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   329篇
  免费   37篇
  国内免费   27篇
化学   275篇
晶体学   4篇
力学   11篇
综合类   3篇
数学   49篇
物理学   51篇
  2023年   4篇
  2021年   4篇
  2019年   7篇
  2018年   14篇
  2017年   8篇
  2016年   10篇
  2015年   8篇
  2014年   14篇
  2013年   29篇
  2012年   16篇
  2011年   12篇
  2010年   12篇
  2009年   16篇
  2008年   19篇
  2007年   19篇
  2006年   13篇
  2005年   15篇
  2004年   9篇
  2003年   10篇
  2002年   12篇
  2001年   11篇
  2000年   10篇
  1999年   5篇
  1998年   4篇
  1997年   7篇
  1996年   4篇
  1994年   2篇
  1993年   3篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   8篇
  1987年   6篇
  1986年   3篇
  1985年   3篇
  1983年   3篇
  1982年   5篇
  1981年   3篇
  1980年   4篇
  1978年   3篇
  1977年   3篇
  1976年   9篇
  1975年   4篇
  1974年   6篇
  1973年   4篇
  1972年   2篇
  1971年   2篇
  1970年   3篇
  1967年   2篇
  1966年   5篇
排序方式: 共有393条查询结果,搜索用时 344 毫秒
81.
The detection of TNT and related nitroaromatic compounds in seawater is of great interest. Electrochemical techniques can be applied for detection purposes since nitroaromatic compounds contain easily reducible nitro groups. In this study, we investigate the performance of thermally reduced graphenes prepared by three different oxidative methods: Hummers, Staudenmaier and Hofmann methods with consequent thermal exfoliation. The Hofmann method‐based graphene was found to exhibit the highest sensitivity in detecting TNT electrochemically. Extended study on the detection of TNT in seawater using the graphene material provided significant improvements in the detection sensitivity. These findings will have profound impacts on the detection of nitroaromatic explosives in seawater.  相似文献   
82.
An evaporation/condensation flow cell was developed and interfaced with the matrix-assistedlaser desorption/ionization (MALDI) time-of-flight mass spectrometer for on-line bioaerosoldetection and characterization, which allows matrix addition by condensation onto the laboratory-generated bioaerosol particles. The final coated particle exiting from the con-denser is then introduced into the aerodynamic particle sizer spectrometer or home-built aerosol laser time-of-flight mass spectrometer, and its aerodynamic size directly effects on the matrix-to-analyte molar ratio, which is very important for MALDI technique. In order to observe the protonated analyte molecular ion, and then determine the classification of bi-ological aerosols, the matrix-to-analyte molar ratio must be appropriate. Four experimental parameters, including the temperature of the heated reservoir, the initial particle size, its number concentration, and the matrix material, were tested experimentally to analyze their influences on the final particle size. This technique represents an on-line system of detec-tion that has the potential to provide rapid and reliable identification of airborne biological aerosols.  相似文献   
83.
采用硝酸-双氧水对槲寄生全药及煎煮液进行湿法消解,用电感耦合等离子体原子发射光谱法(ICP-AES)同时测定试样中Cu,Mg,Zn,Mn,Ni,Se,K,Na,Ca和Fe等元素的含量。该法的的加标回收率为91.6%~108.9%,变异系数为0.47%~4.59%,具有良好的准确度和精密度。结果表明:槲寄生中含有丰富的K和Ca元素,Na和Mg的含量也相对丰富,为进一步研究槲寄生的药理提供了科学的数据。  相似文献   
84.
The aim of this study is to efficiently utilize catalytic properties of silver nanoparticles and nitrogen doped graphene and their combined synergistic effect. For this purpose, nitrogen doped reduced graphene oxide-silver (NrGO-Ag) nanocomposites were synthesized by a facile, environmentally friendly, one-pot hydrothermal method for the first time and characterized by UV–Vis, FTIR, XRD, XPS, SEM, and TEM. Catalytic activity of the synthesized nanocomposites was tested against 4-nitrophenol (4-NP) and methylene blue (MB) reduction reactions in the presence of NaBH4. Total degradation was achieved in both reactions in 210 and 44 s, and pseudo first order reaction rate constants were calculated as 0.0071 and 0.0322 s−1 for 4-NP and MB reduction reactions, respectively.  相似文献   
85.
