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   1354913篇
  免费   29728篇
  国内免费   7683篇
化学   671676篇
晶体学   14588篇
力学   75585篇
综合类   113篇
数学   244631篇
物理学   385731篇
  2021年   12677篇
  2020年   15918篇
  2019年   16034篇
  2018年   15837篇
  2017年   14485篇
  2016年   29205篇
  2015年   21034篇
  2014年   30366篇
  2013年   74231篇
  2012年   40746篇
  2011年   40772篇
  2010年   39698篇
  2009年   41676篇
  2008年   39282篇
  2007年   36040篇
  2006年   38201篇
  2005年   33204篇
  2004年   32784篇
  2003年   29509篇
  2002年   26677篇
  2001年   27685篇
  2000年   23046篇
  1999年   20382篇
  1998年   18794篇
  1997年   19352篇
  1996年   19229篇
  1995年   18540篇
  1994年   18090篇
  1993年   17600篇
  1992年   17611篇
  1991年   17870篇
  1990年   17086篇
  1989年   17153篇
  1988年   16825篇
  1987年   16748篇
  1986年   15625篇
  1985年   22141篇
  1984年   23458篇
  1983年   19576篇
  1982年   21234篇
  1981年   20463篇
  1980年   19760篇
  1979年   20110篇
  1978年   21425篇
  1977年   21079篇
  1976年   20802篇
  1975年   19514篇
  1974年   19165篇
  1973年   19700篇
  1972年   14196篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Russian Journal of General Chemistry - On the basis of 4-(thien-2-yl)-3-aminopyridine-2(1H)-one, the corresponding chloroacetamide and condensed 1H-pyrido[2,3-b][1,4]oxazine-2(3H)-one were...  相似文献   
12.
A new series of azomethine-functionalized compounds was synthesized from the condensation of 2-hydroxy-1,3-propanediamine and 2-thienylcarboxaldehydes in the presence of a drying agent. The derivatives were spectroscopically characterized by NMR, LC-MS, UV/Vis, IR and elemental analysis. Variable temperature 1H-NMR (−60 to +60 °C) was performed to investigate the effect of solvent polarity; the capability of solvent to form H-bond was found to dramatically influencing the tautomerization process of the desired structures. The calculated thermochemical parameters (ΔH298, ΔG298 and ΔS298) at DFT and MP2 levels of theory explained that 3 b exists in equilibrium with two tautomers. The basis of the electronic absorptions was pursued through Time-Dependent Density-Functional Theory (TD-DFT). Analysis of the structural surfaces was inspected and the molecular electrostatic potential (MEP) demonstrated that the three functionalized compounds were relatively analogous in the electronic distributions. Furthermore, the electrophilic and nucleophilic centers lying on the molecular surfaces were probably playing a key-role in stabilizing the compounds through the nonclassical C−H⋅⋅⋅π interactions and hydrogen bonding. The impact of solvent polarity on absorption spectra were investigated via solvatochromic shifts. For instance, compound 3 c displayed a gradual shift of the maximum absorption to the red area when the solvent polarity was increased, recording a 21 nm of bathochromic shift. In contrast, no significant solvent-effect on 3 a and 3 b was observed. The solvation relation was pursued between Gutmann's donicity numbers the experimental λmax; exhibited almost positive linear performance with a minor oscillation, that ascribe to the possible weak interface between the molecules of solute and designated solvents. The bandgap energy of all products were assessed experimentally using optical absorption spectra following Tauc approach, giving −4.050 ( 3 a ), −3.900 ( 3 b ) and −3.210 ( 3 c ) eV. However, the ΔE were computationally figured out from TD-DFT simulation to be −4.258 ( 3 a ), −4.022 ( 3 b ) and −3.390 ( 3 c ) eV.  相似文献   
13.
Circularly polarized luminescence (CPL) has attracted attention as a next-generation light signal because of its carrying more information compared with normal and linearly polarized lights as well as its potential wide application in information fields. Recently, much attention has been paid to small organic molecules-based CPL emitters because of easy synthesis, fine structural modification at molecular level, and tunable wide range emission wavelength. This review highlights the development of small organic molecules-based CPL emitters in the past 5 years (2017–2021). The progress suggests that small organic molecules-based CPL emitters provide a simple and efficient way to generate CPL.  相似文献   
14.
Li  Zh.  Zhang  Y.  Wang  R.  Jiang  D. 《Journal of Applied Spectroscopy》2022,89(2):371-380
Journal of Applied Spectroscopy - The concentration of heavy metals in drinking water is an important standard for water quality evaluation and water pipeline corrosion detection. This research...  相似文献   
15.
Journal of Thermal Analysis and Calorimetry - The paper focuses on the analytical analysis of the propagation of a normal shock wave in an adiabatic gas flow with nanoparticles. A modified...  相似文献   
16.
Journal of Solid State Electrochemistry - The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small...  相似文献   
17.
Annals of Operations Research - In recent years, operations research in agriculture has improved the harvested yield, reduced the cost and time required for field operations, and maintained...  相似文献   
18.
Physics of the Solid State - Using the X-ray diffraction and electron microscopy methods, the structure and the elemental and phase compositions of hypereutectic alloy Al86Ni2Co6Gd6 (hereinafter,...  相似文献   
19.
Russian Physics Journal - The results of a study of the dislocation structure evolution in polycrystals of homogeneous solid solutions in low-stability states in Cu-Mn-based alloys with FCC crystal...  相似文献   
20.
Russian Physics Journal - Aiming at problems of low probability of interception and poor anti-jamming performance of the multi-output radar, the numerical simulation based on a chaos optimization...  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