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   65692篇
  免费   2191篇
  国内免费   3072篇
系统科学   3677篇
丛书文集   2144篇
教育与普及   2180篇
理论与方法论   527篇
现状及发展   1159篇
研究方法   196篇
综合类   61061篇
自然研究   11篇
  2024年   294篇
  2023年   726篇
  2022年   996篇
  2021年   1196篇
  2020年   760篇
  2019年   322篇
  2018年   1143篇
  2017年   1348篇
  2016年   1042篇
  2015年   1450篇
  2014年   2048篇
  2013年   1985篇
  2012年   2441篇
  2011年   3329篇
  2010年   3143篇
  2009年   3261篇
  2008年   3737篇
  2007年   3756篇
  2006年   2547篇
  2005年   2535篇
  2004年   1924篇
  2003年   1788篇
  2002年   1832篇
  2001年   1928篇
  2000年   1887篇
  1999年   2947篇
  1998年   2604篇
  1997年   2727篇
  1996年   2509篇
  1995年   2155篇
  1994年   2039篇
  1993年   1761篇
  1992年   1482篇
  1991年   1289篇
  1990年   1137篇
  1989年   1015篇
  1988年   818篇
  1987年   536篇
  1986年   295篇
  1985年   108篇
  1984年   34篇
  1983年   9篇
  1982年   10篇
  1981年   7篇
  1979年   5篇
  1974年   6篇
  1973年   5篇
  1971年   7篇
  1970年   4篇
  1966年   3篇
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
21.
Li  Ting  Sun  Yao  Huang  Zhenyu  Wang  Dingkang  Lin  Dongdai 《系统科学与复杂性》2019,32(1):205-233
Journal of Systems Science and Complexity - The GVW algorithm is an efficient signature-based algorithm for computing Gröbner bases. In this paper, the authors consider the implementation of...  相似文献   
22.
23.
A synthesis method for global stability and performance of input constrained linear systems, which uses a linear outputfeedback controller and a static anti-windup compensator is investigated. Different from the traditional two-step anti-windup design procedure, the proposed method synthesizes all controller parameters simultaneously. Sufficient conditions for global stability and minimizing the induced L2 gain are formulated and solved as a linear matrix inequalities(LMIs) optimization problem, which also provides an opportunity to search for a better performance tradeoff between the linear controller and the anti-windup compensator.The well-posedness of the close-loop system is also guaranteed.Simulation results show the effectiveness of the proposed method.  相似文献   
24.
利用樊福卓构造的地区专业化综合指数,结合1998—2012年度安徽省17个主要城市15个产业对安徽省地区近年来的专业化程度进行度量,分析安徽省的地区专业化特征,为安徽省产业布局提供新的理论思路。  相似文献   
25.
We measure and predict states of Activation and Happiness using a body sensing application connected to smartwatches. Through the sensors of commercially available smartwatches we collect individual mood states and correlate them with body sensing data such as acceleration, heart rate, light level data, and location, through the GPS sensor built into the smartphone connected to the smartwatch. We polled users on the smartwatch for seven weeks four times per day asking for their mood state. We found that both Happiness and Activation are negatively correlated with heart beats and with the levels of light. People tend to be happier when they are moving more intensely and are feeling less activated during weekends. We also found that people with a lower Conscientiousness and Neuroticism and higher Agreeableness tend to be happy more frequently. In addition, more Activation can be predicted by lower Openness to experience and higher Agreeableness and Conscientiousness. Lastly, we find that tracking people’s geographical coordinates might play an important role in predicting Happiness and Activation. The methodology we propose is a first step towards building an automated mood tracking system, to be used for better teamwork and in combination with social network analysis studies.  相似文献   
26.
Classical dendritic cells (cDCs) play a pivotal role in the early events that tip the immune response toward persistence or viral control. In vitro studies indicate that HIV infection induces the dysregulation of cDCs through binding of the LILRB2 inhibitory receptor to its MHC-I ligands and the strength of this interaction was proposed to drive disease progression. However, the dynamics of the LILRB2/MHC-I inhibitory axis in cDCs during early immune responses against HIV are yet unknown. Here, we show that early HIV-1 infection induces a strong and simultaneous increase of LILRB2 and MHC-I expression on the surface of blood cDCs. We further characterized the early dynamics of LILRB2 and MHC-I expression by showing that SIVmac251 infection of macaques promotes coordinated up-regulation of LILRB2 and MHC-I on cDCs and monocytes/macrophages, from blood and lymph nodes. Orientation towards the LILRB2/MHC-I inhibitory axis starts from the first days of infection and is transiently induced in the entire cDC population in acute phase. Analysis of the factors involved indicates that HIV-1 replication, TLR7/8 triggering, and treatment by IL-10 or type I IFNs increase LILRB2 expression. Finally, enhancement of the LILRB2/MHC-I inhibitory axis is specific to HIV-1 and SIVmac251 infections, as expression of LILRB2 on cDCs decreased in naturally controlled chikungunya virus infection of macaques. Altogether, our data reveal a unique up-regulation of LILRB2 and its MHC-I ligands on cDCs in the early phase of SIV/HIV infection, which may account for immune dysregulation at a critical stage of the anti-viral response.  相似文献   
27.
28.
29.
Reverberation is significant in shallow water and produces obvious notches in OBC spec-tra. It also degrades the quality of sections and increases the difficulty of processing and interpretation. This ...  相似文献   
30.
The development of new technologically advanced products requires the contribution from a range of skills and disciplines, which are often difficult to find within a single company or organization. Requirements establishment practices in Systems Engineering (SE), while ensuring coordination of activities and tasks across the supply network, fall short when it comes to facilitate knowledge sharing and negotiation during early system design. Empirical observations show that when system-level requirements are not available or not mature enough, engineers dealing with the development of long lead-time sub-systems tend to target local optima, rather than opening up the design space. This phenomenon causes design teams to generate solutions that do not embody the best possible configuration for the overall system. The aim of this paper is to show how methodologies for value-driven design may address this issue, facilitating early stage design iterations and the resolution of early stage design trade-offs. The paper describes how such methodologies may help gathering and dispatching relevant knowledge about the ‘design intent’ of a system to the cross-functional engineering teams, so to facilitate a more concurrent process for requirement elicitation in SE. The paper also describes EVOKE (Early Value Oriented design exploration with KnowledgE maturity), a concept selection method that allows benchmarking design options at sub-system level on the base of value-related information communicated by the system integrators. The use of EVOKE is exemplified in an industrial case study related to the design of an aero-engine component. EVOKE’s ability to raise awareness on the value contribution of early stage design concepts in the SE process has been further verified with industrial practitioners in ad-hoc design episodes.  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