全文获取类型
收费全文 | 422篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 293篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 56篇 |
物理学 | 73篇 |
出版年
2020年 | 4篇 |
2019年 | 4篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 27篇 |
2011年 | 30篇 |
2010年 | 12篇 |
2009年 | 8篇 |
2008年 | 37篇 |
2007年 | 33篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 12篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1935年 | 2篇 |
1932年 | 2篇 |
1930年 | 2篇 |
1924年 | 2篇 |
1923年 | 2篇 |
1909年 | 4篇 |
排序方式: 共有430条查询结果,搜索用时 31 毫秒
131.
Metadynamics is employed to sample the configurations available to calcium carbonate nanoparticles in water, and to map an approximate free energy as a function of crystalline order. These data are used to investigate the validity of bulk and ideal surface energies in predicting structure at the nanoscale. Results indicate that such predictions can determine the structure and morphology of particles as small as 3-4 nm in diameter. Comparisons are made to earlier results on 2 nm particles under constant volume conditions which support nanoconfinement as a mechanism for enhancing the stability of amorphous calcium carbonate. Our results indicate that crystalline calcitelike structure is thermodynamically preferred for nanoparticles as small as 2 nm in the absence of nanoconfinement. 相似文献
132.
A. M. Al-Sabagh D. R. K. Harding N. G. Kandile A. M. Badawi Amira E. El-Tabey 《Journal of Dispersion Science and Technology》2013,34(3):427-438
Eight novel ethoxylated nonionic surfactants were prepared based on oil soluble α-amino acids. The L-phenylalanine and L-leucine were esterified and amidated with cetyl alcohol and palamitic acid, respectively; two amides and two esters of α-amino acids were obtained. The ethylene oxide was condensed with the prepared amides and esters to get three different polyethylene oxide units (40, 60, and 100) as phenylalanine derivatives. The amide and ester of α-L-leucine were ethoxylated at (60 ethylene oxides units). The analytical micro analysise, FTIR, 1H NMR, 13C NMR, mass spectra were carried out to confirm the chemical structures. The surface tension of the water soluble prepared compounds was measured at 25°C, further the surface active properties were determined and calculated. Such that critical micelle concentration (CMC), surface excess (Γmax); area per molecule (Amin), effectiveness (γCMC) free energy of micellization and adsorption (ΔGmic, ΔGad). From the data obtained it was found that the CMC of phenylalanine esters is greater than that obtained for the amide derivatives. The Γmax decreased as the ethylene oxide units (EO) increased. It was found also that the ΔGad was greater than the ΔGmic. The obtained data and discrepancy were discussed on the light of surfactant chemical structure. 相似文献
133.
John Harding 《International Journal of Theoretical Physics》2006,45(6):1079-1090
We provide a method to construct a type of orthomodular structure known as an orthoalgebra from the direct product decompositions of an object in a category that has finite products and whose ternary product diagrams give rise to certain pushouts. This generalizes a method to construct an orthomodular poset from the direct product decompositions of familiar mathematical structures such as non-empty sets, groups, and topological spaces, as well as a method to construct an orthomodular poset from the complementary pairs of elements of a bounded modular lattice.
Mathematics Subject Classifications (2000): 06C15, 81P10, 03G12, 18A30 相似文献
134.
135.
136.
The synthesis of a quinoxaline-appended aza-macrocyclic ligand together with corresponding LnIII complexes are described. The luminescence properties of the complexes show that the quinoxaline unit sensitises both visible (EuIII) and near-IR (NdIII and YbIII) emitting lanthanide ions. UV–Vis absorption and time-resolved photophysical studies together with X-ray structural data suggest that as well as contributing chromophorically, the quinoxaline moiety generally participates in the first coordination sphere of LnIII. The luminescent pH response of the EuIII complex is also reported. The form of the steady state spectrum changes profoundly in the pH range 2–12, implying a change in the coordination environment, which was confirmed with time-resolved lifetime measurements that suggest an increase in europium inner sphere hydration at acidic pH. 相似文献
137.
Helsel AJ Brown AL Yamato K Feng W Yuan L Clements AJ Harding SV Szabo G Shao Z Gong B 《Journal of the American Chemical Society》2008,130(47):15784-15785
Oligoamide macrocycles 1d and 1e, which carry membrane-compatible side chains and contain a hydrophilic, noncollapsible cavity, were found to mediate high ion flux across a lipid bilayer, as demonstrated by results from (23)Na NMR and planar bilayer conductance measurements. The measured transmembrane single channel currents are very high, rivaling those typically associated with pore-forming protein toxins. The obtained results have demonstrated the promise of developing large, highly conducting channels based on nanopores formed by oligoamide macrocycles. 相似文献
138.
