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排序方式: 共有466条查询结果,搜索用时 15 毫秒
101.
At the dissolution of anhydrous bismuth(III) trifluoromethanesulfonate in N,N-dimethylthioformamide (DMTF) a deep red-orange complex, lambda(max) = 457 nm, is formed. Bismuth(III) is reduced by the solvent to a low-valent oxidation state stabilized by the sulfur-coordinating solvent DMTF. The obtained complex is weakly solvated seen by a low EXAFS amplitude and a slightly higher absorption energy of the L(III) edge than of the DMTF-solvated bismuth(III) ion. The EXAFS data reveal a dimeric bismuth complex solvated by a single DMTF molecule, which sulfur atom bridges the bismuth atoms. The Bi-S bond distance is 2.543(2) A, and the Bi...Bi distance is 3.929(7) A giving a Bi-S-Bi angle of 101.2(4) degrees. The very low number of coordinated solvent molecule shows that the lone electron pairs of the reduced bismuth ions are stereochemically active. Cyclic voltammetry investigations provide evidence that at least one bismuth atom in the dimer exists in an oxidation state lower than +III, seen by two peaks at approximately -0.36 and -0.57 V in the reduction half-cycle. The absence of EPR signals excludes the presence of bismuth(II) radicals. 相似文献
102.
Sahre K Eichhorn KJ Günther M Suchaneck G Gerlach G 《Analytical and bioanalytical chemistry》2004,378(2):396-401
Thin polyimide (PI) and polyethersulfone (PES) films are widely used as functional layers for microelectronic sensors. Ion implantation modifies the layer structure and morphology of these polymers and hence results in new mechanical and optical properties. However, ion-modified layers also show a change in sensitivity to moisture uptake under specific conditions. This is important for developing humidity sensors. Therefore, the water sorption ability of such modified polymer layers is studied by spectroscopic ellipsometry under definite relative humidity conditions (1–95%). Swelling data were obtained by fitting procedures based on changes of effective layer thickness and optical constants due to water uptake. Irradiation doses from 0.5 to 5×1015 B+ cm–2 at an energy of 180 keV were used for polymer modification. At irradiation doses from 0.5 to 0.7×1015 B+ cm–2, the maximum out-of-plane swelling is reached. At higher doses >2×1015 B+ cm–2, the swelling decreases and corresponds to values of the pure polymer layers. The wetting properties of the layer surfaces determined by contact angle measurements are important to explain this behavior. 相似文献
103.
Blomberg D Hedenström M Kreye P Sethson I Brickmann K Kihlberg J 《The Journal of organic chemistry》2004,69(10):3500-3508
A beta-turn mimetic in which the four amino acids of a beta-turn have been replaced by a 10-membered ring has been designed, synthesized, and subjected to conformational studies. In the mimetic, the intramolecular CO(i)-HN(i)(+3) hydrogen bond that is often found in beta-turns has been replaced by an ethylene bridge. In addition, the amide bond between residues i and i + 1 was exchanged for a methylene ether isoster. Such a beta-turn mimetic, based on the first four residues of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu), was prepared in 15 steps. The synthesis relied on a beta-azido alcohol prepared in five steps from Cbz-Tyr(tBu)-OH as a key, i-position building block. tert-Butyl bromoacetate, glycine, and a Phe-Leu dipetide were then used as building blocks for positions i + 1, i + 2, and i + 3, respectively. Conformational studies based on (1)H NMR data showed that the beta-turn mimetic was flexible, but that it resembled a type-II beta-turn at low temperature. This low energy conformer closely resembled the structure determined for crystalline Leu-enkephalin. 相似文献
104.
I. Halász A. Kroneisen H. O. Gerlach und P. Walkling 《Fresenius' Journal of Analytical Chemistry》1968,234(2):81-97
Zusammenfassung Probleme der schnellen Flüssigkeits-Chromatographie mit Eingangsdrucken bis 300 at werden diskutiert. Eine Näherungsformel für die Abschätzung der Permeabilität gepackter Säulen (Teilchengröße 30 bis 200 m) wird vorgeschlagen. Vor- und Nachteile verschiedenartiger Hochdruckpumpen werden zusammengefaßt. Eine einfache Regelanordnung zur Glättung der Pumpenpulsation, ein Regelsystem für Druckprogrammierung und ein System für das Einspritzen der Proben unter hohem Druck werden beschrieben. Eine blasenfreie Förderung der Flüssigkeit ohne Entgasen derselben konnte erreicht werden. Die Bandenverbreiterung innerhalb und außerhalb der Kolonne wird besprochen. Die Detektoren werden nach der Art der Anzeige und der Empfindlichkeit klassifiziert.
