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991.
Dr. Dina Christina Tymann Lars Benedix Dr. Lyuba Iovkova Roman Pallach Prof. Dr. Sebastian Henke Dr. David Tymann Prof. Dr. Martin Hiersemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(52):11974-11978
We report on the implementation of the concept of a photochemically elicited two-carbon homologation of a π-donor–π-acceptor substituted chromophore by triple-bond insertion. Implementing a phenyl connector between the slide-in module and the chromophore enabled the synthesis of cylohepta[b]indole-type building blocks by a metal-free annulative one-pot two-carbon ring expansion of the five-membered chromophore. Post-irradiative structural elaboration provided founding members of the indolo[2,3-d]tropone family of compounds. Control experiments in combination with computational chemistry on this multibond reorganization process founded the basis for a mechanistic hypothesis. 相似文献
992.
Christina Fraunhofer Stefan Schwarzmüller James L. Gardiner G. Jeffrey Snyder Oliver Oeckler 《无机化学与普通化学杂志》2020,646(16):1345-1351
In composite materials of NaCl-type Sn12Sb2Te15 with x equivalents of CdI2-type NiTe2 (x = 0.2; 1; 2), both phases are stable from room temperature up to 500 °C without a significant extent of mutual doping. The thermoelectric properties of this model system, complemented by Hall measurements, show clear trends with increasing x. Both electrical and thermal conductivities increase significantly whilst Seebeck coefficients decrease due to an increase in charge carrier concentrations. The overall Figure of merit zT is slightly impaired upon heterostructuring with NiTe2. However, the good reproducibility and cyclability of the measurements renders these composites an intriguing model system to qualitatively examine the applicability of a simple single parabolic band (SPB) model based on Hall-effect data to rather metallic heterostructures. This model is best applicable to composites with lower fractions of NiTe2 and gives the direction for tuning the charge carrier concentrations toward the optimum upon heterostructuring. These findings are in accordance with B-factor analysis and classical effective medium theory for spheroidal precipitates. 相似文献
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An experimental and numerical study on the adequacy of CH as a flame marker in premixed methane flames 总被引:5,自引:0,他引:5
Christina M. Vagelopoulos Jonathan H. Frank 《Proceedings of the Combustion Institute》2005,30(1):241-249
The CH radical is frequently used as a flame marker because it is relatively short-lived and is present over a narrow region in flames. Discontinuities in the CH field are thus often interpreted as localized extinction of the flame. Recently, however, the adequacy of CH laser-induced fluorescence (LIF) as a flame marker was questioned by an experimental study of flame–vortex interactions in highly N2-diluted premixed methane flames. We demonstrate both experimentally and numerically that anomalies in the transient response of CH in this earlier study were due to reactant composition variations in the vortex. In addition, we evaluate the adequacy of CH LIF as a flame marker over a much broader range of conditions. Previous numerical studies showed that heat release rate correlates reasonably well with peak [HCO] and the concentration product [OH][CH2O], but poorly with [CH], in highly N2-diluted premixed methane flames. Here, the correlation between heat release rate and CH is investigated both experimentally, by performing simultaneous measurements of CH, OH, and CH2O LIF, and numerically. We consider undiluted and N2-diluted premixed methane flames over a range of strain rates and stoichiometries. Results are reported for flames subjected to unsteady stretch and reactant composition variations. For all N2-dilution levels considered, the peak CH LIF signal correlates poorly with heat release rate when the stoichiometry of the reactant mixture changes from rich to lean. However, when flames are subjected to stretch, the correlation between CH and heat release rate improves as the N2-dilution level decreases. The correlation is reasonably good for undiluted flames with equivalence ratios of 0.8 < Φ < 1.2. This result is particularly encouraging, given the relevance of undiluted flames to practical applications, and it motivates further investigation of the parameter space for which difficulties may exist in using CH as a flame marker. 相似文献
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Vestislav Apostolov David M.J. Calderbank Paul Gauduchon Christina W. Tønnesen-Friedman 《Inventiones Mathematicae》2008,173(3):547-601
This paper concerns the existence and explicit construction of extremal Kähler metrics on total spaces of projective bundles, which have been studied in many places. We present a unified approach, motivated by the theory of Hamiltonian 2-forms (as introduced and studied in previous papers in the series) but this paper is largely independent of that theory. We obtain a characterization, on a large family of projective bundles, of the ‘admissible’ Kähler classes (i.e., those compatible with the bundle structure in a way we make precise) which contain an extremal Kähler metric. In many cases every Kähler class is admissible. In particular, our results complete the classification of extremal Kähler metrics on geometrically ruled surfaces, answering several long-standing questions. We also find that our characterization agrees with a notion of K-stability for admissible Kähler classes. Our examples and nonexistence results therefore provide a fertile testing ground for the rapidly developing theory of stability for projective varieties, and we discuss some of the ramifications. In particular we obtain examples of projective varieties which are destabilized by a non-algebraic degeneration. 相似文献
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A T-shaped micro reactor was used for the optimisation of reaction conditions for the enantioselective silylcyanation of benzaldehyde catalysed by lanthanide-pybox complexes. Compared to a conventional batch procedure, higher conversion was observed within shorter reaction time. The micro reactor process involving Lu(III) afforded essentially the same enantioselectivity as the batch process (73 vs 76% ee), whereas the enantioselectivity was lower in the micro reactor for catalysts containing Yb(III) (53 compared to 72%). Ce(III) provided very low selectivity in both types of processes (1 and 11% ee, respectively). A study of the effect of additives showed that the enantioselectivity in the Yb catalysed reaction performed in the micro reactor could be increased to 66%, whereas only a minor improvement, to 78% ee, was observed in the reaction with Lu. 相似文献
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