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11.
Tong X Benz L Kemper P Metiu H Bowers MT Buratto SK 《Journal of the American Chemical Society》2005,127(39):13516-13518
Experiments in which mass-selected gold clusters were deposited on a surface have found that the catalytic properties depend strongly on cluster size. However, these experiments have not established definitively that the clusters maintain their size after deposition. We report here work in which we deposit low kinetic energy, mass-selected Aun+ (n = 1-8) clusters on a rutile TiO2(1 x 1) surface and use ultrahigh vacuum scanning tunneling microscopy (UHV-STM) to determine their size and shape. 相似文献
12.
Hoh-Jiear Yan Eli M. Pearce 《Journal of polymer science. Part A, Polymer chemistry》1984,22(11):3319-3334
Polymers containing rigid aromatic structures in the chain backbone usually gave high thermal stability and good flammability resistance. Three glycidyl ethers of epoxy resins were prepared from 2,4-di(p-hydroxystyryl)pyridine (2,4-DGESP), 2,6-di-(p-hydroxystyryl)pyridine (2,6-DGESP), and 2,4,6-tri-(p-hydroxystyryl)pryidine (2,4,6-TGESP) to study the relationships of structure to polymer degradation. To prepare a highly crosslinked material, trimethoxyboroxine (TMB) was used as the curing agent. The relative char yields of the three different resins, as measured by TGA, were 2,4-DGESP ≈ 2,6-DGESP > 2,4,6-TGESP. The char yield of the cured 2,6-DGESP varied with different amounts of the TMB curing agent, and was higher than the uncured 2,6-DGESP. The oxygen index increased as a function of thermal curing time for the 2,6-DGESP epoxy resin. An intermolecular Diels–Alder reaction with 2,6-DGESP is proposed as a primary reaction during thermal curing. 相似文献
13.
S. P. Ting B. J. Bulkin E. M. Pearce T. K. Kwei 《Journal of polymer science. Part A, Polymer chemistry》1981,19(6):1451-1473
Copolymers of styrene with vinylphenyl trifluoromethyl carbinol, p-vinylphenyl trifluoromethyl carbinol, vinylphenyl hexafluorodimethyl carbinol, and p-vinylphenol are conditionally compatible with poly(ethylene oxide), depending on their composition and blending ratios, whereas copolymers of styrene and vinylphenyl methyl carbinol are much less compatible with poly(ethylene oxide), as determined by Tg criteria and differential scanning calorimetry. The crystallinity of poly(ethylene oxide) is changed in the copolymer/poly(ethylene oxide) blends, as indicated by depressions of the poly(ethylene oxide) melting point. Hydrogen-bond formation has been studied in two selected blends by infrared (IR) spectroscopy. Hydrogen bonding dissociation and reassociation as a function of temperature are reported. The conformation changes of poly(ethylene oxide) in the blends, the interaction between copolymer and poly(ethylene oxide) as well as in the reference blend, polystyrene/poly(ethylene oxide), are also investigated. 相似文献
14.
Organic phase conversion of bulk (wurtzite) ZnO to nanophase (wurtzite and zinc blende) ZnO 总被引:1,自引:0,他引:1
Lauren P. Snedeker Aditi S. Risbud Ombretta Masala Jin Ping Zhang Ram Seshadri 《Solid State Sciences》2005,7(12):1500
We describe the all-organic phase conversion of bulk commercial ZnO in the wurtzite modification to sub-30 nm ZnO that we find to be partially in the zinc blende [, a=4.568(3) Å] modification. The conversion involves refluxing ZnO in 2,4-pentanedione (acetylacetone) at 413 K to form the zinc 2,4-pentanedionate, which is decomposed by heating at 573 K in an appropriate high-temperature solvent such as dibenzylether to form nanophase ZnO. This nanophase, partially zinc blende ZnO can also be obtained in a single step by heating commercial zinc 2,4-pentanedionate in refluxing dibenzylether. Thermodiffractometry suggests that the conversion of zinc blende ZnO to wurtzite ZnO commences near 650 K. 相似文献
15.
