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排序方式: 共有461条查询结果,搜索用时 15 毫秒
101.
Władysław Piotrowski Koen Lodefier Slawomir Kubacki Witold Elsner Erik Dick 《Flow, Turbulence and Combustion》2008,81(3):369-394
The present paper evaluates two unsteady transition modelling approaches: the prescribed unsteady intermittency method PUIM,
developed at Cambridge University and the dynamic unsteady intermittency method developed at Ghent University. The methods
are validated against experimental data for the N3-60 steam turbine stator profile for steady and for unsteady inlet flow
conditions. The characteristic features of the test case are moderately high Reynolds number and high inlet turbulence intensity,
which causes bypass transition. The tested models rely both on the intermittency parameter and are unsteady approaches. In
the prescribed method, the time-dependent intermittency distribution is obtained from integral relations. In the dynamic method,
the intermittency distribution follows from time-dependent differential equations. For unsteady computations, self-similar
wake profiles are prescribed at the inlet of the computational domain. Joint validation of the prescribed and the dynamic
unsteady intermittency models against experimental data shows that both methods are able to reproduce the global features
of the periodical evolution of the boundary layer under the influence of a periodically impinging wake. The overall quality
of the dynamic method is better than that of the prescribed method. 相似文献
102.
Multianalytical Study of Patina Formed on Archaeological Metal Objects from Bliesbruck-Reinheim 总被引:1,自引:0,他引:1
Michael Wadsak Ina Constantinides Guido Vittiglio Annemie Adriaens Koen Janssens Manfred Schreiner Freddy C. Adams Philippe Brunella Michel Wuttmann 《Mikrochimica acta》2000,133(1-4):159-164
Patinas naturally formed on archaeological bronze alloys were characterized using light microscopy (LM), micro energy dispersive
X-ray fluorescence analysis (μ-EDXRF), time of flight secondary ion mass spectrometry (TOF-SIMS) and scanning electron microscopy
in combination with energy dispersive X-ray microanalysis (SEM/EDX). The examinations carried out on cross-sections of samples
have shown that in all samples the copper content in the corrosion layer is lower than in the bulk, while an increase of tin
and lead could be observed. Two different types of corrosion were found: first type, a corrosion formation leading to a three
layer structure was observed on lead bronze. The outer layer consists mainly of Cu(II) compounds and soil material, followed
by a fragmented layer of cuprous oxide and the surface layer of the alloy, where a depletion of copper and an enrichment of
tin and high amounts of Cl could be detected. The second type of corrosion is characterized by a two layer structure on the
tin bronze sample consisting of an outer layer with copper containing corrosion products and a layer with cracks, which reveals
a depletion of copper whereas tin and lead are enriched. Also high amounts of Si were detected in this surface layer. 相似文献
103.
Cui-Lian Liu Eduard O. Bobylev Yang Fu David A. Poole III Dr. Koen Robeyns Prof. Dr. Charles-André Fustin Prof. Dr. Yann Garcia Prof. Dr. Joost N. H. Reek Prof. Dr. Michael L. Singleton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(52):11960-11965
Non-covalent interactions are important for directing protein folding across multiple intermediates and can even provide access to multiple stable structures with different properties and functions. Herein, we describe an approach for mimicking this behavior in the self-assembly of metal–organic cages. Two ligands, the bend angles of which are controlled by non-covalent interactions and one ligand lacking the above-mentioned interactions, were synthesized and used for self-assembly with Pd2+. As these weak interactions are easily broken, the bend angles have a controlled flexibility giving access to M2( L1 )4, M6( L2 )12, and M12( L2 )24 cages. By controlling the self-assembly conditions this process can be directed in a stepwise fashion. Additionally, the multiple endohedral hydrogen-bonding sites on the ligand were found to play a role in the binding and discrimination of neutral guests. 相似文献
104.
105.
