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61.
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63.
Stähler M Wynands R Knappe S Kitching J Hollberg L Taichenachev A Yudin V 《Optics letters》2002,27(23):2130
In our recent Letter,(1) Ref. 12 was printed incorrectly. The correct reference is M. Zhu, Coherent population trapping-based frequency standard and method for generating a frequency standard incorporating a quantum absorber that genrates the CPT state with high frequency, U.S. patent 6,359,916 (March 19, 2002). 相似文献
64.
Ruthenium(II)‐Catalyzed CH Activation/Alkyne Annulation by Weak Coordination with O2 as the Sole Oxidant 下载免费PDF全文
M. Sc. Svenja Warratz Dr. Christoph Kornhaaß M. Sc. Ana Cajaraville Benedikt Niepötter Prof. Dr. Dietmar Stalke Prof. Dr. Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2015,54(18):5513-5517
Aerobic oxidative C? H functionalizations of weakly coordinating benzoic acids have been accomplished with versatile ruthenium(II) biscarboxylates under ambient oxygen or air. Mechanistic studies identified the key factors controlling the elementary step of the oxidation of the ruthenium(0) complex. 相似文献
65.
E. Knappe und I. Rohdewald 《Fresenius' Journal of Analytical Chemistry》1965,208(3):195-200
Zusammenfassung Die Trennung bzw. Identifizierung einer grö\eren Zahl technisch bedeutsamer substituierter Amide der AcetessigsÄure gelang durch Kombination von zwei einfachen dünnschichtchromatographischen Anordnungen. Als stationÄre Phasen wurden dabei ImprÄgnierschichten aus Kieselgur mit AdipinsÄurediÄthylenglykolpolyester und Normalschichten aus hochreinem Kieselgel benutzt. Als mobile Phase diente in beiden Anordnungen eine Mischung aus DiisopropylÄther, PetrolÄther, Kohlenstofftetrachlorid, AmeisensÄure und Wasser (50202081). Für die Identifizierung erwiesen sich Mengen von etwa 4–5 g als ausreichend.
Für die gewissenhafte Mitwirkung an unseren experimentellen Arbeiten fühlen wir uns Herrn U. Strauss sehr verbunden.
II. Mitteilung: Knappe, E., u. K. G. Yekundi: diese Z. 203, 87 (1964). 相似文献
Summary Separation resp. identification of a considerable number of technically important substituted amides of acetoacetic acid was achieved by combination of two thin-layer chromatographic runs under simple conditions. Layers of kieselguhr impregnated with adipic acid diethyleneglycol polyester as well as layers of high purity silica gel have been used as stationary phases. The mobile phase in both cases consisted of a mixture of diisopropyl ether, petroleum ether, carbon tetrachloride, formic acid and water (50202081). Quantities of about 4–5 g were sufficient for identification.
Für die gewissenhafte Mitwirkung an unseren experimentellen Arbeiten fühlen wir uns Herrn U. Strauss sehr verbunden.
II. Mitteilung: Knappe, E., u. K. G. Yekundi: diese Z. 203, 87 (1964). 相似文献
66.
67.
First Examples of de Vries‐like Smectic A to Smectic C Phase Transitions in Ionic Liquid Crystals 下载免费PDF全文
Dr. Nadia Kapernaum Carsten Müller Svenja Moors M. Christian Schlick Eugen Wuckert Prof. Dr. Sabine Laschat Prof. Dr. Frank Giesselmann 《Chemphyschem》2016,17(24):4116-4123
In ionic liquid crystals, the orthogonal smectic A phase is the most common phase whereas the tilted smectic C phase is rather rare. We present a new study with five novel ionic liquid crystals exhibiting both a smectic A as well as the rare smectic C phase. Two of them have a phenylpyrimidine core whereas the other three are imidazolium azobenzenes. Their phase sequences and tilt angles were studied by polarizing microscopy and their temperature‐dependent layer spacing as well as their translational and orientational order parameters were studied by X‐ray diffraction. The X‐ray tilt angles derived from X‐ray studies of the layer contraction and the optically measured tilt angles of the five ionic liquid crystals were compared to obtain their de Vries character. Four of our five mesogens turned out to show de Vries‐like behavior with a layer shrinkage that is far less than that expected for conventional materials. These materials can thus be considered as the first de Vries‐type materials among ionic liquid crystals. 相似文献
68.
Dr. Fabian Ehret Dr. Vasileios Filippou Svenja Blickle Dr. Martina Bubrin Dr. Stanislav Záliš Prof. Dr. Wolfgang Kaim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3374-3381
Reaction of [Pt(DMSO)2Cl2] or [Pd(MeCN)2Cl2] with the electron-rich LH=N,N’-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL2] ( 1 ) but dinuclear [Pd2L4] ( 2 ), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L−. The reversibly accessible cations [PtL2]+ and [Pd2L4]+ were also studied, the latter as [Pd2L4][B{3,5-(CF3)2C6H3}4] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [PtII(L−)2] or [Pt.(L )2], [PtII(L0.5−)2]+ or [PtIII(L−)2]+, [(PdII)2(μ-L−)4] or [(Pd1.5)2(μ-L0.75−)4], and [(Pd2.5)2(μ-L−)4]+ or [(PdII)2(μ-L0.75−)4]+. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL2] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd2L4], and the dimetal (Pd24+→Pd25+) instead of ligand (L−→L ) oxidation of the dinuclear palladium compound. 相似文献
69.
Dr. Svenja Neumann Prof. Dr. Oliver S. Wenger Jun.-Prof. Dr. Christoph Kerzig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(12):4115-4123
One-electron reduced metal complexes derived from photoactive ruthenium or iridium complexes are important intermediates for substrate activation steps in photoredox catalysis and for the photocatalytic generation of solar fuels. However, owing to the heavy atom effect, direct photochemical pathways to these key intermediates suffer from intrinsic efficiency problems resulting from rapid geminate recombination of radical pairs within the so-called solvent cage. In this study, we prepared and investigated molecular dyads capable of producing reduced metal complexes via an indirect pathway relying on a sequence of energy and electron transfer processes between a Ru complex and a covalently connected anthracene moiety. Our test reaction to establish the proof-of-concept is the photochemical reduction of ruthenium(tris)bipyridine by the ascorbate dianion as sacrificial donor in aqueous solution. The photochemical key step in the Ru-anthracene dyads is the reduction of a purely organic (anthracene) triplet excited state by the ascorbate dianion, yielding a spin-correlated radical pair whose (unproductive) recombination is strongly spin-forbidden. By carrying out detailed laser flash photolysis investigations, we provide clear evidence for the indirect reduced metal complex generation mechanism and show that this pathway can outperform the conventional direct metal complex photoreduction. The further optimization of our approach involving relatively simple molecular dyads might result in novel photocatalysts that convert substrates with unprecedented quantum yields. 相似文献
70.
A microwave-enhanced copper-catalyzed protocol for N-arylation using water as the solvent is reported. This fast transformation allows the reaction between various amino acids or amino acid esters and a diverse set of substituted aryl bromides in less than 40 min, affording good yields of non-protected N-arylated amino acids with only minor racemization (6% or less). In addition, online ESI-MS and MS/MS analysis were used to "fish-out" an anionic Cu-containing amino acid complex directly from an ongoing N-arylation reaction. 相似文献