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211.
This paper is devoted to present some results on the controllability of the hydrostatic Stokes equations. The first main result
of this paper states that the approximate null controllability of this system holds. This is proved whatever the boundary
conditions are. Then, we extend this result to an exact null controllability result when the boundary conditions are ∂
z
u = 0 (the vertical derivative of the horizontal velocity) at the bottom.
相似文献
212.
Chemically deposited copper oxide thin films: structural, optical and electrical characteristics 总被引:1,自引:0,他引:1
M. T. S. Nair Laura Guerrero Olga L. Arenas P. K. Nair 《Applied Surface Science》1999,150(1-4):143-151
Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu2O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10−4 Ω−1 cm−1 for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m−2 tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10−3 Ω−1 cm−1. These films are also photoconductive. 相似文献
213.
Roxana M. Bîrzoi Dr. Delia Bugnariu Dr. Rafael Guerrero Gimeno Dr. Daniela Lungu Vera Zota Dr. Constantin Daniliuc Dr. Peter G. Jones Prof. Dr. Zoltán Benkõ Dr. László Könczöl László Nyulászi Prof. Dr. Rainer Bartsch Dr. Wolf‐W. du Mont Prof. Dr. Edgar Niecke Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(16):4843-4851
Deprotonation of aminophosphaalkenes (RMe2Si)2C?PN(H)(R′) (R=Me, iPr; R′=tBu, 1‐adamantyl (1‐Ada), 2,4,6‐tBu3C6H2 (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe2Si)2C?P(M)(R′)] with one equivalent of the corresponding P‐chlorophosphaalkenes (RMe2Si)2C?PCl provides bisphosphaalkenes (2,4‐diphospha‐3‐azapentadienes) [(RMe2Si)2C?P]2NR′. The thermally unstable tert‐butyliminobisphosphaalkene [(Me3Si)2C?P]2NtBu ( 4 a ) undergoes isomerisation reactions by Me3Si‐group migration that lead to mixtures of four‐membered heterocyles, but in the presence of an excess amount of (Me3Si)2C?PCl, 4 a furnishes an azatriphosphabicyclohexene C3(SiMe3)5P3NtBu ( 5 ) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P?C double bond and an exocyclic ylidic P(+)? C(?)(SiMe3)2 unit. Using the bulkier iPrMe2Si substituents at three‐coordinated carbon leads to slightly enhanced thermal stability of 2,4‐diphospha‐3‐azapentadienes [(iPrMe2Si)2C?P]2NR′ (R′=tBu: 4 b ; R′=1‐Ada: 8 ). According to a low‐temperature crystal‐structure determination, 8 adopts a non‐planar structure with two distinctly differently oriented P?C sites, but 31P NMR spectra in solution exhibit singlet signals. 31P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6‐tBu3C6H2) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P? N bonds in persistent compounds [(RMe2Si)2C?P]2NMes* ( 11 a , 11 b ). DFT calculations for the parent molecule [(H3Si)2C?P]2NCH3 suggest that the non‐planar distortion of compound 8 will have steric grounds. 相似文献
214.
Sara Goñi Francisca Puertas María Soledad Hernández Marta Palacios Ana Guerrero Jorge S. Dolado Bruno Zanga Fulvio Baroni 《Journal of Thermal Analysis and Calorimetry》2010,102(3):965-973
This research is part of a European project (namely, CODICE project), main objective of which is modelling, at a multi-scale,
the evolution of the mechanical performance of non-degraded and degraded cementitious matrices. For that, a series of experiments
were planned with pure synthetic tri-calcium silicate (C3S) and bi-calcium silicate (C2S) (main components of the Portland cement clinker) to obtain different calcium–silicate–hydrate (C–S–H) gel structures during
their hydration. The characterization of those C–S–H gels and matrices will provide experimental parameters for the validation
of the multi-scale modelling scheme proposed. In this article, a quantitative method, based on thermal analyses, has been
used for the determination of the chemical composition of the C–S–H gel together with the degree of hydration and quantitative
evolution of all the components of the pastes. Besides, the microstructure and type of silicate tetrahedron and mean chain
length (MCL) were studied by scanning electron microscopy (SEM) and 29Si magic-angle-spinning (MAS) NMR, respectively. The main results showed that the chemical compositions for the C–S–H gels
have a CaO/SiO2 M ratio almost constant of 1.7 for both C3S and C2S compounds. Small differences were found in the gel water content: the H2O/SiO2 M ratio ranged from 2.9 ± 0.2 to 2.6 ± 0.2 for the C3S (decrease) and from 2.4 ± 0.2 to 3.2 ± 0.2 for the C2S (increase). The MCL values of the C–S–H gels, determined from 29Si MAS NMR, were 3.5 and 4 silicate tetrahedron, for the hydrated C3S and C2S, respectively, remaining almost constant at all hydration periods. 相似文献
215.
