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81.
Thermal and mechanical properties of chitosan nanocomposites with cellulose modified in ionic liquids 总被引:1,自引:0,他引:1
Aleksandra Grząbka-Zasadzińska Tazdin Amietszajew Sławomir Borysiak 《Journal of Thermal Analysis and Calorimetry》2017,130(1):143-154
In this paper, ionic liquid treatment was applied to produce nanometric cellulose particles of two polymorphic forms. A complex characterization of nanofillers including wide-angle X-ray scattering, Fourier transform infrared spectroscopy, and particle size determination was performed. The evaluated ionic liquid treatment was effective in terms of nanocrystalline cellulose production, leaving chemical and supermolecular structure of the materials intact. However, nanocrystalline cellulose II was found to be more prone to ionic liquid hydrolysis leading to formation larger amount of small particles. Each nanocrystalline cellulose was subsequently mixed with a solution of chitosan, so that composite films containing 1, 3, and 5% mass/mass of nanometric filler were obtained. Reference samples of chitosan and chitosan with micrometric celluloses were also solvent casted. Thermal, mechanical, and morphological properties of films were tested and correlated with properties of filler used. The results of both, tensile tests and thermogravimetric analysis showed a significant discrepancy between composites filled with nanocrystalline cellulose I and nanocrystalline cellulose II. 相似文献
82.
Nathanael Ackerman Cameron Freer Aleksandra Kwiatkowska Rehana Patel 《Annals of Pure and Applied Logic》2017,168(1):19-36
We consider the space of countable structures with fixed underlying set in a given countable language. We show that the number of ergodic probability measures on this space that are -invariant and concentrated on a single isomorphism class must be zero, or one, or continuum. Further, such an isomorphism class admits a unique -invariant probability measure precisely when the structure is highly homogeneous; by a result of Peter J. Cameron, these are the structures that are interdefinable with one of the five reducts of the rational linear order . 相似文献
83.
Aleksandra JankowiakEmilia Obijalska Piotr Kaszynski Adam Pieczonka Victor G. Young Jr. 《Tetrahedron》2011,67(19):3317-3327
Four heterocyclic salts 1a-d were prepared by Ca2+-assisted cyclization of fluoro derivatives 3, and investigated by spectroscopic (NMR and UV), electrochemical, and computational (DFT and MP2) methods. The mechanism for the formation of the cations was investigated at the DFT level of theory. 2-D NMR spectroscopy for 1[ClO4] in DMSOd6 aided with DFT results permitted the assignment of 1H and 13C NMR signals in cations 1. The molecular and crystal structures for 1a[ClO4] [C13H10ClNO4 triclinic, P−1, a=9.6517(12) Å, b=11.0470(13) Å, c=12.2373(15) Å, α=67.615(1)°, β=78.845(2)°, γ=87.559(2)°; V=1183.0(2) Å3, Z=4] and 1d[ClO4] [C12H9ClN2O4 triclinic, P−1, a=5.9525(6) Å, b=8.3141(9) Å, c=12.2591(13) Å, α=73.487(1)°, β=83.814(1)°, γ=83.456(1)°; V=576.07(10) Å3, Z=2] were determined by X-ray crystallography and compared with results of DFT and MP2 calculations. Electrochemical analysis gave the reduction potential order (1b>1c∼1d>1a), which is consistent with computational results. 相似文献
84.
The reaction between 3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridinecarboxaldehyde semicarbazone (pyridoxal-semicarbazone or PLSC) and appropriate chloride, sulfate, nitrate or thiocyanate Cu(II) salts in water/alcohol mixtures resulted in the formation of new copper(II) complexes: [Cu(PLSC)Cl2] (1), [Cu(PLSC)(H2O)(SO4)]2·3H2O (2), [Cu2(PLSC)2(NCS)2](NCS)2 (3), [Cu(PLSC)(NO3)2(CH3OH)] (4) and [Cu(PLSC-2H]NH3·H2O (5). The complexes were characterized by elemental analysis, conductometric measurements and IR spectroscopy, while complexes 1, 2, 3 and 4 were further characterized by single crystal X-ray diffraction. 相似文献
85.
Schmidt H Böttcher C Trampczynska A Clemens S 《Analytical and bioanalytical chemistry》2011,399(3):1355-1361
Nicotianamine (NA) is an important metal chelator, implicated in the intra- and intercellular trafficking of several transition
metal ions in plants. To decipher its roles in physiological processes such as micronutrient acquisition, distribution or
storage, fast and sensitive analytical techniques for quantification of this non-proteinogenic amino acid will be required.
The use of a recombinant Schizosaccharomyces pombe strain expressing a nicotianamine synthase (NAS) gene allowed for the production of [15N3]-NA, which was enriched from cell extracts through cation exchange and used for stable isotope dilution analysis of NA. Such
an approach should be widely applicable to important bioanalytes that are difficult to synthesize. The analytical procedure
comprises mild aqueous extraction and rapid Fmoc derivatization, followed by fast separation using ultra-performance liquid
chromatography (UPLC) and sensitive detection by positive ion electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS)
with a chromatographic cycle time of only 8 min. Derivatization was optimized with respect to incubation time and species
suitable for quantification. The limit of detection was 0.14 to 0.23 pmol in biological matrices with the response being linear
up to 42 pmol. Recovery rates were between 83% and 104% in various biological matrices including fission yeast cells, fungal
mycelium, plant leaves and roots. 相似文献
86.
