全文获取类型
收费全文 | 490篇 |
免费 | 9篇 |
国内免费 | 6篇 |
专业分类
化学 | 300篇 |
晶体学 | 3篇 |
力学 | 17篇 |
数学 | 59篇 |
物理学 | 126篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 24篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1975年 | 10篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1970年 | 4篇 |
排序方式: 共有505条查询结果,搜索用时 203 毫秒
51.
Conductance measurements of 12 quaternary ammonium salts in propylene carbonate (PC) have been made at 25°C. The cations were either tetramethylammonium, tetraethylammonium, or tetra-n-butylammonium, and the concentrations of salt varied from about 2×10–4 to 5×10–3
M. The data were analyzed by the equation of Pitts. The results showed that the benzoate, nitrobenzoate, and pentachlorophenolate salts are completely dissociated. The nitrophenolate, chlorophenolate, methylsulfonate, and nitrate salts are only slightly associated (K
A
from 2.5 to 6.5), while the acetate, phenylacetate, and nitrophenolate salts display somewhat more extensive association, with ionpair association constants from 17 to 45. Limiting molar conductances for the anions were derived. The factors affecting ionic mobilities in this dipolar aprotic solvent are discussed.On leave 1973–1975 from the University of Gdask, Poland. 相似文献
52.
MoN and MoO molecules produced in a hollow cathode discharge have been trapped in Ne, Ar, and Kr matrices at 4.2 and 13 K and investigated by optical spectroscopy. Bands attributed to MoN were identified in the red and blue spectral regions and assigned by comparison with gas phase results to the A4π → X4Σ? (a) and B4Σ → X4Σ? (a) transitions, respectively. The ground state of Mo14N has been identified as 4Σ? with ωe = 1040 cm?1 in an Ar matrix. Absorptions assigned to MoO in the red spectral region form the (0-0) and (1-0) bands of at least one electronic transition, but could not definitely be correlated with the gas phase results. The ground state vibrational frequency for Mo16O in an Ar matrix is 893.5 cm?1. Additionally, Mo2 absorptions centered at 19 305 cm?1 were shown to be part of a vibrational progression with an average spacing of 181 cm?1. 相似文献
53.
54.
Caltagirone C Bates GW Gale PA Light ME 《Chemical communications (Cambridge, England)》2008,(1):61-63
Sulfonamide groups, commonly used as neutral hydrogen bond donors in a wide variety of anion receptors, deprotonate upon addition of certain basic anionic guests in two simple functionalised ureas. 相似文献
55.
Bates CM Stevens F Langford SC Dickinson JT 《Langmuir : the ACS journal of surfaces and colloids》2008,24(14):7193-7199
The dissolution of liquids with low mutual solubility is typically slow. However, drops of sparingly soluble, low-density, low-surface-tension liquids often dissolve rapidly on water due to surface tension instabilities and gradients. We report observations of the motion and dissolution of drops of aliphatic alcohols of a wide range of alkyl chain lengths as they dissolve in water. The alcohol drops are rendered visible by adding small amounts of iodine or other dyes. These drops display dewetting instabilities, fragmentation, fingering, and oscillation. As the length of the alcohol carbon chain increases from n = 4 to n = 9, dissolution slows dramatically. The roles of alcohol solubility and water surface area in promoting rapid dissolution are discussed. 相似文献
56.
The rates of proton transfer from [pyrH]+ (pyr = pyrrolidine) to the binuclear complexes [Fe2S2Cl4]2- and [S2MS2FeCl2]2- (M = Mo or W) are reported. The reactions were studied using stopped-flow spectrophotometry, and the rate constants for proton transfer were determined from analysis of the kinetics of the substitution reactions of these clusters with the nucleophiles Br- or PhS- in the presence of [pyrH]+. In general, Br- is a poor nucleophile for these clusters, and proton transfer occurs before Br- binds, allowing direct measure of the rate of proton transfer from [pyrH]+ to the cluster. In contrast, PhS- is a better nucleophile, and a pathway in which PhS- binds preferentially to the cluster prior to proton transfer from [pyrH]+ usually operates. For the reaction of [Fe2S2Cl4]2- with PhS- in the presence of [pyrH]+ both pathways are observed. Comparison of the results presented in this paper with analogous studies reported earlier on cuboidal Fe-S-based clusters allows discussion of the factors which affect the rates of proton transfer in synthetic clusters including the nuclearity of the cluster core, the metal composition, and the nature of the terminal ligands. The possible relevance of these findings to the protonation sites of natural Fe-S-based clusters, including FeMo-cofactor from nitrogenase, are presented. 相似文献
57.
The absorption spectra and the characteristic emission and excitation spectra of CsI:Na bulk crystals at temperatures between 300 K and 4.2 K are reported. Localized exciton energies were calculated by considering a Born-Haber cycle. The results were compared with the experimental results and the origins of the absorption bands were identified. The characteristic emission spectrum consists of two bands, one peaking around 4200 Å, the other around 3800 Å. The corresponding excitation spectra show that this emission is due to the recombination of a relaxed exciton which was created by transferring an electron from an iodine ion to a substitutional sodium ion in an otherwise perfect CsI lattice. 相似文献
58.
59.
Resonance Raman scattering has been observed from metastable O2 molecules produced in single crystals of NaClO3 by γ-irradiation at 300 K. Evidence that the observed bands are due to O2 is provided by the Raman spectrum of irradiated 18O enriched NaClO3 in which bands due to 16O2, 16O 18O, and 18O2 were identified. The Raman band at 1544 cm?1 ascribed to metastable O2 disappears on bleaching with intense 4880 Å radiation enabling the identification of a weaker band at 1557 cm?1 that is assigned to the stable form of O2. 相似文献
60.
It is found that the forced common turning point procedure is satisfactory for treating the excitation of hydrogen atoms by slow protons evan at an energy of relative motion as low as 30 eV. 相似文献