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941.
Yuning Hong Hao Xiong Jacky Wing Yip Lam Dr. Matthias Häußler Dr. Jianzhao Liu Yong Yu Yongchun Zhong Dr. Herman H. Y. Sung Dr. Ian D. Williams Prof. Kam Sing Wong Prof. Ben Zhong Tang Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1232-1245
Whereas most conventional DNA probes are flat disklike aromatic molecules, we explored the possibility of developing quadruplex sensors with nonplanar conformations, in particular, the propeller‐shaped tetraphenylethene (TPE) salts with aggregation‐induced emission (AIE) characteristics. 1,1,2,2‐Tetrakis[4‐(2‐triethylammonioethoxy)phenyl]ethene tetrabromide (TPE‐ 1 ) was found to show a specific affinity to a particular quadruplex structure formed by a human telomeric DNA strand in the presence of K+ ions, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Steady‐state and time‐resolved spectral analyses revealed that the specific binding stems from a structural matching between the AIE fluorogen and the DNA strand in the folding process. Computational modeling suggests that the AIE molecule docks on the grooves of the quadruplex surface with the aid of electrostatic attraction. The binding preference of TPE‐ 1 enables it to serve as a bioprobe for direct monitoring of cation‐driven conformational transitions between the quadruplexes of various conformations, a job unachievable by the traditional G‐quadruplex biosensors. Methyl thiazolyl tetrazolium (MTT) assays reveal that TPE‐ 1 is cytocompatible, posing no toxicity to living cells. 相似文献
942.
Akhtar Hussain Jose Gracia Dr. Ben E. Nieuwenhuys? Prof. Dr. J. W. Niemantsverdriet Prof. Dr. 《Chemphyschem》2010,11(11):2375-2382
The chemistry of oxygen, hydrogen, water, and other species containing both oxygen and hydrogen atoms on the anatase TiO2 (001) surface is investigated by DFT. The adsorption energy of atoms and radicals depends appreciably on the position and mode of adsorption, and on the coverage. Molecular hydrogen and oxygen interact weakly with the clean surface. However, H2O dissociates spontaneously to give two nonidentical hydroxyl groups, and this provides a model for hydroxylation of TiO2 surfaces by water. The mobility of the hydroxyl groups created by water splitting is initially impeded by a diffusion barrier close to 1 eV. The O2 adsorption energy increases significantly in the presence of H atoms. Hydroperoxy (OOH) formation is feasible if at least two H atoms are present in the direct vicinity of O2. In the adsorbed OOH, the O? O bond is considerably lengthened and thus weakened. 相似文献
943.
Pijper D Saisaha P de Boer JW Hoen R Smit C Meetsma A Hage R van Summeren RP Alsters PL Feringa BL Browne WR 《Dalton transactions (Cambridge, England : 2003)》2010,39(43):10375-10381
A number of manganese-based catalysts employing ligands whose structures incorporate pyridyl groups have been reported previously to achieve both high turnover numbers and selectivity in the oxidation of alkenes and alcohols, using H(2)O(2) as terminal oxidant. Here we report our recent finding that these ligands decompose in situ to pyridine-2-carboxylic acid and its derivatives, in the presence of a manganese source, H(2)O(2) and a base. Importantly, the decomposition occurs prior to the onset of catalysed oxidation of organic substrates. It is found that the pyridine-2-carboxylic acid formed, together with a manganese source, provides for the observed catalytic activity. The degradation of this series of pyridyl ligands to pyridine-2-carboxylic acid under reaction conditions is demonstrated by (1)H NMR spectroscopy. In all cases the activity and selectivity of the manganese/pyridyl containing ligand systems are identical to that observed with the corresponding number of equivalents of pyridine-2-carboxylic acid; except that, when pyridine-2-carboxylic acid is used directly, a lag phase is not observed and the efficiency in terms of the number of equivalents of H(2)O(2) required decreases from 6-8 equiv. with the pyridin-2-yl based ligands to 1-1.5 equiv. with pyridine-2-carboxylic acid. 相似文献
944.
Quantum Phase Transition of the Bosonic Atoms near the Feshbach Resonance in an Optical Lattice 下载免费PDF全文
The quantum phase transition from the Mott insulator to the superfluid phases of the bosonic atoms trapped in an optical lattice, in which the on-site interaction carl be tuned by a Feshbach resonance, is investigated by a variational approach within mean-field theory. We derive an extended Bos~Hubbard model to describe this ultracold atomic system. By theoretical calculation and analysis, the phase diagram is shown clearly, and we find an exciting and novel phenomenon that is the appearance of the Mort insulator-sea (MI-sea). Meanwhile, the experimental feasibility of observing the MI-sea is discussed by analyzing the published data related to the Fashbaeh resonance at present. Finally, the potential application of the MI-sea for quantum information processing and quantum computation is also discussed in detail 相似文献
945.
Sonia Ben Abdelkhalek Sami Kallel Octavio Peña 《Journal of magnetism and magnetic materials》2010,322(21):3416-4067
The structural, magnetic and electrical properties of Cr and Fe simultaneously substituted in the perovskite La0.6Sr0.4Mn1−2xCrxFexO3 have been studied. The presence of Cr and Fe had no significant effect on the structural properties. Curie temperature and saturation magnetization decrease with increase in Cr and Fe contents. For x=0.20 and 0.25, a steep drop of zero field-cooled (ZFC) magnetization at low temperature signifies the formation of cluster- or spin-glass state. A weak hysteresis at low fields seems to be an indication of phase separation. All the resulting magnetization curves can be explained by a superposition of both ferromagnetic and antiferromagnetic components. All the samples are semiconducting throughout the temperature range studied. Resistivity can be described by the adiabatic small polaron hopping and the variable range hopping model. It was found that the transport mechanism is dominated by the VRH model with an increase of Mott localization energy, which explains the increase of resistivity. 相似文献
946.