Symbolverzeichnis at 1 Kilopond/cm2 Druck - c Konzentration - d p Teilchengröße des Trägermaterials [cm] - h Bandenverbreiterung in der Kolonne, HETP [cm] - h gem. L(w/4t R)2 = gemessene Bandenverbreiterung, [cm] - h z r 224DL = Bandenverbreiterung in der Zuleitung, bezogen auf die Kolonnenlänge [cm] - f Pumpfrequenz [sec–1] - l Länge der Zuleitung [cm] - m Masse - p Druckabfall an der Kolonne [1 at = 9,81 · 105 dyn/cm2] - r Radius [cm] - t Zeit - t R Retentionszeit [sec] - u lineare Geschwindigkeit der mobilen Phase [cm] - w Bandenbreite, Achsenschnitt der Wendetangenten an der Basislinie [sec] - C pneumatische Kapazität [cm/dyn oder cm3/at] - D Interdiffusionskoeffizient [cm2sec–1] - F Volumengeschwindigkeit der mobilen Phase [cm3sec–1] - K Permeabilitätskonstante oder Permeabilität [cm2] - L Kolonnenlänge [cm] - V Volumen - Porosität - Viscosität der beweglichen Phase [poise] - 2 Varianz der Bande in Längeneinheiten [cm] Die Autoren möchten der Deutschen Forschungsgemeinschaft, Bad Godesberg, für finanzielle Unterstützung danken, mit der diese Arbeit durchgeführt werden konnte. 相似文献
Summary Problems of speedy liquid chromatography with inlet pressures up to 300 at are discussed. An approximation formula is given for the estimation of the permeability of packed columns with particle sizes between 30–200 m. Advantages and disadvantages of different types of high pressure pumps are summarized. Simple controlling equipments for smoothing the pulsation of high pressure pumps, a device for pressure program and a sample injection system are described. A gas-bubble free flow was achieved without degassing the liquid. Peak broadening effects inside and outside the column are calculated. The detectors are classified due to the kind of their recording and that of their sensitivity.
Symbolverzeichnis at 1 Kilopond/cm2 Druck - c Konzentration - d p Teilchengröße des Trägermaterials [cm] - h Bandenverbreiterung in der Kolonne, HETP [cm] - h gem. L(w/4t R)2 = gemessene Bandenverbreiterung, [cm] - h z r 224DL = Bandenverbreiterung in der Zuleitung, bezogen auf die Kolonnenlänge [cm] - f Pumpfrequenz [sec–1] - l Länge der Zuleitung [cm] - m Masse - p Druckabfall an der Kolonne [1 at = 9,81 · 105 dyn/cm2] - r Radius [cm] - t Zeit - t R Retentionszeit [sec] - u lineare Geschwindigkeit der mobilen Phase [cm] - w Bandenbreite, Achsenschnitt der Wendetangenten an der Basislinie [sec] - C pneumatische Kapazität [cm/dyn oder cm3/at] - D Interdiffusionskoeffizient [cm2sec–1] - F Volumengeschwindigkeit der mobilen Phase [cm3sec–1] - K Permeabilitätskonstante oder Permeabilität [cm2] - L Kolonnenlänge [cm] - V Volumen - Porosität - Viscosität der beweglichen Phase [poise] - 2 Varianz der Bande in Längeneinheiten [cm] Die Autoren möchten der Deutschen Forschungsgemeinschaft, Bad Godesberg, für finanzielle Unterstützung danken, mit der diese Arbeit durchgeführt werden konnte. 相似文献
105.
The solvation of the mercury(II) ion in solvents with different solvation properties, water, dimethylsulfoxide, N,N-dimethylthioformamide, and liquid ammonia, has been studied by means of (199)Hg NMR. The (199)Hg chemical shift shows a pronounced dependence on the coordination number of the mercury(II) ion in the solvates resulting in a difference of over 1200 ppm between basically tetrahedral and octahedral complexes. The chemical shifts can furthermore be associated with electron-pair donor properties of the solvents. The spin-lattice relaxation times of the (199)Hg nucleus in the solvates have been measured at different applied magnetic fields, concentrations, temperatures, and isotope substitutions. Possible mechanisms for the (199)Hg relaxation were proposed and the chemical shielding anisotropy in the solvates has been estimated. The (199)Hg relaxation rates and the anisotropy are correlated with the structure of the solvate complexes in solution obtained from recent LAXS and EXAFS studies. 相似文献
106.
