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   1222篇
  免费   384篇
  国内免费   306篇
化学   1237篇
晶体学   5篇
力学   3篇
数学   4篇
物理学   663篇
  2023年   100篇
  2022年   42篇
  2021年   86篇
  2020年   119篇
  2019年   83篇
  2018年   107篇
  2017年   61篇
  2016年   92篇
  2015年   70篇
  2014年   86篇
  2013年   114篇
  2012年   152篇
  2011年   153篇
  2010年   105篇
  2009年   107篇
  2008年   127篇
  2007年   103篇
  2006年   125篇
  2005年   66篇
  2004年   13篇
  1985年   1篇
排序方式: 共有1912条查询结果,搜索用时 19 毫秒
1.
R. A. Marcus在他开拓性的工作中,考察了溶剂化效应对电子转移过程的影响,并给出了著名的非绝热电子转移速率公式. 本文基于热力学溶剂化势能面的分析,从Rice-Ramsperger-Kassel-Marcus理论的角度重新考察了Marcus的公式. 由类比Rice-Ramsperger-Kassel-Marcus得到的理论,不仅可以适用于线性溶剂化的情形并得到Marcus的速率公式,也同样可以用于非线性溶剂化的情形. 在非线性溶剂化的情形下,会存在溶剂化势能面的多点交叉. 本文平行地考察了Fermi黄金规则给出的相应结果,并对比本工作中所提出的Rice-Ramsperger-Kassel-Marcus类似理论进行了批判性的讨论. 作为例释,考察了二次型溶剂化的情形. 对于这种情形,物理上存在良好的描述方案.  相似文献   
2.
Hu  Duo-Duo  Gao  Qian  Dai  Jing-Cheng  Cui  Ru  Li  Yuan-Bo  Li  Yuan-Ming  Zhou  Xiao-Guo  Bian  Kang-Jie  Wu  Bing-Bing  Zhang  Kai-Fan  Wang  Xi-Sheng  Li  Yan 《中国科学:化学(英文版)》2022,65(4):753-761
Science China Chemistry - A light-induced, nickel-catalyzed three-component arylsulfonation of 1,3-enynes in the absence of photocatalyst is reported. This methodology exhibited mild conditions,...  相似文献   
3.
《中国化学快报》2022,33(8):4048-4052
A series of pyrazolone derivatives bearing a tetrasubstituted chiral center were prepared by virtue of a Lewis acid-catalyzed Friedel-Crafts reaction, in which a chiral copper complexes was employed as the catalyst. This reaction can be carried out smoothly under mild condition to afford the pyrazolone derivatives with high yields (up to 85%) and excellent enantioselectivities (up to 99%).
  1. Download : Download high-res image (90KB)
  2. Download : Download full-size image
  相似文献   
4.
《中国物理 B》2021,30(7):77501-077501
The magnetism and magnetocaloric effect(MCE) of rare-earth-based tungstate compounds R_3 BWO_9(R=Gd,Dy,Ho) have been studied by magnetic susceptibility,isothermal magnetization,and specific heat measurements.No obvious long-range magnetic ordering can be found down to 2 K.The Curie-Weiss fitting and magnetic susceptibilities under different applied fields reveal the existence of weak short-range antiferromagnetic couplings at low temperature in these systems.The calculations of isothermal magnetization exhibit a giant MCE with the maximum changes of magnetic entropy being 54.80 J/kg-K at 2 K for Gd_3 BWO_9,28.5 J/kg-K at 6 K for Dy_3 BWO_9,and 29.76 J/kg-K at 4 K for Ho_3 BWO_9,respectively,under a field change of 0-7 T.Especially for Gd_3 BWO_9,the maximum value of magnetic entropy change(-ΔS_M~(max)) and adiabatic temperature change(-ΔT_(ad)~(max)) are 36.75 J/kg·K and 5.56 K for a low field change of 0-3 T,indicating a promising application for low temperature magnetic refrigeration.  相似文献   
5.
We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues.  相似文献   
6.
We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe5 thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature Tp.Below Tp,the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe5 thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.  相似文献   
7.
许多物理、化学和生物过程发生于气液界面,且受到局域微观结构的深远影响. 不同于液体的体相,分子取向是界面处微观结构突出的不对称特征之一. 本文综述了电子碰撞时间延迟质谱方法和近期取得的进展. 利用这个崭新的方法,不仅可以侦测得到利用小角度X射线或中子散射以及振动和频光谱方法获得的界面微观结构,同时也提供了一种研究气液界面处电子驱动化学反应的实验方案.  相似文献   
8.
Yuan Gao 《中国物理 B》2022,31(10):107304-107304
Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI3 and ScCl2 is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability.  相似文献   
9.
Photocatalytic reduction of CO2 is one important approach to alleviate greenhouse gas emission and energy crisis, which has gained huge attention in the past decades. However, the lack of understanding complex reaction mechanism impedes new catalysts design. It is also very difficult to understand the mechanism by using only experimental approaches. For this concern, theoretical calculations can effectively supplement the experimental deficiency and thus play an important role. Recently theoretical calculations have been performed on adsorption, migration and reduction of CO2 molecule on the photocatalyst surface, leading to useful information that have contributed greatly to this field. This review summarizes recent advances in first-principles calculations about CO2 photoreduction over various semiconductor photocatalysts like metal oxides, sulfides and g-C3N4. The methods, models, adsorption and reaction pathways have been discussed in detail. The perspective about future investigation on the photocatalytic reduction of CO2 using first principles calculations is also presented.  相似文献   
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