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51.
Neumann M Herten DP Dietrich A Wolfrum J Sauer M 《Journal of chromatography. A》2000,871(1-2):299-310
The first capillary array scanner for time-resolved fluorescence detection in parallel capillary electrophoresis based on semiconductor technology is described. The system consists essentially of a confocal fluorescence microscope and a x,y-microscope scanning stage. Fluorescence of the labelled probe molecules was excited using a short-pulse diode laser emitting at 640 nm with a repetition rate of 50 MHz. Using a single filter system the fluorescence decays of different labels were detected by an avalanche photodiode in combination with a PC plug-in card for time-correlated single-photon counting (TCSPC). The time-resolved fluorescence signals were analyzed and identified by a maximum likelihood estimator (MLE). The x,y-microscope scanning stage allows for discontinuous, bidirectional scanning of up to 16 capillaries in an array, resulting in longer fluorescence collection times per capillary compared to scanners working in a continuous mode. Synchronization of the alignment and measurement process were developed to allow for data acquisition without overhead. Detection limits in the subzeptomol range for different dye molecules separated in parallel capillaries have been achieved. In addition, we report on parallel time-resolved detection and separation of more than 400 bases of single base extension DNA fragments in capillary array electrophoresis. Using only semiconductor technology the presented technique represents a low-cost alternative for high throughput DNA sequencing in parallel capillaries. 相似文献
52.
Béraud S Bersch B Brutscher B Gans P Barras F Blackledge M 《Journal of the American Chemical Society》2002,124(46):13709-13715
Residual dipolar couplings (RDC) from partially aligned molecules provide long-range structural data and are thus particularly well adapted to rapid structure validation or protein fold recognition. Extensive measurements in two alignment media can also provide precise de novo structure from RDC alone. We have applied a novel combination of these approaches to the study of methionine sulfoxide reductase (MsrA) from Erwinia chrysanthemi, a 27 kDa enzyme essential for repairing oxidative stress damage. The tertiary fold was initially validated by comparing backbone RDC to expected values from the crystal structure of the homologous MsrA from Escherichia coli. Good agreement was found throughout the chain, verifying the overall topology of the molecule, with the exception of the catalytically important peptide P196-L202, where strong and systematic RDC violation was observed. No evidence for local differential mobility in this region was detected, implying that the structure of the strand differs in the two molecules. We have therefore applied the de novo approach meccano to determine the conformation of this peptide using only RDC. A single conformation is found that is in agreement with all measured data. The aligned peptide can be docked onto the expected covalence of the rest of the template molecule while respecting its strictly defined relative orientation. In contrast to the structure of MsrA from E. coli, the reactive side chain of Cys200 is oriented toward the interior of the molecule and therefore closer to the catalytic Cys53, obviating the need for previously proposed conformational reorganization prior to formation of this disulfide intermediate. This analysis requires only backbone assignment and uses unambiguously assigned and readily measurable structural data, thereby greatly economizing investigation time compared to established nuclear Overhauser effect- (nOe-) based structure calculation methods. 相似文献
53.
Horozov TS Aveyard R Clint JH Neumann B 《Langmuir : the ACS journal of surfaces and colloids》2005,21(6):2330-2341
Vertical emulsion films with particle monolayers at their surfaces have been studied by direct microscope observations. The effects of particle wettability and surface coverage on the structure and stability of water films in octane and octane films in water have been investigated. Monodisperse silica particles (3 microm in diameter) hydrophobized to different extents have been used. It is found that the structure and stability of emulsion films strongly depend on the film type (water-in-oil or oil-in-water), the particle contact angle, the interactions between particles from the same and the opposite monolayer, and the monolayer density. Stable films are observed only when the particle wettability fulfills the condition for stable particle bridges--in agreement with the concept that hydrophilic particles can give stable oil-in-water emulsions, whereas hydrophobic ones give water-in-oil emulsions. In the case of water films with dilute disordered monolayers at their surfaces, the hydrophilic particles are expelled from the film center toward its periphery, giving a dimple surrounded by a ring of particles bridging the film surfaces. In contrast, the thinning of octane films with dilute ordered monolayers at their surfaces finally leads to the spontaneous formation of a dense crystalline monolayer of hydrophobic particles bridging both surfaces at the center of the film. The behaviors of water and octane films with dense close-packed particle monolayers at their surfaces are very similar. In both cases, a transition from bilayer to bridging monolayer is observed at rather low capillary pressures. The implications of the above finding for particle stabilized emulsions are discussed. 相似文献
54.
