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   2650篇
  免费   81篇
  国内免费   21篇
化学   1722篇
晶体学   14篇
力学   36篇
数学   435篇
物理学   545篇
  2023年   17篇
  2022年   46篇
  2021年   65篇
  2020年   50篇
  2019年   70篇
  2018年   66篇
  2017年   54篇
  2016年   80篇
  2015年   98篇
  2014年   81篇
  2013年   178篇
  2012年   147篇
  2011年   184篇
  2010年   131篇
  2009年   128篇
  2008年   189篇
  2007年   151篇
  2006年   185篇
  2005年   156篇
  2004年   101篇
  2003年   92篇
  2002年   94篇
  2001年   38篇
  2000年   37篇
  1999年   29篇
  1998年   25篇
  1997年   28篇
  1996年   36篇
  1995年   26篇
  1994年   16篇
  1993年   17篇
  1992年   15篇
  1991年   16篇
  1990年   8篇
  1989年   10篇
  1988年   8篇
  1987年   11篇
  1986年   8篇
  1985年   7篇
  1984年   6篇
  1982年   6篇
  1980年   5篇
  1979年   5篇
  1978年   6篇
  1977年   2篇
  1976年   2篇
  1975年   7篇
  1974年   4篇
  1972年   2篇
  1969年   2篇
排序方式: 共有2752条查询结果,搜索用时 15 毫秒
111.
A systematic study was conducted on current efficiency (CE), corrosion and structural changes in SnO2-based inert anodes (made of 96wt%SnO2+2wt%Sb2O3+2wt%CuO) on a laboratory Hall-Heroult aluminium cell. The influence of operating parameters and electrolyte composition on the CE and corrosion process were evaluated. The CE was found to be more than 90% and catastrophic corrosion took place at low percent of Al2O3, high percent of LiF, low cryolite ratio and high current densities. From all the structural changes that took place in the SnO2-based inert anodes, we assumed that the most important contribution was due to the migration of CuO towards the outer limits of the constituent grains of SnO2 based ceramic. The complex process occurred during the formation of various phases and their sintering ability both directly depended on Cu/Sb molar ratio.  相似文献   
112.
We examined a series of amino acid-based surfactants with two carboxylic groups separated by a spacer of one, two, or three carbon atoms with sodium and calcium counterions in the premicellar concentration region near the CMC. 1H nuclear magnetic resonance (NMR) spectroscopy and NMR diffusometry techniques were used to study the local environment, association, and translational dynamics of the surfactant's molecules. We measured the self-diffusion coefficients of the micelles, calculated the effective hydrodynamic radii, and determined the temperature region in which the premicelles exist. With an increase in temperature from 295 to 335 K, the premicellar state of the surfactant is replaced by the monomeric state.  相似文献   
113.
We present an option of the experiment with a correlated pair of particles in the entangled state, which provides the effect of a change in the polarization for entangled photons, and demonstrate the reality of all different superposition states and the corresponding vector of the quantum system state; also we analyze possible consequences of this fact. We propose a quantum realism paradigm within the relational paradigm instead of the local realism concept disproved by the experiments on verifying the Bell inequalities. We analyze the results of experimental research of the Leggett inequality violation with respect to the verification of the adequacy of different kinds of nonlocal hidden variable theories and suggest a new way of their evaluation based on the study of the photon cross-correlation suppression after a beam splitter and preparation of quantum squeezed states. We show that the interpretation based on the nonlocal hidden variable theory is inconsistent.  相似文献   
114.
We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wave vector range from zero to 6x10(4) cm-1. We find that the spin polarization lifetime is maximal at a nonzero wave vector, in contrast with expectations based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.  相似文献   
115.
116.
117.
118.
119.
An efficient and practical Pd‐catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3‐ and 1,4‐amino alcohols and 1,3‐diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center  相似文献   
120.
EBC‐162 isolated from Croton insularis, obtained from the northern rainforest of Australia, was structurally affirmed as crotofolin C ( 4 ). Novel oxidative degradation products, EBC‐233 and EBC‐300, which are the first crotofolane endoperoxides, were also isolated. Both endoperoxides were found to be stable intermediates, which are proposed to undergo an unprecedented homo‐Baeyer–Villiger biosynthetic rearrangement to give a new class of 1,14‐seco‐crotofolane diterpenes. Prolonged storage of all isolates assisted in authenticating their natural product status. Anticancer activities of reported compounds are presented.  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