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   542449篇
  免费   18806篇
  国内免费   8682篇
化学   300144篇
晶体学   7681篇
力学   25707篇
综合类   329篇
数学   61738篇
物理学   174338篇
  2022年   5809篇
  2021年   6757篇
  2020年   7480篇
  2019年   7609篇
  2018年   8689篇
  2017年   8345篇
  2016年   12883篇
  2015年   9371篇
  2014年   13194篇
  2013年   27050篇
  2012年   23582篇
  2011年   27533篇
  2010年   19167篇
  2009年   18824篇
  2008年   23700篇
  2007年   23024篇
  2006年   21291篇
  2005年   18761篇
  2004年   16982篇
  2003年   14767篇
  2002年   14396篇
  2001年   16493篇
  2000年   12642篇
  1999年   10334篇
  1998年   8523篇
  1997年   8253篇
  1996年   7928篇
  1995年   7020篇
  1994年   6740篇
  1993年   6358篇
  1992年   7049篇
  1991年   7079篇
  1990年   6670篇
  1989年   6295篇
  1988年   6251篇
  1987年   6113篇
  1986年   5729篇
  1985年   7314篇
  1984年   7380篇
  1983年   5787篇
  1982年   5834篇
  1981年   5789篇
  1980年   5364篇
  1979年   5816篇
  1978年   5966篇
  1977年   5891篇
  1976年   5751篇
  1975年   5281篇
  1974年   5277篇
  1973年   5233篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Journal of Radioanalytical and Nuclear Chemistry - Eco-friendly and low-cost composite, amidoxime-functionalized microcrystalline cellulose/mesoporous silica (MCC/MS-AO), were synthesized by...  相似文献   
2.
3.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
4.
In this study, the transverse relaxation time (T2) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution.  相似文献   
5.
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   
6.
Zhang  Hongchi  Liu  Rui  Li  Hui  Yang  Yang  Zhou  Feng 《Chemistry of Natural Compounds》2022,58(3):541-544
Chemistry of Natural Compounds -  相似文献   
7.
Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the...  相似文献   
8.
Zhang  Bing  Yang  Jie-qin  Liu  Ying  Hu  Bin  Yang  Yang  Zhao  Li  Lu  Qiang 《Cellulose (London, England)》2022,29(12):6565-6578
Cellulose - Heating is essential in various biomass pre-treatments and thermal conversion processes. It is of practical significance to study the characteristics of cellulose-lignin and...  相似文献   
9.
Liu  Shao-Hua  Tian  Bo 《Nonlinear dynamics》2022,108(3):2471-2482
Nonlinear Dynamics - In this paper, a (2+1)-dimensional Caudrey–Dodd–Gibbon–Kotera–Sawada system is investigated in fluid mechanics via the symbolic computation. With the...  相似文献   
10.
The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom.  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