全文获取类型
收费全文 | 2582篇 |
免费 | 524篇 |
国内免费 | 674篇 |
专业分类
化学 | 3032篇 |
晶体学 | 169篇 |
力学 | 20篇 |
综合类 | 7篇 |
物理学 | 552篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 78篇 |
2021年 | 114篇 |
2020年 | 178篇 |
2019年 | 93篇 |
2018年 | 105篇 |
2017年 | 95篇 |
2016年 | 139篇 |
2015年 | 152篇 |
2014年 | 196篇 |
2013年 | 342篇 |
2012年 | 189篇 |
2011年 | 146篇 |
2010年 | 116篇 |
2009年 | 133篇 |
2008年 | 180篇 |
2007年 | 166篇 |
2006年 | 175篇 |
2005年 | 158篇 |
2004年 | 141篇 |
2003年 | 148篇 |
2002年 | 93篇 |
2001年 | 75篇 |
2000年 | 77篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 41篇 |
1996年 | 66篇 |
1995年 | 51篇 |
1994年 | 41篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有3780条查询结果,搜索用时 15 毫秒
121.
A variety of disubstituted (double-comb) polysiloxane polymers have been prepared containing linear, branched, and cyclic oligoethyleneoxide units, –(OCH2CH2)n–, in the side chains and as part of the siloxane backbone. Copolymers, using mixtures of linear ethylene oxide side chains, were also synthesized. These polymers were doped with LiN(SO2CF3)2 (LiTFSI, 1) and conductivities of the polymer-salt complexes were determined as a function of temperature and doping level. The maximum conductivity of these polymers at 25 ° C was 2.99 ×10–4, for a copolymer containing equimolar amounts of side chains with n = 5 and 6. 相似文献
122.
尖晶石构造LiCu0.5Mn1.5O4的合成及其在水溶液中对Li+的抽出/嵌入反应董殿权钟杰柳敦雷刘亦凡*(青岛化工学院化学工程系青岛266042)关键词尖晶石,Li-Cu-Mn复合氧化物,合成,锂离子交换1997-09-17收稿,1997-12-2... 相似文献
123.
124.
Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate (MEC) have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^+ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^+ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions. 相似文献
125.
Marco Arfelli Giovanni Cossu Giulia Mattogno Carla Ferragina Maria Antonietta Massucci 《Journal of inclusion phenomena and macrocyclic chemistry》1990,9(2):161-170
X-ray photoelectron spectroscopy provides evidence that when [Cu(phen)2]2+(phen = 1,10-phenanthroline) is diffused between the layers of -zirconium phosphate, the complex species does not remain intact after intercalation, but some Cu-N bonds are broken, replaced with Cu-O bonds and the released nitrogen atoms can now interact with the PO3-OH groups of the host. XPS also provides evidence for coordination of the Cu2+ ions when they are diffused by ion exchange in the phenanthroline--zirconium phosphate intercalation compound. Although Cu2+ and phen are in a 1 : 1 molar ratio in the interlayer region of the host, so that a 1 : 1 coordination could be expected between the two species, the characteristic peaks of the uncoordinated phenanthroline, even though at a low intensity, are still present. The differences between the two Cu(II)-intercalation compounds are discussed. 相似文献
126.
V.?S.?Leshinlevasi@highp.chem.msu.ru" title="levasi@yandex.ru levasi@highp.chem.msu.ru" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author N.?E.?Sorokina V.?V.?Avdeev 《Russian Journal of Electrochemistry》2005,41(5):572-575
Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H2SO4 and H3PO4 acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H2SO4, a mixture of compounds of intercalation steps I and II forms in 60% H2SO4, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H2SO4 solutions. The threshold concentration of H2SO4 intercalation is ∼2%. With the decrease in active intercalate (H2SO4) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d
i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H3PO4 concentration in solution, d
i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev. 相似文献
127.
