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   6904篇
  免费   211篇
  国内免费   552篇
系统科学   1431篇
丛书文集   117篇
教育与普及   1894篇
理论与方法论   142篇
现状及发展   59篇
研究方法   3篇
综合类   3979篇
自然研究   42篇
  2022年   30篇
  2021年   47篇
  2018年   52篇
  2017年   66篇
  2016年   67篇
  2015年   77篇
  2014年   148篇
  2013年   81篇
  2012年   95篇
  2011年   136篇
  2010年   118篇
  2009年   90篇
  2008年   135篇
  2007年   281篇
  2006年   387篇
  2005年   552篇
  2004年   297篇
  2003年   427篇
  2002年   251篇
  2001年   262篇
  2000年   230篇
  1999年   220篇
  1998年   136篇
  1997年   89篇
  1996年   82篇
  1995年   65篇
  1994年   79篇
  1993年   134篇
  1992年   119篇
  1991年   112篇
  1990年   96篇
  1989年   124篇
  1988年   178篇
  1987年   191篇
  1986年   231篇
  1985年   224篇
  1984年   239篇
  1983年   222篇
  1982年   214篇
  1981年   183篇
  1980年   154篇
  1979年   71篇
  1964年   34篇
  1959年   67篇
  1958年   80篇
  1957年   53篇
  1956年   55篇
  1955年   64篇
  1954年   30篇
  1946年   33篇
排序方式: 共有7667条查询结果,搜索用时 15 毫秒
21.
临床中我已经运用张颖清教授创立的全息胚诊疗法广泛治病,其有效率达90%以上。现将运用全息生物学方法治疗糖尿病患者的情况报告如下。根据临床记录,只要病人所患疾病不是处于后期(根据其血糖含量),其有效率为95%。约半年后,同一病人回医院寻求其他方式的治疗,同时检查其血糖含量,发现他们体内保持了稳定而正常的血糖,病情没有恶化。采用全息生物诊疗法,经过平均两个月的一系列洽疗,即能生效。据我观察,血糖含量从320mg/dl下降到160mg/dl。经过四个月的继续治疗,病人体内的血糖含量能仍保持在120mg/dl至160mg/dl之  相似文献   
22.
最低环境代价生存是人类可持续发展的原动力   总被引:7,自引:0,他引:7  
本文从科学的实在主义研究方法论出发 ,对当今可持续发展理论提出质疑。研究结果发现了许多关于可持续发展的悖论。得出可持续发展的科学哲学语言———可持续发展就是“不可持续发展” ,不可持续发展就是“最好的可持续发展” ;进一步证实 :最低限度的环境代价生存可以使人类社会获得可持续发展的原动力。  相似文献   
23.
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   
24.
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   
25.
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   
26.
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   
27.
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   
28.
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   
29.
30.
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   
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