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   20677篇
  免费   1240篇
  国内免费   1044篇
系统科学   1897篇
丛书文集   548篇
教育与普及   202篇
理论与方法论   304篇
现状及发展   939篇
研究方法   31篇
综合类   19039篇
自然研究   1篇
  2024年   47篇
  2023年   122篇
  2022年   249篇
  2021年   330篇
  2020年   235篇
  2019年   183篇
  2018年   938篇
  2017年   965篇
  2016年   716篇
  2015年   553篇
  2014年   755篇
  2013年   748篇
  2012年   1159篇
  2011年   1862篇
  2010年   1729篇
  2009年   1455篇
  2008年   1615篇
  2007年   1850篇
  2006年   930篇
  2005年   890篇
  2004年   786篇
  2003年   697篇
  2002年   677篇
  2001年   607篇
  2000年   461篇
  1999年   424篇
  1998年   282篇
  1997年   278篇
  1996年   267篇
  1995年   235篇
  1994年   169篇
  1993年   140篇
  1992年   124篇
  1991年   132篇
  1990年   100篇
  1989年   88篇
  1988年   72篇
  1987年   40篇
  1986年   28篇
  1985年   8篇
  1984年   1篇
  1981年   9篇
  1980年   1篇
  1979年   2篇
  1967年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
111.
The characterization of non-stationary signal requires joint time and frequency information. However, time and frequency are a pair of non-commuting variables that cannot constitute a joint probability density in the time-frequency plane. The time-frequency distributions have difficult interpretation problems arising from negative and complex values or spurious components. In this paper, we get time-frequency information from the marginal distributions in rotated directions in the time-frequency plane. The rigorous probability interpretation of the marginal distributions is without any ambiguities. This time-frequency transformation is similar to the computerized axial tomography (CT or CAT) and is applied to signal analysis and signal detection and reveals a lot of advantages especially in the signal detection of the low signal/noise (S/N).  相似文献   
112.
The participation of non-state actors in implementation processes is often understood as a means to increase compliance efficiency. But the implementation of spatial policies frequently focuses on pre-established goals, processes and instruments and thus renders difficult open discourse and shared decision-making. This paper introduces conflict pattern analysis (CPA) as a tool that supports the analysis of the actual actor constellation in order to define efficient approaches that avoid common problems of participatory processes. CPA is a semi-formalised method that helps to identify key-actors, their relations and interaction amongst each other as well as their core beliefs, interests and resources. It aggregates this information to interaction patterns that can be compared, classified and linked to different participatory methods on a theoretically informed basis. Particularly on the local and regional level, this could be the first step for successful (participatory) implementation strategies.  相似文献   
113.
In this paper, we introduce a new class of generalized convex function, namely, a-pseudounivex function, by combining the concepts of pseudo-univex and α-invex functions. Further, we establish some relationships between vector variational-like inequality problems and vector optimization problems under the assumptions of α-pseudo-univex functions. Results obtained in this paper present a refinement and improvement of previously known results.  相似文献   
114.
刘瑛 《山西科技》2007,(1):128-129
文章介绍了UPS在实际应用中的供电方案及UPS系统的测试内容。  相似文献   
115.
张颖 《枣庄师专学报》2007,24(3):99-102
心理健康教育的重要性随着社会的发展日趋突出,荣格的思想受到越来越多人的重视。荣格的人格结构论、人格动力论及人格发展论三方面对目前心理健康教育有重要的影响。  相似文献   
116.
语言的模糊性运用于各种文体的分析,是近些年来中西方语言学家所关注的研究话题.本文介绍了有关模糊语言的研究概况,在收集的大量外交语言的基础上,从词汇、句法、篇章三个层面分析了模糊语言在政治外交语言中的应用,并由此得出外交语言的真正意图.  相似文献   
117.
Image-based gait analysis as a means of biometric identification has attracted much research attention. Most of the existing methods focus on human identification, posture analysis and movement tracking. There have been few investigations on measuring the carried load based on the carrier's gait characteristics by automatic image processing. Nevertheless, this measurement is very useful in a number of applications, such as the study of the carried load on the postural development of children and adolescence. In this paper, we investigate how to automatically estimate the carried weight from a sequence of images. We present a method to extract human gait silhouette based on an observation that humans tend to minimize the energy during motion. We compute several angles of body leaning and determine the relationship of the carried weight, the leaning angles and the centroid location according to a human kinetic study. Our weight determination method has been verified successfully by experiments.  相似文献   
118.
The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.  相似文献   
119.
研究了金属间化合物快速凝固薄带的成型过程和影响薄带质量的工艺参数。提出了熔体在喷嘴处进行层流流动的经验关系式,给出了金属间化合物快速凝固薄带制备的最佳工艺参数。  相似文献   
120.
本文利用微积分方法,推导出自然数同政幂级数的求和公式。  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