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   4516篇
  免费   144篇
  国内免费   41篇
化学   2892篇
晶体学   28篇
力学   108篇
数学   967篇
物理学   706篇
  2023年   32篇
  2022年   98篇
  2021年   114篇
  2020年   99篇
  2019年   112篇
  2018年   96篇
  2017年   70篇
  2016年   150篇
  2015年   115篇
  2014年   136篇
  2013年   248篇
  2012年   264篇
  2011年   303篇
  2010年   196篇
  2009年   170篇
  2008年   285篇
  2007年   216篇
  2006年   227篇
  2005年   232篇
  2004年   214篇
  2003年   145篇
  2002年   150篇
  2001年   49篇
  2000年   48篇
  1999年   63篇
  1998年   50篇
  1997年   35篇
  1996年   72篇
  1995年   38篇
  1994年   34篇
  1993年   31篇
  1992年   31篇
  1991年   32篇
  1990年   14篇
  1989年   19篇
  1988年   17篇
  1987年   22篇
  1986年   20篇
  1985年   22篇
  1984年   28篇
  1982年   34篇
  1981年   29篇
  1980年   12篇
  1979年   21篇
  1978年   34篇
  1977年   18篇
  1976年   24篇
  1975年   11篇
  1974年   16篇
  1973年   14篇
排序方式: 共有4701条查询结果,搜索用时 0 毫秒
951.
952.
A numerical method used for solving a two-phase flow problem as found in typical oil recovery is investigated in the setting of physics-based two-level operator splitting. The governing equations involve an elliptic differential equation coupled with a parabolic convection-dominated equation which poses a severe restriction for obtaining fully implicit numerical solutions. Furthermore, strong heterogeneity of the porous medium over many length scales adds to the complications for effectively solving the system. One viable approach is to split the system into three sub-systems: the elliptic, the hyperbolic, and the parabolic equation, respectively. In doing so, we allow for the use of appropriate numerical discretization for each type of equation and the careful exchange of information between them. We propose to use the multiscale finite volume element method (MsFVEM) for the elliptic and parabolic equations, and a nonoscillatory difference scheme for the hyperbolic equation. Performance of this procedure is confirmed through several numerical experiments.  相似文献   
953.
954.
955.
Upon treatment with H2O2/KOH in EtOH or with Na2CO3/H2O2 in acetone, cycloalkylidene‐α‐(4‐arylthiazol‐2‐yl)acetonitriles afforded 2‐(4‐arylthiazol‐2‐yl)‐1‐oxaspiro[2.5]octane‐2‐carboxamides and 2‐(4‐arylthiazol‐2‐yl)‐1‐oxaspiro[2.4]heptane‐2‐carboxamides in excellent yields (76–100%). J. Heterocyclic Chem., 2011.  相似文献   
956.
957.
The human proteome is composed of a diverse and heterogeneous range of gene products/proteoforms/protein species. Because of the growing amount of information about proteoforms generated by different methods, we need a convenient approach to make an inventory of the data. Here, we present a database of proteoforms that is based on information obtained by separation of proteoforms using 2DE followed by shotgun ESI–LC–MS/MS. The database's principles and structure are described. The database is called “2DE-pattern” as it contains multiple isoform-centric patterns of proteoforms separated according to 2DE principles. The database can be freely used at http://2de-pattern.pnpi.nrcki.ru .  相似文献   
958.
A new catalytic system based on triarylstibines for C-arylation of unsaturated compounds is proposed. It was found for a model reaction, the C-arylation of methyl acrylate, that in the presence of equimolar amounts of peroxide and catalytic amounts of a palladium compound (4 mol%), triarylstibines can act as mild efficient arylating agents.  相似文献   
959.
Berberis darwinii Hook (Berberidaceae) has yielded the lactams (±)-nuevamine (7) and (±)-lennoxamine (8). Nuevamine is the first known isoindoloisoquinoline alkaloid, while lennoxamine is an isoindolobenzazepine structurally related to (±)-chilenine (3).  相似文献   
960.
Motivated by applications in universal data compression algorithms we study the problem of bounds on the sizes of constant weight covering codes. We are concerned with the minimal sizes of codes of lengthn and constant weightu such that every word of lengthn and weightv is within Hamming distanced from a codeword. In addition to a brief summary of part of the relevant literature, we also give new results on upper and lower bounds to these sizes. We pay particular attention to the asymptotic covering density of these codes. We include tables of the bounds on the sizes of these codes both for small values ofn and for the asymptotic behavior. A comparison with techniques for attaining bounds for packing codes is also given. Some new combinatorial questions are also arising from the techniques.Part of this work was done while the first and third authors were visiting Bellcore. The third author was supported in part by National Science Foundation under grant NCR-8905052. Part of this work was presented in the Coding and Quantization Workshop at Rutgers University, NJ, October 1992.  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