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851.
Ilia I. Sadykov Dr. Vitaly L. Sushkevich Dr. Frank Krumeich Dr. Rob Jeremiah G. Nuguid Prof. Dr. Jeroen A. van Bokhoven Dr. Maarten Nachtegaal Dr. Olga V. Safonova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202214032
Operando X-ray absorption spectroscopy identified that the concentration of Fe2+ species in the working state-of-the-art Pt−FeOx catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe2+ sites. The active Fe2+ species are presumably Fe+2O−2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe3+) and metallic iron (Fe0) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe2+ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle. 相似文献
852.
853.
Min Ji Kim Diana J. Wang Karina Targos Uriel A. Garcia Alison F. Harris Ilia A. Guzei Zachary K. Wickens 《Angewandte Chemie (International ed. in English)》2023,62(21):e202303032
Cyclopropanes are desirable structural motifs with valuable applications in drug discovery and beyond. Established alkene cyclopropanation methods give rise to cyclopropanes with a limited array of substituents, are difficult to scale, or both. Herein, we disclose a new cyclopropane synthesis through the formal coupling of abundant carbon pronucleophiles and unactivated alkenes. This strategy exploits dicationic adducts derived from electrolysis of thianthrene in the presence of alkene substrates. We find that these dielectrophiles undergo cyclopropanation with methylene pronucleophiles via alkenyl thianthrenium intermediates. This protocol is scalable, proceeds with high diastereoselectivity, and tolerates diverse functional groups on both the alkene and pronucleophile coupling partners. To validate the utility of this new procedure, we prepared an array of substituted analogs of an established cyclopropane that is en route to multiple pharmaceuticals. 相似文献
854.
We investigate sums \(J(\vec {x})\) and \(L(\vec {x})\) of pairs of normalized Saalschützian \({}_4F_3(1)\) hypergeometric series, and develop a theory of relations among these J and L functions. The function \(L(\vec {x})\) has been studied extensively in the literature and has been shown to satisfy a number of two-term and three-term relations with respect to the variable \(\vec {x}\). More recent works have framed these relations in terms of Coxeter group actions on \(\vec {x}\) and have developed a similar theory of two-term and three-term relations for \(J(\vec {x})\). In this article, we derive “mixed” three-term relations, wherein any one of the L (respectively, J) functions arising in the above context may be expressed as a linear combination of two of the above J (respectively, L) functions. We show that, under the appropriate Coxeter group action, the resulting set of three-term relations (mixed and otherwise) among J and L functions partitions into eighteen orbits. We provide an explicit example of a relation from each orbit. We further classify the eighteen orbits into five types, with each type uniquely determined by the distances (under a certain natural metric) between the J and L functions in the relation. We show that the type of a relation dictates the complexity (in terms of both number of summands and number of factors in each summand) of the coefficients of the J and L functions therein. 相似文献
855.
D. D. Kul’minskii V. I. Ponomarenko A. S. Karavaev M. D. Prokhorov 《Technical Physics》2016,61(5):639-647
We propose a system of concealed information transfer based on a delayed feedback oscillator with switchable chaotic regimes. The proposed system is analyzed numerically and experimentally. The dependences of the bit error rate during transmission of a binary information signal on the signal-to-noise ratio, attenuation of the signal in the communication channel, and the duration of the time interval during which a bit is transferred are constructed. The high stability of the system to noise and amplitude distortions of a signal in the communication channel is demonstrated. 相似文献
856.
Dymon J Wibby R Kleingardner J Tanski JM Guzei IA Holbrey JD Larsen AS 《Dalton transactions (Cambridge, England : 2003)》2008,(22):2999-3006
A range of new alkylpyridinium and imidazolium carborane salts with [nido-C(2)B(9)H(12)](-), [closo-CB(11)H(12)](-), and [RC(2)B(11)H(11)](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C(2)B(9)H(12)](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB(11)H(12)](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed. 相似文献
857.
Ilia Krasikov 《Constructive Approximation》2008,28(2):113-125
T. Erdelyi, A.P. Magnus and P. Nevai conjectured that for
the orthonormal Jacobi polynomials
satisfy the inequality
[Erdelyi et al., Generalized Jacobi weights, Christoffel functions, and Jacobi polynomials. SIAM J. Math. Anal., 25 (1994),
602-614.]. Here we will confirm this conjecture in the ultraspherical case
even in a stronger form by giving very explicit upper bounds. We also show that
for a certain choice of
such that the interval
contains all the zeros of
Slightly weaker bounds are given for polynomials of odd degree. 相似文献
858.
An efficient asymmetric synthesis of the 22nd amino acid L-pyrrolysine has been accomplished. The key stereogenic centers were installed by an asymmetric conjugate addition reaction. A Staudinger/aza-Wittig cyclization was used to form the acid-sensitive pyrroline ring. Pyrrolysine was synthesized in 13 steps in 20% overall yield. 相似文献
859.
Aurelia Visa Maria Mracec Bianca Maranescu Valentin Maranescu Gheorghe Ilia Adriana Popa Mircea Mracec 《Chemistry Central journal》2012,6(1):1-8
Background
Biosensors have attracted increasing attention as reliable analytical instruments in in situ monitoring of public health and environmental pollution. For enzyme-based biosensors, the stabilization of enzymatic activity on the biological recognition element is of great importance. It is generally acknowledged that an effective immobilization technique is a key step to achieve the construction quality of biosensors.Results
A novel disposable biosensor was constructed by immobilizing laccase (Lac) with silica spheres on the surface of multi-walled carbon nanotubes (MWCNTs)-doped screen-printed electrode (SPE). Then, it was characterized in morphology and electrochemical properties by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The characterization results indicated that a high loading of Lac and a good electrocatalytic activity could be obtained, attributing to the porous structure, large specific area and good biocompatibility of silica spheres and MWCNTs. Furthermore, the electrochemical sensing properties of the constructed biosensor were investigated by choosing dopamine (DA) as the typical model of phenolic compounds. It was shown that the biosensor displays a good linearity in the range from 1.3 to 85.5 ??M with a detection limit of 0.42 ??M (S/N = 3), and the Michaelis-Menten constant (Km app) was calculated to be 3.78 ??M.Conclusion
The immobilization of Lac was successfully achieved with silica spheres to construct a disposable biosensor on the MWCNTs-doped SPE (MWCNTs/SPE). This biosensor could determine DA based on a non-oxidative mechanism in a rapid, selective and sensitive way. Besides, the developed biosensor could retain high enzymatic activity and possess good stability without cross-linking reagents. The proposed immobilization approach and the constructed biosensor offer a great potential for the fabrication of the enzyme-based biosensors and the analysis of phenolic compounds. 相似文献860.
Lara C. Spencer Ilia A. Guzei Tebogo V. Segapelo James Darkwa 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(11):m317-m319
The title compound, [PdCl2(C21H17N3)], is a member of a sequence of Pd, Pt and Co dichloride complexes bearing polysubstituted (pyrazol‐1‐ylmethyl)pyridine ligands. It is shown that there is a correlation between the steric bulkiness of the bidentate (pyrazol‐1‐ylmethyl)pyridine ligands and the Pd—Npyrazole distances, i.e. the larger the ligand, the longer the bond. In contrast, no trend is observed between the steric properties of the ligand and the Pd—Npyridine bond lengths. 相似文献