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   573篇
  免费   9篇
  国内免费   6篇
化学   380篇
晶体学   10篇
力学   40篇
数学   24篇
物理学   134篇
  2022年   4篇
  2021年   6篇
  2019年   11篇
  2018年   7篇
  2016年   4篇
  2015年   9篇
  2014年   13篇
  2013年   29篇
  2012年   22篇
  2011年   25篇
  2010年   21篇
  2009年   23篇
  2008年   34篇
  2007年   27篇
  2006年   24篇
  2005年   22篇
  2004年   16篇
  2003年   20篇
  2002年   20篇
  2001年   14篇
  2000年   11篇
  1999年   11篇
  1998年   9篇
  1997年   14篇
  1996年   9篇
  1995年   8篇
  1994年   7篇
  1993年   9篇
  1992年   14篇
  1991年   10篇
  1990年   9篇
  1989年   8篇
  1988年   12篇
  1987年   16篇
  1986年   9篇
  1985年   10篇
  1984年   7篇
  1983年   4篇
  1982年   3篇
  1981年   5篇
  1980年   6篇
  1979年   4篇
  1978年   4篇
  1977年   3篇
  1976年   8篇
  1975年   6篇
  1974年   5篇
  1973年   3篇
  1972年   3篇
  1968年   2篇
排序方式: 共有588条查询结果,搜索用时 78 毫秒
51.
In all-trans-neurosporene, whose level is lower than the level by one vibrational quantum, the following two steps of vibrational relaxation from the mixed vibronic states were identified, in the order, stimulated emission stimulated emission transient absorption. The stimulated emission patterns were simulated by the use of Franck–Condon factors in the transitions from the pair of mixed vibronic levels down to the ground vibronic levels. The vibronic levels of the mixed and state were characterized theoretically based on the diabatic approximation.  相似文献   
52.
Metallic Na was formed in/on NaCl single crystals by irradiating them with a variety of radiation sources, namely, 21 MeV electron pulses, an electron beam of 30 keV and photon fluxes in the VUV region. The physical states were analysed using several methods, optical absorption, lifetime measurement of positron annihilation, Auger electron spectroscopy and UV photoelectron spectroscopy. Metallic Na was obtained in different physical states; clusters were formed in bulk, thin layers (islands) and thick layers on the surface.  相似文献   
53.
This paper shares results from a secondary analysis of data from the participation of Japanese, Singaporean, and U.S. students in the International Project on Mathematical Attainment (IPMA). IPMA was a longitudinal study to assess the mathematics achievement of primary students from their first year of schooling through the end of fifth grade. Tests were constructed to enable achievement on the same items to be assessed over multiple years, thus permitting the assessment of growth in achievement throughout primary school. Achievement is compared to the grade at which the content is introduced so that achievement can be related to students’ opportunity to learn.  相似文献   
54.
55.
We propose a new search algorithm to solve the equation for a fixed value of . By parametrizing min, this algorithm obtains and (if they exist) by solving a quadratic equation derived from divisors of . By using several efficient number-theoretic sieves, the new algorithm is much faster on average than previous straightforward algorithms. We performed a computer search for 51 values of below 1000 (except ) for which no solution has previously been found. We found eight new integer solutions for and in the range of .

  相似文献   

56.
57.
We have developed a new magneto-optical measurement system using a rotational cavity system equipped with a millimeter vector network analyzer and a 14 T solenoid type super conducting magnet. The measurement can be performed in the transmission configuration down to 1.6 K. The results of the precise angular dependence measurement of quasi-one-dimensional organic conductor (DMET)2I3 using the new system are shown, and its Fermi surface will be discussed in connection with the previous reports.  相似文献   
58.
59.
The effect of inelastic scattering on the electron reflection in multi-quantum barriers (MQBs) has been examined using the damped resonant tunnelling model for the first time. The electron reflectivity in the virtual barrier region for unstrained GalnAs/InP MQB deteriorates below 100% by about 10% for phase relaxation time of 0.22ps. We propose a strain-compensated GalnAs/GalnP MQB which not only has virtual barrier 4 times as high as that of an unstrained MQB, but whose reflectivity deterioration is reduced to less than 5% in comparison with 10% for unstrained MQB for the same phase relaxation time. We have also successfully grown a Ga0.25In0.75As (1.5% compressive) well/Ga0.25In0.75P (1.2% tensile) barrier short-period superlattice with six wells by chemical beam epitaxy, which exhibits the possibility of fabrication of the strain-compensated MQBs.  相似文献   
60.
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