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   308591篇
  免费   2182篇
  国内免费   887篇
化学   133475篇
晶体学   4107篇
力学   18242篇
综合类   4篇
数学   64589篇
物理学   91243篇
  2021年   1409篇
  2020年   1565篇
  2019年   1653篇
  2018年   18614篇
  2017年   19180篇
  2016年   11582篇
  2015年   3405篇
  2014年   3212篇
  2013年   7292篇
  2012年   12371篇
  2011年   26350篇
  2010年   15736篇
  2009年   16172篇
  2008年   21214篇
  2007年   26037篇
  2006年   5976篇
  2005年   12821篇
  2004年   9222篇
  2003年   9191篇
  2002年   6355篇
  2001年   5955篇
  2000年   4550篇
  1999年   3280篇
  1998年   2355篇
  1997年   2378篇
  1996年   2400篇
  1995年   2121篇
  1994年   2077篇
  1993年   1894篇
  1992年   2337篇
  1991年   2429篇
  1990年   2259篇
  1989年   2227篇
  1988年   2201篇
  1987年   2212篇
  1986年   2012篇
  1985年   2483篇
  1984年   2516篇
  1983年   2013篇
  1982年   2032篇
  1981年   1863篇
  1980年   1857篇
  1979年   2148篇
  1978年   2237篇
  1977年   2093篇
  1976年   2054篇
  1975年   1917篇
  1974年   1891篇
  1973年   1980篇
  1972年   1283篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
2.
Chromatographia - We developed a simple, rapid, ecological RP-HPLC method for the estimation of Pitavastatin (PIT), Fenofibrate (FEN), and their impurities in a novel fixed dose combination. We...  相似文献   
3.
Molecular Diversity - The preparation, characterization and application of hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for...  相似文献   
4.

In the present research, magnesium aluminate spinel was prepared as catalyst support using a novel, facile, and efficient mechanochemical method. The Co-promoted catalysts with 20 wt.% of Ni were fabricated using an impregnation route and the samples were analyzed by the X-ray diffraction (XRD), N2 adsorption/desorption (BET), temperature-programmed reduction and desorption (H2-TPR and O2-TPD), and field emission scanning electron microscopy (FESEM) tests. The results confirmed that all samples have a mesoporous structure with a high specific surface area and the presence of cobalt caused complete CH4 oxidation at low temperatures, and no side reactions were observed. The results indicated that the 3%Co-20%Ni/MgAl2O4 catalyst was the optimal sample among the prepared catalysts, owing to the improvement of reduction features and oxygen mobility. The 50 and 90% of methane conversion was obtained at 530 and 600 °C, respectively. Also, the influence of calcination temperature, GHSV, and feed ratio was determined on the catalytic activity. The obtained outcomes revealed that the calcination temperature has a significant effect on the textural properties and catalytic efficiency. The sample calcined at 700 °C showed the weakest performance, which was related to the sintering of particles at high temperatures. The catalytic stability showed that the 3%Co-20%Ni/MgAl2O4 has acceptable stability during 600 min time of reaction.

Graphical abstract
  相似文献   
5.
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial...  相似文献   
6.
Journal of Structural Chemistry - A new polymorph of the [ReCl3(MeCN)(PPh3)2] complex is synthesized and characterized by single crystal X-ray diffraction (XRD). Its recrystallization from the...  相似文献   
7.
Journal of Structural Chemistry - Atomic and electronic structures of cyclic organosilicon compound 9,9,10,10-tetraethynyl-9,10-dihydrodisilaanthracene are studied by the density functional theory....  相似文献   
8.
Molecular Diversity - A new series of azo chromene dyes were synthesized via a facile cyclocondensation reaction of (E)-1,2-diphenyl-1-diazene and 4-aminocoumarin with 1:2 molar ratio catalyzed by...  相似文献   
9.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
10.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

  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