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   1158篇
  免费   1篇
  国内免费   14篇
化学   421篇
晶体学   1篇
力学   45篇
数学   312篇
物理学   394篇
  2018年   9篇
  2014年   13篇
  2013年   35篇
  2012年   30篇
  2011年   33篇
  2010年   35篇
  2009年   17篇
  2008年   40篇
  2007年   27篇
  2006年   39篇
  2005年   29篇
  2004年   31篇
  2003年   25篇
  2002年   32篇
  2001年   25篇
  2000年   24篇
  1999年   18篇
  1998年   21篇
  1997年   14篇
  1996年   24篇
  1995年   22篇
  1994年   25篇
  1993年   35篇
  1992年   27篇
  1991年   19篇
  1990年   28篇
  1989年   26篇
  1988年   20篇
  1987年   17篇
  1986年   19篇
  1985年   30篇
  1984年   19篇
  1983年   13篇
  1982年   26篇
  1981年   23篇
  1980年   13篇
  1979年   26篇
  1978年   21篇
  1977年   17篇
  1976年   26篇
  1975年   22篇
  1974年   16篇
  1973年   18篇
  1972年   19篇
  1971年   15篇
  1970年   19篇
  1969年   18篇
  1968年   13篇
  1967年   11篇
  1966年   9篇
排序方式: 共有1173条查询结果,搜索用时 15 毫秒
111.
There are several theorems describing the intricate relationship between flatness and associated primes over commutative Noetherian rings. However, associated primes are known to act badly over non-Noetherian rings, so one needs a suitable replacement. In this paper, we show that the behavior of strong Krull primes most closely resembles that of associated primes over a Noetherian ring. We prove an analogue of a theorem of Epstein and Yao characterizing flat modules in terms of associated primes by replacing them with strong Krull primes. Also, we partly generalize a classical equational theorem regarding flat base change and associated primes in Noetherian rings. That is, when associated primes are replaced by strong Krull primes, we show containment in general and equality in many special cases. One application is of interest over any Noetherian ring of prime characteristic. We also give numerous examples to show that our results fail if other popular generalizations of associated primes are used in place of strong Krull primes.  相似文献   
112.
A polygonal measure is the sum of finitely many real constant density measures supported on triangles in ?. Given a finite set S ? ?, we study the existence of polygonal measures spanned by triangles with vertices in S, all of whose harmonic moments vanish. We show that for generic S, the dimension of the linear space of such measures is \(\left( {_2^{|S| - 3} } \right)\) . We also investigate the situation in which the density for such measure takes on only values 0 or ±1. This corresponds to pairs of polygons of unit density having the same logarithmic potential at ∞. We show that such (signed) measures do not exist for |S| ≤ 5, but that for each n ≥ 6 one can construct an S, with |S| = n, giving rise to such a measure.  相似文献   
113.
114.
Potential Analysis - Assume that a bounded domain Ω??N (N ≥ 2) has the property that there exists a signed measure µ with compact support in Ω such that, for every...  相似文献   
115.
The notion of hyperderivability is introduced and discussed which allows us to obtain, in particular, formulas for the derivatives of the Martinelli-Bochner integrals.  相似文献   
116.
In this paper we discuss a general approach to studying asymptotic properties of statistical estimators in stochastic programming. The approach is based on an extended delta method and appears to be particularly suitable for deriving asymptotics of the optimal value of stochastic programs. Asymptotic analysis of the optimal value will be presented in detail. Asymptotic properties of the corresponding optimal solutions are briefly discussed.  相似文献   
117.
118.
The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100 °C for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10 Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid‐phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the size‐dependence of contact point conductivity is incorporated to rationalize this trend.  相似文献   
119.
120.
Conclusions Reaction of 1,2,2,6,6-pentamethyl-3,5-dimethylene-4-piperidone with bulky nucleophiles possessing two heteroatom-proton bonds at the nucleophilic center affords six- and seven-membered saturated heterocycles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 667–671, March, 1989.  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