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   500篇
  免费   6篇
化学   340篇
晶体学   8篇
力学   3篇
数学   7篇
物理学   148篇
  2022年   6篇
  2020年   7篇
  2019年   6篇
  2018年   7篇
  2017年   5篇
  2016年   9篇
  2015年   7篇
  2014年   13篇
  2013年   16篇
  2012年   10篇
  2011年   19篇
  2010年   19篇
  2009年   11篇
  2008年   19篇
  2007年   25篇
  2006年   33篇
  2005年   24篇
  2004年   19篇
  2003年   19篇
  2002年   21篇
  2001年   10篇
  2000年   8篇
  1999年   4篇
  1998年   4篇
  1997年   6篇
  1996年   9篇
  1995年   5篇
  1994年   14篇
  1993年   4篇
  1992年   8篇
  1991年   7篇
  1990年   5篇
  1989年   11篇
  1987年   6篇
  1986年   3篇
  1985年   5篇
  1984年   12篇
  1983年   7篇
  1982年   8篇
  1981年   10篇
  1980年   4篇
  1979年   5篇
  1978年   9篇
  1977年   6篇
  1976年   5篇
  1975年   3篇
  1974年   3篇
  1973年   6篇
  1968年   5篇
  1967年   3篇
排序方式: 共有506条查询结果,搜索用时 0 毫秒
501.
Kaori Yagi 《Tetrahedron》2006,62(20):4933-4940
CuCN-catalyzed reaction of the (1R)-isomer of 4-cyclopentene-1,3-diol monoacetate with TBDPSO(CH2)6MgCl produced an SN2-type product regioselectively in high yield. Mitsunobu inversion of the product and subsequent Claisen rearrangement furnished aldehyde with the two side chains, from which the title compounds were synthesized efficiently.  相似文献   
502.
The influence of shearing on the magnetic properties and domain structure of 0.5 mm thick non-oriented electrical steel was studied. In the region from 1 to 1.4 mm from the sheared edge, a striped domain pattern that indicated the existence of elastic strain was observed. From the degradation tendency of flux density with respect to shearing width, the width of the degraded region near the edge increased as the magnetic field decreased. These results suggested that the change in the flux density at high magnetic fields over 300 A/m were mainly dependent on the characteristics of the edge vicinity where the domain pattern was influenced by shearing.  相似文献   
503.
504.
As a new method, stable-isotope dilution activation analysis has been developed. When an element consists of at least two stable isotopes which are converted easily to the radioactive nuclides through nuclear reactions, the total amount of the element (xg) can be determined by irradiating simultaneously the duplicated sample containing small amounts of either enriched isotope (y g), and by using the following equation. $${{x = y\left( {{M \mathord{\left/ {\vphantom {M {M*}}} \right. \kern-\nulldelimiterspace} {M*}}} \right)\left[ {\left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)\left( {{{\theta _2^* } \mathord{\left/ {\vphantom {{\theta _2^* } {\theta _2 }}} \right. \kern-\nulldelimiterspace} {\theta _2 }}} \right) - \left( {{{\theta _1^* } \mathord{\left/ {\vphantom {{\theta _1^* } {\theta _1 }}} \right. \kern-\nulldelimiterspace} {\theta _1 }}} \right)} \right]} \mathord{\left/ {\vphantom {{x = y\left( {{M \mathord{\left/ {\vphantom {M {M*}}} \right. \kern-\nulldelimiterspace} {M*}}} \right)\left[ {\left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)\left( {{{\theta _2^* } \mathord{\left/ {\vphantom {{\theta _2^* } {\theta _2 }}} \right. \kern-\nulldelimiterspace} {\theta _2 }}} \right) - \left( {{{\theta _1^* } \mathord{\left/ {\vphantom {{\theta _1^* } {\theta _1 }}} \right. \kern-\nulldelimiterspace} {\theta _1 }}} \right)} \right]} {\left[ {1 - \left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)} \right]}}} \right. \kern-\nulldelimiterspace} {\left[ {1 - \left( {{{R*} \mathord{\left/ {\vphantom {{R*} R}} \right. \kern-\nulldelimiterspace} R}} \right)} \right]}}$$ Where M and M* are atomic weights of the element to be determined and the enriched isotope used as a spike,θ 1 andθ 2 are natural abundances of two stable isotopes in the element,θ 1 * andθ 2 * are isotopic compositions of the above isotopes in the enriched isotope, and R and R* are counting ratios of gamma-rays emitted by two radionuclides produced in the sample and the isotopic mixture. Neither calibration standard nor correction of irradiation conditions are necessary for this method. Usefulness of the present method was verified by photon activations of Ca, Zn and Ce using isotopically enriched48ca,68Zn and142Ce.  相似文献   
505.
A grid-averaged Lagrangian (GAL) model for dispersed particle motion in multiphase turbulent flow is presented to provide a large eddy simulation (LES) model for multiphase turbulent flow in which a quite large number of particles are involved. The GAL model is based on an averaging operation for a Lagrangian-type equation of motion of a particle over a computational grid volume and a procedure of reallocation of a dispersed particle cloud with its centroid movement to each grid. The model is therefore a mixed Eulerian–Lagrangian model which can effectively reduce computational time compared with existing Lagrangian-type models, without losing the advantage of Lagrangian-type models that they can properly describe the dynamical evolution of particles. Since the GAL model adopts the grid-volume averaging operation it can easily provide an effective SGS model for LES modeling of multiphase turbulent flow. The validity of the multiphase LES model developed, which is named the GAL-LES model, is confirmed through its application to a particle plume, in which the present model is found to simulate large-eddy motion usually observed in a jet and plume, and to give good agreements with experimental data.  相似文献   
506.
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