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   92532篇
  免费   462篇
  国内免费   398篇
化学   26384篇
晶体学   912篇
力学   6929篇
数学   32532篇
物理学   16469篇
无线电   10166篇
  2022年   100篇
  2021年   107篇
  2020年   130篇
  2019年   128篇
  2018年   11885篇
  2017年   11518篇
  2016年   7085篇
  2015年   1001篇
  2014年   504篇
  2013年   728篇
  2012年   4382篇
  2011年   11865篇
  2010年   6970篇
  2009年   6937篇
  2008年   7358篇
  2007年   9819篇
  2006年   395篇
  2005年   1730篇
  2004年   1873篇
  2003年   2248篇
  2002年   1169篇
  2001年   318篇
  2000年   356篇
  1999年   213篇
  1998年   249篇
  1997年   188篇
  1996年   255篇
  1995年   172篇
  1994年   147篇
  1993年   179篇
  1992年   133篇
  1991年   122篇
  1990年   121篇
  1989年   122篇
  1988年   132篇
  1987年   121篇
  1986年   103篇
  1985年   158篇
  1984年   163篇
  1983年   119篇
  1982年   112篇
  1981年   115篇
  1980年   121篇
  1979年   120篇
  1978年   109篇
  1977年   83篇
  1976年   80篇
  1975年   66篇
  1974年   63篇
  1973年   91篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number of trials and derive the probability generating functions. The present work extends several properties of distributions of orderk and leads us a new type of geneses of the discrete distributions.  相似文献   
272.
273.
 We prove that for any simple theory which is constructed via Fr?issé-Hrushovski method, if the forking independence is the same as the d-independence then the stable forking property holds. Received: 22 January 2001 / Published online: 19 December 2002 This article is part of the author's D-Phil thesis, written at the University of Oxford and supported by the Ministry of Higher Education of Iran. The author would like to thank the Institute for Studies in Theoretical Physics and Mathematics (IPM), Tehran, Iran, for its financial support whilst working on this article. Mathematics Subject Classification (2000): 03C45 Key words or phrases: Generic structures – Fr?issé-Hrushovski method – Predimension – Simple theories – Stable theories – Stable forking conjecture  相似文献   
274.
The classical economic order quantity (EOQ) model assumes that items produced are of perfect quality and that the unit cost of production is independent of demand. However, in realistic situations, product quality is never perfect, but is directly affected by the reliability of the production process. In this paper, we consider an EOQ model with imperfect production process and the unit production cost is directly related to process reliability and inversely related to the demand rate. In addition, a numerical example is given to illustrate the developed model. Sensitivity analysis is also performed and discussed.  相似文献   
275.
276.
Problem-structuring techniques are an integral aspect of ‘Soft-OR’. SSM, SAST, Strategic Choice, and JOURNEY Making, all depend for their success on a group developing a shared view of a problem through some form of explicit modelling. The negotiated problem structure becomes the basis for problem resolution. Implicit to this process is an assumption that members of the group share and build their knowledge about the problem domain. This paper explores the extent to which this assumption is reasonable. The research is based on detailed records from the use of JOURNEY Making, where it has used special purpose Group Support software to aid the group problem structuring. This software continuously tracks the contributions of each member of the group and thus the extent to which they appear to be ‘connecting’ and augmenting their own knowledge with that of other members of the group. Software records of problem resolution in real organisational settings are used to explore the sharing of knowledge among senior managers. These explorations suggest a typology of knowledge sharing. The implications of this typology for problem structuring and an agenda for future research are considered.  相似文献   
277.
§ 1 IntroductionInthispaperwediscusstheglobalclassicalsolutionofamultidimensionalquasistationaryproblem .Theproblemcomesfromthediscussionofagrowthmodelofselfmaintainingprotocell(see [1— 3])inmultidimensionalcase .Theprotocellcanbevisualizedashavingaporousst…  相似文献   
278.
 The inner radius of univalence of a domain D with Poincaré density ρ D is the possible largest number σ such that the condition ∥ S f D  = sup w∈ D ρ D (w) −2S f (z) ∥ ≤ σ implies univalence of f for a nonconstant meromorphic function f on D, where S f is the Schwarzian derivative of f. In this note, we give a lower bound of the inner radius of univalence for strongly starlike domains of order α in terms of the order α. The author was partially supported by the Ministry of Education, Grant-in-Aid for Encouragement of Young Scientists, 11740088. A part of this work was carried out during his visit to the University of Helsinki under the exchange programme of scientists between the Academy of Finland and the JSPS. Received November 26, 2001; in revised form September 24, 2002 Published online May 9, 2003  相似文献   
279.
280.
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