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   9741篇
  免费   2205篇
  国内免费   1692篇
化学   4833篇
晶体学   96篇
力学   588篇
综合类   119篇
数学   1164篇
物理学   6838篇
  2024年   10篇
  2023年   94篇
  2022年   155篇
  2021年   217篇
  2020年   293篇
  2019年   212篇
  2018年   224篇
  2017年   261篇
  2016年   333篇
  2015年   396篇
  2014年   541篇
  2013年   788篇
  2012年   602篇
  2011年   737篇
  2010年   665篇
  2009年   754篇
  2008年   821篇
  2007年   845篇
  2006年   734篇
  2005年   676篇
  2004年   493篇
  2003年   552篇
  2002年   477篇
  2001年   371篇
  2000年   350篇
  1999年   309篇
  1998年   254篇
  1997年   223篇
  1996年   194篇
  1995年   151篇
  1994年   154篇
  1993年   112篇
  1992年   111篇
  1991年   95篇
  1990年   50篇
  1989年   71篇
  1988年   43篇
  1987年   39篇
  1986年   20篇
  1985年   48篇
  1984年   26篇
  1983年   15篇
  1982年   34篇
  1981年   17篇
  1980年   10篇
  1979年   14篇
  1977年   7篇
  1976年   10篇
  1974年   4篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 434 毫秒
11.
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.  相似文献   
12.
We obtained the azo‐imine ligand (2,2′‐[4‐(5‐methoxy salicylidene‐4‐iminophenylazo)phenylimino]diethanol) (HL) and its Cu (II) complex (CuL) from the ethanol solution. The complex Cu(L)2 was obtained as single crystals from the CH3OH solution and structurally characterized. The electronic and photoluminescence properties of the ligand and its Cu (II) complex were investigated both in DMF solution and solid state. The oxidation and reduction behaviours of the compounds were studied in the solution and found that the redox processes are irreversible. Thermal studies show that the ligand has higher thermal stability than the CuL complex. Single crystals of the complex were obtained from slow evaporation of a DMF solution of the complex. Crystals of the complex showed a diffraction pattern; however, the structure of the complex was able to be solved.  相似文献   
13.
A generalization of the Mattis-Nam model Mattis and Nam (1972) [7], which takes into account a correlated hopping and pairing of electrons, is proposed, its exact solution is obtained. In the framework of the model the stability of the zero energy Majorana fermions localized at the boundaries is studied in the chain in which electrons interact through both the on-site Hubbard interaction and the correlated hopping and pairing. The ground-state phase diagram of the model is calculated, the region of existence of topological states is determined. It is shown that low-energy excitations destroy bonds between electrons in the chain, leading to an insulator state.  相似文献   
14.
利用高温固相法成功制备了Er~(3+)单掺、Er~(3+)/Yb~(3+)共掺杂Ca_(12)Al_(14)O_(32)F_2上转换发光样品。在980 nm激光激发下,Er~(3+)单掺和Er~(3+)/Yb~(3+)共掺杂样品均呈现出较强的绿光(528,549 nm)和较弱的红光(655 nm)发射,分别归因于Er~(3+)离子的~2H_(11/2),~4S_(3/2)→~4I_(15/2)和~4F_(9/2)→~4I_(15/2)能级跃迁。随着Er离子浓度的增加,单掺杂样品上转换发光强度先增大后减小,最佳掺杂浓度为0.8%。共掺杂Yb~(3+)后,Er~(3+)的发光强度明显增大。还原气氛下合成的样品上转换发光强度增大约两倍,可能和笼中阴离子基团变化有关。发光强度和激发光功率的关系表明所得上转换发射为双光子吸收过程,借助Er~(3+)-Yb~(3+)体系能级结构详细讨论了上转换发射的跃迁机制。  相似文献   
15.
One of the most important multipartite entangled states, Greenberger–Horne–Zeilinger state (GHZ), serves as a fundamental resource for quantum foundation test, quantum communication and quantum computation. To increase the number of entangled particles, significant experimental efforts should been invested due to the complexity of optical setup and the difficulty in maintaining the coherence condition for high-fidelity GHZ state. Here, we propose an ultra-integrated scalable on-chip GHZ state generation scheme based on frequency combs. By designing several microrings pumped by different lasers, multiple partially overlapped quantum frequency combs are generated to supply as the basis for on-chip polarization-encoded GHZ state with each qubit occupying a certain spectral mode. Both even and odd numbers of GHZ states can be engineered with constant small number of integrated components and easily scaled up on the same chip by only adjusting one of the pump wavelengths. In addition, we give the on-chip design of projection measurement for characterizing GHZ states and show the reconfigurability of the state. Our proposal is rather simple and feasible within the existing fabrication technologies and we believe it will boost the development of multiphoton technologies.  相似文献   
16.
17.
电子、激子和声子等量子态在固体中的行为早已被人们所熟知. 然而,当体系的尺寸只有纳米量级的时候,已有的固体理论常常不能适用,需要新的低维物理理论的建立. 我们系统研究了低维体系限域量子态(包括电子、激子和声子)的行为对环境、应力、压力及光的响应和性质的调控. 较早认识到低维体系之显著的表面-体积比对量子态性质调控之有效性,系统地揭示了低维体系的一系列由表面和应力决定的新颖性质,证明了低维体系的表面和应力效应同量子限域效应同等重要. 本文概况了如下五个方面的结果:(1)一种使用应力效应调控电子能带结构的方法和(2)一种使用表面效应调控电子能带结构的方法(这两个方法都可将低维体系能带从间接能隙调控至直接能隙能带结构);(3)一种低维体系表面掺杂方法,该方法将在低维体系掺杂中取代传统方法;(4)量子点表面诱导的光致异构现象;(5)基于表面自催化半导体低维结构的形成机理. 希望我们的研究工作有助于促进低维体系在光电子、纳电子、环境、能源、生物和医学等领域的应用.  相似文献   
18.
Through a solid‐state reaction, a practically phase pure powder of Ba3V2S4O3 was obtained. The crystal structure was confirmed by X‐ray single‐crystal and synchrotron X‐ray powder diffraction (P63, a=10.1620(2), c=5.93212(1) Å). X‐ray absorption spectroscopy, in conjunction with multiplet calculations, clearly describes the vanadium in charge‐disproportionated VIIIS6 and VVSO3 coordinations. The compound is shown to be a strongly correlated Mott insulator, which contradicts previous predictions. Magnetic and specific heat measurements suggest dominant antiferromagnetic spin interactions concomitant with a weak residual ferromagnetic component, and that intrinsic geometric frustration prevents long‐range order from evolving.  相似文献   
19.
20.
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