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   9089篇
  免费   223篇
  国内免费   555篇
系统科学   1434篇
丛书文集   161篇
教育与普及   1857篇
理论与方法论   127篇
现状及发展   361篇
研究方法   526篇
综合类   5359篇
自然研究   42篇
  2021年   38篇
  2018年   44篇
  2017年   64篇
  2016年   64篇
  2015年   73篇
  2014年   145篇
  2013年   77篇
  2012年   315篇
  2011年   426篇
  2010年   166篇
  2009年   76篇
  2008年   347篇
  2007年   465篇
  2006年   588篇
  2005年   736篇
  2004年   463篇
  2003年   580篇
  2002年   386篇
  2001年   362篇
  2000年   391篇
  1999年   257篇
  1998年   127篇
  1997年   78篇
  1996年   78篇
  1995年   60篇
  1994年   72篇
  1993年   130篇
  1992年   121篇
  1991年   120篇
  1990年   95篇
  1989年   121篇
  1988年   177篇
  1987年   189篇
  1986年   225篇
  1985年   215篇
  1984年   234篇
  1983年   215篇
  1982年   209篇
  1981年   179篇
  1980年   149篇
  1979年   73篇
  1964年   34篇
  1960年   27篇
  1959年   85篇
  1958年   133篇
  1957年   89篇
  1956年   81篇
  1955年   100篇
  1954年   58篇
  1946年   32篇
排序方式: 共有9867条查询结果,搜索用时 31 毫秒
41.
本文研究了乙烷和丙烷的混合裂解,并与乙烷、丙烷单独裂解进行了比较。解决了微分方程组的刚性问题,提出了混合裂解反应动力学模型。明确了三种选择性的概念,即;真实选择性、迭加选择性和总选择性,从而澄清了国际上对于选择性有正偏差和负偏差的不同观点。为乙烯生产提供了有效利用乙烷和丙烷的分析评价方法。  相似文献   
42.
The purpose of this paper is to develop a high speed detection scheme for moving and / or stationary point targets in a multitarget environment as registered in an IR image sequence. An iterative approximate 3-D line searching algorithm based upon the geometric representation of lines (for non-maneuvering targets in space) in a 3-D space is derived. The convergency of the algorithm is proved. An analysis is performed of the theoretical detection performance of the algorithm. The statistical experiment results show high effectiveness and computational efficiency of the algorithm in the case of low SNR. The idea may be employed to satisfy the real-time processing requirement of an IR system.  相似文献   
43.
STABILITY CRITERIA FOR A CLASS OF UNCERTAINSYSTEMS WITH TIME—DELAY   总被引:1,自引:0,他引:1  
Some stability criteria are obtained for a class of uncertain systems with time-delay usingLyapunov functional and analytic techniques. It is easy to check the criteria by making use of theboundedness of the uncertainties.  相似文献   
44.
This paper investigates the impact of a secondary market, where retailers can buy and sell excessinventories, on the supply chain. We develop a two-period model with a single manufacturer and tworetailers. At the beginning of the first period the retailers order and receive products from themanufacturer, but at the beginning of the second period, they can trade surplus products betweenthemselves in the secondary market. We investigate the impact of the correlated dependence ofretailers' demand on both the quantity effect and the allocation effect under the secondary market.Lastly,we study potential strategies for the manufacturer to increase sales with the existence of thesecondary market.  相似文献   
45.
A subset of S of the vertex set of a graph G is called acyclic if the subgraph it induces in G contains no cycles. S is called an acyclic dominating set of G if it. is both acyclic and dominating. The minimum cardinality of an acyclic dominating set, denoted by 7a(G), is called the acyclic domination number of G. S. M. Hedetniemi et al. on 2000 introduced the concept of acyclic domination and posed the following open problem: Is -ya(G) < <5(G) for any graph whose diameter is two? In this paper, we give a counterexample which disproves the problem.  相似文献   
46.
With time-based competition and rapid technology advancements, effective manufacturingscheduling and supply chain coordination are critical to quickly respond to changing marketconditions. These problems, however, are difficult in view of inherent complexity and variousuncertainties involved. Based on a series of results by the authors, decomposition and coordination byusing Lagrangian relaxation is identified in this paper as an effective way to control complexity anduncertainty.A manufacturing scheduling problem is first formulated within the job shop context withuncertain order arrivals, processing times, due dates, and part priorities as a separable optimizationproblem. A solution methodology that combines Lagrangian relaxation, stochastic dynamicprogramming, and heuristics is developed. Method improvements to effectively solve large problemsare also highlighted. To extend manufacturing scheduling within a factory to coordinate autonomicmembers across chains of suppliers, a decentralized supply chai  相似文献   
47.
It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations.  相似文献   
48.
It has been reported that the single crystal of relaxor ferroelectrics (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) with the compositions near the morphotropic phase boundary (MPB, 0.28相似文献   
49.
1. INTRODUCTION As the development of technologies of digital signal processing and integrated circuits, the structure of wireless communication system has been improved. Many schemes for software defined radio (SDR) systems have been developed since 1995, and they can be divided into five tiers of solutions according to their developing history and their definitions[1]. The five tiers are conventional hardware-implemented scheme; software-controlled radio scheme; SDR, that implements m…  相似文献   
50.
Good.  B 桑林岗 《世界科学》1991,13(8):18-19
电子学T模型又要出现,新型的电子管为集装在硅片中的不再发热的显微器件。  相似文献   
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