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11.
K. E. Whittaker L. Ciaffoni G. Hancock P. L. Hurst R. Peverall G. A. D. Ritchie 《Applied physics. B, Lasers and optics》2014,116(1):157-168
Studies into the suitability of a novel, widely tunable telecom L-band (1,563–1,613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for cavity ring-down spectroscopy (CRDS) are presented. The spectrometer comprised of a 36.6?cm long linear cavity with ring-down times varying between 19–26 μs across the 50 nm DS-DBR wavelength range due to changes in the cavity mirror reflectivities with wavelength. The potential of such a broadband, high-resolution CRD spectrometer was illustrated by investigating several transitions of CO2 in air, a 5 % calibrated mixture and breath samples. Allan variance measurements at a single wavelength indicated an optimal minimum detectable absorption coefficient (α min) of 3 × 10?10 cm?1 over 20 s. 相似文献
12.
Ultrasonic absorption in polymer gel dosimeters was investigated. An ultrasonic interferometer was used to study the frequency (f) dependence of the absorption coefficient (alpha) in a polyacrylamide gel dosimeter (PAG) in the frequency range 5-20 MHz. The frequency dependence of ultrasonic absorption deviated from that of an ideal viscous fluid. The presence of relaxation mechanisms was evidenced by the frequency dependence of alpha/f(2) and the dispersion in ultrasonic velocity. It was concluded that absorption in polymer gel dosimeters is due to a number of relaxation processes which may include polymer-solvent interactions as well as relaxation due to motion of polymer side groups.The dependence of ultrasonic absorption on absorbed dose and formulation was also investigated in polymer gel dosimeters as a function of pH and chemical composition. Changes in dosimeter pH and chemical composition resulted in a variation in ultrasonic dose response curves. The observed dependence on pH was considered to be due to pH induced modifications in the radiation yield while changes in chemical composition resulted in differences in polymerisation kinetics. 相似文献
13.
Emel Önal Cheng Zhang Derya Davarcı Ümit İşci Guillaume Pilet Andrew K. Whittaker Fabienne Dumoulin 《Tetrahedron letters》2018,59(6):521-523
A cyclotriphosphazene substituted with six 3,5-bis(trifluoromethyl) benzyloxy units was designed as a novel 19F MRI contrast agent. The resulting molecule has 36 magnetically equivalent fluorine atoms and exhibited suitable MRI properties with high imaging sensitivity, confirming the proof-of-concept as a convenient scaffold for the production of new 19F MRI contrasts agents. 相似文献
14.
Gass IA Milios CJ Whittaker AG Fabiani FP Parsons S Murrie M Perlepes SP Brechin EK 《Inorganic chemistry》2006,45(14):5281-5283
The microwave-assisted reaction of Fe(O2CMe)2 with salicylaldoxime (saoH2) in pyridine produces an octametallic cluster in crystalline form in 2 min. The core describes a cube encapsulated in a tetrahedron, while sao2- exhibits a novel coordination mode. 相似文献
15.
Rucker RP Whittaker AM Dang H Lalic G 《Journal of the American Chemical Society》2012,134(15):6571-6574
A method for highly selective anti-Markovnikov hydroamination of terminal alkenes is reported. The one-pot procedure involves hydroboration of the alkene followed by a novel electrophilic amination of the alkyl borane catalyzed by an NHC-Cu complex. Terminal alkenes are successfully transformed into tertiary alkyl amines in the presence of a variety of functional groups in yields ranging from 80 to 97% with excellent regioselectivity. Results of a preliminary study of the reaction mechanism are also described. 相似文献
16.
17.
Dr. Clelia Cogliati Dr. Laura Ragona Dr. Mariapina D'Onofrio Prof. Ulrich Günther Dr. Sara Whittaker Dr. Christian Ludwig Dr. Simona Tomaselli Dr. Michael Assfalg Prof. Henriette Molinari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(37):11300-11310
The investigation of multi‐site ligand–protein binding and multi‐step mechanisms is highly demanding. In this work, advanced NMR methodologies such as 2D 1H–15N line‐shape analysis, which allows a reliable investigation of ligand binding occurring on micro‐ to millisecond timescales, have been extended to model a two‐step binding mechanism. The molecular recognition and complex uptake mechanism of two bile salt molecules by lipid carriers is an interesting example that shows that protein dynamics has the potential to modulate the macromolecule–ligand encounter. Kinetic analysis supports a conformational selection model as the initial recognition process in which the dynamics observed in the apo form is essential for ligand uptake, leading to conformations with improved access to the binding cavity. Subsequent multi‐step events could be modelled, for several residues, with a two‐step binding mechanism. The protein in the ligand‐bound state still exhibits a conformational rearrangement that occurs on a very slow timescale, as observed for other proteins of the family. A global mechanism suggesting how bile acids access the macromolecular cavity is thus proposed. 相似文献
18.
Hui Hui Lee-Wang Idriss Blakey Traian V. Chirila Hui Peng Firas Rasoul Andrew K. Whittaker Bronwin L. Dargaville 《Macromolecular Symposia》2010,296(1):229-232
The possibility of employing self-healing gels as potential artificial vitreous substitutes is being explored. Advancement of traditional synthetic hydrogels as vitreous substitutes is hindered by their fragmentation upon injection into the vitreous cavity leading ultimately to inflammation. Preliminary work involved developing first generation self-healing gels, using amphiphilic tri-block copolymers of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPG-PEG-PPG) as the building block. Eight linear self-healing gels are synthesized by tethering an ureidopyrimidinone system to synthetically modified PPG-PEG-PPG via the formation of a bis-urea as a linker. The reversible nature of the hydrogen bonds permits alteration of their physical properties by changing the environment, yet retaining desirable characteristics. Despite low solubility in water, these polymers demonstrated associating behaviour under the investigated conditions, which is encouraging. Future generations of self-healing gels should involve the selection of a more hydrophilic core and/or star-like polymers to facilitate gel formation and strengthen the network. 相似文献
19.
Richard Law Oliver Barker John J. Barker Thomas Hesterkamp Robert Godemann Ole Andersen Tara Fryatt Steve Courtney Dave Hallett Mark Whittaker 《Journal of computer-aided molecular design》2009,23(8):459-473
Fragment-based drug discovery (FBDD) represents a change in strategy from the screening of molecules with higher molecular
weights and physical properties more akin to fully drug-like compounds, to the screening of smaller, less complex molecules.
This is because it has been recognised that fragment hit molecules can be efficiently grown and optimised into leads, particularly
after the binding mode to the target protein has been first determined by 3D structural elucidation, e.g. by NMR or X-ray
crystallography. Several studies have shown that medicinal chemistry optimisation of an already drug-like hit or lead compound
can result in a final compound with too high molecular weight and lipophilicity. The evolution of a lower molecular weight
fragment hit therefore represents an attractive alternative approach to optimisation as it allows better control of compound
properties. Computational chemistry can play an important role both prior to a fragment screen, in producing a target focussed
fragment library, and post-screening in the evolution of a drug-like molecule from a fragment hit, both with and without the
available fragment-target co-complex structure. We will review many of the current developments in the area and illustrate
with some recent examples from successful FBDD discovery projects that we have conducted. 相似文献
20.