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   143篇
  免费   15篇
  国内免费   35篇
化学   76篇
晶体学   1篇
力学   6篇
综合类   1篇
数学   41篇
物理学   68篇
  2023年   4篇
  2022年   1篇
  2021年   1篇
  2019年   3篇
  2018年   4篇
  2017年   2篇
  2016年   2篇
  2015年   3篇
  2014年   5篇
  2013年   9篇
  2012年   15篇
  2011年   3篇
  2010年   8篇
  2009年   13篇
  2008年   12篇
  2007年   6篇
  2006年   4篇
  2005年   7篇
  2004年   8篇
  2003年   6篇
  2002年   5篇
  2001年   9篇
  2000年   12篇
  1999年   10篇
  1998年   5篇
  1997年   4篇
  1996年   3篇
  1995年   6篇
  1994年   4篇
  1993年   7篇
  1992年   4篇
  1991年   2篇
  1990年   2篇
  1988年   1篇
  1985年   2篇
  1984年   1篇
排序方式: 共有193条查询结果,搜索用时 78 毫秒
91.
In this article the solution of dynamical equation of motion of IBM-Ⅱ in continuous variable representation is discussed.With appropriate transformation and approximation,the on-phase part of system manifests the vibration-rotation mode and the off-phase part the 'scissor mode',ect.In the last section the energy spectrum of 156Gd is calculated.The result can well reproduce the algebraic result of IBM-Ⅱ.  相似文献   
92.
Nonlinear local Lyapunov exponent (NLLE) is applied to quantitatively determine the local predictability limit of chaotic systems. As an example, we find that the local predictability limit of Henon attractor varies considerably with time, and some underlying phase-spatial structure does not appear. The local predictability limit of initially adjacent points in phase space may be completely different. This will cause difficulties in making the long-time analogue forecast.  相似文献   
93.
Some authors consider the ψ(4415) to be the 4S or 5S excited tate of a cc pair. Starting from this assumption, we study he decays of the ψ(4415) to DD, D*D*, DSDS, DS*DS*, and get the corresponding branching ratios in terms of the Quark-Pair-Creation (QPC) model. Compared with the experimental data, we find that the results of 4S state agree much better than those of the 5S state. Therefore, it is more reasonable to assume the ψ(4415) to be a 4S state.  相似文献   
94.
Some authors consider the ψ(4415) to be the 4S or 5S excited state of a c-c pair.Starting from this assumption,we study the decays of the ψ(4415) to DD,D*D-*,DsD-s,D*SD*S~,and get the corresponding branching ratios in terms of the Quark-Pair-Creation (QPC) model.Compared with the experimental data,we find that the results of 4S state agree much better than those of the 5S state.Therefore,it is more reasonable to assume the ψ(4415) to be a 4S state.  相似文献   
95.

Background  

Our previous work described the neural processes of motor response inhibition during a stop signal task (SST). Employing the race model, we computed the stop signal reaction time (SSRT) to index individuals' ability in inhibitory control. The pre-supplementary motor area (preSMA), which shows greater activity in individuals with short as compared to those with long SSRT, plays a role in mediating response inhibition. In contrast, the right inferior prefrontal cortex (rIFC) showed greater activity during stop success as compared to stop error. Here we further pursued this functional differentiation of preSMA and rIFC on the basis of an intra-subject approach.  相似文献   
96.
研究了不同剂量12C6+离子辐照对中兰1号、BC-04-477、塔城3种苜蓿M1代个体在低温胁迫下存活率、过氧化氢酶(CAT)及过氧化物酶(POD)活性的影响。在辐照剂量为400 Gy时,中兰1号低温胁迫组存活率、CAT活性比未辐照的对照分别提高了33.3%,56.3%,POD活性与未辐照的对照无差异;在辐照剂量为400 Gy时,BC-04-477低温胁迫组存活率、CAT及POD活性比未辐照的对照组分别提高了33.3%,69.2%,5.1%;塔城在辐照剂量为800 Gy时,低温胁迫组的存活率、CAT及POD活性比未辐照的对照组分别提高了25%,26%,22.8%。以上结果表明,12C6+离子辐照可以提高中兰1号、BC-04-477、塔城的低温环境的存活能力,提高苜蓿抗寒性能。  相似文献   
97.