Afshin Nabiyan Johannes Bernhard Max Dr. Christof Neumann Magdalena Heiland Prof. Dr. Andrey Turchanin Prof. Dr. Carsten Streb Prof. Dr. Felix Helmut Schacher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):16924-16929
An effective strategy to enhance the performance of inorganic semiconductors is moving towards organic-inorganic hybrid materials. Here, we report the design of core–shell hybrid materials based on a TiO2 core functionalized with a polyampholytic (poly(dehydroalanine)-graft-(n-propyl phosphonic acid acrylamide) shell (PDha-g-PAA@TiO2). The PDha-g-PAA shell facilitates the efficient immobilization of the photosensitizer Eosin Y (EY) and enables electronic interactions between EY and the TiO2 core. This resulted in high visible-light-driven H2 generation. The enhanced light-driven catalytic activity is attributed to the unique core–shell design with the graft copolymer acting as bridge and facilitating electron and proton transfer, thereby also preventing the degradation of EY. Further catalytic enhancement of PDha-g-PAA@TiO2 was possible by introducing [Mo3S13]2− cluster anions as hydrogen-evolution cocatalyst. This novel design approach is an example for a multi-component system in which reactivity can in future be independently tuned by selection of the desired molecular or polymeric species. 相似文献
55.
Ernst Richard Neumann 《Mathematische Annalen》1941,118(1):276-285
Ohne Zusammenfassung 相似文献
56.
A. W. Dumanskiij O. W. Neumann H. Arnfelt R. K. Abrams O. Schales und W. Specht 《Fresenius' Journal of Analytical Chemistry》1939,116(3-4):143-145
Ohne Zusammenfassung 相似文献
57.
Transition Metal Substituted Acylphosphanes and Phosphaalkenes. 17. Synthesis and Structure of the μ-Isophosphaalkyne Complexes [(η5-C5H5)2(CO)2Fe2(μ-CO)(μ-C?PC6H2R3)] (R = Me, iPr, tBu) . Condensation of (η5-C5H5)2(CO)2Fe2(μ-CO)(μ-CSMe)}+SO3CF3? ( 6 ) with 2,4,6-R3C6H2PH(SiMe3) ( 7 ) ( a : R = Me, b : R = iPr, c : R = tBu) affords the complexes (η5-C5H5)2(CO)2Fe2(μ-CO)(η-C?PC6H2R3-2,4,6) ( 9 a–c ) with edge-bridging isophosphaalkyne ligands as confirmed by the x-ray structure analysis of 9 a . 相似文献
58.
59.
Direct Access to Aryl Bis(trifluoromethyl)carbinols from Aryl Bromides or Fluorosulfates: Palladium‐Catalyzed Carbonylation 下载免费PDF全文
Katrine Domino Cedrick Veryser Benjamin A. Wahlqvist Cecilie Gaardbo Dr. Karoline T. Neumann Prof.Dr. Kim Daasbjerg Prof. Dr. Wim M. De Borggraeve Prof. Dr. Troels Skrydstrup 《Angewandte Chemie (International ed. in English)》2018,57(23):6858-6862
A palladium‐catalyzed carbonylative approach for the direct conversion of (hetero)aryl bromides into their α,α‐bis(trifluoromethyl)carbinols is described, and it employs only stoichiometric amounts of carbon monoxide and trifluoromethyltrimethylsilane. In addition, aryl fluorosulfates proved highly compatible with these reaction conditions. The method is tolerant of a diverse set of functional groups, and it is adaptable to late‐stage carbon‐isotope labeling. 相似文献
60.
Haoquan Li Dr. Helfried Neumann Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10050-10056
A benign and efficient palladium‐catalyzed aminocarbonylation reaction of allylic alcohols is presented. The generality of this novel process is demonstrated by the synthesis of β,γ‐unsaturated amides including aliphatic, cinnamyl, and terpene derivatives. The choice of ligand is crucial for optimal carbonylation processes: Whereas in most cases the combination of PdCl2 with Xantphos ( L6 ) gave best results, sterically hindered substrates performed better in the presence of simple triphenylphosphine ( L10 ), and primary anilines gave the best results using cataCXium® PCy ( L8 ). The reactivity of the respective catalyst system is significantly enhanced by addition of small amounts of water. Mechanistic studies and control experiments revealed a tandem allylic alcohol amination/C?N bond carbonylation reaction sequence. 相似文献