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71.
72.
Andrews PC Deacon GB Junk PC Kumar I Silberstein M 《Dalton transactions (Cambridge, England : 2003)》2006,(40):4852-4858
Two synthetic approaches to the formation of bismuth(III) carboxylates have been explored and compared. Ph(3)Bi was reacted with a series of carboxylic acids (RCO(2)H) of varying pK(a) and functionality (R = PhCH[double bond, length as m-dash]CH, o-MeOC(6)H(4), m-MeOC(6)H(4), o-H(2)NC(6)H, o-O(2)NC(6)H(4), p-O(2)NC(6)H(4), 2-(C(5)H(4)N)) under reflux conditions in toluene and solvent-free. The thermochemical profiles of the solvent-free reactions were also studied by DSC-TGA. All reactions produced the tri-substituted bismuth carboxylates in comparable yields and purity with the exceptions of picolinic acid and p-nitrobenzoic acid. 2-Picolinic acid exclusively formed the di-substituted complex, [PhBi(2-(C(5)H(4)N)CO(2))(2)](4), by both methods, while p-nitrobenzoic acid gave the tri-substituted complex through reflux and the di-substituted complex under solvent-free conditions. Two of the complexes were structurally authenticated by single crystal X-ray diffraction: [PhBi(2-(C(5)H(4)N)CO(2))(2)](4) is tetrameric formed through five membered chelate rings involving the pyridyl N and O(-C) rather than the less stable carboxylate (-CO(2)) chelates, while [Bi(o-MeOC(6)H(4)CO(2))(3)](infinity), is a polymer in which dimeric units, constructed around two chelating and one unsymmetrical bridging carboxylate on each Bi centre, are then joined together through longer intermolecular Bi-O bridging bonds. 相似文献
73.
Cole ML Deacon GB Forsyth CM Konstas K Junk PC 《Dalton transactions (Cambridge, England : 2003)》2006,(27):3360-3367
Treatment of calcium or strontium with 2.0 equivalents of N,N-bis(o-methylphenyl)formamidine (o-TolFormH), N,N-bis(2,6-dimethylphenyl)formamidine (XylFormH) or N,N-bis(o-phenylphenyl)formamidine (o-PhPhFormH) in the presence of 1.0 equivalent of Hg(C6F5)2 in tetrahydrofuran (thf) affords the bis(formamidinate) complexes [Ca(o-TolForm)2(thf)2] (1), [Ca(XylForm)2(thf)2] (2), [Ca(o-PhPhForm)2(thf)2].thf (3), [Sr(o-TolForm)2(thf)3] (4), [Sr(XylForm)2(thf)3].3thf (5) and [Sr(o-PhPhForm)2(thf)3].2thf (6). Analogous reactions with barium were generally unsatisfactory but [Ba(o-PhPhForm)2(thf)3].2thf (7) was successfully prepared. Compounds 1-7 have been characterised by various spectroscopic methods (1H, 13C{1H} NMR and IR), elemental analyses and, for 1, 2 and 4-6, X-ray crystallography. The calcium complexes are monomeric and six-coordinate with either transoid octahedral or trigonal prismatic geometry, whilst the larger radius of strontium accommodates an additional thf solvent donor to give seven-coordinate structures with two types of coordination polyhedra. 相似文献
74.
This work describes the first approach in the development of a comprehensive classification method for bitterness of small molecules. The data set comprises 649 bitter and 13 530 randomly selected molecules from the MDL Drug Data Repository (MDDR) which are analyzed by circular fingerprints (MOLPRINT 2D) and information-gain feature selection. The feature selection proposes substructural features which are statistically correlated to bitterness. Classification is performed on the selected features via a na?ve Bayes classifier. The substructural features upon which the classification is based are able to discriminate between bitter and random compounds, and thus we propose they are also functionally responsible for causing the bitter taste. Such substructures include various sugar moieties as well as highly branched carbon scaffolds. Cynaropicrine contains a number of the substructural features found to be statistically associated with bitterness and thus was correctly predicted to be bitter by our model. Alternatively, both promethazine and saccharin contain fewer of these substructural features, and thus the bitterness in these compounds was not identified. Two different classes of bitter compounds were identified, namely those which are larger and contain mainly oxygen and carbon and often sugar moieties, and those which are rather smaller and contain additional nitrogen and/or sulfur fragments. The classifier is able to predict 72.1% of the bitter compounds. Feature selection reduces the number of false-positives while also increasing the number of false negatives to 69.5% of bitter compounds correctly predicted. Overall, the method presented here presents both one of the largest databases of bitter compounds presently available as well as a relatively reliable classification method. 相似文献
75.
