首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14099篇
  免费   45篇
  国内免费   58篇
系统科学   158篇
丛书文集   36篇
教育与普及   51篇
理论与方法论   114篇
现状及发展   4701篇
研究方法   788篇
综合类   8003篇
自然研究   351篇
  2013年   125篇
  2012年   332篇
  2011年   765篇
  2010年   143篇
  2008年   379篇
  2007年   422篇
  2006年   426篇
  2005年   456篇
  2004年   504篇
  2003年   391篇
  2002年   439篇
  2001年   315篇
  2000年   355篇
  1999年   236篇
  1992年   214篇
  1991年   164篇
  1990年   174篇
  1989年   186篇
  1988年   180篇
  1987年   194篇
  1986年   180篇
  1985年   255篇
  1984年   186篇
  1983年   150篇
  1982年   123篇
  1981年   127篇
  1980年   141篇
  1979年   348篇
  1978年   266篇
  1977年   249篇
  1976年   226篇
  1975年   241篇
  1974年   311篇
  1973年   285篇
  1972年   238篇
  1971年   343篇
  1970年   482篇
  1969年   330篇
  1968年   315篇
  1967年   324篇
  1966年   350篇
  1965年   225篇
  1964年   98篇
  1959年   108篇
  1958年   209篇
  1957年   118篇
  1956年   130篇
  1955年   101篇
  1954年   85篇
  1948年   127篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Linear models are invariant under non-singular, scale-preserving linear transformations, whereas mean square forecast errors (MSFEs) are not. Different rankings may result across models or methods from choosing alternative yet isomorphic representations of a process. One approach can dominate others for comparisons in levels, yet lose to another for differences, to a second for cointegrating vectors and to a third for combinations of variables. The potential for switches in ranking is related to criticisms of the inadequacy of MSFE against encompassing criteria, which are invariant under linear transforms and entail MSFE dominance. An invariant evaluation criterion which avoids misleading outcomes is examined in a Monte Carlo study of forecasting methods.  相似文献   
2.
Recent years have seen an increasing cross-fertilization between the fields of decision analysis and forecasting. Decision-analytic models often require forecasts as inputs, and aspects of the Bayesian decision-theoretic framework underlying decision analysis have proved useful to forecasting, particularly in contexts where subjective judgemental inputs are required. This paper describes the use of decision tree analysis for forecasting and illustrates its use for corporate divisional forecasting and planning. A specialized decision-analytic technique, acts as events, is also described and illustrated to forecast a new product's earnings. Conclusions are drawn about the applicability of decision analysis for forecasting.  相似文献   
3.
1.0MeV208Pb离子在非晶Si中的投影射程RP和射程偏差ΔRP作为注量和温度二者的函数用背散射法进行测定.注量的变化范围为5×1013~7×1014cm-2.注入是在室温和t=-120℃下完成的.由由实验所确定的投影射程,射程偏差与注量或温度无关,并且分别等于295和72.2nm.与TRIM86的计算结果相比较,发现RP的偏离为18%,而ΔRP的偏离为36%.RP和ΔRP二者与注量及温度的无关性,排除了所观察到的与TRIM的矛盾是由于注入期间辐射增强扩散或离子束混合效应而引起的解释。  相似文献   
4.
    
Synthesis is a creative and mysterious process in which a chaotic array of concepts, what might be called a mess, is cognitively ‘engaged’ with a problem domain to produce as many interpretations as can validly be derived for effective decision‐making purposes. The benefits of engaging concepts into a mess are that it allows the problem to be viewed through multiple lenses simultaneously, which affords a holistic vantage point for richer problem interpretation. By deliberately shifting the underlying concept held by actors and provoking the movement of concepts, better interpretations might lead to more useful decision making. Although research has discussed the possibility of using synthesis through case studies, we argue that there is a need to formally develop methodologies in this area for the purpose of fostering and solving complex problems. To demonstrate this, we provide a speculative case study to illustrate how this approach may be usefully applied. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
5.