Carruthers C Ronson TK Sumby CJ Westcott A Harding LP Prior TJ Rizkallah P Hardie MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(33):10286-10296
A series of clathrate and metal complexes with cyclotriveratrylene-like molecular host ligands show a similar dimeric homomeric inclusion motif in which a ligand arm of one host is the intra-cavity guest of another and vice versa. This "hand-shake" motif is found in the trinuclear transition metal complex [Cu(3)Cl(6)(1)]CH(3)CN1.5 H(2)O in which 1 is tris(4-[2,2',6',2'-terpyridyl]benzyl)cyclotriguaiacylene; in the self-included M(4)L(4) tetrahedral metallo-supramolecular assembly [Ag(4)(2)(4)] (BF(4))(4) in which 2 is tris-(2-quinolylmethyl)cyclotriguaiacylene; in the 1D coordination chains [Ag(4)]ReO(4) CH(3)CN and [Ag(5)]SbF(6)3 DMFH(2)O in which 4 is tris(1H-imidazol-1-yl)cyclotriguaiacylene and 5 is tris{4-(2-pyridyl)benzyl}cyclotriguaiacylene; and in the acetone clathrate of tris{4-(2-pyridyl)benzyl-amino}cyclotriguaiacylene. Clathrates of ligands 2 and 5 do not show the same dimeric motif, although 2 has an extended homomeric inclusion motif that gives a hexagonal network. 相似文献
139.
Benchmark calculations of (19)F nuclear magnetic shielding constants are presented for a set of 28 molecules. Near-quantitative accuracy (ca. 2 ppm deviation from experiment) is achieved if (1) electron correlation is adequately treated by employing the coupled-cluster singles and doubles (CCSD) model augmented by a perturbative correction for triple excitations [CCSD(T)], (2) large (uncontracted) basis sets are used, (3) gauge-including atomic orbitals are used to ensure gauge-origin independence, (4) calculations are performed at accurate equilibrium geometries [obtained from CCSD(T)/cc-pVTZ calculations correlating all electrons], and (5) vibrational averaging and temperature corrections via second-order vibrational perturbation theory (VPT2) are included. For the CCSD(T)/13s9p4d3f calculations corrected for vibrational effects, mean and standard deviation from experiment are -1.9 and 1.6 ppm, respectively. Less elaborate theoretical treatments result in larger errors. Consideration of relative shifts can reduce the mean deviation (through an appropriately chosen reference compound), but does not change the standard deviation. Density-functional theory calculations of absolute and relative (19)F nuclear magnetic shielding constants are found to be, at best, as accurate as the corresponding Hartree-Fock self-consistent-field calculations and are not improved by consideration of vibrational effects. Molecular systems containing fluorine-oxygen, fluorine-nitrogen, and fluorine-fluorine bonds are found to be more challenging than the other investigated molecules for the considered theoretical methods. 相似文献
140.
Yann Sarazin Joseph A. Wright Duncan A.J. Harding Eddy Martin Timothy J. Woodman David L. Hughes Manfred Bochmann 《Journal of organometallic chemistry》2008,693(8-9):1494-1501
The synthesis of a series of binuclear zinc complexes with Cl, N and O bridges is reported. The reaction of EtZnCl with B(C6F5)3 in the presence of hexamethylbenzene affords the arene complex [Zn(μ-Cl)(C6F5)(η-C6Me6)]2 in which the C6Me6 ligand may be regarded as η3-bonded. The comproportionation of Zn[N(SiMe3)2]2 with ZnBut2 or Zn(C6F5)2 · toluene gave [ButZn{μ-N(SiMe3)2}]2 and [C6F5Zn{μ-N(SiMe3)2}]2, respectively, with three-coordinate zinc. The reaction of ZnEt2 with C6F5OH in the presence of pyridine gave [EtZn(μ-OC6F5)(py)]2, while ZnMe2 and C6F5OH followed by recrystallisation from THF gave [Zn(OC6F5)(μ-OC6F5)(THF)2]2 with five-coordinate zinc in a trigonal-bipyramidal geometry. The structures of these compounds have been determined. 相似文献