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   40390篇
  免费   944篇
  国内免费   769篇
化学   21048篇
晶体学   750篇
力学   1752篇
综合类   41篇
数学   4060篇
物理学   14452篇
  2022年   436篇
  2021年   469篇
  2020年   457篇
  2019年   475篇
  2018年   660篇
  2017年   574篇
  2016年   860篇
  2015年   574篇
  2014年   926篇
  2013年   1845篇
  2012年   1803篇
  2011年   2205篇
  2010年   1605篇
  2009年   1635篇
  2008年   1825篇
  2007年   1774篇
  2006年   1625篇
  2005年   1380篇
  2004年   1278篇
  2003年   1108篇
  2002年   1064篇
  2001年   1449篇
  2000年   1075篇
  1999年   879篇
  1998年   659篇
  1997年   623篇
  1996年   559篇
  1995年   511篇
  1994年   492篇
  1993年   425篇
  1992年   501篇
  1991年   490篇
  1990年   477篇
  1989年   430篇
  1988年   450篇
  1987年   433篇
  1986年   380篇
  1985年   444篇
  1984年   474篇
  1983年   348篇
  1982年   388篇
  1981年   377篇
  1980年   318篇
  1979年   401篇
  1978年   380篇
  1977年   396篇
  1976年   393篇
  1975年   343篇
  1974年   322篇
  1973年   340篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.  相似文献   
2.
3.
Saleh  Z. M.  Nasser  H.  Özkol  E.  Günöven  M.  Abak  K.  Canli  S.  Bek  A.  Turan  R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting...  相似文献   
4.
5.
6.
In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC4H3X ( 1 X ), SiC4H2X2 ( 2 X ), SiC4HX3 ( 3 X ), and SiC4X4 ( 4 X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔEs-t, a possible indication of stability), and band gap (ΔEH-L) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X . Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F . The trend of divalent angle () for each X is 4 X > 1 X > 3 X > 2 X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔEs-t and ΔEH-L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry.  相似文献   
7.
Palladium and molybdenum polycrystalline layers (clusters) have been deposited in a stainless steel UHV system onto a layer of alumina (Al2O3). This layer has been prepared by high temperature oxidation of an aluminium layer. The interaction of this system with nitrogen has been investigated at room temperature by an FEM technique. Under these conditions nitrogen spillover from molybdenum to palladium has been observed.  相似文献   
8.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
9.
10.
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