全文获取类型
收费全文 | 508743篇 |
免费 | 21667篇 |
国内免费 | 9698篇 |
专业分类
化学 | 283719篇 |
晶体学 | 5820篇 |
力学 | 24108篇 |
综合类 | 449篇 |
数学 | 59294篇 |
物理学 | 166718篇 |
出版年
2022年 | 3714篇 |
2021年 | 6138篇 |
2020年 | 7968篇 |
2019年 | 7893篇 |
2018年 | 8875篇 |
2017年 | 8453篇 |
2016年 | 13144篇 |
2015年 | 9597篇 |
2014年 | 13514篇 |
2013年 | 26571篇 |
2012年 | 23443篇 |
2011年 | 27370篇 |
2010年 | 18879篇 |
2009年 | 18516篇 |
2008年 | 23179篇 |
2007年 | 22195篇 |
2006年 | 20526篇 |
2005年 | 17926篇 |
2004年 | 16045篇 |
2003年 | 13774篇 |
2002年 | 12528篇 |
2001年 | 14473篇 |
2000年 | 10898篇 |
1999年 | 8952篇 |
1998年 | 7423篇 |
1997年 | 7310篇 |
1996年 | 7030篇 |
1995年 | 6527篇 |
1994年 | 6338篇 |
1993年 | 6002篇 |
1992年 | 6480篇 |
1991年 | 6510篇 |
1990年 | 6150篇 |
1989年 | 5815篇 |
1988年 | 5698篇 |
1987年 | 5501篇 |
1986年 | 5218篇 |
1985年 | 6647篇 |
1984年 | 6698篇 |
1983年 | 5310篇 |
1982年 | 5395篇 |
1981年 | 5343篇 |
1980年 | 4898篇 |
1979年 | 5313篇 |
1978年 | 5438篇 |
1977年 | 5346篇 |
1976年 | 5295篇 |
1975年 | 4877篇 |
1974年 | 4847篇 |
1973年 | 4848篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Jose M. Guisan Gloria Fernandez-Lorente Javier Rocha-Martin Daniel Moreno-Gamero 《Current Opinion in Green and Sustainable Chemistry》2022
Different strategies for the preparation of efficient and robust immobilized biocatalysts are here reviewed. Different physico-chemical approaches are discussed.i.- The stabilization of enzyme by any kind of immobilization on pre-existing porous supports.ii.- The stabilization of enzymes by multipoint covalent attachment on support surfaces.iii.- Additional stabilization of immobilized-stabilized enzyme by physical or chemical modification with polymers.These three strategies can be easily developed when enzymes are immobilized in pre-existing porous supports. In addition to that, these immobilized-stabilized derivatives are optimal to develop enzyme reaction engineering and reactor engineering. Stabilizations ranging between 1000 and 100,000 folds regarding diluted soluble enzymes are here reported. 相似文献
2.
Nonlinear Dynamics - In this paper, an economic competition between two firms that want to maximize the weighted-average social welfare and own profits is proposed. This kind of competition is... 相似文献
3.
Crystallography Reports - The review presents the important unique results of the cycle of research led by M.V. Kovalchuk on the fundamental patterns of protein interactions and the protein... 相似文献
4.
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
5.
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
6.
Rui Feng Zi-Ying Li Zhao-Quan Yao Zi-Ang Guo Yi-Nan Zhang Hao-Xiang Sun Wei Li Xian-He Bu 《中国科学:化学(英文版)》2022,65(1):128-134
The rational designability and chemical tunability of metal-organic frameworks(MOFs)are enabling tributes to efficaciously enhance their room temperature phosphorescence(RTP)performance.A family of stable anionic MOFs,[Zn2(4,5-ImDC)2]M2(NKU-132,M=(CH3)2NH2or(CH2CH3)2NH2),featuring significant RTP have been synthesized.By rational cation selection and in-situ replacement from dimethylammonium to diethylammonium,the phosphorescence lifetime is increased from 30.88 to126.3 ms,along with less sensitivity to air.This work provides an anti-quenching and lifetime tuning example for RTP-MOFmaterials via facile host-guest chemistry. 相似文献
7.
In this paper,we consider the deformed Hermitian-Yang-Mills equation on closed almost Hermitian manifolds.In the case of the hypercritical phase,we derive a priori estimates under the existence of an admissible C-subsolution.As an application,we prove the existence of solutions for the deformed Hermitian-Yang-Mills equation under the condition of existence of a supersolution. 相似文献
8.
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
9.
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
10.