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   350652篇
  免费   56521篇
  国内免费   43382篇
化学   160584篇
晶体学   2836篇
力学   16183篇
综合类   1112篇
数学   30452篇
物理学   108297篇
综合类   131091篇
  2024年   1465篇
  2023年   4986篇
  2022年   7929篇
  2021年   8779篇
  2020年   9354篇
  2019年   11368篇
  2018年   10811篇
  2017年   11295篇
  2016年   14527篇
  2015年   15125篇
  2014年   17917篇
  2013年   21741篇
  2012年   23957篇
  2011年   25674篇
  2010年   24021篇
  2009年   23605篇
  2008年   18378篇
  2007年   17031篇
  2006年   14869篇
  2005年   14000篇
  2004年   12629篇
  2003年   10029篇
  2002年   9261篇
  2001年   8710篇
  2000年   7592篇
  1999年   10234篇
  1998年   9086篇
  1997年   8885篇
  1996年   8932篇
  1995年   8361篇
  1994年   7956篇
  1993年   7241篇
  1992年   6327篇
  1991年   5708篇
  1990年   4798篇
  1989年   4394篇
  1988年   4024篇
  1987年   2684篇
  1986年   2298篇
  1985年   1589篇
  1984年   1396篇
  1983年   644篇
  1982年   1110篇
  1981年   902篇
  1980年   888篇
  1979年   599篇
  1978年   578篇
  1977年   686篇
  1976年   1108篇
  1972年   570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.
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   
3.
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   
4.
Two series of novel alternating copolyoxamides (PAnT-alt-n2 and PAn2-alt-62) are synthesized via solution/solid-state polycondensation (SSP). The alternating structures are analyzed carefully with 1H NMR and 13C NMR spectra. The melting behaviors, thermal stabilities, crystal structures and crystallinities are systematically evaluated by DSC, TGA and WAXD. The results reveal that these alternating copolyoxamides possess almost perfect alternating chain structures and have high melting temperature (Tm > 270 °C), high crystallinity (Xc > 32%) and high decomposition temperature (T5 > 405 °C) as well as low saturated water absorption (<3.5 wt%), which suggests that they have high potential as engineering plastic of high heat resistant.  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.
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   
8.
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.  相似文献   
9.
Journal of Radioanalytical and Nuclear Chemistry - This study presents a time-efficient method of analysing 210Pb, 210Bi, and 210Po in natural waters. The optimum pH (1.00), temperature...  相似文献   
10.
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