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   6613篇
  免费   219篇
  国内免费   551篇
系统科学   1425篇
丛书文集   112篇
教育与普及   1819篇
理论与方法论   127篇
现状及发展   61篇
研究方法   3篇
综合类   3794篇
自然研究   42篇
  2021年   38篇
  2018年   51篇
  2017年   68篇
  2016年   71篇
  2015年   85篇
  2014年   150篇
  2013年   83篇
  2012年   105篇
  2011年   125篇
  2010年   116篇
  2009年   77篇
  2008年   116篇
  2007年   273篇
  2006年   382篇
  2005年   538篇
  2004年   287篇
  2003年   407篇
  2002年   227篇
  2001年   256篇
  2000年   224篇
  1999年   213篇
  1998年   132篇
  1997年   76篇
  1996年   80篇
  1995年   62篇
  1994年   75篇
  1993年   130篇
  1992年   117篇
  1991年   115篇
  1990年   98篇
  1989年   116篇
  1988年   176篇
  1987年   189篇
  1986年   222篇
  1985年   214篇
  1984年   230篇
  1983年   213篇
  1982年   205篇
  1981年   178篇
  1980年   149篇
  1979年   67篇
  1964年   34篇
  1960年   24篇
  1959年   61篇
  1958年   81篇
  1957年   47篇
  1956年   48篇
  1955年   57篇
  1954年   25篇
  1946年   32篇
排序方式: 共有7383条查询结果,搜索用时 15 毫秒
41.
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   
42.
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   
43.
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   
44.
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   
45.
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   
46.
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   
47.
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   
48.
1 Results Amphiphilic block copolymers are capable of forming supramolecular assemblies resembling those observed in nature,such as spherical micelles,worm micelles,and vesicles.Changing the solvent composition,ionic strength or pH of the polymer solution may induce the self-assembly of block copolymers or trigger the transition between the geometries of noncovalent assemblies.In the current work,we have synthesised starlike amphiphilic block copolymers having hydrophobic poly(methyl methacrylate),PMMA,core,and hydrophilic poly(acrylic acid),PAA,shell.The self-assembling characteristics of these polymers have been investigated in aqueous solutions by light scattering and direct visualisation by cryo-transmission electron microscopy (cryoTEM)[1]. Computer simulations along with the theoretical predictions made for the star-like system based on mean-field theory have been used to support the experimental observations[2]. The association of the starlike macromolecules resembles that of charged biopolymers,such as actin,since a balance between attractive and repulsive forces is required for the formation of cylindrical assemblies and can be manipulated by changing the pH or the ionic strength of the solvent[3].  相似文献   
49.
Progress on nuclear liquid gas phase transition (LGPT) or critical behavior has been simply reviewed and some signals of LGPT in heavy ion collisions, especially in NIMROD data, are focused. These signals include the power-law charge distribution, the largest fluctuation of the fragment observables, the nuclear Zipf law, caloric curve and critical exponent analysis etc.  相似文献   
50.
“研究”是探求事物的真相、性质、规律的行为,既可以是教学方法也可以是学习方法,为学生构建了开放合作的学习环境。本文通过对高职英语阅读中加强目标语国家文化“研究”的认识,说明建立高职英语阅读研究性教学是应当而且是必须的,并认为高职英语阅读研究性教学理念应贯穿整个教学体系。  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