cannot handle the uncertainties and fuzziness in real life. For example, Tomatoes could be classified into the Fruit category, but could be also regarded as the Vegetable category. To deal with the fuzzy nature of taxonomy, Chen and Huang developed a novel knowledge discovering model to mine fuzzy multi-level sequential patterns, where the relationships from one level to another can be represented by a value between 0 and 1. In their work, a generalized sequential patterns (GSP)-like algorithm was developed to find fuzzy multi-level sequential patterns. This algorithm, however, faces a difficult problem since the mining process may have to generate and examine a huge set of combinatorial subsequences and requires multiple scans of the database. In this paper, we propose a new efficient algorithm to mine this type of pattern based on the divide-and-conquer strategy. In addition, another efficient algorithm is developed to discover fuzzy cross-level sequential patterns. Since the proposed algorithm greatly reduces the candidate subsequence generation efforts, the performance is improved significantly. Experiments show that the proposed algorithm is much more efficient and scalable than the previous one. In mining real-life databases, our works enhance the model's practicability and could promote more applications in business. 相似文献
63.
The benefits of simultaneous consideration of siting and sizing of distribution centers have been well acknowledged in supply
chain design. Most formulations assume that the potential DC sites are known and the decision on location is to select sites
from the finite potential DC sites. However, the quality of this discrete version problem depends on the selection of potential
DC sites. In this paper we present a planar version of the problem, which assumes that there is no a priori knowledge of DC
sites and DCs can be located anywhere in the plane. The goal of the problem is to simultaneously find locations and sizing
of DC sites. The solution of the planar problem provides a lower bound for the discrete problem. The objective of the problem
is to minimize the total of inbound and outbound transportation costs and distribution center construction costs—which include
its fixed charge cost and concave sizing cost. The problem is initially formulated as a nonlinear programming model. We then
reformulate it as a set covering problem after establishing certain key properties. A greedy drop heuristic and a column generation
heuristic are developed to solve the problem. Computational experiments are provided. 相似文献
64.
This paper considers a production/inventory system where items produced/purchased are of different qualities: Types A and B. Type A items are of perfect quality, and Type B items are of imperfect quality; but not necessarily defective; and have a lower selling price. The percentage of Type A (the yield rate) is assumed to be a random variable with known probability distribution. The electronics industry gives good examples of such situations. We extend the classical single period (newsvendor) and the economic order quantity (EOQ) models by accounting for random supply and for imperfect quality (Type B) items which are assumed to have their own demand and cost structure. We develop mathematical models and prove concavity of the expected profit function for both situations. We also present detailed analysis and numerical results. We focus on comparing the profitability of the novel proposed models with models from the literature (and derivatives of these models) that develop the optimal order quantity based on the properties of Type A items only (and ignore Type B items). We find that accounting for Type B items can significantly improve profitability. 相似文献
65.
In this paper, two new algorithms are presented to solve multi-level multi-objective linear programming (ML-MOLP) problems through the fuzzy goal programming (FGP) approach. The membership functions for the defined fuzzy goals of all objective functions at all levels are developed in the model formulation of the problem; so also are the membership functions for vectors of fuzzy goals of the decision variables, controlled by decision makers at the top levels. Then the fuzzy goal programming approach is used to achieve the highest degree of each of the membership goals by minimizing their deviational variables and thereby obtain the most satisfactory solution for all decision makers. 相似文献
66.
We propose a formulation and solution procedure for optimizing the fleet size and freight car allocation under uncertainty demands. There are important interactions between decisions on sizing a rail–car fleet and utilizing that fleet. Consequently, the optimum use of empty rail–cars for demands response in the length of the time periods one of advantages the proposed model. The model also provides rail network information such as yard capacity, unmet demands, and number of loaded and empty rail–car at any given time and location. Consequently, the model helping managers or decision makers of any train company for planning and decision making. We propose two-stage solution procedure for solve rail–car fleet sizing problem. Numerical examples are given to illustrate the model and solution methodology. 相似文献
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