A new photoelectron spectroscopic method is described directed towards the measurement of the photoelectron spectra of trapped ions. An electrostatic retarding field electron energy analyser incorporating a channel plate is included with an ion trap in a strong magnetic field. The form of photoelectron spectrum is shown to be strongly influenced by a elastic scattering effects which can be enhanced by using an electron trapping potential well. The resultant spectra then have a particularly simple and useful form. 相似文献
16.
Binoy K. Bordoloi Eli M. Pearce L. Blight B. R. Currell R. Merrall R. A. M. Scott C. Stillo 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):383-406
Liquid sulfur–olefinic reactions at 140°C forming crosslinked polysulfide polymers have been investigated. A systematic approach to the characterization and some structure–property studies on these new polymeric materials has been presented. The olefinic systems of interest are endo-and exo-dicyclopentadiene and an oligomeric alkenyl polysulfide. Equimolar S8–olefinic system copolymers are amorphous and they show no tendency for sulfur crystallization. A correlation has been drawn between chemical structure and glass transition temperature of the copolymers and terpolymers. Mechanical properties and, in particular, chemical stress relaxation of the crosslinked polysulfide polymers have been investigated. 相似文献
17.
S. H. Kim Eli M. Pearce T. K. Kwei 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3167-3180
The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH2 moiety which was protected by SnCl5?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc. 相似文献
18.
Timothy S. Keizer Lauren J. De Pue Sean Parkin David A. Atwood 《Journal of Cluster Science》2002,13(4):609-620
Various Salen ligands (Salen(
t
Bu)H2=N, N-ethylenebis(3,5-di-tertbutyl(2-hydroxy)benzylidenimine) were used to prepare borosilyl and -O bridged borosilyl compounds having the formula, L{B(OSiMe3)2}2 (L=Salen(
t
Bu) (1), Salpen(
t
Bu) (2), Salben(
t
Bu) (3), Salhen(
t
Bu) (4) and L(BOSiMe3)2(-O) (L=Salen(
t
Bu) (5) and Salben(
t
Bu) (6)). In the case of 5 and 6 the formation of the B–O–B linkage takes precedence over the formation of a B–O–Si linkage. All of the compounds were characterized by Mp, elemental analysis, 1H and 11B NMR, IR, MS and in the case of 1, 2, and6 by X-ray crystallography. 相似文献
19.
A. Raith W. T. Perkins N. J. G. Pearce T. E. Jeffries 《Fresenius' Journal of Analytical Chemistry》1996,355(7-8):789-792
Laser ablation inductive coupled plasma – mass spectrometry (LA-ICP-MS) was used to analyse minor and trace elements in the hard parts of a shellfish, representing the environmental changes. A large, long-lived bivalve such as Arctica islandica can produce historical records of trace element fluctuations in seawater. Analytical traverses using LA-ICP-MS were performed from the inner to the outer wall of the shell at different locations. The development of the UV laser system now offers spatial resolution of craters of 10 m diameter, enabling several analyses between the various growthbands. The elemental changes between growthbands of the shell are discussed, showing the potential for precise determination of heavy-metal pollution over the years. 相似文献
20.
A. Raith W. T. Perkins N. J. G. Pearce T. E. Jeffries 《Analytical and bioanalytical chemistry》1996,355(7-8):789-792
Laser ablation inductive coupled plasma – mass spectrometry (LA-ICP-MS) was used to analyse minor and trace elements in the hard parts of a shellfish, representing the environmental changes. A large, long-lived bivalve such as Arctica islandica can produce historical records of trace element fluctuations in seawater. Analytical traverses using LA-ICP-MS were performed from the inner to the outer wall of the shell at different locations. The development of the UV laser system now offers spatial resolution of craters of 10 μm diameter, enabling several analyses between the various growthbands. The elemental changes between growthbands of the shell are discussed, showing the potential for precise determination of heavy-metal pollution over the years. 相似文献