全文获取类型
收费全文 | 1255651篇 |
免费 | 29593篇 |
国内免费 | 7585篇 |
专业分类
化学 | 614504篇 |
晶体学 | 14196篇 |
力学 | 73295篇 |
综合类 | 102篇 |
数学 | 237235篇 |
物理学 | 353497篇 |
出版年
2021年 | 12884篇 |
2020年 | 15857篇 |
2019年 | 15985篇 |
2016年 | 27338篇 |
2015年 | 20590篇 |
2014年 | 30235篇 |
2013年 | 74006篇 |
2012年 | 34830篇 |
2011年 | 29493篇 |
2010年 | 35486篇 |
2009年 | 38389篇 |
2008年 | 29731篇 |
2007年 | 24738篇 |
2006年 | 32137篇 |
2005年 | 24229篇 |
2004年 | 26310篇 |
2003年 | 25392篇 |
2002年 | 26806篇 |
2001年 | 24757篇 |
2000年 | 22447篇 |
1999年 | 18945篇 |
1998年 | 18249篇 |
1997年 | 18921篇 |
1996年 | 18962篇 |
1995年 | 18383篇 |
1994年 | 17902篇 |
1993年 | 17380篇 |
1992年 | 16899篇 |
1991年 | 17246篇 |
1990年 | 16496篇 |
1989年 | 16584篇 |
1988年 | 16177篇 |
1987年 | 16234篇 |
1986年 | 15091篇 |
1985年 | 21657篇 |
1984年 | 23111篇 |
1983年 | 19297篇 |
1982年 | 21089篇 |
1981年 | 20324篇 |
1980年 | 19634篇 |
1979年 | 19767篇 |
1978年 | 21204篇 |
1977年 | 20818篇 |
1976年 | 20497篇 |
1975年 | 19182篇 |
1974年 | 18799篇 |
1973年 | 19318篇 |
1972年 | 13859篇 |
1968年 | 11926篇 |
1967年 | 12305篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Palamarchuk I. V. Shulgau Z. T. Sergazy Sh. D. Zhulikeeva A. M. Seilkhanov T. M. Kulakov I. V. 《Russian Journal of General Chemistry》2022,92(9):1692-1705
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.
Dr. Kifah S. M. Salih 《ChemistryOpen》2022,11(2):e202100237
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.
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.
Avramenko Andriy A. Shevchuk Igor V. Dmitrenko Nataliia P. Skitsko Ivan F. 《Journal of Thermal Analysis and Calorimetry》2022,147(22):12709-12719
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.
Zlámalová M. Pitňa Lásková B. Vinarčíková M. Zukalová M. Kavan L. 《Journal of Solid State Electrochemistry》2022,26(3):639-647
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.
Utamima Amalia Reiners Torsten Ansaripoor Amir H. 《Annals of Operations Research》2022,316(2):955-977
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.
Potekaev A. I. Klopotov A. A. Trishkina L. I. Cherkasova T. V. Kulagina V. V. Tazin I. D. 《Russian Physics Journal》2022,65(1):114-122
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