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   253篇
  免费   1篇
化学   74篇
力学   3篇
数学   89篇
物理学   88篇
  2019年   5篇
  2014年   7篇
  2013年   8篇
  2012年   6篇
  2011年   5篇
  2010年   3篇
  2009年   5篇
  2008年   3篇
  2007年   7篇
  2006年   3篇
  2005年   3篇
  2004年   4篇
  2003年   4篇
  2002年   9篇
  2001年   3篇
  1994年   5篇
  1992年   5篇
  1990年   5篇
  1989年   5篇
  1988年   3篇
  1986年   3篇
  1984年   3篇
  1983年   6篇
  1982年   3篇
  1981年   5篇
  1979年   4篇
  1977年   6篇
  1976年   5篇
  1975年   4篇
  1974年   5篇
  1973年   7篇
  1972年   4篇
  1971年   4篇
  1970年   2篇
  1969年   3篇
  1964年   2篇
  1960年   3篇
  1959年   2篇
  1932年   2篇
  1930年   11篇
  1929年   8篇
  1928年   4篇
  1927年   5篇
  1925年   2篇
  1922年   2篇
  1914年   2篇
  1911年   2篇
  1909年   3篇
  1903年   6篇
  1885年   2篇
排序方式: 共有254条查询结果,搜索用时 19 毫秒
101.
102.
Weighting is a common methodology in survey statistics to increase accuracy of estimates or to compensate for non-response. One standard approach for weighting is calibration estimation which represents a common numerical problem. There are various approaches in the literature available, but quite a number of distance-based approaches lack a mathematical justification or are numerically unstable. In this paper we reformulate the calibration problem as a system of nonlinear equations. Although the equations are lacking differentiability properties, one can show that they are semismooth and the corresponding extension of Newton’s method is applicable. This is a mathematically rigorous approach and the numerical results show the applicability of this method.  相似文献   
103.
104.
105.
106.
107.
108.
In a new oxidative route, Ag+[Al(ORF)4]? (RF=C(CF3)3) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)n]+ salts (n=2, 3) with the weakly coordinating [Al(ORF)4]? anion in quantitative yield. The In+ salt and the known analogous Ga+[Al(ORF)4]? were used to synthesize a series of homoleptic PR3 phosphane complexes [M(PR3)n]+, that is, the weakly PPh3‐bridged [(Ph3P)3In–(PPh3)–In(PPh3)3]2+ that essentially contains two independent [In(PPh3)3]+ cations or, with increasing bulk of the phosphane, the carbene‐analogous [M(PtBu3)2]+ (M=Ga, In) cations. The MI? P distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2‐TZVPP, MP2/def2‐TZVPP, and SCS‐MP2/def2‐TZVPP levels.  相似文献   
109.
Extreme events that change global society have been characterized as black swans. The frequency-size distributions of many natural phenomena are often well approximated by power-law (fractal) distributions. An important question is whether the probability of extreme events can be estimated by extrapolating the power-law distributions. Events that exceed these extrapolations have been characterized as dragon-kings. In this paper we consider extreme events for earthquakes, volcanic eruptions, wildfires, landslides and floods. We also consider the extreme event behavior of three models that exhibit self-organized criticality (SOC): the slider-block, forest-fire, and sand-pile models. Since extrapolations using power-laws are widely used in probabilistic hazard assessment, the occurrence of dragon-king events have important practical implications.  相似文献   
110.
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