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121.
Helmreich M Ermilov EA Meyer M Jux N Hirsch A Röder B 《Journal of the American Chemical Society》2005,127(23):8376-8385
The synthesis and photophysical studies of a fullerene [6:0]-hexaadduct that carries 12 pyropheophorbide a units are reported. The synthesis started with the malonate 1, which was coupled under template conditions to C(60)() to give the hexaadduct 2. After removal of the protecting group with acid the dodecakis amino-substituted precursor compound 3 was generated. 3 was not isolated but directly reacted with the N-succinimid ester 4 of pyropheophorbide a (5), which delivered the desired fullerene [6:0]-hexaadduct 6 in excellent yield. The photophysical properties of 6 were studied and compared with those of the fullerene [5:1]-hexaadduct 7 with six pyropheophorbide a groups and the bispyropheophorbide a-fullerene [5:1]-hexaadduct 8. The pyropheophorbide a units in 6 undergo after light absorption very efficient energy transfer as well as partly excitonic interaction. The last process results in formation of energy traps, which could be resolved experimentally. Compared to the reference compounds 7 and 8, 6 has a higher probability of trap formation due to a higher local concentration of dye molecules and shorter distances between them. As a consequence, the excitation energy is delivered rapidly (within 23 ps) to the traps, resulting in decreases of the fluorescence, intersystem crossing, and singlet oxygen quantum yields in comparison with the values of the reference compounds. 相似文献
122.
Christa Gensch und Gerhart Jander 《Fresenius' Journal of Analytical Chemistry》1950,130(2-3):200-209
Zusammenfassung Die gleichzeitige quantitative Bestimmung des Ammoniaks und der Phosphorsäure durch eine einzige konduktometrische Titration mit Natronlauge ist nicht nur bei reinen Substanzen, sondern auch bei technischen Düngemittelproben, bzw. in Gegenwart gewisser Fremdsubstanzen möglich.Von den im Handel üblichen Düngesalzen und Mischdüngern sind in Tab. 8 diejenigen zusammengestellt, die hinsichtlich ihres Ammoniakund Phosphorsäuregehaltes nach der beschriebenen konduktometrischen Methode analysiert werden können. Die Tabelle erhebt keinen Anspruch auf Vollständigkeit. — Bezüglich der erreichten Genauigkeit sei noch einmal in Tab. 9 eine kurze Übersicht gegeben. 相似文献
123.
Thomas Gensch M. Sandra Churio Silvia E. Braslavsky Kurt Schaffner 《Photochemistry and photobiology》1996,63(6):719-725
The primary quantum yield, Φ1700, for the photoconver-sion of the red-absorbing form of phytochrome, Pr, to the set of primary intermediates, Ii700, was redetermined by laser-induced optoacoustic spectroscopy at very low excitation laser fluences. The Ii700 value obtained is in the range of ΦPfr reported for the complete phototransformation Pr→ Pfr (J. M. Kelly and C. Lagarias, 1985, Biochemistry 24 , 4003–6010). An energy level of ca 150 kJ/ mol was found for the intermediates Ii700, i.e. ca 85% of the 0–0 level of Pr. Furthermore, a molecular expansion of 7 mL/mol (equivalent to 11 Å3/molecule) was determined for the Pr→ Ii700 transformation. It reflects the protein reorganization induced by the geometrical pho-toisomerization of the chromophore, which results in changes of bonding interactions, in particular between the chromophore and its protein surrounding. 相似文献
124.
Timo A. Kinder René Pior Dr. Sebastian Blomeyer Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Norbert W. Mitzel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(23):5899-5903
Chlorogermane (C2F5)3GeCl with very electronegative pentafluoroethyl groups was converted with LiCH2P(tBu)2 to obtain the intramolecular frustrated Lewis pair (FLP) (C2F5)3GeCH2P(tBu)2, a neutral, germanium-based FLP. Its reactivity was compared to its silicon homologue (C2F5)3SiCH2P(tBu)2. Both FLPs cleave NO but give cyclic (Si) and open-chain oxides (Ge). In reactions with HCl both FLPs gave the same adduct type in the solid state, while the proton seems more mobile in solution in the germanium case. Reactions with PhCNO and Me3SiCHN2 result in ring-type adducts. The structures of (C2F5)3GeCH2P(tBu)2 and of five adducts with substrates were elucidated by X-ray diffraction. The study clearly showed the germanium compound to have a more moderate Lewis acidity compared to the silicon analogue. 相似文献
125.
