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11.
It has been shown that tert-butyldimethylsilylated (Z) 2-carboethoxymethylene cycloalkanols are readily desilylated with concomitant cyclization to give the corresponding butenolides. The (E) isomers are desilylated, but not cyclized under these conditions. 相似文献
12.
The utility of organoboranes in the synthesis of a wide variety of functional groups is now well established.1 There have been, however, only a limited number of reports where an organoborane containing a β-functionalized carbon was utilized in organic synthesis. Part of the reason for this is the difficulty in preparing β-functional organoboranes and their tendency to undergo elimination under a variety of reaction conditions.2 Those β-functionalized organoboranes utilized synthetically, which we could find in the literature are the β-ethoxy3, 1, and β-carboethoxyvinyl-boranes4, 2, of Zweifel and coworkers and the trans-β-tert-butyldimethylsilyloxy organoborane, 3, of Corey and Ravindranathan,5 who proposed this system as a potential precursor to prostanoids. 相似文献
13.
Julie P. Vanegas Lucas E. Peisino Dr. Salvador Pocoví‐Martínez Dr. Ramón J. Zaragozá Dr. Elena Zaballos‐García Dr. Julia Pérez‐Prieto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16248-16255
Gold nanoparticles capped with simple adenosine derivatives can form colloidal aggregates in nonpolar solvents. Theoretical calculations indicate the formation of organic channels by the supramolecular assembly of the nanoparticles by means of hydrogen bonds between the adenine moieties. The aggregates were only negligibly sensitive to nPrOH, iPrOH, and tBuOH, whereas some showed a similar response to MeOH and EtOH, and others showed high selectivity toward MeOH. DNA nucleoside derivatives (1‐(2‐deoxy‐β‐D ‐ribofuranosyl)‐5‐methyluracil and 2′,3′‐O‐isopropylideneadenosine) as well as thymine and other aromatic compounds such as pyrene derivatives (pyrene, 1‐chloropyrene, 1‐hydroxypyrene, (1‐pyrenyl)methanol, and 2‐hydroxynapthalene) did not induce disassembly of the nanoparticle aggregates. Data suggest that the nucleoside channels allow access to alcohols according to their size, and an efficient interaction between the alcohol and the adenine units destabilizes the hydrogen bonds, which eventually leads to nanoparticle disassembly. 相似文献
14.
Freezing Capture of Polymorphic Aggregates of Bolaamphiphilic L‐Valine‐Based Molecular Hydrogelators 下载免费PDF全文
Dr. Vicent J. Nebot Dr. Santiago Díaz‐Oltra Dr. Johan Smets Susana Fernández Prieto Dr. Juan F. Miravet Dr. Beatriu Escuder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5762-5767
Nanostructured xerogels have been prepared by the freeze‐drying of hydrogels and aggregates formed by bolaamphiphilic L ‐valine derivatives after aging under different environmental conditions. A wide variety of shapes and sizes has been achieved by a simple methodology. These nanostructures have been studied by SEM and WAXD and a dramatic influence of structural flexibility on the kinetics of aggregation has been observed. Such flexibility and a modulation of the hydrophobic effect have shown a profound influence in the packing of these compounds and revealed a high degree of polymorphism. 相似文献
15.
Dr. Bidyut B. Sarma Jonglack Kim Jonas Amsler Dr. Giovanni Agostini Dr. Claudia Weidenthaler Norbert Pfänder Dr. Raul Arenal Dr. Patricia Concepción Dr. Philipp Plessow Prof. Dr. Felix Studt Dr. Gonzalo Prieto 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5855-5864
Realizing the full potential of oxide-supported single-atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one-pot combination of Ru1/CeO2 and Rh1/CeO2 SACs enables a highly selective olefin isomerization-hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double-bond migration and anti-Markovnikov α-olefin hydrosilylation, respectively. First-principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single-pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio-selectivity (>95 %) even from industrially-relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide-supported single-atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes. 相似文献
16.
J. Lí nares M. V. P Rez R. E. La Fuente X. Prieto C. Montero L. Gato J. I. Rodriguez C. G mez-Reino 《Fiber and Integrated Optics》1993,12(3):231-245
An experimental analysis of graded-index (GRIN) planar waveguides produced by ion exchange in soda-lime glass is presented. This study is based on a recent model describing nonlinear diffusion. Likewise the modal coupling between planar waveguides, produced in the same substrate, is analyzed in order to design efficient integrated optical components. Finally, waveguiding structures induced by Kerr effect in glass are proposed and analyzed. 相似文献
17.
