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731.
732.
Alexis Kotland Imane Hadef Jean‐Hugues Renault Mahmoud Hamzaoui Agathe Martinez Nicolas Borie Arnaud Guilleret Romain Reynaud Jane Hubert 《Journal of separation science》2013,36(8):1362-1369
Sophorolipids represent an important class of natural surfactants with a variety of environmental, cosmetic, and pharmaceutical applications. Despite their promising physicochemical and biological properties, the use of sophorolipids is hampered by the lack of information regarding their individual structure‐activity relationships. The major difficulty in isolating pure sophorolipids arises from the high complexity of crude fermentation media composition and from their strong structural similarities. In this work, a centrifugal partition chromatography method was developed in an original gradient elution mode for the separation of sophorolipids produced by the yeast Candida bombicola. Experiments were realized by using three sets of solvent systems composed of n‐heptane, ethyl acetate, n‐butanol, methanol, and water in different proportions. The separation was performed at 5 mL/min in the ascending mode by increasing progressively the polarity of the organic mobile phase. In these conditions, more than 80% of the sophorolipids present in the initial crude fermentation extract were eluted successively from the most hydrophobic lactone forms to the most hydrophilic acid forms. The structures of the isolated sophorolipids were further elucidated by HPLC and NMR analyses. 相似文献
733.
Stability is a particular problem for biopharmaceutical products because the efficacy of peptides and proteins as therapeutic or diagnostic agents can be affected during preparation, shipping, and storage. A particular formulation may have no immediately apparent effect on physical or chemical stability, and the time required for these studies at ambient temperature can be very lengthy because chemical reactions proceed relatively slowly at low temperatures. Undoubtedly, accelerated and stress testing of stability can provide useful information for future product development. The many methods used to study kinetics in aqueous solution may be experimental or computational. Experimental approaches may be isothermal or non-isothermal. Non-linear and linear regression methods can be used to analyze data from these experimental approaches, and the Monte Carlo method could be useful to obtain information about uncertainties in experimental data.The purpose of this review is to describe and to discuss options for the accelerated study of peptide and protein drugs. These options are not necessarily the same as those used for regulatory testing to set expiration dates. We also review statistical techniques to estimate kinetic parameters (rate constant, activation energy, and pre-exponential factor). Further, we establish the advantages and the limitations of both thermal approaches. We analyze and discuss all aspects using the most recent examples of peptide and protein stability. 相似文献
734.
The total synthesis of enantiopure 4-epi-(+)-codonopsinine was achieved in 10 steps starting from D-ribose as a chiral building block. The key step involved a highly stereoselective nucleophilic addition of a Grignard reagent to a protected ribosylamine. Synthesis of the N-desmethyl derivative and its p-tolyl analogue was also accomplished, and the compounds were assayed against α-fucosidase. 相似文献
735.
Braulio Insuasty Alberto Insuasty Alexis Tigreros Jairo Quiroga Rodrigo Abonia Manuel Nogueras Justo Cobo Marcos Derita Susana Zacchino 《Journal of heterocyclic chemistry》2011,48(2):347-350
This work describes the synthesis and antifungal evaluation of 5‐arylidene‐(Z)‐2‐(1,1‐dicyanomethylene)‐1,3‐thiazol‐4‐ones 5 obtained from the reaction of 2‐(1,1‐dicyanomethylene)‐1,3‐thiazol‐4‐one 3 and benzaldehydes 4. The starting material 3 was synthesized by a condensation reaction of rhodanine 1 and malononitrile 2. The structures of the obtained products were established by IR, NMR, mass spectrometry, and elemental analysis. J. Heterocyclic Chem., (2011). 相似文献
736.
Mihaela Popovici Johan Swerts Kazuyuki Tomida Dunja Radisic Min‐Soo Kim Ben Kaczer Olivier Richard Hugo Bender Annelies Delabie Alain Moussa Christa Vrancken Karl Opsomer Alexis Franquet Malgorzata A. Pawlak Marc Schaekers Laith Altimime Sven Van Elshocht Jorge A. Kittl 《固体物理学:研究快报》2011,5(1):19-21
Crystalline rutile TiO2 films were grown by atomic layer deposition on oxidized Ru electrodes using a titanium methoxide as the metal precursor and O3 as the oxidant. A protective layer of ~0.3 nm TiO2 grown with H2O as the oxidant was first deposited in order to avoid etching of the Ru bottom electrode by the O3 used for the growth of the TiO2 (bulk) layer. Electrical evaluation of the capacitor stacks with TiO2 as dielectric, RuO2/Ru and Pt as the bottom and top electrodes respectively, resulted in superior characteristics of the rutile phase as compared to the anatase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
737.