126.
Andrea Berlich Beate Flemmig Gunther Wittstock 《Journal of Solid State Electrochemistry》2001,6(1):29-38
A polymer-modified electrode can be formed from 2-mercaptobenzoxazole (MBO) on glassy carbon (GC) electrodes in aqueous solution.
Film formation occurs during prolonged cycling with positive scan limits above +600 mV vs. SCE. The main redox process is
the oxidation of MBO to bis(benzoxazolyl) disulfide and the re-reduction to MBO. However, several side reactions including
polymerization are observed. A density functional calculation of the MBO radical shows that there is a considerable spin density
not only at the sulfur atom but also at the nitrogen atom and at some of the carbon atoms. Therefore ring-ring coupling products
other than the disulfide can be formed which may further react to the polymer film. Notably, FTIR spectra indicate substitution
at the nitrogen atom. The coupling would explain the occurrence of both thione and bridging sulfur as well as amine and imine
nitrogen in the formed polymer. These binding states in the film have been identified by X-ray photoelectron spectroscopy
(XPS). Elemental sulfur could not be detected by cyclic voltammetry or XPS of cooled samples. The polymer film is not redox
active and non-conducting, as illustrated by the self-limiting growth and the diminishing currents during the potentiodynamic
film growth. The film is impermeable for anions. At pH 7 the film is permeable for cations, while it is impermeable for anions
and cations at pH 4.
Electronic Publication 相似文献
127.
M. Sc. Stefan Mattsson Prof. Dr. Beate Paulus M. Sc. Frenio A. Redeker Dr. habil. Helmut Beckers Prof. Dr. Sebastian Riedel Dr. Carsten Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3318-3324
The cohesive energy of α-fluorine, with C2/c space group symmetry, was calculated at benchmark quality by applying the method of increments. The known experimental X-ray structure data needed to be refined, since the reported intramolecular bond length was unrealistically large. At the CCSD(T) level, including corrections for zero-point energy, the basis set superposition error, and extrapolated to the complete basis set limit, a cohesive energy of −8.72 kJ mol−1 was calculated, which agrees well with the 0 K-extrapolated experimental value of −8.35 kJ mol−1. 1 Comparison of the C2/c structure with a Cmca structure, isotypic to that of chlorine, bromine, and iodine reveals that the origin of the different structure of solid fluorine, compared to the heavier halogens, is the lack of significantly stabilizing σ-hole interactions. In addition, the wave numbers of the stretching mode in solid fluorine were calculated at coupled cluster level and compared to newly recorded Raman spectra of condensed fluorine. Both experiment and calculation indicate a slight up-shift for the stretching mode by 2 or 5 cm−1, respectively, with respect to a free F2 molecule in the gas phase. 相似文献
128.
Robin F. Weitkamp Beate Neumann Hans‐Georg Stammler Berthold Hoge 《Angewandte Chemie (International ed. in English)》2019,58(41):14633-14638
The reaction of a strongly basic phosphazene (Schwesinger base) with water afforded the corresponding metastable hydroxide trihydrate [OH(OH2)3]? salt. This is the first hydroxide solvate that is not in contact with a cation and furthermore one of rare known water‐stabilized hydroxide anions. Thermolysis in vacuum results in the decomposition of the hydroxide salt and quantitative liberation of the free phosphazene base. This approach was used to synthesize the Schwesinger base from its hydrochloride salt after anion exchange in excellent yields of over 97 %. This deprotonation method can also be used for the phosphazene‐base‐catalyzed preparation of the Ruppert–Prakash reagent Me3SiCF3 using fluoroform (HCF3) as the trifluoromethyl building block and sodium hydroxide as the formal deprotonation agent. 相似文献
129.
130.