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   73920篇
  免费   1673篇
  国内免费   278篇
化学   38294篇
晶体学   487篇
力学   2107篇
综合类   13篇
数学   17423篇
物理学   17547篇
  2023年   349篇
  2022年   333篇
  2021年   518篇
  2020年   705篇
  2019年   640篇
  2018年   2079篇
  2017年   2240篇
  2016年   2395篇
  2015年   1939篇
  2014年   1817篇
  2013年   3685篇
  2012年   5725篇
  2011年   4942篇
  2010年   3468篇
  2009年   2938篇
  2008年   2928篇
  2007年   2762篇
  2006年   2504篇
  2005年   6232篇
  2004年   5475篇
  2003年   3615篇
  2002年   1695篇
  2001年   1218篇
  2000年   1029篇
  1999年   820篇
  1998年   626篇
  1997年   502篇
  1996年   626篇
  1995年   451篇
  1994年   529篇
  1993年   468篇
  1992年   626篇
  1991年   536篇
  1990年   569篇
  1989年   464篇
  1988年   461篇
  1987年   391篇
  1986年   365篇
  1985年   484篇
  1984年   440篇
  1983年   349篇
  1982年   349篇
  1981年   364篇
  1980年   290篇
  1979年   301篇
  1978年   298篇
  1977年   281篇
  1976年   343篇
  1974年   288篇
  1973年   309篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
91.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed.  相似文献   
92.
Book Review     
Structural Chemistry -  相似文献   
93.
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA.  相似文献   
94.
95.
The exponential functional of simple, symmetric random walks with negative drift is an infinite polynomial Y = 1 + ξ1 + ξ1ξ2 + ξ1ξ2ξ3 + ⋯ of independent and identically distributed non-negative random variables. It has moments that are rational functions of the variables μ k = E k ) < 1 with universal coefficients. It turns out that such a coefficient is equal to the number of permutations with descent set defined by the multiindex of the coefficient. A recursion enumerates all numbers of permutations with given descent sets in the form of a Pascal-type triangle. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
96.
Periodica Mathematica Hungarica - In our paper we study the usage of partially defined Boolean functions (PDBFs) for generating cryptographically strong Boolean functions. A PDBF can be considered...  相似文献   
97.
A note on a generalized Douglas space   总被引:1,自引:0,他引:1  
Periodica Mathematica Hungarica -  相似文献   
98.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents.  相似文献   
99.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d h (i) of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d h (1) and d′ h (3) , were measured, d h (1) =(244±3) pC/N and d′ h (3) =(92±1) pC/N. The hydrostatic piezoelectric coefficient d h (3) for orthogonal axis system was calculated to be d h (3) =(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d h (1) equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d h ) mean corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d h ) mean =136 pC/N.  相似文献   
100.
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