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   6967篇
  免费   211篇
  国内免费   577篇
系统科学   1433篇
丛书文集   181篇
教育与普及   1849篇
理论与方法论   147篇
现状及发展   59篇
研究方法   3篇
综合类   4041篇
自然研究   42篇
  2021年   50篇
  2020年   29篇
  2019年   35篇
  2018年   59篇
  2017年   73篇
  2016年   70篇
  2015年   92篇
  2014年   165篇
  2013年   91篇
  2012年   120篇
  2011年   142篇
  2010年   122篇
  2009年   99篇
  2008年   134篇
  2007年   280篇
  2006年   393篇
  2005年   595篇
  2004年   319篇
  2003年   414篇
  2002年   227篇
  2001年   269篇
  2000年   240篇
  1999年   219篇
  1998年   135篇
  1997年   91篇
  1996年   88篇
  1995年   65篇
  1994年   79篇
  1993年   137篇
  1992年   120篇
  1991年   114篇
  1990年   98篇
  1989年   116篇
  1988年   182篇
  1987年   189篇
  1986年   225篇
  1985年   215篇
  1984年   234篇
  1983年   213篇
  1982年   208篇
  1981年   178篇
  1980年   150篇
  1979年   69篇
  1964年   34篇
  1959年   64篇
  1958年   81篇
  1957年   48篇
  1956年   50篇
  1955年   60篇
  1946年   32篇
排序方式: 共有7755条查询结果,搜索用时 0 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.
127个愿望     
8 岁生日的那天,祖父送给他一件特别的礼物—一张世界地图。那红红绿绿的颜色引起了他极大的兴趣,特别是那上面标注的一个个城市、一处处美丽的山水风景,令他飘逸的思绪随之上下纵横驰骋,渴望抵达的翅膀,在那上面一次次自由地翱翔。多少次不停地翻看,每次都令他心潮起伏。终于在 15岁那年,他写下了气势不凡的《一生的志愿》,他写道:“我要到尼罗河、亚马逊河和刚果河探险;要登上珠穆朗玛峰、乞力马扎罗山和麦金利峰;驾驭大象、骆驼、鸵鸟和野马;探访马可· 7波罗和亚力山大一世走过的路;主演一部《人猿泰山》那样的电影; 12驾…  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.
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   
30.
“克隆人”相继“出世”世界上首个克隆婴儿“夏娃”还未验明正身,“克隆人二号”便接踵而至。美国时间1月4日,邪教组织雷尔教派成员、“克隆援助”公司总裁、法国女科学家布里吉特·布瓦瑟利耶对法新社说,第二个克隆宝宝已经降临人间,她的“父母”是一对荷兰女同性恋者。据雷尔教派下属的“克隆援助”公司发言人加利透露,“克隆人二号”于“当地时间”1月3日晚间诞生,但是她并没有说明这个“当地”究竟是哪里?不过,“当地”是某个北欧国家。加利说:“第二个克隆婴儿已经诞生,这是千真万确的。她的父母拥有荷兰国籍,但宝宝并非在荷兰所生。”  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