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101.
Simone Dill Jochen Glaser Markus Strbele Sonja Tragl H.‐Jürgen Meyer 《无机化学与普通化学杂志》2004,630(7):987-992
Beyond the Conventional Number of Electrons in M6X12 Type Metal Halide Clusters: W6Cl18, (Me4N)2[W6Cl18], and Cs2[W6Cl18] Black octahedral single crystals of W6Cl18 were obtained by reducing WCl4 with graphite in a silica tube at 600 °C. The single crystal structure refinement (space group R 3¯, Z = 3, a = b = 1498.9(1) pm, c = 845.47(5) pm) yielded the W6Cl18 structure, already reported on the basis of X‐ray powder data. (Me4N)2[W6Cl18] and Cs2[W6Cl18] were obtained from methanolic solutions of W6Cl18 with Me4NCl and CsCl, respectively. The structure of (Me4N)2[W6Cl18] was refined from X‐ray single crystal data (space group P 3¯m1, Z = 1, a = b = 1079.3(1) pm, c = 857.81(7) pm), and the structure of Cs2[W6Cl18] was refined from X‐ray powder data (space group P 3¯, Z = 1, a = b = 932.10(7) pm, c = 853.02(6) pm). The crystal structure of W6Cl18 contains molecular W6Cl18 units arranged as in a cubic closest packing. The structures of (Me4N)2[W6Cl18] and Cs2[W6Cl18] can be considered as derivatives of the W6Cl18 structure in which 2/3 of the W6Cl18 molecules are substituted by Me4N+ ions and Cs+ ions, respectively. The conventional number of 16 electrons/cluster is exceeded in these compounds, with 18 electrons for W6Cl18 and 20 electrons for (Me4N)2[W6Cl18] and Cs2[W6Cl18]. Cs2[W6Cl18] exhibits temperature independent paramagnetic behaviour. 相似文献
102.
The sorption of metal ions (e.g. Cd2+, Cu2+, Ni2+ and Pb2+) from aqueous solution on the anion exchange resin Amberlite IRA-904 modified with tetrakis(4-carboxyphenyl)porphyrin (TCPP) was studied in batch equilibrium experiments. The influence of operating variables such
as initial pH and contact time between solution and the resin on the equilibrium parameters was measured. The selectivity
order of investigated metal ions was evaluated as follows: Pb2+ > Ni2+ > Cu2+ > Cd2+. The matrix cations, such as Mg2+ and Ca2+, exhibit very low affinity for TCPP-modified resin. The rate uptake of the sorption procedure is predominantly controlled
by film diffusion. The best retention kinetic was observed for lead where half the saturation of the TCPP-modified sorbent
was achieved in less than 5 min.
Author for correspondence. E-mail: kryspyrz@chem.uw.edu.pl
Received November 20, 2002; accepted January 26, 2003
Published online May 5, 2003 相似文献
103.
The only molecules that are currently known to fold into unique three-dimensional conformations and perform sophisticated functions are biological polymers - proteins and some RNA molecules. Our aim is to create a nonbiological sequence-specific polymer that folds in aqueous solution. Toward that end, we synthesized sequence-specific 30mer, 45mer, and 60mer peptoid oligomers (N-substituted glycine polymers) consisting of 15mer units we chained together by disulfide and oxime linkages to mimic the helical bundle structures commonly found in proteins. Because these 15mer sequences were previously shown to form defined helical structures that aggregate together at submillimolar concentrations, we expected that by covalently linking multiple 15mers together, they might fold as helical bundles. To probe whether they folded, we used fluorescence resonance energy transfer (FRET) reporter groups. We found that certain constructs fold up with a hydrophobic core and have cooperative folding transitions. Such molecules may ultimately provide a platform for designing specific functions resembling those of proteins. 相似文献
104.
ab initio MO calculations have been performed on the cis and trans isomers of the crotyl cation, free radical and anion in each of two orientations of the Me rotor about the allylic framework. In agreement with available experimental data, both the crotyl cation and free radical prefer trans skeletal geometries. On the other hand, the cis isomer of the crotyl anion is found to be more stable than the trans, the same preference as has been noted for alkali metal allyl organometallics in solution, but opposite to that recently reported for the free (gas phase) anion. The Me groups are predicted to eclipse the partial double bond for the trans isomers of all three systems and for the cis cation. These results are rationalized with the aid of perturbation MO theory. 相似文献
105.
H. G. Kilian 《Colloid and polymer science》1961,176(1):49-62
Zusammenfassung Es wird an Hand von röntgenographischen Messungen an verschiedenen Hochpolymeren gezeigt, daß es durch die spezielle Bauart des Makromoleküls bedingte, anisotrope Kristallstrukturen gibt, die allgemein beim Kristallisieren abgeschreckter Proben eingenommen werden. Dabei ist vorausgesetzt, daß durch das Abschrecken die Kristallisation der betreffenden Hochpolymeren ganz oder auch nur teilweise unterdrückt werden kann. Es werden die Ursachen für die stufenweise Kristallisation der angegebenen Polymeren beim Tempern diskutiert. Die Zunahme der Langperiode während des Strukturwechsels Pseudostruktur Kristallstruktur wird dem selektiven Aufschmelzen der kleinsten Teilchen bei gleichzeitigem Wachsen der stabilen Kristalle zugeschrieben. Dies führt zu der Auffassung, daß das Schmelzen der Hochpolymeren in einem Temperaturintervall von der mittleren Kristallitgröße und von der Kristallitgrößenverteilung abhängt. Beide Größen können i. a. durch unterschiedliche thermische Vorbehandlung der Proben verändert werden, wie es am Beispiel des Polyurethans und des Terephthalsäureglykolesters gezeigt wird. Das Schmelzverhalten verschieden verzweigter Polyäthylene, des Teflons und eines Copolymerisates dieses Polymeren mit Hexafluorpropylen kann durch eine Theorie vonFlory qualitativ richtig wiedergegeben werden. Hierbei werden die mittlere Kristallitgröße und die Kristallitgrößenverteilung durch den Einbau nicht kristallisationsfähiger Atomgruppen in das Makromolekül entscheidend bestimmt. Der Schmelzvorgang selbst wird als eine Umwandlung 1. Ordnung angesehen. Copolymere werden als spezielles Zweikomponentensystem aufgefaßt. Diese schmelzen prinzipiell in einem Temperaturintervall.Ich danke der Deutschen Forschungsgemeinschaft für die Bereitstellung eines Teils der Geriäte und sachlichen Mittel. 相似文献
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