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   56798篇
  免费   1780篇
  国内免费   3310篇
系统科学   5593篇
丛书文集   1544篇
教育与普及   486篇
理论与方法论   220篇
现状及发展   299篇
研究方法   3篇
综合类   53722篇
自然研究   21篇
  2024年   73篇
  2023年   226篇
  2022年   460篇
  2021年   509篇
  2020年   614篇
  2019年   468篇
  2018年   434篇
  2017年   558篇
  2016年   633篇
  2015年   1119篇
  2014年   2197篇
  2013年   1811篇
  2012年   2958篇
  2011年   3502篇
  2010年   2769篇
  2009年   3086篇
  2008年   3378篇
  2007年   4571篇
  2006年   4290篇
  2005年   4057篇
  2004年   3728篇
  2003年   3245篇
  2002年   2630篇
  2001年   2246篇
  2000年   1758篇
  1999年   1610篇
  1998年   1218篇
  1997年   1208篇
  1996年   1067篇
  1995年   920篇
  1994年   845篇
  1993年   770篇
  1992年   650篇
  1991年   582篇
  1990年   519篇
  1989年   421篇
  1988年   348篇
  1987年   225篇
  1986年   124篇
  1985年   39篇
  1984年   9篇
  1982年   1篇
  1981年   6篇
  1955年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
用自适应控制法控制混沌Rossler系统和混沌Duffing系统,数值计算2个受控系统的Lyapunov指数,表明自适应法可控制混沌Rossler系统到达确定的定常态,不能控制混沌Duffing系统到达定常态而可控制到一系列周期态,并用Matlab进行数值仿真,观察和验证受控Rossler系统和受控Duffing系统的可控性和稳定性。  相似文献   
992.
讨论系统数字频响分析中的线性、时不变、因果、稳定、奇偶虚实分解及其对应等推导求解的条件,明确了如何正确应用这些条件.  相似文献   
993.
皖南传统聚落的生态适应性   总被引:2,自引:0,他引:2  
以景观生态的视角,对皖南传统聚落的选址、布局以及巷道空间、单体建筑形态等进行了分析与研究,以对当代建筑设计有所启迪.  相似文献   
994.
机床高速主轴系统的动力学特性   总被引:7,自引:0,他引:7  
基于Riccatti传递矩阵法,对正在研制的MK2120A型内圆磨床的高速主轴系统进行了动力特性分析,不同规格砂轮对主轴系统的固有频率影响可忽略不计,而不同规格的皮带轮对多统的高阶固有频率影响很大;经过结构动态设计,使主轴临界转速与额定转速之间呈合理布置,确保主轴系统具有优良的动力学品质。研究表明:此方法计算简单,精度较高,计算主轴系统回转效应快捷有效。  相似文献   
995.
This paper deals with the use of optimal control techniques in large-scale water distribution networks. According to the network characteristics and actual state of the water supply system in China, the implicit model, which may be solved by utilizing the hierarchical optimization method,is established. In special, based on the analyses of the water supply system containing variable-speed pumps, a software tool has been developed successfully. The application of this model to the city of Shenyang (China) is compared to experiential strategy. The results of this study show that the developed model is a very promising optimization method to control the large-scale water sup-ply systems.  相似文献   
996.
以壮族地区双语制为主要考察对象,提供新的材料,并从新的角度进行探讨。结论要点是:一是壮族地区双语现象的量化分析结果;二是双语制给壮语语音、词汇、语法系统带来了明显的影响;三是双语制给汉语有关方言的语音、词汇、语法系统也带来了明显的影响;四是双语制需要有与之相适应的语文政策。  相似文献   
997.
与相应的审美氛围、审美风范双向对生并走向整生的民族审美活动循环圈 ,构成民族生态审美场。民族生态审美场是民族生态审美学的整体对象 ,它的逻辑结构统观化整生化展开 ,构成当代民族生态审美学的理论体系  相似文献   
998.
This paper introduces the in-car navigation system prototype development and test results under the context of Singapore. In the system, integrated GPS/DR is used for continuous vehicle positioning. A digital road network map database is built for the whole Singapore. The database is designed to support map matching, route determination, and route guidance functions. The prototype system demonstrates GPS positioning of the vehicle in real-time, tracking the vehicle onto a digital map with fix updates every one or two seconds.With the map matched vehicle location on the map, voice and/or text guidance is provide to the driver. The vehicle position can also be transferred to control centre through communication data link for the purpose of fleet management.  相似文献   
999.
This paper presents a study on species diversity and its ecological service function in the plateau area in western Sichuan. The results show that species diversity in the plantations on the cutover land has a tendency to increase and that its ecological service function is to be improved with stand age growing. The species diversity in forest communities is also gradually increased on different succession stage till reaching a climax level. But the species diversity in the climax community is slightly decreased before it reaches a relatively constant status. Ecological service function of diversity is gradually strengthened with the progress of succession. In addition, species diversity in a stand in a similar site and at a same age differs among forest types. Species diversity index within a coniferous and broad-leaved mixed forest is larger than that within a coniferous forest. Meanwhile, species diversity enriches as the tree density increases.  相似文献   
1000.
Highways in mountainous areas are easy to be damaged by such natural disasters as debris flows and landslides and disaster reduction decision support system (DRDSS) is one of the important means to mitigate these disasters. Guided by the theories and technologies of debris flow and landslide reduction and supported by geographical information system (GIS), remote sensing and database techniques, a DRDSS against debris flow and landslide along highways in mountainous areas has been established on the basis of such principles as pertinence, systematicness, effectiveness, easy to use, open and expandability. The system consists of database, disaster analysis models and decisions on reduction of debris flows and landslides, mainly functioning to zone disaster dangerous degree, analyze debris flow activity,simulate debris flow deposition and diffusion, analyze landslide stability, select optimal highway renovation scheme and plan disaster prevention and control ergineering. This system has been applied successfully to the debris flow and landslide treatment works along Palongzangbu Section of Sichuan-Tibet Highway.  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