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   5539篇
  免费   351篇
  国内免费   101篇
化学   820篇
晶体学   33篇
力学   146篇
综合类   84篇
数学   1118篇
物理学   1325篇
无线电   2465篇
  2024年   2篇
  2023年   13篇
  2022年   31篇
  2021年   104篇
  2020年   114篇
  2019年   30篇
  2018年   37篇
  2017年   109篇
  2016年   139篇
  2015年   157篇
  2014年   259篇
  2013年   314篇
  2012年   255篇
  2011年   386篇
  2010年   352篇
  2009年   365篇
  2008年   409篇
  2007年   394篇
  2006年   349篇
  2005年   273篇
  2004年   253篇
  2003年   263篇
  2002年   218篇
  2001年   182篇
  2000年   160篇
  1999年   107篇
  1998年   124篇
  1997年   102篇
  1996年   110篇
  1995年   74篇
  1994年   72篇
  1993年   44篇
  1992年   26篇
  1991年   28篇
  1990年   18篇
  1989年   15篇
  1988年   12篇
  1987年   12篇
  1986年   18篇
  1985年   18篇
  1984年   16篇
  1983年   6篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1976年   4篇
  1970年   1篇
  1969年   1篇
  1967年   2篇
  1966年   1篇
排序方式: 共有5991条查询结果,搜索用时 15 毫秒
781.
Let D be a directed graph; the (l,ω)-Independence Number of graph D, denoted by αl,ω(D), is an important performance parameter for interconnection networks. De Bruijn networks and Kautz networks, denoted by B(d,n) and K(d,n) respectively, are versatile and efficient topological structures of interconnection networks. For l=1,2,…,n, this paper shows that αl,d−1(B(d,n))=dn,αl,d−1(K(d,n))=αl,d(K(d,n))=dn+dn−1 if d≥3 and nd−2. In particular, the paper shows the exact value of the Independence Number for B(d,1) and B(d,2) for any d. For the generalized situation, the paper obtains a lower bound αl,d−1(B(d,n))≥d2 if n≥3 and d≥5.  相似文献   
782.
783.
In this paper, a new monotonicity, MM-monotonicity, is introduced, and the resolvent operator of an MM-monotone operator is proved to be single valued and Lipschitz continuous. With the help of the resolvent operator, an equivalence between the variational inequality VI(C,F+G)(C,F+G) and the fixed point problem of a nonexpansive mapping is established. A proximal point algorithm is constructed to solve the fixed point problem, which is proved to have a global convergence under the condition that FF in the VI problem is strongly monotone and Lipschitz continuous. Furthermore, a convergent path Newton method, which is based on the assumption that the projection mapping C(⋅)C() is semismooth, is given for calculating εε-solutions to the sequence of fixed point problems, enabling the proximal point algorithm to be implementable.  相似文献   
784.
In this paper we generalize classical LqLq, q≥pqp, estimates of the gradient to the Orlicz space for weak solutions of quasilinear elliptic equations of p-Laplacian type.  相似文献   
785.
786.
787.
Five pathways leading to the deamination of cytosine (to uracil) after formation of its deprotonated radical cation are investigated in the gas phase, at the UB3LYP/6‐311G(d,p) level of theory, and in bulk aqueous solvent. The most favorable pathway involves hydrogen‐atom transfer from a water molecule to the N3 nitrogen of the deprotonated radical cation, followed by addition of the resulting hydroxyl radical to the C4 carbon of the cytosine derivative. Following protonation of the amino group (N4), the C4? N4 bond is broken with elimination of the NH3?+ radical and formation of a protonated uracil. The rate‐determining step of this mechanism is hydrogen‐atom transfer from a water molecule to the cytosine derivative. The associated free energy barrier is 70.2 kJ mol?1.  相似文献   
788.
Stokes–Einstein (SE) and Stokes–Einstein–Debye (SED) relations in the neat ionic liquid (IL) [C2mim][NTf2] and IL/chloroform mixtures are studied by means of molecular dynamics (MD) simulations. For this purpose, we simulate the translational diffusion coefficients of the cations and anions, the rotational correlation times of the C(2)? H bond in the cation C2mim+, and the viscosities of the whole system. We find that the SE and SED relations are not valid for the pure ionic liquid, nor for IL/chloroform mixtures down to the miscibility gap (at 50 wt % IL). The deviations from both relations could be related to dynamical heterogeneities described by the non‐Gaussian parameter α(t). If α(t) is close to zero, at a concentration of 1 wt % IL in chloroform, both relations become valid. Then, the effective radii and volumes calculated from the SE and SED equations can be related to the structures found in the MD simulations, such as aggregates of ion pairs. Overall, similarities are observed between the dynamical properties of supercooled water and those of ionic liquids.  相似文献   
789.
For the sets , 1?p<∞, of positive finite Borel measures μ on the real axis with the set of algebraic polynomials P dense in Lp(R,dμ), we establish a majorization principle of their “boundaries,” i.e. for every there exists such that dμ/dν?1. A corresponding principle holds for the sets , p>0, of non-negative upper semi-continuous on R functions (weights) w such that P is dense in the space : For every there exists such that w?ω.  相似文献   
790.
It is proved that the Hörmander and spaces (Ω1Rn, Ω2Rm open sets, 1?p<∞, ki Beurling-Björck weights, k=k1k2) are isomorphic whereas the iterated spaces and are not if 1<pq<∞. A similar result for weighted Lp-spaces of entire analytic functions is also obtained. Finally a result on iterated Besov spaces is given: and are not isomorphic when 1<q≠2<∞.  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