József Lörinczi Christian Maes Koen Vande Velde 《Probability Theory and Related Fields》1998,112(1):121-147
We study local transformations of Gibbs measures. We establish sufficient conditions for the quasilocality of the images
and obtain results on the existence and continuity properties of their relative energies. General results are illustrated
by simple examples.
Received: 11 November 1997 / Revised version: 20 February 1998 相似文献
106.
In this paper, we classify the generalized quadrangles of order (s,t), s ≠ 1 ≠ t, which admit the natural action of PSL(2,s) × PSL(2,s) on a subGQ of order (s,1). This generalizes a recent result of J. De Kaey and H. Van Maldeghem 3 , by whom the classification was obtained for the case s = t. © 2005 Wiley Periodicals, Inc. J Combin Designs. 相似文献
107.
M. A. Vandyck 《General Relativity and Gravitation》1989,21(1):79-89
The study of the problem of defining, in the theory of supergravity, the notion of a spacetime symmetry is continued. The connection with the formalism of superspace is explicitly considered, and the geometrical significance of the definition given in Parts I and II of this series of papers is emphasized. 相似文献
108.
Capturing the Genesis of an Active Fischer–Tropsch Synthesis Catalyst with Operando X‐ray Nanospectroscopy
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Ilse K. van Ravenhorst Charlotte Vogt Heiko Oosterbeek Koen W. Bossers José G. Moya‐Cancino Dr. Ir. Alexander P. van Bavel Ad M. J. van der Eerden Dr. David Vine Prof. Dr. Frank M. F. de Groot Dr. Florian Meirer Prof. Dr. Ir. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2018,57(37):11957-11962
A state‐of‐the‐art operando spectroscopic technique is applied to Co/TiO2 catalysts, which account for nearly half of the world's transportation fuels produced by Fischer–Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra‐ and interparticular heterogeneities previously believed not to occur in particles under 200 μm. These heterogeneities are strongly dependent on changes in H2/CO ratio, but also on changes thereby induced on the Co and Ti valence states. We have captured the genesis of an active FTS particle over its propagation to steady‐state operation, in which microgradients lead to the gradual saturation of the Co/TiO2 catalyst surface with long chain hydrocarbons (i.e., organic film formation). 相似文献
109.
De Smet K Pleysier A Vankelecom IF Jacobs PA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(1):334-338
Although transition-metal complexes are very attractive as homogeneous catalysts in fine chemistry, their high prices often limit their applications. A means to recycle those catalysts would solve this problem and would simultaneously facilitate the downstream purification of the product. This is now realized in a new concept in which homogeneous catalysis is coupled to dialysis. The advantages of homogeneous catalysis (off-the-shelf catalysts, high activities and selectivities) are thus combined with those of heterogeneous catalysis (easy catalyst separation from product solution, reuse of catalyst, and possibility for continuous operation). Since the heart of the process is the membrane, self-prepared membranes were preferred as they allow a better control and understanding of the separation characteristics. Rhodamine B was used as a probe molecule to define the working conditions of the membrane. The concept is proven to work for two relevant chiral reactions: a hydrogenation with Ru-BINAP and a hydrogen transfer reaction with Ru-TsDPEN [BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine); TsDPEN= tosyl-N,N'-diphenyl-1,2-ethanediamine]. 相似文献
110.
C2-Symmetric bicyclo[2.2.1]hepta-2,5-dienes with various substituents (R=Bn, i-Bu, c-Hex, allyl) are prepared starting from the corresponding enantiomerically pure bis-triflate (R=OTf). These chiral ligands are tested and compared in rhodium(I)-catalyzed 1,4- and 1,2-addition of phenylboronic acid to cyclic enones and aryl aldehydes, respectively. Some interesting reactivity and selectivity effects due to the introduction of sterically demanding or olefinic substituents are reported. Moreover, remarkably high catalytic activity is observed for the rhodium(I)-catalyzed 1,2-addition. 相似文献