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   96175篇
  免费   3652篇
  国内免费   2149篇
化学   36992篇
晶体学   957篇
力学   7683篇
综合类   74篇
数学   33809篇
物理学   22461篇
  2024年   67篇
  2023年   405篇
  2022年   727篇
  2021年   790篇
  2020年   765篇
  2019年   771篇
  2018年   10997篇
  2017年   10700篇
  2016年   6948篇
  2015年   1715篇
  2014年   1406篇
  2013年   1740篇
  2012年   5483篇
  2011年   12153篇
  2010年   6729篇
  2009年   7062篇
  2008年   7712篇
  2007年   9716篇
  2006年   1211篇
  2005年   2078篇
  2004年   2115篇
  2003年   2379篇
  2002年   1444篇
  2001年   580篇
  2000年   567篇
  1999年   549篇
  1998年   473篇
  1997年   443篇
  1996年   492篇
  1995年   366篇
  1994年   287篇
  1993年   312篇
  1992年   198篇
  1991年   226篇
  1990年   183篇
  1989年   160篇
  1988年   146篇
  1987年   130篇
  1986年   127篇
  1985年   102篇
  1984年   100篇
  1983年   66篇
  1982年   73篇
  1981年   61篇
  1980年   72篇
  1979年   54篇
  1978年   47篇
  1914年   45篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
This paper provides a quantitative and comparative economic and risk approach to strategic quality control in a supply chain, consisting of one supplier and one producer, using a random payoff game. Such a game is first solved in a risk-neutral framework by assuming that both parties are competing with each other. We show in this case that there may be an interior solution to the inspection game. A similar analysis under a collaborative framework is shown to be trivial and not practical, with a solution to the inspection game being an ‘all or nothing’ solution to one or both the parties involved. For these reasons, the sampling random payoff game is transformed into a Neyman–Pearson risk constraints game, where the parties minimize the expected costs subject to a set of Neyman–Pearson risk (type I and type II) constraints. In this case, the number of potential equilibria can be large. A number of such solutions are developed and a practical (convex) approach is suggested by providing an interior (partial sampling) solution for the collaborative case. Numerical examples are developed to demonstrate the procedure used. Thus, unlike theoretical approaches to the solution of strategic quality control random payoff games, the approach we construct is both practical and consistent with the statistical risk Neyman–Pearson approach.  相似文献   
122.
The mass spectrum ofcb meson is investigated with an effective quark-antiquark potential of the form -αc/r +Ar νwith ν varying from 0.5 to 2.0. TheS andP-wave masses, pseudoscalar decay constant, weak decay partial widths in spectator model and the lifetime ofB cmeson are computed. The properties calculated here are found to be in good agreement with other theoretical and experimental values at potential index,ν = 1  相似文献   
123.
The regression problem in learning theory is investigated with least square Tikhonov regularization schemes in reproducing kernel Hilbert spaces (RKHS). We follow our previous work and apply the sampling operator to the error analysis in both the RKHS norm and the L2 norm. The tool for estimating the sample error is a Bennet inequality for random variables with values in Hilbert spaces. By taking the Hilbert space to be the one consisting of Hilbert-Schmidt operators in the RKHS, we improve the error bounds in the L2 metric, motivated by an idea of Caponnetto and de Vito. The error bounds we derive in the RKHS norm, together with a Tsybakov function we discuss here, yield interesting applications to the error analysis of the (binary) classification problem, since the RKHS metric controls the one for the uniform convergence.  相似文献   
124.
This paper considers efforts to improve in-patient flows, a particularly urgent issue in the National Health Service (NHS). The context is described and related to reasons why OR has been making relatively little contribution. The paper argues that large complex models may often be unnecessary and even get in the way of providing clear insight and guidance for problem owners. The importance of understanding the generic working of systems to lead to improvement, and the limitations of simply describing them, is stressed. It is demonstrated that some very simple models can be of significant practical value in understanding and managing complex systems, changing mindsets and driving collection and use of operationally valuable data. Recommendations for more effective engagement with the NHS are offered.  相似文献   
125.
126.
127.
This note introduces a refinement to a previously proposed tabu search algorithm for vehicle routing problems with time windows. This refinement yields new best known solutions on a set of benchmark instances of the multi-depot, the periodic and the site-dependent vehicle routing problems with time windows.  相似文献   
128.
129.
The spin polarized β-emitting nuclei12B (I π=1+,T 1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift.  相似文献   
130.
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