全文获取类型
收费全文 | 1530篇 |
免费 | 35篇 |
国内免费 | 6篇 |
专业分类
化学 | 1020篇 |
晶体学 | 4篇 |
力学 | 31篇 |
数学 | 220篇 |
物理学 | 296篇 |
出版年
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 33篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 81篇 |
2012年 | 79篇 |
2011年 | 75篇 |
2010年 | 43篇 |
2009年 | 39篇 |
2008年 | 65篇 |
2007年 | 62篇 |
2006年 | 80篇 |
2005年 | 61篇 |
2004年 | 67篇 |
2003年 | 63篇 |
2002年 | 50篇 |
2001年 | 32篇 |
2000年 | 42篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 29篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 23篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1975年 | 8篇 |
1974年 | 16篇 |
1973年 | 16篇 |
1968年 | 9篇 |
排序方式: 共有1571条查询结果,搜索用时 31 毫秒
31.
By deuteration of the OH group, it has been shown that two bands, at 1665 and 1630 cm−1 (CCl4), in the IR spectra of 5-hydroxychromones are associated with the H-bonded CO stretching vibration. Nuclear deuteration of 5-hydroxy-2-methylchromone (1) under acidic conditions gave a tri- and a hexadeutero derivative; the latter, isotopically substituted at C-3, shows a single CO band at 1649 cm−1. Hydrolysis of 3-acetyl-5-hydroxy-2-methylchromone with sodium carbonate in deuterium oxide furnished 5-hydroxy-2-trideuteromethylchromone-3-d which also exhibits a single CO absorption. Partial incorporation of O18 into the CO group of 1 results in a single νC=O18 at 1593 cm−1. It is suggested that the doublet CO absorption of 5-hydroxychromones arises from a Fermi resonance involving a low-energy vibrational mode of the vinyl proton on the nuclear C-3 position. 相似文献
32.
The replacement of phenylethanethiolate (SC2Ph) ligands on 1.1 nm (core diameter) Au38(SC2Ph)24 monolayer-protected clusters (MPCs) with varied amounts of triphenylphosphine (PPh3) is investigated in methylene chloride. UV-vis spectra suggest that changes in the MPC Au core size occur when large amounts (> 10 equiv moles per cluster) of PPh3 are reacted with Au38(SC2Ph)24. 1H and 31P NMR spectra following the addition of smaller amounts (< 5 equiv moles) of PPh3 indicate that the reaction liberates a AuISC2Ph complex, as opposed to a SC2Ph thiol, disulfide, or anion. A 1H NMR kinetic study shows that the exchange is surprisingly rapid, even faster than exchanges of thiolates with other thiolates, at room temperature and in air. The reaction is slowed when cooled or conducted under Ar. The difference in potentials of the initial one-electron voltammetric reduction and oxidation of Au38(SC2Ph)24 decreases slightly upon reaction with small amounts of PPh3. 相似文献
33.
Rammile Ettelaie Brent S. Murray Emma L. James 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):195-206
To a first approximation, the primary structure of many food proteins maybe thought of as a sequence of short hydrophobic and hydrophilic blocks. The influence of this type of structure on the steric-stabilising properties of such proteins has been considered here. In line with previous studies, using Self-Consistent-Field calculations, it has been shown that the presence of such protein molecules can lead to attraction and consequently bridging flocculation of colloidal particles. In the low adsorption energy limit for the hydrophobic groups (−1kBT), it is found that the steric potential is significantly influenced by the changes in the number of adsorbed segments, as two surfaces are brought together. This is in contrast to the well-known results in the literature for the high adsorption limiting cases, where the number of such segments remains constant. In particular, the changes in the number of adsorbed hydrophobic units are observed not to be a monotonic function of the separation distance, but increase or decrease in reasonable accord with the oscillatory nature of the steric interactions, observed for various block sizes. Effects of the addition of a moderately sized hydrophilic side chain to the above molecules have also been studied. It is found that, in principle, such a modification can lead to a purely repulsive steric potential in solutions of these hybrid biopolymers. At the hydrophilic side chain sizes considered here, the surface affinity of the molecules is observed not to be drastically different compared to those of unmodified proteins. 相似文献
34.
Whittle M Murray BS Dickinson E Pinfield VJ 《Journal of colloid and interface science》2000,225(2):273-284
Preflocculated ferric hydroxide flocs were subjected to either a simple shear flow or a two-dimensional straining flow, and their motion was optically observed. Digital image analysis was applied to extract information on orientation and deformation from the digitized frames. It was found that the simple shear flow led to a rotation of the flocs whose motion can be understood from the behavior of a solid ellipsoid. In the extensional flow, no continuous rotation occurred and flocs were broken apart along the axis of straining. The rupture forces estimated from an ellipsoid model were found to be in the range of 0.1 N/m(2). Copyright 2000 Academic Press. 相似文献
35.
Tynan E Jensen P Kelly NR Kruger PE Lees AC Moubaraki B Murray KS 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3440-3447
We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4'-dicarboxy-2,2'-bipyridine ligand, H(2)dcbp: alpha-[Co(dcbp)(H(2)O)(2)], 1; beta-[Co(dcbp)(H(2)O)(2)], 2, [Ni(dcbp)(H(2)O)(2)], and [[Mn(dcbp)].1/2DEF], 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1:1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6(4)8(2)-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water-carboxylate double helices in , and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm(-3)(1.654 vs. 1.940 g cm(-3), respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1-3 and has a (4.6(2))(4(2).6)(4(3).6(6).8(6)) Schlafli notation. Magnetic susceptibility studies performed on 1, 2, [[Mn(dcbp)].1/2DMF] 5 (DMF = dimethylformamide) and [[Mn(dcbp)].2H(2)O] 6 reveal very weak antiferromagnetic coupling between the metal centres in each case. 相似文献
36.
Redl FX Black CT Papaefthymiou GC Sandstrom RL Yin M Zeng H Murray CB O'Brien SP 《Journal of the American Chemical Society》2004,126(44):14583-14599
We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mossbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements. 相似文献
37.
Beker H Boggild H Boissevain J Cherney M Dodd J Esumi S Fabjan CW Fields DE Franz A Hansen KH Holzer EB Humanic TJ Jacak BV Jayanti R Kalechofsky H Kobayashi T Kvatadze R Lee YY Leltchouk M Lörstad B Maeda N Medvedev A Miake Y Miyabayashi A Murray M Nagamiya S Nishimura S Noteboom E Pandey SU Piuz F Polychronakos V Potekhin M Poulard G Sakaguchi A Sarabura M Shigaki K Simon-Gillo J Sondheim W Sugitate T Sullivan JP Sumi Y van Hecke H Willis WJ Wolf K Xu N 《Physical review letters》1995,74(17):3340-3343
38.
39.
40.