Veronica V. Tomina Gabriella R. Yurchenko Alexandr K. Matkovsky Yuriy L. Zub Aljosa Kosak Aleksandra Lobnik 《Journal of fluorine chemistry》2011,132(12):1146-1151
Hydrolysis and polycondensation reactions of tetraethoxysilane (TEOS) with 3,3,3-trifluoropropyl-trimethoxysilane (TFMS) or 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFES) were used to synthesize xerogels functionalized with fluorine-containing groups. According to transmission electron microscopy, the skeletons of synthesized polysiloxane xerogels have globular structures and consist of agglomerates of particles with fluorinated groups on their surfaces. FTIR spectroscopy showed that primary xerogel particles possess spatial polysiloxane networks, with fluorinated groups along with silanol groups and water in the surface layer. According to thermal analyses, the water content was 3–8 wt.%, and it decreased with increasing length of the fluorinated chain. Thermal destruction of the surface layer starts above 300 °C. The sorbents that were obtained were predominantly mesoporous materials with well-developed porous structures (SBET = 400–960 m2 g−1, Vs = 0.66–0.93 cm3 g−1). The influence of the TEOS/functional silane ratio and the natures of the functional groups on the structural and adsorptive properties were shown. The samples synthesized are organophilic. The affinity for n-hexane increases with increasing length of the fluorine-containing chain (PFES) and the content of fluorinated groups in the surface layer. The hybrid organic–inorganic materials that were obtained can be used for adsorption of hydrocarbons, including oil, from water. 相似文献
87.
Phenol adsorption on closed carbon nanotubes 总被引:1,自引:0,他引:1
Pacholczyk A Terzyk AP Wiśniewski M Gauden PA Wesołowski RP Furmaniak S Szcześ A Chibowski E Kruszka B 《Journal of colloid and interface science》2011,361(1):288-292
We present the results of systematic studies of phenol adsorption on closed commercially available, unmodified carbon nanotubes. Phenol adsorption is determined by the value of tube-specific surface area, the presence of small amount of surface groups influence adsorption only in very small amount. Phenol can be applied as a probe molecule for comparative analysis of tube surface areas. Tube curvature influences adsorption from solution, i.e., we observe increasing adsorption energy (and slower desorption process) with the decrease in tube curvature. This is in full accordance with molecular simulation results. 相似文献
88.
Woźnica M Butkiewicz A Grzywacz A Kowalska P Masnyk M Michalak K Luboradzki R Furche F Kruse H Grimme S Frelek J 《The Journal of organic chemistry》2011,76(9):3306-3319
In the present work, the validity of the helicity rule relating the absolute configuration of the bridgehead carbon atom in bicyclic β-lactams to the sign of the 220 nm band observed in their electronic circular dichroism (ECD) spectra is examined for ring-expanded cephalosporin analogues. To this end, a series of model compounds with a seven-membered ring condensed with the β-lactam unit was synthesized. A key step of their synthesis was either the ring-closing metathesis (RCM) or the free radical cyclization leading to the seven-membered ring with an S, O, or C atom at the 6 position in the bicyclic skeleton. To investigate the scope and limitations of the simple, empirically established helicity rule, a combination of ECD spectroscopy, variable-temperature ECD measurements, X-ray analysis, and time-dependent density functional theory (TD-DFT) calculations was used. A comparison of the experimental ECD spectra with the spectra simulated by TD-DFT calculations gives a reasonable interpretation of the Cotton effects observed in the 240-215 nm spectral range. The results suggest that the helicity rule does not apply to the investigated compounds because of the planarity of their amide chromophore. Thus, these compounds do not constitute an exception to the rule that was established for bi- and polycyclic β-lactams with the nonplanar amide chromophore only. 相似文献
89.
This paper presents the results of experimental studies of hydrogen-bonded 2-pyridone crystal IR spectra. Spectral studies have demonstrated the existence of two anhydrous solid-state phases of each compound, namely the α and the β phases. Hydrogen bonds in the high-temperature α phase of these crystals have been estimated to be 40% stronger than the hydrogen bonds in the β phase, which are stable at room temperature. The mechanism of the phase transition in the solid-state 2-pyridone is proposed on the basis of the IR spectral data. This was possible by taking into account small changes in the geometry of heterocyclic molecular skeletons, which accompany the electron density redistribution in the hydrogen bonds occurring during the transition. The phase transition is connected with a partial change in the hydrogen bond nature from the N(+)-H···O(-) in the α phase, to the N-H···O hydrogen bonds in the β phase crystals. 相似文献
90.
Synthesis of iminosugar-based affinity-based proteomics probes for use in probing exo-α-glycosidase activity. 相似文献