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   15288篇
  免费   994篇
  国内免费   506篇
系统科学   1444篇
丛书文集   255篇
教育与普及   199篇
理论与方法论   304篇
现状及发展   913篇
研究方法   46篇
综合类   13625篇
自然研究   2篇
  2024年   61篇
  2023年   135篇
  2022年   181篇
  2021年   204篇
  2020年   148篇
  2019年   78篇
  2018年   811篇
  2017年   833篇
  2016年   545篇
  2015年   280篇
  2014年   319篇
  2013年   293篇
  2012年   570篇
  2011年   1298篇
  2010年   1155篇
  2009年   849篇
  2008年   935篇
  2007年   1264篇
  2006年   398篇
  2005年   528篇
  2004年   415篇
  2003年   376篇
  2002年   331篇
  2001年   300篇
  2000年   309篇
  1999年   498篇
  1998年   466篇
  1997年   512篇
  1996年   448篇
  1995年   360篇
  1994年   331篇
  1993年   283篇
  1992年   289篇
  1991年   234篇
  1990年   230篇
  1989年   188篇
  1988年   144篇
  1987年   115篇
  1986年   59篇
  1985年   9篇
  1984年   1篇
  1978年   2篇
  1968年   1篇
  1967年   1篇
  1957年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We consider the stability of a random Riccati equation with a Markovian binary jump coefficient. More specifically, we are concerned with the boundedness of the solution of a random Riccati difference equation arising from Kalman filtering with measurement losses. A sufficient condition for the peak covariance stability is obtained which has a simpler form and is shown to be less conservative in some cases than a very recent result in existing literature. Furthermore, we show that a known sufficient condition is also necessary when the observability index equals one.  相似文献   
82.
In the present paper, we focus on constructive spherical codes. By employing algebraic geometry codes, we give an explicit construction of spherical code sequences. By making use of the idea involved in the proof of the Gilbert-Varshamov bound in coding theory, we construct a spherical code sequence in exponential time which meets the best-known asymptotic bound by Shamsiev and Wyner.  相似文献   
83.
针对临近空间单粒子效应进行了数值模型仿真和特征尺寸为0.1 μm的反相器电路的脉冲注入模拟研究。数值仿真结果表明器件临界电荷随着工作电压的降低而减小,敏感横截面随着临界电荷的降低而逐渐增大。临近空间微电子器件的单粒子翻转概率随敏感横截面增大而上升,但其又随临近空间高度的增加而下降。此外,利用SPICE软件脉冲注入模拟观察到了反相器电路的单粒子翻转现象。所得结论有助于深入研究临近空间的单粒子效应并为器件抗辐射加固提供了理论依据。  相似文献   
84.
在现行的理工科教学中,matlab的应用已经成为一个重要的内容。尤其在电子类的核心专业课信号与系统中,matlab的作用更加值得教师关注。文章就信号与系统这一课程中牵涉到的一些典型matlab程序,进行了注解和说明。试图在信号与系统和matlab的应用两方面找到了一个更为恰当的结合点,使学生和教师在专业知识和应用性工具方面,得到一个更好的处理方式。  相似文献   
85.
86.
文章阐明了循环经济的基本概念和基本理论,在分析我国交通运输业可持续发展面临的诸多问题后,结合循环经济模式对我国交通运输可持续发展战略进行了研究。  相似文献   
87.
陈颖琪  Lin  Guixu  Wang  Feng  Hu  Jianling  Tan  Zhiming 《高技术通讯(英文版)》2007,13(3):297-301
A multiple MIPS 4Kc processor cores based interrupt processing system is introduced. The interrupt controller plays a key role in the high definition television (HDTV) system-on-a-chip (SoC) platform, especially when it is a multiple processor system. Based on a general introduction to the whole HDTV SoC platform, a layered interrupt controller and its implementation are discussed in detail. The proposed scheme was implemented in our FPGA verification board. The results indicate that our scheme is reliable and efficient. Meanwhile, as a functional intellectual property (IP), the interrupt controller has reusability and expandability with the layered structure.  相似文献   
88.
The philosophical analysis of chemistry has advanced at such a pace during the last dozen years that the existence of philosophy of chemistry as an autonomous discipline cannot be doubted any more. The present paper will attempt to analyse the experience of philosophy of chemistry at the, so to say, meta-level. Philosophers of chemistry have especially stressed that all sciences need not be similar to physics. They have tried to argue for chemistry as its own type of science and for a pluralistic understanding of science in general. However, when stressing the specific character of chemistry, philosophers do not always analyse the question ‘What is science?’ theoretically. It is obvious that a ‘monistic’ understanding of science should not be based simply on physics as the epitome of science, regarding it as a historical accident that physics has obtained this status. The author’s point is that the philosophical and methodological image of science should not be chosen arbitrarily; instead, it should be theoretically elaborated as an idealization (theoretical model) substantiated on the historical practice of science. It is argued that although physics has, in a sense, justifiably obtained the status of a paradigm of science, chemistry, which is not simply a physical science, but a discipline with a dual character, is also relevant for elaborating a theoretical model of science. The theoretical model of science is a good tool for examining various issues in philosophy of chemistry as well as in philosophy of science or science studies generally.  相似文献   
89.
It is well known that considering a non-Euclidean Minkowski metric in Multidimensional Scaling, either for the distance model or for the loss function, increases the computational problem of local minima considerably. In this paper, we propose an algorithm in which both the loss function and the composition rule can be considered in any Minkowski metric, using a multivariate randomly alternating Simulated Annealing procedure with permutation and translation phases. The algorithm has been implemented in Fortran and tested over classical and simulated data matrices with sizes up to 200 objects. A study has been carried out with some of the common loss functions to determine the most suitable values for the main parameters. The experimental results confirm the theoretical expectation that Simulated Annealing is a suitable strategy to deal by itself with the optimization problems in Multidimensional Scaling, in particular for City-Block, Euclidean and Infinity metrics.  相似文献   
90.
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   
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