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排序方式: 共有59条查询结果,搜索用时 15 毫秒
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Günther Kraft Dieter Lindenberger Heinz Beck 《Fresenius' Journal of Analytical Chemistry》1976,282(2):119-121
Zusammenfassung Die Intensität des flammenabsorptionsspektrometrischen Cr-Signals hängt in einer sehr komplexen Weise von der Wertigkeit des Chroms und der Flammentemperatur ab. Ferner ist ein ausgeprägter Kalium-Einfluß vorhanden. Alle diese Schwierigkeiten können am besten dadurch eliminiert werden, daß in der Lachgasflamme gearbeitet und die Analysenlösung mit einer höheren K-Konzentration gepuffert wird.
Effect of valency on the determination of chromium by flame absorption spectrometry
The intensity of the chromium signal in AAS depends in a very complex manner strongly on the valency of the Cr and the flame temperature. It is furthermore influenced by potassium, if present. The best way to overcome all these interferences is to use the nitrous oxide flame and to buffer the solution with a higher concentration of potassium.相似文献
3.
Tamam L Kraack H Sloutskin E Ocko BM Pershan PS Ulman A Deutsch M 《The journal of physical chemistry. B》2005,109(25):12534-12543
The molecular-scale structure and phase behavior of single-component Langmuir films of 4'-methyl-4-mercaptobiphenyl (MMB) and 4'-perfluoromethyl-4-mercaptobiphenyl (FMMB) on mercury were studied using surface tensiometry, grazing incidence X-ray diffraction, and X-ray reflectivity. At low coverages, a condensed but in-plane disordered single layer of surface-parallel molecules is found for both compounds. At high coverages, both compounds exhibit in-plane-ordered phases of standing-up molecules. For MMB, the biphenyl core dominates the structure, yielding a centered-rectangular unit cell with an area A(x) of 21.8 A(2)/molecule, with molecules tilted by approximately 14 degrees from the surface normal in the nearest-neighbor direction, and a coherence length xi of >1000 A for the crystalline domains. For FMMB, the perfluoromethyl group dominates the structure, yielding a hexagonal unit cell with untilted molecules, an area A(x) of 24.2 A(2)/molecule, and a much smaller xi of approximately 110 A. The structure is discussed in comparison with self-assembled monolayers of MMB on crystalline Au(111) and similar-length alkanethiolate SAMs on Au(111) and on mercury. The differences in the structure are discussed and traced to the differences in the substrate's surface structure, and in the molecular cross section and rigidity. 相似文献
4.
Shafi KV Ulman A Lai J Yang NL Cui MH 《Journal of the American Chemical Society》2003,125(14):4010-4011
We present a new route for the preparation of gamma-alumina and YAG nanoparticles. Metal salts of ethylhexanoic acids provide good solubility in hydrocarbon solvents and allow efficient ultrasonication. The sonication product is an alumioxane gel, which can reversibly collapse and reform, depending on the solvent used. The dried gel nanoparticles are calcined at temperatures significantly lower than those used in conventional syntheses, resulting in gamma-alumina nanoparticles. This is due to the complete mixing of elements at the atomic level and the small size of the formed nanoparticles. 相似文献
5.
Chr v. Faber du Faur K. H. Lindenberger 《Zeitschrift für Physik A Hadrons and Nuclei》1962,169(2):286-288
For the halflife of the 1,49 MeV state in Co57 an upper limit of 3,0 × 10?10 sec. has been found. 相似文献
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The hyperfine structures of the z7P3 and z7P4 states of 95Mo and 97Mo have been investigated by levelcrossing spectroscopy. A fit of the experimental signal curves yields the magnetic and electric hfs coupling constants: 95Mo z7P3 |A| = 86.19(10) MHz, |B|=5.2(30) MHz, A/B095Mo z7P4 |A|=64.05(30) MHz, |B|=4.3(30) MHz, A/B<0; 97Mo z7P3|A|= 88.0(1) MHz, |B|=60.0(20) MHz, A/B<0; 97Mo z7P4 |A|=65.4(3) MHz, |B|=50.0(50) MHz, A/B0. For the ratio of the electric quadrupole moments we fine 97Q/95 Q= -11.5(70). 相似文献
9.
Mark B. Fischer Donald F. Gaines Jeffrey A. Ulman 《Journal of organometallic chemistry》1982,231(1):55-62
Reaction of 2-XB5H8 (X Cl, Br) with Naco(CO)4 produces the transiently stable 2-[Co(CO)4]B5H8. The similar 2-[(η5-C5H5)Fe(CO)2]B5H8, which exhibits much greater thermal stability, is prepared by reaction of LiB5H8 with (η5-C5H5)Fe(CO)2I. Reactions of CO2(CO)8 with B5H9 under a variety of conditions produce 2-[Co(CO)4]B5H8 along with an inseparable impurity that appears to be 1-[Co(CO)4]B5H8. 相似文献
10.
Wyatt Cole Stephanie L. Hemmingson Audrey C. Eisenberg Catherine A. Ulman Joseph M. Tanski Yutan D. Y. L. Getzler 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(1):65-69
Four 2,2′‐bisindolylmethanes (BIMs), a useful class of polyindolyl species joined to a central carbon, were synthesized using salicylaldehyde derivatives and simple acid catalysis; these are 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐6‐methylphenol, (IIa), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐dichlorophenol, (IIb), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4‐nitrophenol, (IIc), and 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐di‐tert‐butylphenol, (IId). BIMs (IIa) and (IIb) were characterized crystallographically as the dimethyl sulfoxide (DMSO) disolvates, i.e. C26H24N2O·2C2H6OS and C25H20Cl2N2O·2C2H6OS, respectively. Both form strikingly similar one‐dimensional hydrogen‐bonding chain motifs with the DMSO solvent molecules. BIM (IIa) packs into double layers of chains whose orientations alternate every double layer, while (IIb) forms more simply packed chains along the a axis. BIM (IIa) has a remarkably long c axis. 相似文献