全文获取类型
收费全文 | 5546篇 |
免费 | 600篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 1073篇 |
理论与方法论 | 279篇 |
现状及发展 | 887篇 |
研究方法 | 29篇 |
综合类 | 3875篇 |
自然研究 | 6篇 |
出版年
2024年 | 1篇 |
2021年 | 1篇 |
2018年 | 729篇 |
2017年 | 735篇 |
2016年 | 432篇 |
2015年 | 33篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 272篇 |
2011年 | 959篇 |
2010年 | 818篇 |
2009年 | 457篇 |
2008年 | 511篇 |
2007年 | 768篇 |
2006年 | 15篇 |
2005年 | 51篇 |
2004年 | 128篇 |
2003年 | 155篇 |
2002年 | 64篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1975年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有6149条查询结果,搜索用时 15 毫秒
1.
C. Baroni Urbani G. S. Boyan A. Blarer J. Billen T. M. Musthak Ali 《Cellular and molecular life sciences : CMLS》1994,50(1):63-71
The Indian antHarpegnathos saltator may be unique among insects in using its jumping capacity not only as an escape mechanism but also as a normal means of locomotion, and for catching its prey in flight. High-speed cinematography used to analyse the various phases of the jump suggests thatHarpegnathos employs a novel jumping mechanism to mediate these behaviours: namely the synchronous activation of its middle and hindlegs. Electrophysiological recordings from muscles or nerves in pairs of middle and hindlegs show remarkably synchronous activity during fictive jumping, supporting the synchronous activation hypothesis.Harpegnathos is not the only ant to jump, and a cladistic analysis suggests that jumping behaviour evolved independently three times during ant evolutionary history. 相似文献
2.
An Fe-based amorphous alloy was found to significantly enhance the reductive degradation of an azo dye in aqueous solution. The surface-area normalized rate constant was up to 2.0 L m-2 min-1 at room temperature,an order of magnitude larger than any previously reported value. The activation energy of the degradation process was calculated according to the Arrhenius equation,and a much lower value than those previously reported was obtained. Valence band measurement indicated that a depressed valence band maximum and a widened empty band were established in the amorphous ribbon. The unique structure of the amorphous alloy is important-it may reduce the activation energy of the degradation process and enhance the activity of the electrons,thus accelerating the degradation process. 相似文献
3.
Automatically allocation of more attention to negative stimuli is called emotional negativity bias. An event-related potentials (ERPs) experiment investigated whether or not this bias was altered by positive mood arousal. The results suggested that the attention bias towards negative stimuli was attenuated when positive information was accessible. 相似文献
4.
延长油田东部裸眼井区早期测井资料普遍只有自然电位(SP)、自然伽马(GR)及梯度电阻率(R2.5)三条曲线,因缺失声波(AC)、地层电阻率(RT)等测井曲线,难以满足精细油藏地质研究需求。东部裸眼井区开发时间长、单井产量低,重新测井缺乏可行性及经济性。采用长短期记忆循环神经网络(Long Short-Term Memory,LSTM)进行缺失测井曲线重构是一种经济有效方法,适用于地层测井序列数据。然而延长油田东部浅层油藏上覆黄土层段测井数据信号干扰大,直接应用模型精度较差。针对此问题,本文采用考虑地质分层约束的LSTM模型进行缺失测井曲线的重构,通过分层数据截取每口井长6层段测井数据作为样本数据,既保留了LSTM模型处理序列数据的优势,同时又避免了上覆黄土层测井数据对模型的干扰。利用裸眼井区完整测井数据进行模型训练优化和验证,讨论了考虑地质分层约束的LSTM测井曲线重构精度,结果表明通过引入地质分层约束,模型重构测井曲线精度更高。应用优化后模型实现裸眼井区50口仅有GR、SP、R2.5三条曲线数据井的AC、RT曲线重构,对50口井的142个射孔段进行二次解释,对比试油解释结论符合率达到89.4%,验证了该方法对测井曲线重构的实用性和有效性。 相似文献
5.