The aim of this work is to improve the mechanical properties of AISI 4140 steel substrates by using a TiN[BCN/BN]n/c-BN multilayer system as a protective coating. TiN[BCN/BN]n/c-BN multilayered coatings via reactive r.f. magnetron sputtering technique were grown, systematically varying the length period (Λ) and the number of bilayers (n) because one bilayer (n = 1) represents two different layers (tBCN + tBN), thus the total thickness of the coating and all other growth parameters were maintained constant. The coatings were characterized by Fourier transform infrared spectroscopy showing bands associated with h-BN bonds and c-BN stretching vibrations centered at 1400 cm−1 and 1100 cm−1, respectively. Coating composition and multilayer modulation were studied via secondary ion mass spectroscopy. Atomic force microscopy analysis revealed a reduction in grain size and roughness when the bilayer number (n) increased and the bilayer period decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period (Λ) was 80 nm (n = 25), yielding the relative highest hardness (∼30 GPa) and elastic modulus (230 GPa). The values for the hardness and elastic modulus are 1.5 and 1.7 times greater than the coating with n = 1, respectively. The enhancement effects in multilayered coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain increased hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayered coatings taking into account the thickness reduction at individual single layers that make up the multilayered system. The Hall-Petch model based on dislocation motion within layered and across layer interfaces has been successfully applied to multilayered coatings to explain this hardness enhancement. 相似文献
18.
Piñeiro A Prieto G Ruso JM Verdes PV Sarmiento F 《Journal of colloid and interface science》2009,329(2):351-356
Using grazing incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy (AFM) it has been recently demonstrated that linear fluorocarbon-hydrocarbon diblocks (FnHm) self-assemble in water/air interfaces forming elongated and circular hemimicelles. Those structures have been observed for diblocks with at least eight fluorinated carbons. Based on the lack of a collapse pressure for F6H16, and due to the fact that no stable surface pressure values are reached under compression, it has been concluded that these molecules do not form stable monolayers. It has been also suggested that F6H16 and shorter diblocks desorb from the water surface under compression. It is not easy to accept that a significant concentration of so hydrophobic molecules can be stable in aqueous solution even when the employed experimental techniques were not able to clearly detect a well defined structure on the interface. In the present work the adsorption and arrangement of F6H16 and F6H10 at the water surface are studied by molecular dynamics (MD) simulations as a function of the available area per molecule. Starting from a random mixture, the spontaneous formation of elongated hemimicelles is observed for both systems when the area per molecule is higher than approximately 50 A(2). For intermediate areas two pseudo-phases, one rich in hydrocarbons and the other with higher fluorocarbon concentration, are formed. For the systems with less than approximately 30 A(2) available per molecule the formation of multilayers is observed. This is the first time that the dynamics and structure of perfluoroalkane (PFA) films, and in particular of hemimicelles on a liquid surface, are observed and characterized at atomic level. 相似文献
19.
Kevin E. O’Shea Ailette Aguila K. Vinodgopal Prashant V. Kamat 《Research on Chemical Intermediates》1998,24(6):695-705
The oxidation of dimethyl methylphosphonate (DMMP) was examined under ultrasonic conditions (640 kHz) in oxygen saturated
aqueous solutions. Acetic acid, formic acid, methylphosphonic acid, phosphate, and oxalic acid have been identified as the
major products produced during the sonolytic irradiation of DMMP. The initial rates of oxidation were determined as a function
of initial DMMP concentration. The kinetic behavior of the system is consistent with the Langmuir-Hinshelwood model implying
oxidative processes occur at or near the gas-liquid interface during cavitation. Mechanistic implications and conclusions
are discussed based on the product distributions and kinetic parameters. 相似文献
20.
Luis A. Arias David Arbelo Arnaldo Alzrreca Jos A. Prieto 《Journal of heterocyclic chemistry》2001,38(1):29-33
Alkylphenyl sulfones 3 are appropriate synthons for the synthesis of 2‐phenylsulfonyl alkylidene pyrro‐lidine or piperidine derivatives 1 in good to moderate yields. The lithium alkyl sulfones 4 are first reacted with the desired protected lactams and then subjected to acidic methanolysis to afford the unusual enam‐ines 1a‐e . NMR studies (COSY 1H‐1H, COSY 1H‐13C, NOE) showed the Z enamines to exist in a dynamic equilibrium with the corresponding imines 2 . The stereochemistry of the described compounds was confirmed by molecular calculations. 相似文献