Chillemi G Barone V D'Angelo P Mancini G Persson I Sanna N 《The journal of physical chemistry. B》2005,109(18):9186-9193
In this paper, we present a state-of-the-art 100 ns molecular dynamics simulation of a cadmium(II) aqueous solution that highlights a very flexible ion first coordination shell which transits between hexa- and heptahydrated complexes. From this investigation, a dynamical picture of the water exchange process emerges that takes place through an associative mechanism for the solvent substitution reaction. Our procedure starts from the generation of an effective two-body potential from quantum mechanical ab initio calculations in which the many-body ion-water terms are accounted for by the polarizable continuum method (PCM). This approach is computationally very efficient and has allowed us to carry out extremely long molecular dynamics simulations, indispensable to reproduce the dynamic properties of the cadmium(II) aqueous solution. Quantum mechanical ab initio calculations of the hexa- and heptahydrated complexes extracted from MD configurations have revealed stable minima for both clusters with the water molecules arranged in T(h)() and C(2) symmetries in the hexa- and heptahydrated complexes, respectively, with a slight energetic preference for the heptahydrated one. Finally, a comparison of the calculated hexa- and heptahydrated cluster IR and Raman spectra with the experimental data in the literature, has demonstrated that the IR spectroscopy is not able to distinguish between the two species, whereas the Raman spectrum of the Cd(2+)-(H(2)O)(7) cluster provides a better agreement with the experimental data. 相似文献
107.
Unusual surface structures of Na on Ni (110) occur in which evenly spaced Na atoms are positioned incoherently with respect to the Ni substrate atoms along troughs in the close packed direction of the substrate surface. In the first case considered for coverages between about 0.25 and 0.31 monolayers, alternate troughs on the Ni(110) surface contain incoherent rows of Na atoms. The rows are randomly out of phase with one another and in addition the interatomic spacing between Na atoms in these rows varies inversely with the coverage. The second case concerns coverages from about 0.64 to 0.71 monolayers where every trough contains an incoherent row of Na atoms and the rows are in phase with one another. The interpretation of the one-dimensionally incoherent sodium structures and their dependency on the two-fold symmetry of the substrate discussed in this study may have applicability to surface structures observed in other similar LEED adsorption studies. 相似文献
108.
Ostwald Wo. Hückel E. Henning F. Franck J. Gerlach W. Paneth F. Minkowsky R. Sponer H. Günther P. Katz I. R. Deckert A. Winter H. Münder W. Krebs P. Hecht W. Winkel A. Schulz H. Gramm H. Günther-Schulze A. Fischer J. Heimerle A. Seiler Fr. Oppenheimer Karl Kuhn R. Elsner Fr. Plücker W. Dietrich E. Kaminer S. Rassow B. Loesche A. 《Analytical and bioanalytical chemistry》1924,65(8):323-323
Analytical and Bioanalytical Chemistry - 相似文献
109.
Robert F. Gerlach Kenneth M. Mackay Brian K. Nicholson 《Journal of organometallic chemistry》1979,178(2):C30-C32
The room-temperature reaction of NaCo(CO)4 with halogermanes, or Co2(CO)8 with GeH4, gives GeCo4(CO)14 which is assigned a Ge[Co2(CO)7]2 structure on infrared evidence. This new species eliminates one CO at 50°C to give (CO)4CoGeCO3(CO)9 and adds further CO(CO)4- to give anionic [GeCo6(CO)n]2-. 相似文献
110.
Ingmar Polenz Friedrich Georg Schmidt Stefan Spange 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):687-695
The brutto rate of the imine base/isocyanate (IBI)‐mediated radical polymerization of methyl methacrylate (MMA) can be significantly increased by use of ionic liquid (IL) traces. At least, catalytic amounts of IL influence both the value of the brutto polymerization rate νBr,0 and the necessary reaction temperature of the used IBI mixture. Combinations of 2‐phenyl‐2‐oxazoline (POX) or 1‐methyl pyrazole (1MP) with isocyanates are IBI systems that usually do not initiate MMA at room temperature. By adding traces of 1‐ethyl‐3‐methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([Emim]FAP), polymethyl methacrylate (PMMA) with high average molecular weight can be obtained whereas the initiator mixture (imine base/isocyanate) concentration can be decreased by a factor of 10. The polymerization kinetics of several IBI combinations in the presence of ILs has been determined and a comparison to non‐IL containing initiator mixtures is given. Additionally, the temperature dependence of the IL‐containing polymerizations was measured. The interaction of the IL with MMA and the individual IBI initiator components is studied by means of attenuated total reflection Fourier transformation middle infrared spectroscopy (ATR FT MIR). Furthermore, the IBI brutto polymerization rate constants kBr,0 were brought into relation to the IL hydrogen bond donating ability α. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献