COMPARISON OF TWO METHODS OF OPERATING THEATRE PLANNING: APPLICATION IN BELGIAN HOSPITAL 总被引:3,自引:0,他引:3
Sondes CHAABANE~ Nadine MESKENS~ Alain GUINET~ Marius LAURENT~ ~LAMIH laboratory Valenciennes University Valenciennes Cedex France ~MAAD Laboratory FUCAM Mons Belgium ~LIESP Laboratory INSA-Lyon France ~CHU de TIVOLI La Louvière Belgium 《系统科学与系统工程学报(英文版)》2008,17(2):171-186
Operating Theatre is the centre of the hospital management's efforts. It constitutes the most expensive sector with more than 10% of the intended operating budget of the hospital. To reduce the costs while maintaining a good quality of care, one of the solutions is to improve the existent planning and scheduling methods by improving the services and surgical specialty coordination or finding the best estimation of surgical case durations. The other solution is to construct an effective surgical case plan and schedule. The operating theatre planning and scheduling is the two important steps, which aim to make a surgical case programming with an objective of obtaining a realizable and efficient surgical case schedule. This paper focuses on the first step, the operating theatre planning problem. Two planning methods are introduced and compared. Real data of a Belgian university hospital "Tivoli" are used for the experiments. 相似文献
6.
This paper further investigates cluster synchronization in a complex dynamical network with two-cluster. Each cluster contains a number of identical dynamical systems, however, the subsystems composing the two clusters can be different, i.e., the individual dynamical system in one cluster can differ from that in the other cluster. Complete synchronization within each cluster is possible only if each node from one cluster receives the same input from nodes in other cluster. In this case, the stability condition of one-cluster synchronization is known to contain two terms: the first accounts for the contribution of the inner-cluster coupling structure while the second is simply an extra linear term, which can be deduced by the "same-input" condition. Applying the connection graph stability method, the authors obtain an upper bound of input strength for one cluster if the first account is known, by which the synchronizability of cluster can be scaled. For different clusters, there are different upper bound of input strength by virtue of different dynamics and the corresponding cluster structure. Moreover, two illustrative examples are presented and the numerical simulations coincide with the theoretical analysis. 相似文献
7.
In this paper, the joint production and recycling problem is investigated for a hybrid manufacturing and remanufacturing system where brand-new products are produced in the manufacturing plant and recycled products are remanufactured into as-new products in the remanufacturing facility. Both the brand-new products and remanufactured products are used to satisfy customer demands. Returns of used products that are recycled from customers are assumed to be stochastic and nonlinearly price-dependent. A mathematical model is proposed to maximize the overall profit of the system through simultaneously optimizing the production and recycling decisions, subject to two capacity constraints — the manufacturing capacity and the remanufacturing capacity. Based on Lagrangian relaxation method, subgradient algorithm and heuristic algorithm, a solution approach is developed to solve the problem. A representative example is presented to illustrate the system, and managerial analysis indicates that the uncertainties in demand and return have much influence on the production and recycling policy. In addition, twenty randomly produced examples are solved, and computational results show that the solution approach can obtain very good solutions for all examples in reasonable time. 相似文献
8.
Most inventory researches assume that production level can fluctuate arbitrarily. However, large fluctuation of the production
level in many firms may be much costly. This paper addresses the coordinating pricing and inventory control problem in a bounded
production system with uncertain yield, in which the production level is constrained between a maximum and minimum level in
each period and the price can be adjusted dynamically. We show that the optimal policy is the interval base-stock-list-price
policy. Also, we study the impact of the production bounds and uncertainty of the yield on the production system. Numerical
experiments are also performed to study the impact of parameters on the system. 相似文献
9.
Yutaka Baba 《系统科学与系统工程学报(英文版)》2010,19(4):496-503
We study an M/PH/1 queue with phase type working vacation and vacation interruption where the vacation time follows a phase
type distribution. The server serves the customers at a lower rate in a vacation period. The server comes back to the regular
busy period at a service completion without completing the vacation. Such policy is called vacation interruption. In terms
of quasi birth and death process and matrix-geometric solution method, we obtain the stationary queue length distribution.
Moreover we obtain the conditional stochastic decomposition structures of queue length and waiting time when the service time
distribution in the regular busy period is exponential. 相似文献
10.
<正> In this paper,a two-scale finite element approach is proposed and analyzed for approximationsof Green's function in three-dimensions.This approach is based on a two-scale finite elementspace defined,respectively,on the whole domain with size H and on some subdomain containing singularpoints with size h (h H).It is shown that this two-scale discretization approach is very efficient.In particular,the two-scale discretization approach is applied to solve Poisson-Boltzmann equationssuccessfully. 相似文献