Oxidative dimerizations of some naphthalene derivatives were studied. With vanadium oxytrichloride either a new C-C bond formation occured or the reagent caused chlorination of the ring. Attempts to induce photochemically a new C-C bond failed.
Versuche zur Herstellung einiger Binaphthalin-Derivate
Zusammenfassung Die oxidative Dimerisierung einiger Naphthalinderivate wurde untersucht. Mit Vanadiumoxytrichlorid wird eine neue C-C-Bindung gebildet, es wurde jedoch auch Chlorierung des Naphthalinringes beobachtet. Versuche zur photochemischen Bildung einer C-C-Bindung scheiterten.
  相似文献   
86.
The incoherent radiation emanating out of the tokamak plasmas gives vital information about the electron temperature. Electron cyclotron emission (ECE) is a powerful diagnostic tool for the measurement of electron temperature due to many advantages such as the high spatial and temporal resolutions. This paper presents the sixteen channel superheterodyne radiometer as an electron cyclotron emission diagnostic to measure the electron temperature on HT-7 tokamak.  相似文献   
87.
用热扩散法将客体LiCI组装进入主体FER沸石孔道生成的客/主体材料中,客体与主体骨架在一定温度下发生相互作用,诱导该沸石发生相转变.XRD,FT-IR,TG/DTA/DTG等方法表征该客/主体材料相变过程证明,相变起始温度500℃,500~600℃生成LiAISi3O8,800℃的相变产物主要为β-石英,LiAIsi3O8的相对含量随LiCI的组装量增多而增加.  相似文献   
88.
Exposure to BPS induced glycerophospholipid fatty acid remodeling, which might be useful in toxicity evaluation for bisphenols-induced hepatic diseases.  相似文献   
89.
Summary A new binuclear NiII complex, [{(TPA)Ni(-Cl)}2]-(ClO4)2·H2O (1), where TPA = tris(2-pyridyl-methyl) amine, has been prepared and characterized. The X-ray crystal structure and variable temperature magnetic susceptibility (4–300 K) of the complex have been determined. The two NiII atoms of (1) are in a distorted octahedral environment and are bridged by Cl atoms. Ni-Cl distances are 2.363(6) and 2.503(7) Å, and the Ni-Cl-Ni angle is 92.7(2)°. The metal atoms are separated by a non-bonding distance of 3.523 Å.The effective magnetic moment of (1) increases slightly with decreasing temperature and appears to reach a maximum before decreasing. The observed data were fitted to the Heisenberg model and the results indicate that there is a ferromagnetic interaction (positive J) and weak antiferromagnetic intermolecular interaction (negative ).  相似文献   
90.
New syntheses of oxazolo[4,5—d]pyridazine derivatives7 and11 were achieved by the cyclization of substituted N-pyridazin-5-ylformamide oximes6 and10. Under mild reaction conditions the transformations of the substituted amino group at position 2 of the oxazolo[4,5—d]pyridazine system7 occured to produce the compounds11, 14, and15, while under more drastic reaction conditions the nucleophilic attack at carbon at position 2 followed by the ring opening of the oxazole part of the molecule was observed to give the compounds13, 16, 17 and18.
Transformationen von N-Heteroarylformamidinen und N-Heteroarylformamidinoximen. Neue Synthesen und Transformationen von Oxazolo[4,5—d]pyridazinen
Zusammenfassung Mittels Cyclisierung substituierter N-Pyridazin-5-ylformamidoxime6 und10 wurden neue Synthesemöglichkeiten von Oxazolo[4,5—d]pyridazinderivaten erschlossen. Bei milden Reaktionsbedingungen trat Transformation der substituierten Aminogruppe an Position 2 des Oxazolo[4,5—d]pyridazin-Systems unter Bildung der Verbindungen11, 14 und15 ein, währenddessen unter drastischeren Reaktionsbedingungen ein nucleophiler Angriff am Kohlenstoff-2, gefolgt von einer Ringöffnung unter Bildung der Verbindungen13, 16, 17 und18 eintrat.
  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