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   217203篇
  免费   2640篇
  国内免费   625篇
化学   120951篇
晶体学   3772篇
力学   8472篇
综合类   11篇
数学   21634篇
物理学   65628篇
  2020年   1921篇
  2019年   2106篇
  2018年   2414篇
  2017年   2495篇
  2016年   3804篇
  2015年   2442篇
  2014年   3850篇
  2013年   9815篇
  2012年   7213篇
  2011年   8967篇
  2010年   6147篇
  2009年   6070篇
  2008年   7925篇
  2007年   7899篇
  2006年   7567篇
  2005年   6858篇
  2004年   6265篇
  2003年   5761篇
  2002年   5497篇
  2001年   6352篇
  2000年   4813篇
  1999年   3671篇
  1998年   2926篇
  1997年   2888篇
  1996年   2812篇
  1995年   2611篇
  1994年   2501篇
  1993年   2305篇
  1992年   2969篇
  1991年   2869篇
  1990年   2799篇
  1989年   2806篇
  1988年   2852篇
  1987年   2862篇
  1986年   2695篇
  1985年   3509篇
  1984年   3531篇
  1983年   2762篇
  1982年   2945篇
  1981年   2966篇
  1980年   2742篇
  1979年   3070篇
  1978年   3053篇
  1977年   3147篇
  1976年   2985篇
  1975年   2698篇
  1974年   2669篇
  1973年   2611篇
  1972年   1776篇
  1968年   1741篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
71.

The adsorption and photocatalytic degradation of Ethyl methylphosphonate (EMPA) on powdery TiO2 film has experimentally investigated using attenuated total reflection-infrared Fourier transform spectroscopy (ATR-FTIR) in ambient condition. Characteristic IR frequency as P-O-C vibration mode as EtO was observed by EMPA adsorbed at the surface of TiO2. By TiO2 photocatalysis, the adsorbed EMPA was decomposed to methyl phosphonic acid and phosphoric acid. The increment of IR intensity of which is assigned to Ti–O-P-O-Ti of EMPA was accompanied with increasing the IR peak intensity assigned to MPA. About that, we suggest that the appearance of the Ti–O-P-O-Ti of EMPA by the TiO2 photocatalysis is regarded as acceleration of the hydrolysis of EMPA by the surface OH groups of TiO2. The plausible adsorption structure and the photocatalytic reaction mechanism of EMPA at the surface of TiO2 photocatalyst were elucidated.

  相似文献   
72.
73.
74.
75.
Journal of Thermal Analysis and Calorimetry - The operating temperature of Li-ion batteries used in modern electric vehicles should be maintained within an allowable range to avoid thermal runaway...  相似文献   
76.
77.
78.
79.
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.  相似文献   
80.
Following a thermal reduction method, platinum nanoparticles were synthesized and stabilized by polyvinylpyrrolidone. The colloidal platinum nanoparticles were stable for more than 3 months. The micrograph analysis unveiled that the colloidal platinum nanoparticles were well dispersed with an average size of 2.53 nm. The sol–gel‐based inverse micelle strategy was applied to synthesize mesoporous iron oxide material. The colloidal platinum nanoparticles were deposited on mesoporous iron oxide through the capillary inclusion method. The small‐angle X‐ray scattering analysis indicated that the dimension of platinum nanoparticles deposited on mesoporous iron oxide (Pt‐Fe2O3) was 2.64 nm. X‐ray photoelectron spectroscopy (XPS) data showed that the binding energy on Pt‐Fe2O3 surface decreased owing to mesoporous support–nanoparticle interaction. Both colloidal and deposited platinum nanocatalysts improved the degradation of methyl orange under reduction conditions. The activation energy on the deposited platinum nanocatalyst interface (2.66 kJ mol?1) was significantly lowered compared with the one on the colloidal platinum nanocatalyst interface (40.63 ± 0.53 kJ mol?1).  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