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   2967篇
  免费   242篇
  国内免费   376篇
化学   124篇
晶体学   2篇
力学   59篇
综合类   48篇
数学   2782篇
物理学   570篇
  2024年   4篇
  2023年   42篇
  2022年   56篇
  2021年   64篇
  2020年   78篇
  2019年   84篇
  2018年   73篇
  2017年   82篇
  2016年   93篇
  2015年   92篇
  2014年   149篇
  2013年   182篇
  2012年   140篇
  2011年   152篇
  2010年   130篇
  2009年   186篇
  2008年   248篇
  2007年   199篇
  2006年   181篇
  2005年   164篇
  2004年   123篇
  2003年   145篇
  2002年   140篇
  2001年   92篇
  2000年   115篇
  1999年   99篇
  1998年   89篇
  1997年   69篇
  1996年   67篇
  1995年   31篇
  1994年   38篇
  1993年   26篇
  1992年   16篇
  1991年   13篇
  1990年   8篇
  1989年   11篇
  1988年   7篇
  1987年   6篇
  1986年   7篇
  1985年   16篇
  1984年   10篇
  1982年   8篇
  1981年   8篇
  1980年   13篇
  1979年   4篇
  1978年   5篇
  1977年   5篇
  1976年   4篇
  1974年   3篇
  1936年   4篇
排序方式: 共有3585条查询结果,搜索用时 453 毫秒
181.
A symbolic algorithm based on the generalized Lucas polynomials of first kind is used in order to compute the Newton sum rules for the zeros of polynomial eigenfunctions of linear differential operators with polynomial coefficients.  相似文献   
182.
F. P. Gardiner gave a sufficient condition for a sequence to be a Hamilton sequence for an extremal Beltrami coefficient. In this note, we shall consider the converse problem, proving that the condition is not necessary.

  相似文献   

183.
Let be a real Banach space partially ordered by a closed convex cone with nonempty interior . We study the continuation method for the monotone operator which satisfies




for all , , where . Thompson's metric is among the main tools we are using.  相似文献   
184.
Generalized Steiner systems GS(2, 4, v, g) were first introduced by Etzion and were used to construct optimal constant weight codes over an alphabet of size g + 1 with minimum Hamming distance 5, in which each codeword has length v and weight 4. Etzion conjectured that the necessary conditions v 1 (mod 3) and v ; 7 are also sufficient for the existence of a GS(2,4,v,2). Except for the example of a GS(2,4,10,2) and some recursive constructions given by Etzion, nothing else is known about this conjecture. In this paper, Weil's theorem on character sum estimates is used to show that the conjecture is true for any prime power v 7 (mod 12) except v = 7, for which there does not exist a GS(2,4,7,2).  相似文献   
185.
We study (set-valued) mappings of bounded -variation defined on the compact interval I and taking values in metric or normed linear spaces X. We prove a new structural theorem for these mappings and extend Medvedev's criterion from real valued functions onto mappings with values in a reflexive Banach space, which permits us to establish an explicit integral formula for the -variation of a metric space valued mapping. We show that the linear span GV (I;X) of the set of all mappings of bounded -variation is automatically a Banach algebra provided X is a Banach algebra. If h:I× X Y is a given mapping and the composition operator is defined by (f)(t)=h(t,f(t)), where tI and f:I X, we show that :GV (I;X) GV (I;Y) is Lipschitzian if and only if h(t,x)=h0(t)+h1(t)x, tI, xX. This result is further extended to multivalued composition operators with values compact convex sets. We prove that any (not necessarily convex valued) multifunction of bounded -variation with respect to the Hausdorff metric, whose graph is compact, admits regular selections of bounded -variation.  相似文献   
186.
基于本实验室提出一种新型以势能形式表达的分子距边矢量, 深入地系统研究了核磁共振碳-13谱化学位移和(CSS)规律以及分子拓扑指数矢量在定量结构波谱关系(QSSR)中的应用. 借助多种计量化学方法包括多元线性回归、逐步多元回归、主成分回归、主筛选回归等进行分子拟模和定量相关研究, 发现烷烃13C NMR 化学位移和(CSS)与其分子距边矢量及路径长度指数有良好线性相关性, 回归方程及其统计参数为:CSS=bν+cp3=∑mj=0bjνj+b11p3=b0ν+b1ν1+b2ν2+b3ν3+b4ν4+b5ν5+b6ν6+b7ν7+b8ν8+b9ν9+b10ν10+b11p3=-13.576+22.179ν1+28.407ν2+25 .950ν3+26.690ν4+14.498ν5+5.726ν6-5.379ν7-3.214ν8-15.021ν9 -25.710ν10+12.278p3 n=63, R=0.997, EV=99.68%, RMS=3.7348, SD=4.1 18, F= 773.116, U=144228.844, Q=864.938; CV: R2CV=0.980, EV=98.83%, RMS=7.126 1, SDCV=7.634, FCV=221.720, UCV=142121.891, QCV=2971 .896.结果良好.  相似文献   
187.
We build examples of Norden metrics on × S 1, where R 2 n n is either a pseudosphere or a pseudohyperbolic space. These turn out to be locally conformal to flat anti-Kählerian metrics, strongly non anti-Kählerian, and with a parallel Lee form. Conversely, any connected complete anti-Hermitian manifold possessing these properties is shown to be locally analytically homothetic to × S 1.  相似文献   
188.
Densely Continuous Forms in Vietoris Hyperspaces   总被引:2,自引:0,他引:2  
For countably paracompact normal spaces X and locally compact separable metric spaces Y, a characterization is given for the closure of the set of densely continuous forms from X to Y in the hyperspace of nonempty closed subsets of X × Y under the Vietoris topology. This shows that for such X having no isolated points, every closed subset of X × R that is dense over X can be Vietoris approximated by a semicontinuous function on X.  相似文献   
189.
Let be a real number such that and its conjugate exponent . We prove that for an operator defined on with values in a Banach space, the image of the unit ball determines whether belongs to any operator ideal and its operator ideal norm. We also show that this result fails to be true in the remaining cases of . Finally we prove that when the result holds in finite dimension, the map which associates to the image of the unit ball the operator ideal norm is continuous with respect to the Hausdorff metric.

  相似文献   

190.
Let q 2 be an integer. Then –q gives rise to a number system in , i.e., each number n has a unique representation of the form n = c 0 + c 1 (–q) + ... + c h (–q) h , with c i {0,..., q – 1}(0 i h). The aim of this paper is to investigate the sum of digits function q (n) of these number systems. In particular, we derive an asymptotic expansion for
and obtain a Gaussian asymptotic distribution result for q (n) – q (–n). Furthermore, we prove non-differentiability of certain continuous functions occurring in this context. We use automata and analytic methods to derive our results.  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