Two New Silicate-Chlorides with Divalent Europium: LiEu3[SiO4]Cl3 and Li7Eu8[SiO4]4Cl7 LiEu3[SiO4]Cl3 was prepared by reaction of LiCl with Eu2SiO4 and Li7Eu8[SiO4]4Cl7 from Li with Eu2O3, SiO2 and LiCl. The crystal structures of LiEu3[SiO4]Cl3 (Pmna, a = 946.95(13); b = 699.52(8); c = 1 368.0(2) pm; Z = 4; R1 = 0.0325, R2w = 0.0642) and Li7Eu8[SiO4]4Cl7 (P21/c; a = 851.85(5); b = 948.62(7); c = 1 679.0(2) pm; β = 96.221(8)°; Z = 2; R1 = 0.0352, R2w = 0.0744) were determined from four-circle diffractometer data. LiEu3[SiO4]Cl3 contains [Li(SiO4)2] units and LiCl6 octahedra while in Li7Eu8[SiO4]4Cl7 larger ?lithosilicate”? groups are found. In both structures, the Eu2+ ions are coordinated mostly eightfold by O2? and Cl? ligands. 相似文献
128.
Alkylidynephosphanes and -arsanes. I [P ≡ C? S]?[Li(dme)3]+ – Synthesis and Structure O,O′-Diethyl thiocarbonate and bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide dissolved in 1,2-dimethoxyethane, react below 0°C to give ethoxy trimethylsilane and tris(1,2-dimethoxyethane-O,O′)lithium 2λ3-phosphaethynylsulfanide – [P≡C? S]? [Li(dme)3]+ – ( 1a ). Apart from bis(trimethylsilyl)sulfane or carbon oxide sulfide, dark red concentrated solutions of λ3-phosphaalkyne 1 are also obtained from reactions of carbon disulfide with bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide or with the homologous lithoxy-methylidynephosphane ( 2 ) [1]. The ir spectrum shows two absorptions at 1762 and 747 cm?1 characteristic for the P≡C and C? S stretching vibrations. The nmr parameters {δ(31P) ? 121.3; δ(13C) 190.8 ppm; 1JCP 18.2 Hz} resemble much more values of diorganylamino-2λ3-phosphaalkynes than those of bis(1,2-dimethoxyethane-O,O′)lithoxy-methylidyne-phosphane ( 2a ). As found by an X-ray structure analysis (P21/c; a = 1192.6(16); b = 1239.1(19); c = 1414.8(26) pm; β = 105.91(13)° at ?100 ± 3°C; Z = 4 formula units; wR = 0.064) of pale yellow crystals (mp. + 16°C) isolated from the reaction with O,O′-diethyl thiocarbonate, the solid is built up of separate [P≡C? S]? and [Li(dme)3]+ ions. Typical bond lengths and angles are: P≡C 155.5(11); C? S 162.0(11); Li? O 206.4(17) to 220.3(20) pm; P≡C? S 178.9(7)°. 相似文献
129.
Karolina Kucharska Marta Pilz Krzysztof Bielec Tomasz Kalwarczyk Patrycja Ku
ma Robert Hoyst 《Molecules (Basel, Switzerland)》2021,26(12)
The oxazole yellow dye, YOYO-1 (a symmetric homodimer), is a commonly used molecule for staining DNA. We applied the brightness analysis to study the intercalation of YOYO-1 into the DNA. We distinguished two binding modes of the dye to dsDNA: mono-intercalation and bis-intercalation. Bis-intercalation consists of two consecutive mono-intercalation steps, characterised by two distinct equilibrium constants (with the average number of base pair per binding site equals 3.5): and , respectively. Mono-intercalation dominates at high concentrations of YOYO-1. Bis-intercalation occurs at low concentrations. 相似文献
130.
Michael F. Rectenwald Joshua R. Gaffen Prof. Arnold L. Rheingold Dr. Alexander B. Morgan Prof. John D. Protasiewicz 《Angewandte Chemie (International ed. in English)》2014,53(16):4173-4176
The functionalized catecholate, tetraethyl (2,3‐dihydroxy‐1,4‐phenylene)bis(phosphonate) (H2‐DPC), has been used to prepare a series of lithium salts Li[B(DPC)(oxalato)], Li[B(DPC)2], Li[B(DPC)F2], and Li[P(DPC)3]. The phosphoryl‐rich character of these anions was designed to impart flame‐retardant properties for their use as potential flame‐retardant ions (FRIONs), additives, or replacements for other lithium salts for safer lithium‐ion batteries. The new materials were fully characterized, and the single‐crystal structures of Li[B(DPC)(oxalato)] and Li[P(DPC)3] have been determined. Thermogravimetric analysis of the four lithium salts show that they are thermally stable up to around 200 °C. Pyrolysis combustion flow calorimetry reveals that these salts produce high char yields upon combustion. 相似文献