The α-Zn2P2O7 compound was obtained by conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, solid
state 31P NMR MAS, and electrical impedance spectroscopy. The solid state 31P MAS NMR, performed at 121.49 MHz, shows three isotropic resonances at −21.1, −18.8, and −15.8 ppm, confirming the non-equivalency
of the three PO4 groups in the α-Zn2P2O7 form. They are characterized by different chemical shift tensor parameters with the local geometrical features of the tetrahedra.
Electrical impedance measurements of β-Zn2P2O7, form stable for temperature greater than 403 K, were performed as a function of both temperature and frequency. The electrical
conduction and dielectric relaxation have been studied. The AC conductivity obeys the universal power law. The approximation
type correlated barrier hopping model explains the universal behavior of the n exponent. The impedance plane plot shows semicircle arcs at different temperatures, and an electrical equivalent circuit
has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance R
p and constant phase elements CPE. The simulated spectra show a good correlation with the experimental data. 相似文献
947.
In natural waters, fluoride ions are necessary and beneficial for the human being. At higher level of F− in water, it is toxic and detrimental to human health, leading to serious problems such as dental and skeleton fluorosis.
According to the World Health Organization, the acceptable concentrations of fluoride in potable water are in the range of
0.7–1.5 mg L−1. Various treatment technologies for fluoride removal from water have been used such as ion exchange, adsorption and membrane
processes. In the present study, removal of fluoride ions from aqueous solutions was investigated using a polyamide thin film
composite nanofiltration membrane denoted as HL 2514 T from Osmonics Company. Through this membrane, the mechanism of transport
was investigated. The Kedem–Katchelsky model was applied in order to determine phenomenological parameters σ and P
s, respectively, the reflection coefficient of the membrane and the solute permeability of ions. The convective and diffusive
parts of the mass transfer were quantified. The retention of monovalent and bivalent salts by this membrane shows that it
is negatively charged. In the second part, retention of fluoride anions was investigated. Results show that the retention
of fluoride by HL membrane exceeds 80%. The influence of the chemical parameters (feed concentration and ionic strength) and
the physical parameters (applied pressure and recovery) on the elimination of fluoride was studied. 相似文献
948.
Hisham Ben Hamidane Huan He Oleg Yu. Tsybin Mark R. Emmett Christopher L. Hendrickson Alan G. Marshall Yury O. Tsybin 《Journal of the American Society for Mass Spectrometry》2009,20(6):1182-1192
The rules for product ion formation in electron capture dissociation (ECD) mass spectrometry of peptides and proteins remain
unclear. Random backbone cleavage probability and the nonspecific nature of ECD toward amino acid sequence have been reported,
contrary to preferential channels of fragmentation in slow heating-based tandem mass spectrometry. Here we demonstrate that
for amphipathic peptides and proteins, modulation of ECD product ion abundance (PIA) along the sequence is pronounced. Moreover,
because of the specific primary (and presumably secondary) structure of amphipathic peptides, PIA in ECD demonstrates a clear
and reproducible periodic sequence distribution. On the one hand, the period of ECD PIA corresponds to periodic distribution
of spatially separated hydrophobic and hydrophilic domains within the peptide primary sequence. On the other hand, the same
period correlates with secondary structure units, such as α-helical turns, known for solution-phase structure. Based on a number of examples, we formulate a set of characteristic features
for ECD of amphipathic peptides and proteins: (1) periodic distribution of PIA is observed and is reproducible in a wide range
of ECD parameters and on different experimental platforms; (2) local maxima of PIA are not necessarily located near the charged
site; (3) ion activation before ECD not only extends product ion sequence coverage but also preserves ion yield modulation;
(4) the most efficient cleavage (e.g. global maximum of ECD PIA distribution) can be remote from the charged site; (5) the
number and location of PIA maxima correlate with amino acid hydrophobicity maxima generally to within a single amino acid
displacement; and (6) preferential cleavage sites follow a selected hydrogen spine in an α-helical peptide segment. Presently proposed novel insights into ECD behavior are important for advancing understanding of
the ECD mechanism, particularly the role of peptide sequence on PIA. An improved ECD model could facilitate protein sequencing
and improve identification of unknown proteins in proteomics technologies. In structural biology, the periodic/preferential
product ion yield in ECD of α-helical structures potentially opens the way toward de novo site-specific secondary structure determination of peptides and
proteins in the gas phase and its correlation with solution-phase structure. 相似文献
949.
Yixin Zhao Philip Larimer Richard T. Pressler Dr. Ben W. Strowbridge Prof. Dr. Clemens Burda Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(13):2407-2410
Light rather than electrical current : The inner or outer surfaces of glass micropipettes can be coated with nanoparticles of a narrow‐band‐gap semiconductor. When visible or near‐infrared light is used for excitation, these micropipettes (labeled PE Stim in the image) can activate nearby neurons (labeled *) in brain tissue without the damage associated with electrical stimulation.
950.
Doris Grumelli Dr. Carolina Vericat Dr. Guillermo Benítez Dr. José M. Ramallo‐López Dr. Lisandro Giovanetti Dr. Félix Requejo Dr. M. Sergio Moreno Dr. Alejandro González Orive Alberto Hernández Creus Dr. Roberto C. Salvarezza Dr. 《Chemphyschem》2009,10(2):370-373
Attractive combination: Biopolymer‐modified nanoparticles which combine magnetic properties with biocompatibility are prepared and delivered following a three‐step strategy (see figure): i) Adsorption of thiol‐capped metal nanoparticles on graphite, ii) electrochemical modification, iii) potential‐induced delivery of the modified nanoparticles to the electrolyte.