理论模拟结合实验研究了16-keV Cl-离子穿越不同厚度(7和12 μm)的Al2O3微孔膜的物理过程,发现负离子传输中并不存在与正离子传输类似的明显的导向现象。在只考虑散射过程的情况下,模拟出的穿透粒子角分布及电荷态分布与实验结果符合很好,出射的Cl-离子沿初束方向分布;Cl0、Cl+离子沿微孔轴向分布。仔细分析了不同出射粒子的角分布,发现出射的Cl+在微孔轴向与初束方向之间分布;经单次散射出射的Cl0沿微孔轴向分布,而经多次散射出射的Cl0向初束方向移动。发现了Cl-离子穿越不同厚度的具有相同微孔直径的Al2O3微孔时,较厚的膜出射的Cl+/Cl0比例低。理论分析显示,这是由散射过程的特性造成的,随着微孔膜厚度的增加,出射的Cl0中经单次碰撞的比例变小,而多次散射出射的比例增加,从而导致Cl+离子转化为Cl0的几率要远大于Cl0转化为Cl+离子的几率,使得长的微孔出射的粒子中Cl+/Cl0比例低。  相似文献   
98.
ICP光源中载气压力对等离子体辐射强度的影响   总被引:1,自引:2,他引:1  
为了提高ICP光源等离子体的辐射强度,利用常规同心气动雾化器,增大载气压力,提高样品溶液的雾化效率,并且通过释放掉部分气溶胶的方法,以合适的流速将样品送入等离子体焰。经过测量水样品中元素Ca,Si,Sr和Zn的谱线强度表明,在常规条件下载气压力为0.05 MPa时有谱线峰值强度;当释放掉部分气溶胶以后,在0.07 MPa的载气压力下测得的峰值强度分别提高了38%,79%,45%和70%。另外,使用较高的载气压力并不影响等离子体辐射的稳定性。  相似文献   
99.
ROLF MEYER  TAE-KYU HA 《Molecular physics》2013,111(22):3263-3276
New ab initio results on the 21D potential energy surface of malonaldehyde and a quantum mechanical treatment of the hydrogen transfer motion and its interaction with all vibrations are presented. An explicit approximate reaction path, close to the minimum energy path but matching the reactive normal mode near equilibrium, allows one to predict the ground state tunnelling frequency even when using small basis sets. With a barrier of 1144 cm?1 (3.27kcal mol-1) the tunnelling splitting is predicted to be 22.0cm?1 for the parent species and 3.8 cm?1 for the species deuterated in the hydrogen bond, in good agreement with the observed values 21.6 and 2.9 cm?1, respectively. Predicted energy levels for excited states of the hydrogen transfer motion and for the non-reactive vibrations suggest a re-examination of the vibrational spectra and an extension of the number of vibrational factors in the basis set to improve the results for the vibrationally excited states.  相似文献   
100.
In modelling the retention of ultrafiltration membranes, diffusive fluxes across the membrane have usually been neglected, mainly due to evidence derived from using symmetric track-etched membranes. The present paper reexamines this matter specifically for the case of “real” asymmetric membranes. A critical literature review on the use of irreversible thermodynamic (IT), hydrodynamic and Stefan-Maxwell (S-M) models is presented. It is shown that all three approaches yield the same basic retention equation for the case of non-negligible diffusive solute-flux. It is also shown that, for membranes with a coefficient close to one, a much simpler equation gives results almost identical to the more rigorous basic equation just mentioned. Furthermore an overview of available literature data indicates that diffusive fluxes do play a non-negligible role in the functioning of asymmetric ultrafiltration membranes. Further work is needed in order to predict solute transport properties in hydrodynamic terms. A simplified Stefan-Maxwell approach seems the appropriate tool for future work in studying multicomponent solutions.  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