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   1386篇
  免费   74篇
  国内免费   59篇
化学   31篇
晶体学   1篇
力学   96篇
综合类   3篇
数学   1154篇
物理学   234篇
  2024年   2篇
  2023年   12篇
  2022年   13篇
  2021年   24篇
  2020年   49篇
  2019年   58篇
  2018年   51篇
  2017年   43篇
  2016年   57篇
  2015年   25篇
  2014年   77篇
  2013年   194篇
  2012年   35篇
  2011年   58篇
  2010年   58篇
  2009年   79篇
  2008年   71篇
  2007年   70篇
  2006年   61篇
  2005年   53篇
  2004年   63篇
  2003年   57篇
  2002年   57篇
  2001年   28篇
  2000年   29篇
  1999年   23篇
  1998年   28篇
  1997年   31篇
  1996年   12篇
  1995年   4篇
  1994年   13篇
  1993年   11篇
  1992年   9篇
  1991年   8篇
  1989年   4篇
  1988年   5篇
  1987年   5篇
  1986年   4篇
  1985年   4篇
  1984年   3篇
  1982年   1篇
  1981年   2篇
  1980年   7篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1976年   4篇
  1975年   3篇
  1974年   3篇
  1973年   1篇
排序方式: 共有1519条查询结果,搜索用时 31 毫秒
61.
Let LB be a sequent calculus of the first-order classical temporal logic TB with time gaps. Let, further, LBJ be the intuitionistic counterpart of LB. In this paper, we consider conditions under which a sequent is derivable in the calculus LBJ if and only if it is derivable in the calculus LB. Such conditions are defined for sequents with one formula in the succedent (purely Glivenko -classes) and for sequents with the empty succedent (Glivenko -classes).  相似文献   
62.
We prove a uniform bound for the density, p t (x), of the solution at time t(0, 1] of a 1-dimensional stochastic differential equation, under hypoellipticity conditions. A similar bound is obtained for an expression involving the distributional derivative (with respect to x) of p t (x). These results are applied to extend the Itô formula to the composition of a function (satisfying slight regularity conditions) with a hypoelliptic diffusion process in the spirit of the work of Föllmer et al. (5)  相似文献   
63.
The radial wave functions of inner electron shell and outer electron shell of a Ne atom were obtained by the approximate analytical method and tested by calculating the ground state energy of the Ne atom. The equivalent volume of electron cloud and the refractive index of Ne were calculated. The calculated refractive index agrees well with the experimental result. Relationship between the refractive index and the wave function of Ne was discovered. Supported by the New Star Program of Beijing Science and Technology, China (Grant No. 952870400), the Beijing Municipal Commission of Education, and the Excellent Young Teachers Program of Ministry of Education, China  相似文献   
64.
Differential equations and maps are the most frequently studied examples of dynamical systems and may be considered as continuous and discrete time-evolution processes respectively. The processes in which time evolution takes place on Cantor-like fractal subsets of the real line may be termed as fractal-time dynamical systems. Formulation of these systems requires an appropriate framework. A new calculus calledF α-calculus, is a natural calculus on subsetsF⊂ R of dimension α,0 < α ≤ 1. It involves integral and derivative of order α, calledF α-integral andF α-derivative respectively. TheF α-integral is suitable for integrating functions with fractal support of dimension α, while theF α-derivative enables us to differentiate functions like the Cantor staircase. The functions like the Cantor staircase function occur naturally as solutions ofF α-differential equations. Hence the latter can be used to model fractal-time processes or sublinear dynamical systems. We discuss construction and solutions of some fractal differential equations of the form
whereh is a vector field andD F,t α is a fractal differential operator of order α in timet. We also consider some equations of the form
whereL is an ordinary differential operator in the real variablex, and(t,x)F × Rn whereF is a Cantor-like set of dimension α. Further, we discuss a method of finding solutions toF α-differential equations: They can be mapped to ordinary differential equations, and the solutions of the latter can be transformed back to get those of the former. This is illustrated with a couple of examples.  相似文献   
65.
Shinya Harusawa 《Tetrahedron》2004,60(51):11911-11922
A novel measuring method (electroimmunoassay) of 17β-estradiol (E2) in urine or blood was proposed on the basis of a competition between E2 and a labeled E2 against an immobilizing antibody. To evaluate the principle, 3-{4-[17β-hydroxy-1,3,5(10)-estratrien-3-yloxy]butyldisulfanyl}-N-(6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclopentadecen-2-yl) succinamic acid (1) was designed and synthesized as a novel aminobenzo-15-crown-5-containing E2 tethered with disulfide linkage. Two thiol-intermediates 5b and 19c were efficiently synthesized from mercaptosuccinic acid 7 and 4,4′-dithiodibutyric acid 12, respectively. Formations of disulfide linkages from less reactive thiols were examined and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) could be employed for the formation of an unsymmetrical disulfide 20c from 5b and 19c. Then, removal of TMS- and allyl-protecting groups in 20c successfully afforded the crown ether-containing E21.  相似文献   
66.
In this paper we show that the Cahn–Hilliard stochastic PDE has a function valued solution in dimension 4 and 5 when the perturbation is driven by a space-correlated Gaussian noise. We study the regularity of the trajectories of the solution and the absolute continuity of its law at some given time and position. This is done by showing a priori estimates which heavily depend on the specific equation, and by proving general results on stochastic and deterministic integrals involving general operators on smooth domains of d which are parabolic in the sense of Petrovskii, and do not necessarily define a semi-group of operators. These last estimates might be used in a more general framework.  相似文献   
67.
For two covariant differential *-calculi, the twisted cyclic cocycle associated with the volume form is represented in terms of commutators for some self-adjoint operator and some *-representation of the underlying *-algebra.  相似文献   
68.
Elliptic Equations with Degenerate Coercivity: Gradient Regularity   总被引:2,自引:0,他引:2  
In this paper, we prove higher integrability results for the gradient of the solutions of some elliptic equations with degenerate coercivity whose prototype is where for example, a(x,u)=(1+|u|)−θ with θ ∈ (0,1). We study the same problem for minima of functionals closely related to the previous equation.  相似文献   
69.
The space-fractional telegraph equation is analyzed and the Fourier transform of its fundamental solution is obtained and discussed.A symmetric process with discontinuous trajectories, whose transition function satisfies the space-fractional telegraph equation, is presented. Its limiting behaviour and the connection with symmetric stable processes is also examined.  相似文献   
70.
For a domain in and a Hilbert space of analytic functions on which satisfies certain conditions, we characterize the commuting -tuples of operators on a separable Hilbert space  such that is unitarily equivalent to the restriction of to an invariant subspace, where is the operator -tuple on the Hilbert space tensor product  . For the unit disc and the Hardy space , this reduces to a well-known theorem of Sz.-Nagy and Foias; for a reproducing kernel Hilbert space on such that the reciprocal of its reproducing kernel is a polynomial in and  , this is a recent result of Ambrozie, Müller and the second author. In this paper, we extend the latter result by treating spaces for which ceases to be a polynomial, or even has a pole: namely, the standard weighted Bergman spaces (or, rather, their analytic continuation) on a Cartan domain corresponding to the parameter in the continuous Wallach set, and reproducing kernel Hilbert spaces for which is a rational function. Further, we treat also the more general problem when the operator is replaced by ,  being a certain generalization of a unitary operator tuple. For the case of the spaces on Cartan domains, our results are based on an analysis of the homogeneous multiplication operators on , which seems to be of an independent interest.

  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