    
In this paper, I argue that the fragmented state and uneven maturity of current systems science will render it increasingly inadequate for meeting the future needs of the engineering and practice disciplines depending on it. I explain that it is not the case that System Science is a holistic discipline in contrast with the reductionism of classical science, but that Systems Science has both reductionistic and holistic dimensions, dealt with respectively by two “movements” within systems science, which I will designate as “Complexity Science” and “Systems Research”.  I argue that in many situations the internal workings of a system can be satisfactorily addressed with the mainly reductionistic methods of Complexity Science, whereas when external factors play a significant role, the mainly holistic methods of Systems Research are brought to the fore. This suggest that Complexity Science and Systems Research are not really as disjunct as often portrayed, but represent special cases under a wider conception that would hold across a spectrum of ratios between ‘internal complexity’ and ‘external complexity’ of the system of interest, and that would entail a differential emphasis on reductionistic and holistic methods based on contextual factors. Such a wider conception could not only help to unify systems science, but would also support analysis and intervention in the ‘middle ground’ between these polar types. This is relevant for Systems Engineering and Practice because as the world's complexity grows engineers and practitioners will increasingly have to deal with situations that are complex both internally and externally. This suggests an increasingly urgent need for the development of the envisioned ‘wider conception’ of systems in which we can deal in an elegant and principled way with shifts in the balance between internal and external complexity.  In this paper I propose that a scientific general theory of systems could provide such a wider conception, and that it could serve as a basis for the unification of systems science, provide support for the scientific maturation of the discipline, and extend the capability and utility of systems science in important ways. I present approaches and frameworks that would support the development of such a theory, present wide‐ranging evidence suggesting that we are in a favourable position for developing one, and indicate important areas to focus on in future research.  相似文献   
6.
Tracking mobile nodes in dynamic and noisy conditions of industrial environments has provided a paradigm for many issues inherent in the area of distributed control systems in general and wireless sensor networks in particular. Due to the dynamic nature of the industrial environments, a practical tracking system is required that is adaptable to the changes in the environment. More specifically, given the limited resources of wireless nodes and the challenges created by harsh industrial environments there is a need for a technique that can modify the configuration of the system on the fly as new wireless nodes are added to the network and obsolete ones are removed. To address these issues, two cluster-based tracking systems, one static and the other dynamic, are proposed to organize the overall network field into a set of tracking zones, each composed of a sink node and a set of corresponding anchor nodes. To manage the wireless nodes activities and inter and intra cluster communications, an agent-based technique is employed. To compare the architectures, we report on a set of experiments performed in JADE (Java Agent Development Environment). In these experiments, we compare two agent-based approaches (dynamic and static) for managing clusters of wireless sensor nodes in a distributed tracking system. The experimental results corroborate the efficiency of the static clusters versus the robustness and effectiveness of the dynamic clusters.  相似文献   
7.
The FIFA World Cup? is the most profitable worldwide event. The FIFA publishes global statistics of this competition which provide global data about the players and teams during the competition. This work is focused on the extraction of behavioural patterns for both, players and teams strategies, through the automated analysis of this dataset. The knowledge and models extracted in this work could be applied to soccer leagues or even it could be oriented to sport betting. However, the main contribution is related to the study on several automatic knowledge extraction techniques, such as clustering methods, and how these techniques can be used to obtain useful behavioural models from a global statistics dataset. The information provided by the clustering algorithms shows similar properties which have been combined to define the models, making the human interpretation of these statistics easier. Finally, the most successful teams strategies have been analysed and compared.  相似文献   
8.
Company bankruptcies cost billions of dollars in losses to banks each year. Thus credit risk prediction is a critical part of a bank's loan approval decision process. Traditional financial models for credit risk prediction are no longer adequate for describing today's complex relationship between the financial health and potential bankruptcy of a company. In this work, a multiple classifier system (embedded in a multiple intelligent agent system) is proposed to predict the financial health of a company. In our model, each individual agent (classifier) makes a prediction on the likelihood of credit risk based on only partial information of the company. Each of the agents is an expert, but has limited knowledge (represented by features) about the company. The decisions of all agents are combined together to form a final credit risk prediction. Experiments show that our model out-performs other existing methods using the benchmarking Compustat American Corporations dataset.  相似文献   
9.
The purpose of this paper is to review recent developments in critical theory on the political function of the public sphere and the emancipatory potential of new social movements. This work is shown to be relevant to systemic decisions made under conditions of public conflict. Normative models for the self-understanding of actors engaged in self-limiting emancipatory struggles in modern societies are reviewed and related to the concerns of Critical Systems Thinking.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号