全文获取类型
收费全文 | 298篇 |
免费 | 10篇 |
国内免费 | 1篇 |
学科分类
数理化 | 309篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 16篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 6篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1997年 | 2篇 |
1996年 | 9篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1968年 | 2篇 |
1965年 | 2篇 |
1962年 | 2篇 |
1939年 | 4篇 |
排序方式: 共有309条查询结果,搜索用时 9 毫秒
71.
Alkynyl-substituted phenyldithiafulvenes have been found to act as versatile building blocks for the construction of π-conjugated molecular rods, shape-persistent macrocycles (SPMs), and conducting polymers. Through Cu(I)-catalyzed alkynyl homocoupling, a series of linear-shaped π-extended tetrathiafulvalene analogues (exTTFs) carrying conjugated oligoynes (ranging from diyne to hexayne) as the central π-bridge were readily prepared. The solid-state properties and reactivities of diyne- and tetrayne-centered exTTFs were characterized by X-ray crystallography and differential scanning calorimetry (DSC), while the electronic properties of the oligoyne-exTTFs were elucidated by UV-vis absorption spectroscopy and density functional theory (DFT) calculations. Cyclic voltammetric analysis showed that the terminal phenyldithiafulvene groups of the oligyne-exTTFs could undergo oxidative coupling to form tetrathiafulvalene vinylogue (TTFV)-linked polymer wires. Through a different synthetic route involving oxidative dimerization and Pd/Cu-catalyzed alkynyl homocoupling, the acetylenic phenyldithiafulvene precursors led to shape-persistent macrocycles where the formation of trimeric macrocycles was particularly favored due to the small ring strain incurred. Finally, spectroelectrochemical studies on these oligoyne and TTF hybrid materials disclosed electrochromic and molecular redox-controlled switching properties applicable to molecular electronic and optoelectronic devices. 相似文献
72.
Jérôme Girard Priscilla S. Brunetto Olivier Braissant Zarko Rajacic Nina Khanna Regine Landmann Alma U. Daniels Katharina M. Fromm 《Comptes Rendus Chimie》2013,16(6):550-556
A silver polystyrene sulfonate polyelectrolyte was synthesized, showing a spontaneous reduction of silver ions to silver nanoparticles over a period of approximately 1 month. A follow-up of the nanoparticle formation via scanning electron microscopy (SEM) reveals migration of the nanoparticles towards the cracks of the polymer over time, leading to a self-healing process of the nanocomposite. Antibacterial tests show excellent antibacterial activity of our compound, which allows us to use this compound e.g. for external medical applications. 相似文献
73.
74.
75.
J. E. Daniels D. Pontoni Rui Ping Hoo V. Honkim?ki 《Journal of synchrotron radiation》2010,17(4):473-478
Combined small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) is a powerful technique for the study of materials at length scales ranging from atomic/molecular sizes (a few angstroms) to the mesoscopic regime (~1 nm to ~1 µm). A set‐up to apply this technique at high X‐ray energies (E > 50 keV) has been developed. Hard X‐rays permit the execution of at least three classes of investigations that are significantly more difficult to perform at standard X‐ray energies (8–20 keV): (i) in situ strain analysis revealing anisotropic strain behaviour both at the atomic (WAXS) as well as at the mesoscopic (SAXS) length scales, (ii) acquisition of WAXS patterns to very large q (>20 Å?1) thus allowing atomic pair distribution function analysis (SAXS/PDF) of micro‐ and nano‐structured materials, and (iii) utilization of complex sample environments involving thick X‐ray windows and/or samples that can be penetrated only by high‐energy X‐rays. Using the reported set‐up a time resolution of approximately two seconds was demonstrated. It is planned to further improve this time resolution in the near future. 相似文献
76.
