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   1066篇
  免费   50篇
  国内免费   6篇
化学   690篇
晶体学   2篇
力学   45篇
数学   197篇
物理学   188篇
  2023年   13篇
  2022年   17篇
  2021年   38篇
  2020年   26篇
  2019年   21篇
  2018年   17篇
  2017年   25篇
  2016年   49篇
  2015年   40篇
  2014年   47篇
  2013年   56篇
  2012年   58篇
  2011年   74篇
  2010年   30篇
  2009年   36篇
  2008年   63篇
  2007年   67篇
  2006年   75篇
  2005年   56篇
  2004年   43篇
  2003年   31篇
  2002年   36篇
  2001年   14篇
  2000年   14篇
  1999年   13篇
  1998年   12篇
  1997年   8篇
  1996年   6篇
  1995年   7篇
  1994年   6篇
  1993年   6篇
  1992年   7篇
  1991年   3篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1987年   3篇
  1986年   5篇
  1985年   6篇
  1984年   12篇
  1983年   5篇
  1981年   7篇
  1980年   11篇
  1979年   9篇
  1978年   5篇
  1977年   6篇
  1976年   6篇
  1975年   3篇
  1974年   5篇
  1972年   4篇
排序方式: 共有1122条查询结果,搜索用时 31 毫秒
81.
We prove the existence of small amplitude quasi-periodic solutions for quasi-linear and fully nonlinear forced perturbations of the linear Airy equation. For Hamiltonian or reversible nonlinearities we also prove their linear stability. The key analysis concerns the reducibility of the linearized operator at an approximate solution, which provides a sharp asymptotic expansion of its eigenvalues. For quasi-linear perturbations this cannot be directly obtained by a KAM iteration. Hence we first perform a regularization procedure, which conjugates the linearized operator to an operator with constant coefficients plus a bounded remainder. These transformations are obtained by changes of variables induced by diffeomorphisms of the torus and pseudo-differential operators. At this point we implement a Nash–Moser iteration (with second order Melnikov non-resonance conditions) which completes the reduction to constant coefficients.  相似文献   
82.
In this paper the question of finding infinitely many solutions to the problem −Δu+a(x)u=|u|p−2uΔu+a(x)u=|u|p2u, in RNRN, u∈H1(RN)uH1(RN), is considered when N≥2N2, p∈(2,2N/(N−2))p(2,2N/(N2)), and the potential a(x)a(x) is a positive function which is not required to enjoy symmetry properties. Assuming that a(x)a(x) satisfies a suitable “slow decay at infinity” condition and, moreover, that its graph has some “dips”, we prove that the problem admits either infinitely many nodal solutions or infinitely many constant sign solutions. The proof method is purely variational and allows to describe the shape of the solutions.  相似文献   
83.
84.
We present some multiplicity results concerning semilinear elliptic Dirichlet problems with jumping nonlinearities where the jumping condition involves a set of high eigenvalues not including the first one. Using a variational method we show that the number of solutions may be arbitrarily large provided the number of jumped eigenvalues is large enough. Indeed, we prove that for every positive integer $k$ there exists a positive integer $n(k)$ such that, if the number of jumped eigenvalues is greater than $n(k),$ then the problem has at least a solution which presents $k$ peaks. Moreover, we describe the asymptotic behaviour of the solutions as the number of jumped eigenvalues tends to infinity; in particular, we analyse some concentration phenomena of the peaks (near points or suitable manifolds), we describe the asymptotic profile of the rescaled peaks, etc $\ldots $   相似文献   
85.
86.
Provided that 13C‐detected NMR experiments are either preferable or complementary to 1H detection, we report here tools to determine Cα? C′, C′? N, and Cα? Hα residual dipolar couplings on the basis of the CON experiment. The coupling constants determined on ubiquitin are consistent with the subset measured with the 1H‐detected HNCO sequences. Since the utilization of residual dipolar couplings may depend on the mobility of the involved nuclei, we also provide tools to measure longitudinal and transverse relaxation rates of N and C′. This new set of experiments is a further development of a whole strategy based on 13C direct‐detection NMR spectroscopy for the study of biological macromolecules.  相似文献   
87.
Within group invariance theory we consider a constructive approach in order to define numerical transformation methods. These are initial-value methods for the solution of boundary value problems governed by ordinary differential equations. Here we consider the class of free boundary value problems governed by the most general second-order equation in normal form. For this class of problems the main theorem is concerned with the definition of an iterative transformation method. The definition of a noniterative method, applicable to a subclass of the original class of problems, follows as a corollary. Therefore, the proposed constructive approach allows us to establish a unifying framework for noniterative and iterative transformation methods.  相似文献   
88.
89.
90.
Current density plots of closed‐shell intermolecular H? H interactions characterized by a bond critical point (BCP) show two vortices separated by a saddle, a pattern which allows for a clear definition of a pair current strength. This H? H current strength turns out to be roughly related to the potential energy density at the BCP and then to the dissociation energy. The same pattern is also recognizable, at least for an azimuthal orientation of a field perpendicular to the H? H line, for the intramolecular interactions previously investigated to propose the H? H bonding. In the case of the H atoms of the bay region of polycyclic aromatic hydrocarbons, the current of the H? H delocalized diatropic vortex gives a quantitative indication of stabilization; however, on rotation of the field and the subsequent onset of a bay‐delocalized paratropic vortex (a typical signature of antiaromaticity), the diatropic vortex can be reshaped or it can even disappear, consistently with its smallness, and thus showing the effect of other more relevant interactions. © 2015 Wiley Periodicals, Inc.  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