Billon A Picaut J Foy C Valeau V Sakout A 《The Journal of the Acoustical Society of America》2008,123(6):4040-4043
This paper presents an extension of a diffusion model for room acoustics to handle the atmospheric attenuation. This phenomenon is critical at high frequencies and in large rooms to obtain correct acoustic predictions. An additional term is introduced in the diffusion equation as well as in the diffusion constant, in order to take the atmospheric attenuation into account. The modified diffusion model is then compared with the statistical theory and a cone-tracing software. Three typical room-acoustic configurations are investigated: a proportionate room, a long room and a flat room. The modified diffusion model agrees well with the statistical theory (when applicable, as in proportionate rooms) and with the cone-tracing software, both in terms of sound pressure levels and reverberation times. 相似文献
738.
Molecular imaging by Mid-IR laser ablation mass spectrometry 总被引:1,自引:0,他引:1
Akos Vertes Peter Nemes Bindesh Shrestha Alexis A. Barton Zhaoyang Chen Yue Li 《Applied Physics A: Materials Science & Processing》2008,93(4):885-891
Mid-IR laser ablation at atmospheric pressure (AP) produces a mixture of ions, neutrals, clusters, and particles with a size
distribution extending into the nanoparticle range. Using external electric fields the ions can be extracted and sampled by
a mass spectrometer. In AP infrared (IR) matrix-assisted laser desorption ionization (MALDI) experiments, the plume was shown
to contain an appreciable proportion of ionic components that reflected the composition of the ablated target and enabled
mass spectrometric analysis. The detected ion intensities rapidly declined with increasing distance of sampling from the ablated
surface to ∼4 mm. This was rationalized in terms of ion recombination and the stopping of the plume expansion by the background
gas. In laser ablation electrospray ionization (LAESI) experiments, the ablation plume was intercepted by an electrospray.
The neutral particles in the plume were ionized by the charged droplets in the spray and enabled the detection of large molecules
(up to 66 kDa). Maximum ion production in LAESI was observed at large (∼15 mm) spray axis to ablated surface distance indicating
a radically different ion formation mechanism compared to AP IR-MALDI. The feasibility of molecular imaging by both AP IR-MALDI
and LAESI was demonstrated on targets with mock patterns.
Presented at the 9-th International Conference on Laser Ablation, 2007 Tenerife, Canary Islands, Spain 相似文献
739.
Ghasemi SA Goedecker S Baratoff A Lenosky T Meyer E Hug HJ 《Physical review letters》2008,100(23):236106
Atomistic simulations considering larger tip structures than hitherto assumed reveal novel dissipation mechanisms in noncontact atomic force microscopy. The potential energy surfaces of realistic silicon tips exhibit many energetically close local minima that correspond to different structures. Most of them easily deform, thus causing dissipation arising from hysteresis in force versus distance characteristics. Furthermore, saddle points which connect local minima can suddenly switch to connect different minima. Configurations driven into metastability by the tip motion can thus suddenly access lower energy structures when thermal activation becomes allowed within the time required to detect the resulting average dissipation. 相似文献
740.
Yeljair Monascal Eliana Gallardo Loriett Cartaya Alexis Maldonado Yenner Bentarcurt Gabriel Chuchani 《Molecular physics》2018,116(2):194-203
Keto–enol tautomeric equilibrium and the mechanism of thermal conversion of 2- and 4-hydroxyacetophenone in gas phase have been studied by means of electronic structure calculations using density functional theory (DFT). A topological analysis of electron density evidence that the structure of keto and enol forms of 2-hydroxyacetophenone are stabilised by a relatively strong intramolecular hydrogen bond. 2- and 4-hydroxyacetophenone undergo deacetylation reactions yielding phenol and ketene. Two possible mechanisms are considered for these eliminations: the process takes place from the keto form (mechanism A), or occurs from the enolic form of the substrate (mechanism B). Quantum chemical calculations support the mechanism B, being found a good agreement with the experimental activation parameters. These results suggest that the rate-limiting step is the reaction of the enol through a concerted, non-synchronous, semi-polar, four-membered cyclic transition state (TS). The most advanced reaction coordinate in the TS is the rupture of O1···H1 bond, with an evolution in the order of 79.7%–80.9%. Theoretical results also suggest a three-step mechanism for the phenyl acetate formation from 2-hydroxyacetophenone. 相似文献