全文获取类型
收费全文 | 9226篇 |
免费 | 658篇 |
国内免费 | 567篇 |
专业分类
化学 | 6280篇 |
晶体学 | 147篇 |
力学 | 313篇 |
综合类 | 1篇 |
数学 | 180篇 |
物理学 | 3530篇 |
出版年
2024年 | 8篇 |
2023年 | 412篇 |
2022年 | 150篇 |
2021年 | 203篇 |
2020年 | 517篇 |
2019年 | 243篇 |
2018年 | 279篇 |
2017年 | 425篇 |
2016年 | 468篇 |
2015年 | 442篇 |
2014年 | 507篇 |
2013年 | 593篇 |
2012年 | 512篇 |
2011年 | 428篇 |
2010年 | 488篇 |
2009年 | 473篇 |
2008年 | 333篇 |
2007年 | 424篇 |
2006年 | 651篇 |
2005年 | 367篇 |
2004年 | 255篇 |
2003年 | 313篇 |
2002年 | 292篇 |
2001年 | 491篇 |
2000年 | 223篇 |
1999年 | 398篇 |
1998年 | 195篇 |
1997年 | 44篇 |
1996年 | 34篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1974年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
101.
102.
《Mendeleev Communications》2023,33(4):466-468
The syntheses and characterization of novel propargyl ethers of N-(hydroxymethyl)nitramines that contain from one to four nitramine units are reported. All nitramine-functionalized ethers were well characterized by IR and multinuclear NMR spectroscopy as well as CHN analysis, and the X-ray crystal structures of two of them are described. For ethers bearing two or three nitramine units, the standard molar enthalpies of formation at 298.15 K were determined from the experimental standard molar energies of combustion in oxygen measured by static bomb combustion calorimetry 相似文献
103.
《Mendeleev Communications》2023,33(4):494-496
A new method for selective C(5)–H alkylation of 2-substituted furans with tertiary and secondary alkyl bromides under photoinduced by visible light (∼460 nm) palladium catalysis has been developed. The method is relied on the use of available Pd(PPh3)4 catalyst under mild conditions (30 ± 5 °C, K2CO3 as base), tolerates to various functional groups in furanic substrates and provides from good to excellent yields of alkylated products. 相似文献
104.
《Mendeleev Communications》2023,33(3):387-389
A new method for deoxygenation of fluoroalkyl-substituted alcohols involves derivatization of the hydroxy group with pentafluoropyridine followed by photoredox catalyzed reduction of the obtained hetaryl ethers using γ-terpinene as a source of hydrogen. The initial alcohols can be easily obtained by nucleophilic fluoroalkylation of the corresponding aldehydes. 相似文献
105.
《Mendeleev Communications》2023,33(2):153-156
Exploring the free energy surface of the R–NHC coupling reaction in the key intermediates of the Mizoroki–Heck and cross-coupling catalytic cycles has been conducted by the methods of biased and unbiased molecular dynamics. Molecular dynamics simulations were carried out both in vacuum and in a polar solvent, with the following main observations on the influence of the media: (1) the solvent prevents the dissociation of the solvate ligand, so the R–NHC coupling proceeds in a four-coordination complex (rather than in a three-coordination one, as in the case of a gas-phase reaction); (2) in the condensed phase, the potential barrier of the reaction is significantly higher compared to the same process in vacuum (17.7 vs. 21.8 kcal mol-1); (3) polar solvent stabilizes the R–NHC coupling product. The reaction in a polar medium is exergonic (ΔG = −3.9 kcal mol-1), in contrast to the in vacuum modeling, where the process is endergonic (ΔG = 0.4 kcal mol-1). 相似文献
106.
《Mendeleev Communications》2023,33(2):221-224
Small anionic liposomes were electrostatically adsorbed on the surface of larger cationic liposomes thus forming multi- compartment complexes composed exclusively of natural and synthetic lipids. The complexes contained two dozen anionic liposomes per a single cationic liposome and showed low cytotoxicity and ability to enzyme-induced bio-degradation. The liposomal multi-compartment complexes demonstrate great application potential as containers for drug encapsulation and delivery. 相似文献
107.
《Mendeleev Communications》2023,33(2):231-233
A short simple synthesis of spinazarins (2,3-dihydroxy-naphthazarins or 2,3,5,8-tetrahydroxy-1,4-naphtho-quinones) from available 2,3-dichloronaphthazarin derivatives involves replacement of chlorine atoms with azido groups followed by their acidic hydrolysis. The procedure can be used for the preparative synthesis of natural biologically active spinazarins and their analogues. 相似文献
108.
《Mendeleev Communications》2023,33(2):215-217
The local mobility and diffusion of Li+, Na+, and Cs+ cations in Nafion 117 membrane were explored by 7Li, 23Na, and 133Cs spin relaxation and pulsed field gradient NMR techniques. It was shown that the macroscopic mass transfer of cations is controlled by ion motion near sulfonate groups. Lithium and sodium cations, whose hydrated energy is higher than the water hydrogen bond energy, are moving together with water molecules, but cesium cations possessing a low hydrated energy are jumping directly between the neighboring sulfonate groups. 相似文献
109.
《Mendeleev Communications》2023,33(2):240-242
A series of new cationic amphiphiles based on diethanolamine esters with Gly, βAla, GABA, Lys, Orn amino acid residues in the hydrophilic block were prepared. The sample containing the Lys residue showed the best activity against gram-positive and gram-negative bacteria. For model membranes comprising combinations of DOPC, DOPG and DOPE phospholipids, the sample can electrostatically bind to the surface of a bacterial cell and destroy it by formation of through defects. 相似文献
110.
《Mendeleev Communications》2023,33(2):249-251
The reactions between Ph3As and ω-bromoalkanoic acids with the length of polymethylene fragment n = 5, 7, 9 afford quaternary arsonium salts. Their treatment with alkali gives biologically active arsenobetaines. Solvent-free reactions of Ph3P or Ph3As with 2,3-dibromopropionic acid lead to the corresponding arsonium and phosphonium salts bearing (CH2)2COOH substituent. 相似文献