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961.
962.
We investigate inner shearing constraints for a direct one-dimensional beam model coarsely describing warping. In particular, we study how they affect the field equations for the elastic buckling of open thin-walled beams. We show that the distinction between the axes of the shear centres and of the centroids is crucial for the kinematics of the beam, and to derive expression of reactive actions, hence of buckling critical conditions. We also show how a suitable definition of the warping inertial action and properly introduced inner shearing constraints yield the field equations of the literature for the beam in a general dynamic setting. 相似文献
963.
Gabriella Butera Claudio De Pasquale Antonella Maccotta Giuseppe Alonzo Pellegrino Conte 《Cellulose (London, England)》2011,18(6):1499-1507
Use of crude oil derivatives such as diesel and gasoline is becoming unsuitable due to their detriment to environment and
to the increasing worldwide energy demand which is driving crude oil reservoirs towards exhaustion. Replacement of diesel
and gasoline with biofuels (i.e. biodiesel and bioethanol, respectively) is very desirable. In fact, biofuels are not only
environmentally sustainable, but also potentially inexhaustible due to the large amounts of waste biomasses from which they
can be retrieved. In the present study, a model compound (micro-crystalline cellulose) was dissolved in phosphoric acid and
converted at 80 °C to glucose, thereby providing the possible substrate for fermentation to bioethanol. Results revealed that
after 1 h heating, the reaction had the largest glucose yield as compared to similar studies done by using other acid catalysts.
In addition, the temperature applied here was from 40 to 60 °C lower than those already reported in literature for acid-driven
cellulose degradations. Phosphoric acid allowed both glucose and levulinic acid achievement. The latter is usually used to
synthesize fuel additives, catalysts, solvents and herbicides, thereby enhancing the added value of the conversion of cellulose
to glucose in phosphoric acid. Finally, 1H T1 NMR relaxometry showed its suitability to monitor cellulose degradation. The advantages of relaxomety are its quickness since
only few minutes are needed to obtain relaxograms, and the possibility to use raw mixtures without the needing of sample preparation. 相似文献
964.
Dr. Amit Kumar Sarnali Sanfui Dr. Giuseppe Sciortino Prof. Jean-Didier Maréchal Prof. Eugenio Garribba Prof. Sankar Prasad Rath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(35):7869-7880
cis and trans-copper(II) porphyrin dimers have been synthesized, in which two CuII porphyrin macrocycles are bridged through a rigid ethene linker for possible through-space and through-bond spin-couplings between the paramagnetic CuII centers. It has been found that the two macrocycles come closer after 1 e− oxidation, however, they move far apart upon further 1 e− oxidation leading to transformation of the cis to the trans isomer. Detailed investigations are performed here on the interactions between the two porphyrin macrocycles, between two unpaired spins of closely spaced CuII centers, and also between the unpaired spins of metal and porphyrin π–cation radicals. Spectroscopic investigations along with the X-ray structure of the 2 e−-oxidized complex displayed strong electronic communications through the bridge between two porphyrin π–cation radicals. The counterion I9− is stabilized in an unusual trigonal-pyramidal structure in the 2 e−-oxidized complex in which the central iodide ion is bound with four iodine (I2) molecules. Variable-temperature magnetic study revealed strong antiferromagnetic coupling between the two porphyrin π–cation radical spins (Jr–r) in the 2 e−-oxidized complex. DFT calculations suggest stabilization of the triplet state, which is also in good agreement with the experiment. Ab initio molecular dynamics allowed the variation of the structural details to be followed upon stepwise oxidations and also the final isomerization process including its associated energy barrier. 相似文献
965.
Dr. Daniele Maiolo Dr. Andrea Pizzi Dr. Alessandro Gori Dr. Lara Gazzera Dr. Nicola Demitri Dr. Alessandro Genoni Dr. Fulvio Baggi Dr. Fabio Moda Prof. Dr. Giancarlo Terraneo Prof. Dr. Francesca Baldelli Bombelli Prof. Dr. Pierangelo Metrangolo Prof. Dr. Giuseppe Resnati 《ChemistryOpen》2020,9(2):253-260
Here, we demonstrate that introduction of halogen atoms at the tyrosine 10 phenol ring of the DSGYEV sequence derived from the flexible amyloid-β N-terminus, promotes its self-assembly in the solid state. In particular, we report the crystal structures of two halogen-modified sequences, which we found to be stabilized in the solid state by halogen-mediated interactions. The structural study is corroborated by Non-Covalent Interaction (NCI) analysis. Our results prove that selective halogenation of an amino acid enhances the supramolecular organization of otherwise unstructured biologically-relevant sequences. This method may develop as a general strategy for stabilizing highly polymorphic peptide regions. 相似文献
966.
967.
Giancarlo Sorrentino Giuseppe Ceriello Antonio Cavaliere Mara de Joannon Raffaele Ragucci 《Proceedings of the Combustion Institute》2021,38(4):5393-5402
New scenarios for energy systems pointed out the importance of designing innovative combustion systems. In this context, high levels of internal dilution and preheating show interesting features related to low emissions, smooth temperature gradients, absence of visible flame and large fuel and load flexibility. Those characteristics are very difficult to obtain simultaneously with conventional combustion processes in the same device.The large-scale utilization of such novel concepts relies on the developments of proper modeling tools that should consider the multiple physical phenomena involved under distributed ignition. A challenging modeling aspect is related to the strong coupling between fluid-dynamics and kinetic time scales that implies the use of detailed mechanisms. Moreover, the heat transfer mechanisms and the heat loss at walls play key roles.In this context, tabulated chemistry methods are viable solutions to represent the thermo-chemical pattern in combustion systems with internal recirculation. However, the identification of adequate controlling variables for these systems is not trivial. In fact, in addition to mixture fraction and progress variable, an internal dilution and a heat loss parameter must be considered, leading to a 4-dimensional thermo-chemical manifold, with an inherent increase of computational costs.In this work a novel tabulation procedure is proposed in order to represent such comprehensive manifold taking into account the primary role of the internal recirculation on system reactivity.Moreover, a reduction of the thermo-chemical manifold was carried out by exploiting active interconnections between experiments and computations and embedding physical and process constraints based on measurable quantities obtained from experiments. These constrains are related to minimum ignition and maximum attainable process temperatures, heat loss through the surroundings and recirculation rate. The reliability of the proposed approach was assessed by comparing the reduced manifolds to the measured data for a cyclonic burner operating under massive internal dilution levels. 相似文献
968.
Giuseppe Bruno Archimede Rotondo Giovanni Grassi Francesco Foti Francesco Risitano Francesco Nicol 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(7):o496-o497
The title compound, C18H15BrN2O5, a promising N‐protected α‐amino acid, was synthesized directly from an unusual bromo dipole and a 4‐(arylmethylene)oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph‐set motifs driven by the most important hydrogen bonds are described. 相似文献
969.