Stephanie L. Daniels Johnpeter N. Ngunjiri Jayne C. Garno 《Analytical and bioanalytical chemistry》2009,394(1):215-223
Individual ferritin molecules can be sensitively detected using magnetic sample modulation (MSM) combined with contact mode
atomic force microscopy (AFM). To generate an oscillating magnetic field, an alternating current (AC) was applied to a solenoid
placed within the base of the AFM sample stage. When a modulated electromagnetic field is applied to samples, ferromagnetic
and paramagnetic nanomaterials are induced to vibrate. The flux of the AC electromagnetic field causes the ferritin samples
to vibrate with corresponding rhythm and periodicity of the applied field. This motion can be detected and mapped using contact
mode AFM with a soft, nonmagnetic cantilever. Changes in the phase and amplitude of the periodic motion of the sample are
sensed by the tip to selectively map vibrating magnetic nanomaterials. Particle lithography was used to create nanopatterned
test platforms of ferritin for MSM measurements. Regularly spaced structures of proteins provide precise reproducible dimensions
for multiple successive surface measurements at dimensions of tens of nanometers.
Figure Ring patterns of ferritin were used as nanoscale test platforms to characterize magnetic properties at the level of individual
proteins with AFM imaging
相似文献
Jayne C. GarnoEmail: |
77.
An analytical method for the determination of UV filter substances in fish tissue has been developed and validated using benzophenone-3,
3-(4-methylbenzylidene)-camphor, 2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate and 2-ethylhexyl 3-(methoxyphenyl)-2-propenoate
as target analytes. The fish fillets were homogenised and extracted by Soxhlet extraction. The extracts were run through a
clean-up process including gel permeation chromatography followed by solid-phase extraction. Quantification of the compounds
was performed using liquid chromatography with tandem mass spectrometric detection. Blank fish as well as spiked blank fish
were analysed to validate the analytical method. The analytical method developed has the multiple advantages of enabling separation,
simultaneous identification and quantification of each of the four selected compounds in a single run. Contamination of blank
samples and abnormally high concentrations in spiked samples were avoided by taking extensive precautions during the fish
preparation procedure. The method was validated in accordance with internationally accepted criteria, such as specificity,
accuracy and repeatability. The combination of LC with tandem mass spectrometry ensures a high level of specificity. The accuracy
of the method was reported as the mean recovery rate for the analytes in the sample matrix. Mean recoveries were in the range
86–108%. The precision is expressed as the relative standard deviation, and in all but one of the cases was 20% or below.
The accuracy of the method allows residue analyses to be performed on biological matrices at ng/g levels. The determined limit
of quantification for each analyte was 8 ng/g fish. For all spiking levels ≥8 ng/g, relative standard deviations were ≤ 20%. 相似文献
78.
Experiments on spherical particles in a 3D annular shear cell vibrated from below and sheared from above show a hysteretic freezing or melting transition. Under sufficient vibration a crystallized state is observed, which can be melted by sufficient shear. The critical line for this transition coincides with equal kinetic energies for vibration and shear. The force distribution is double peaked in the crystalline state and single peaked with an approximately exponential tail in the disordered state. Continuous relations between pressure and volume (with dP/dV>0) exist for a continuum of partially and/or intermittently melted states over a range of parameters. 相似文献
79.
Sauerbrey S Majhi PK Daniels J Schnakenburg G Brändle GM Scherer K Streubel R 《Inorganic chemistry》2011,50(3):793-799
Metalation reactions were studied of a sterically demanding imidazole derivative, namely, 1-tert-butylimidazole (1), with different metalation reagents and subsequent reaction with diphenylchlorophosphane. The reaction product, 1-tert-butyl-2-diphenylphosphino-imidazole (2), was subjected to oxidation and complexation reactions to yield the corresponding products Ph(2)(Imi)P-E (E = O (3), S (4), Se (5), W(CO)(5) (8)) and in the case of borane-THF the N-BH(3) coordination product 10 was obtained. The analytical data of the new compounds are discussed, including X-ray diffraction studies of 3-5. 相似文献
80.
Recent experiments in low-intensity fluorescence spectrometry, flash photolysis and continuous photolysis at 300°K in an aqueous medium have provided data for uracil and thymine from which all the pertinent phenomenological characteristics (Φfl0′, Φisc0′, Φ′chem) of the 0′ level can be evaluated. It is necessary to postulate considerable internal conversion 1S → 0S with τic ≈ 1–2 × 10−12 sec, this process correlating with the dielectric relaxation time of water. 相似文献