A microfluidic SELEX prototype 总被引:5,自引:0,他引:5
Hybarger G Bynum J Williams RF Valdes JJ Chambers JP 《Analytical and bioanalytical chemistry》2006,384(1):191-198
Aptamers are nucleic acid binding species capable of recognizing a wide variety of targets ranging from small organic molecules
to supramolecular structures, including organisms. They are isolated from combinatorial libraries of synthetic nucleic acid
by an iterative process referred to as SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Here we describe
an automated microfluidic, microline-based assembly that uses LabView-controlled actuatable valves and a PCR machine, and
which is capable of the selection and synthesis of an anti-lysozyme aptamer as verified by sequence analysis. The microfluidic
prototype described is 1) a simple apparatus that is relatively inexpensive to assemble, making automated aptamer selection
accessible to many investigators, and 2) useful for the continued “morphing” of macro→meso→microfabricated structures until
a convergence to a few functional systems evolves and emerges, partly or completely achieving simpler, smaller and more rapid
SELEX applications. 相似文献
76.
Kurdyumov AV Lin N Hsung RP Gullickson GC Cole KP Sydorenko N Swidorski JJ 《Organic letters》2006,8(2):191-193
[reaction: see text] A Lewis acid-catalyzed formal cycloaddition of alpha,beta-unsaturated aldehydes with 6-methyl-4-hydroxy-2-pyrone, 1,3-diketones, and vinylogous silyl esters is described here. 相似文献
77.
Anna Dall’Acqua Klaus Deckelnick Glen Wheeler 《Calculus of Variations and Partial Differential Equations》2013,48(3-4):293-313
In the class of surfaces with fixed boundary, critical points of the Willmore functional are naturally found to be those solutions of the Euler-Lagrange equation where the mean curvature on the boundary vanishes. We consider the case of symmetric surfaces of revolution in the setting where there are two families of stable solutions given by the catenoids. In this paper we demonstrate the existence of a third family of solutions which are unstable critical points of the Willmore functional, and which spatially lie between the upper and lower families of catenoids. Our method does not require any kind of smallness assumption, and allows us to derive some additional interesting qualitative properties of the solutions. 相似文献
78.
Morris RH Bencsik M Nestle N Galvosas P Fairhurst D Vangala A Perrie Y McHale G 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):159-167
MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl-sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar. 相似文献
79.
Direct thermally induced reactions between rare earth metals (Ln = Y,Ce, Dy, Ho, and Er) activated by Hg metal and 3,5‐diphenylpyrazole (Ph2pzH) or 3,5‐di‐tert‐butylpyrazole (tBu2pzH) yielded either homoleptic complexes [Lnn(R2pz)3n] or a heteroleptic complex [Ln(Ph2pz)3(Ph2pzH)2] From Ph2pzH, [Ce3(Ph2pz)9], [Dy2(Ph2pz)6], [Ho2(Ph2pz)6], and [Y(Ph2pz)3(Ph2pzH)2] were isolated. The first has a bowed trinuclear Ce3 backbone with two η2 pyrazolate ligands on the terminal metal atoms and one on the middle, and bridging by both μ‐η2:η2 and μ‐η2:η5 ligands between the terminal and the central Ce atoms. Although both the Dy and Ho complexes are dinuclear, the former has the rare μ‐η2:η1 bridging whilst the latter has μ‐η2:η2 bridging. Thus the dysprosium complex is seven‐coordinate and the holmium is eight‐coordinate, in contrast to any correlation with Ln3+ ionic radii, and the series has a remarkable structural discontinuity. The heteroleptic Y complex is eight coordinate with three chelating Ph2pz and two transoid unidentate Ph2pzH ligands. From tBu2pzH, dimeric [Ln2(tBu2pz)4] (Ln = Ce, Er) were isolated and are isomorphous with eight coordinate Ln atoms ligated by two chelating terminal tBu2pz and two μ‐η2:η2 tBu2pz donor groups. They are also isomorphous with previously reported La, Nd, Yb, and Lu complexes. 相似文献
80.
Highly [1 1 1]-oriented rhombohedral hetero-structure epitaxy of cubic SiGe semiconductor on trigonal c-plane sapphire was achieved and characterized with two new advanced X-ray diffraction methods to control the formation of primary-twin crystals. The formation of twin crystals on (1 1 1) plane was controlled with growth parameters such that the volume percentage of primary-twin crystal was reduced from 40% to 0.3% compared to the majority single crystal. The control of stacking faults can yield single-crystalline semiconductors without defects or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. In this study, about 94% of all epitaxial layers were fabricated in a single-crystalline phase. We propose the temperature-dependent alignment model of energetically favored majority single-crystalline SiGe layer on c-plane sapphire. This study shows that nearly single-crystalline cubic semiconductors can be grown in the [1 1 1] orientation on the basal (0 0 0 1) planes of selected trigonal crystal substrates. 相似文献