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   142079篇
  免费   23799篇
  国内免费   15200篇
化学   96237篇
晶体学   1686篇
力学   9530篇
综合类   987篇
数学   17713篇
物理学   54925篇
  2024年   150篇
  2023年   2717篇
  2022年   3052篇
  2021年   4669篇
  2020年   5570篇
  2019年   5406篇
  2018年   4703篇
  2017年   4445篇
  2016年   6753篇
  2015年   6482篇
  2014年   7925篇
  2013年   10584篇
  2012年   12741篇
  2011年   13507篇
  2010年   9152篇
  2009年   8769篇
  2008年   9395篇
  2007年   8600篇
  2006年   7714篇
  2005年   6560篇
  2004年   4903篇
  2003年   3861篇
  2002年   3543篇
  2001年   2888篇
  2000年   2681篇
  1999年   2942篇
  1998年   2558篇
  1997年   2344篇
  1996年   2417篇
  1995年   2063篇
  1994年   1959篇
  1993年   1593篇
  1992年   1424篇
  1991年   1325篇
  1990年   1085篇
  1989年   815篇
  1988年   663篇
  1987年   523篇
  1986年   505篇
  1985年   447篇
  1984年   328篇
  1983年   229篇
  1982年   199篇
  1981年   139篇
  1980年   103篇
  1979年   71篇
  1978年   58篇
  1976年   52篇
  1975年   44篇
  1974年   54篇
排序方式: 共有10000条查询结果,搜索用时 429 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
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   
6.
Bo  Luo  Gao  Wei  Yu  Yuguo  Chen  Xiaojun 《Nonlinear dynamics》2022,110(1):281-311
Nonlinear Dynamics - The perovskite solar cell (PSC) is one of the most promising photovoltaic candidates along with the highly increasing demand for green electricity. One of the main concerns...  相似文献   
7.
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   
8.
Fan  K.  Lu  R. S.  Liang  K. K.  Hou  Z. C. 《High Energy Chemistry》2022,56(4):264-269
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was...  相似文献   
9.
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