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   475篇
  免费   22篇
  国内免费   111篇
化学   470篇
晶体学   10篇
力学   3篇
综合类   1篇
物理学   124篇
  2024年   1篇
  2022年   5篇
  2021年   8篇
  2020年   12篇
  2019年   13篇
  2018年   8篇
  2017年   13篇
  2016年   8篇
  2015年   10篇
  2014年   18篇
  2013年   35篇
  2012年   29篇
  2011年   35篇
  2010年   18篇
  2009年   38篇
  2008年   25篇
  2007年   29篇
  2006年   31篇
  2005年   14篇
  2004年   30篇
  2003年   20篇
  2002年   15篇
  2001年   19篇
  2000年   19篇
  1999年   18篇
  1998年   17篇
  1997年   22篇
  1996年   11篇
  1995年   18篇
  1994年   12篇
  1993年   11篇
  1992年   9篇
  1991年   10篇
  1990年   12篇
  1989年   6篇
  1988年   5篇
  1982年   1篇
  1981年   1篇
  1977年   1篇
  1974年   1篇
排序方式: 共有608条查询结果,搜索用时 15 毫秒
101.
High-quality and crack-free Y2O3 single crystals containing low concentrations of Tm3+, Tb3+ and Yb3+ were obtained. The crystals were grown in the form of monocrystalline fibers by using a floating zone method with laser heating (laser-heated pedestal growth).  相似文献   
102.
采用光催化法对造纸废水的处理进行了研究.探讨了光催化反应机理,比较了光催化剂的活性顺序,讨论了复相光催化剂的组成、用量、试液pH值、光照时间与COD、色度去除率的关系.实验结果表明:采用WO3/α-Fe2O3/W为复相光催化剂,其组成为WO3:α-Fe2O3:W=75:24:1,当其用量为0.500g、pH=6.5、光照22h,造纸废水的COD和色度去除率分别达到68.3%和71.2%.  相似文献   
103.
104.
CCD-ICP-AES内标法同时测定化肥中12种有害元素   总被引:1,自引:0,他引:1  
研究了采用CCD-ICP-AES同时测定化肥中As、Cd、Co、Cr、Cu、Hg、Mo、Ni、Pb、Sb、Se和Zn等12种有害元素的方法.采用微波消解法处理样品,加入Y作为内标,消除了化肥基体对测定结果的干扰效应.方法对化肥中各元素的测定回收率在81.6%~120%之间,测定精密度在0.7%~13.8%之间.用该法测定了两种国家标准物质.  相似文献   
105.
摘 要:基于第一性原理的计算方法,建立了本征石墨烯、空位石墨烯及钇( Y)掺杂空位石墨烯模型,并计算了CO、NO在三类石墨烯表面的吸附过程. 从表面能、吸附结构、吸附能和态密度四个方面进行分析讨论,研究掺杂Y对CO、NO气体吸附性能的影响. 结果表明:CO、NO与本征石墨烯之间的吸附为弱的物理吸附,掺杂Y后增强了材料表面对CO、NO的吸附效果,最大吸附能分别为7.414eV、6.702eV,属于化学吸附;掺杂Y使空位石墨烯费米能级附近有了更多的活跃电子,其吸附NO后体系由半金属转变为金属特性,该特性能为开发更加优良的石墨烯气敏材料提供理论支持.  相似文献   
106.
Xenon trioxide (XeO3) forms adducts with triphenylphosphine oxide, dimethylsulfoxide, pyridine-N-oxide, and acetone by coordination of the ligand oxygen atoms to the XeVI atom of XeO3. The crystalline adducts were characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. Unlike solid XeO3, which detonates when mechanically or thermally shocked, solid (C5H5NO)3(XeO3)2, [(C6H5)3PO]2XeO3, and [(CH3)2SO]3(XeO3)2 are insensitive to mechanical shock. The [(CH3)2SO]3(XeO3)2 adduct slowly decomposes over several days to (CH3)2SO2, Xe, and O2. All three complexes undergo rapid deflagration when ignited by a flame. Both [(C6H5)3PO]2XeO3 and (C5H5NO)3(XeO3)2 are room-temperature stable and the [(CH3)2CO]3XeO3 complex dissociates at room temperature to form a stable solution of XeO3 in acetone. The xenon coordination sphere of [(C6H5)3PO]2XeO3, a distorted square-pyramid, provides the first example of a five-coordinate XeO3 complex with only two Xe- - -O adduct bonds. The xenon coordination spheres of the remaining adducts are distorted octahedra, comprised of three Xe- - -O secondary bonds that are approximately trans to the primary Xe−O bonds of XeO3. Quantum-chemical calculations were used to assess the nature of the Xe- - -O adduct bonds, which are described as predominantly electrostatic bonds between the nucleophilic oxygen atoms of the bases and the σ-holes of the electrophilic xenon atoms.  相似文献   
107.
《中国化学快报》2020,31(10):2849-2853
A magnetic mesoporous expanded perlite-based (EPd-APTES@Fe3O4) composite was designed and synthesized as a novel adsorbent for enrichment of rare earth ions in aqueous solution. Effect of various factors including the pH of solution, contact time and adsorbent dosage on the adsorption behaviors of yttrium(III) by the EPd-APTES@Fe3O4 nano-material composites from aqueous solution was investigated. The maximum adsorption capacity of the as-prepared materials for yttrium(III) ions was 383.2 mg/g. Among the various isotherm models, the Freundlich isotherm model could well described for the adsorption of the rare earth ions at pH 5.5 and 298.15 K. The kinetic analysis indicated that the adsorption process followed the pseudo-second order kinetics model, and the rate-determining step might be chemical adsorption. Thermodynamic parameters declared that the adsorption process was endothermic. In addition, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and the quantum chemical calculation indicated that the yttrium(III) ions were captured on the EPd-APTES@Fe3O4 surface mainly by coordination with functional group of -NH2. More importantly, the adsorption-desorption studies indicated that the EPd-APTES@Fe3O4 nano-material composites had a high stability and good recyclability.  相似文献   
108.
本文采用中阶梯光栅光谱仪,直流等离子体光谱法测定高纯(99.99%)氯化镧、氧化钇中稀土杂质元素,由于仪器具有很高的色散率,因而方法具有灵敏度高、干扰少的特点。  相似文献   
109.
We report the results of a wide experimental study of the irreversible modulated microwave absorption as a function of temperature, applied magnetic field and modulation amplitude in the YBa2Cu3Ox single crystals. To analyze the experimental data the model of the microwave power dissipation by the flux lines has been developed taking into account thermal fluctuations, the distributions of currents and vortices over a sample. We have obtained the information about regimes of vortex motion in the different areas of the HT phase diagram and estimated the values of flux flow viscosity and critical current density.  相似文献   
110.
Chemiluminescence has been observed in the reduction of perchloric aqueous solutions of XeO3 with Eu2+ ions, Fast (several seconds) consumption of EuII occurs when the ratio of the initial concentrations of the reactants (Eu2+]0 : [XeO3]0 < 6; however, the chemiluminescence remains sufficiently bright and prolonged (up to –10 min after nearly complete oxidation of EuII to EuIII). The assumption was made that intermediates in the reduction of XeO3 participate in the chemiluminescent stages of the process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2909–2911, December, 1996.  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