In this paper we consider a linear KdV equation posed on a bounded interval. We study the behavior of the cost of null controllability when two boundary controls are employed. By means of suitable Carleman inequalities and a new exponential dissipation estimate, we prove that uniform null controllability with respect to the dispersion coefficient holds, contrary to the case when one control is used at the left end-point of the interval. 相似文献
216.
Nanovehicles are a new class of molecular machines consisting of a molecular scale chassis, axles, and wheels, that can roll across solid surfaces with structurally defined directions making them of interest to synthetic chemists, surface scientists, chemical engineers, and the general car enthusiast. In this tutorial review, following a brief introduction to the development of nanomachines, our recent progress on the nanovehicle project is presented including the design, synthesis, and testing of a series of nanocars, nanotrucks, and motorized nanocars. 相似文献
217.
218.
In this paper, we analyze how to update incomplete Cholesky preconditioners to solve least squares problems using iterative methods when the set of linear relations is updated with some new information, a new variable is added or, contrarily, some information or variable is removed from the set. Our proposed method computes a low-rank update of the preconditioner using a bordering method which is inexpensive compared with the cost of computing a new preconditioner. Moreover, the numerical experiments presented show that this strategy gives, in many cases, a better preconditioner than other choices, including the computation of a new preconditioner from scratch or reusing an existing one. 相似文献
219.
Dr. Susana Ibáñez Dr. Antonio Guerrero Dr. Macarena Poyatos Prof. Eduardo Peris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10566-10575
A rational synthetic procedure for the preparation of a series of pyrene‐based neutral and dicationic bis‐azole compounds is reported. The method allows the tailored design of pyrene‐based azoles with different substituents at the nitrogen atoms of the heterocycles, for which the relative conformation of the resulting bis‐azoles can be easily controlled. The bis‐azoliums were used for the preparation of the related diplatinum complexes by reaction with [{Pt(ppy)(μ‐Cl)2}2] (ppy=2‐phenylpyridinate). The X‐ray molecular structure of one of the resulting compounds, a diplatinum(II) bis(N‐heterocyclic carbene) complex, is described. Studies on the photophysical properties of all new species are described. The emission of the bis‐azole‐based compounds seems to be independent of their substitution patterns, which basically indicates that physical properties such as solubility, melting point, and viscosity can be fine‐tuned while maintaining the luminescence properties. Finally, the energies associated with the HOMO and LUMO levels suggest that this family provides versatility to match the energy levels of a wide range of host materials, which is important for the preparation of organic light‐emitting devices. 相似文献
220.
Baer T Guerrero A Davalos JZ Bodi A 《Physical chemistry chemical physics : PCCP》2011,13(39):17791-17801
The dissociation dynamics of Sn(CH(3))(4)(+), Sn(CH(3))(3)Cl(+), and Sn(CH(3))(3)Br(+) were investigated by threshold photoelectron photoion spectrometry using an electron imaging apparatus (iPEPICO) at the Swiss Light Source. The tetramethyltin ion was found to dissociate via Sn(CH(3))(4)(+) → Sn(CH(3))(3)(+) + CH(3) → Sn(CH(3))(2)(+) + 2CH(3), while the trimethyltin halide ions dissociated via methyl loss at low energies, and a competitive halogen loss at somewhat higher energies. The 0 K methyl loss onset for the three ions was found to be 9.410 ± 0.020 eV, 10.058 ± 0.020 eV, and 9.961 ± 0.020 eV, respectively. Statistical theory could not reproduce the observed onsets for the halogen loss steps in the halotrimethyltin ions. The halide loss signal as a function energy mimicked the excited state threshold photoelectron spectrum, from which we conclude that the halide loss from these ions takes place on an isolated excited state potential energy surface, which we describe by time dependent density functional calculations. The sequential loss of a second methyl group in the Sn(CH(3))(4)(+) ion, observed at about 3 eV higher energies than the first one, is also partially non-statistical. The derived product energy distribution resulting from the loss of the first methyl group is two-component with about 50% being statistical and the remainder associated with high translational energy products that peak at 2 eV. Time dependent DFT calculations show that a dissociative ?B state lies in the vicinity of the experimental measurements. We thus propose that 50% of the Sn(CH(3))(4)(+) ions produced in this energy range internally convert to the ?X state, on which they dissociate statistically, while the remainder dissociate directly from the repulsive ?B state leading to high kinetic energy products. 相似文献