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991.
Quantum dot solar cells. harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films 总被引:2,自引:0,他引:2
Robel I Subramanian V Kuno M Kamat PV 《Journal of the American Chemical Society》2006,128(7):2385-2393
By using bifunctional surface modifiers (SH-R-COOH), CdSe quantum dots (QDs) have been assembled onto mesoscopic TiO(2) films. Upon visible light excitation, CdSe QDs inject electrons into TiO(2) nanocrystallites. Femtosecond transient absorption as well as emission quenching experiments confirm the injection from the excited state of CdSe QDs into TiO(2) nanoparticles. Electron transfer from the thermally relaxed s-state occurs over a wide range of rate constant values between 7.3 x 10(9) and 1.95 x 10(11) s(-1). The injected charge carriers in a CdSe-modified TiO(2) film can be collected at a conducting electrode to generate a photocurrent. The TiO(2)-CdSe composite, when employed as a photoanode in a photoelectrochemical cell, exhibits a photon-to-charge carrier generation efficiency of 12%. Significant loss of electrons occurs due to scattering as well as charge recombination at TiO(2)/CdSe interfaces and internal TiO(2) grain boundaries. 相似文献
992.
Gonçalves DP Ladame S Balasubramanian S Sanders JK 《Organic & biomolecular chemistry》2006,4(17):3337-3342
A series of cationic porphyrins carrying 1-3 meso-N-pyridinium groups has been synthesised, and their binding to G-quadruplex DNA has been explored by surface plasmon resonance (SPR) and circular dichroism spectroscopy. Two trans substituents appear to be sufficient for tight binding; preferential binding to the anti-parallel intramolecular human telomeric DNA was observed for the A2trans and A3 porphyrins. The A2trans is able to induce the formation of an anti-parallel G-quadruplex in a K+ free solution, mimicking the effect of a molecular chaperone. 相似文献
993.
DeLongchamp DM Jung Y Fischer DA Lin EK Chang P Subramanian V Murphy AR Fréchet JM 《The journal of physical chemistry. B》2006,110(22):10645-10650
The thin film microstructure development of functionalized oligothiophenes with branched, thermally removable groups at each end of conjugated cores with five, six, and seven thiophene rings was monitored during their thermal conversion from solution processible precursors to insoluble semiconductor products. The change in end group character provides a comparison of branched vs linear end group functionalization in oligothiophenes. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy confirmed that branched alpha-, omega-substitutions of the precursors strongly influenced the packing of the conjugated core. The quinque- and sexithiophene precursors oriented perpendicular to the substrate, whereas the septithiophene precursor oriented parallel to the substrate, providing one of the first examples of length dependence in oligothiophene orientation. This dependence may be due to a packing mismatch between the conjugated cores and the branched end groups. The convertible septithiophene exhibits four distinct microstructures as it converts from precursor to product that correlate strongly with its field-effect hole mobility in field-effect transistors. The extent of septithiophene order and the surface-relative orientation of its ordered phases clearly influence field-effect transistor performance. 相似文献
994.
Sidik RA Anderson AB Subramanian NP Kumaraguru SP Popov BN 《The journal of physical chemistry. B》2006,110(4):1787-1793
An experimental and theoretical study of electroreduction of oxygen to hydrogen peroxide is presented. The experimental measurements of nitrided Ketjenblack indicated an onset potential for reduction of approximately 0.5 V (SHE) compared to the onset potential of 0.2 V observed for untreated carbon. Quantum calculations on cluster models of nitrided and un-nitrided graphite sheets show that carbon radical sites formed adjacent to substitutional N in graphite are active for O2 electroreduction to H2O2 via and adsorbed OOH intermediate. The weak catalytic effect of untreated carbon is attributed to weaker bonding of OOH to the H atom-terminated graphite edges. Substitutional N atoms that are far from graphite sheet edges will be active, and those that are close to the edges will be less active. Interference from electrochemical reduction of H atoms on the reactive sites is considered, and it is shown that in the potential range of H2O2 formation the reactive sites are not blocked by adsorbed H atoms. 相似文献
995.
pKa prediction using group philicity 总被引:1,自引:0,他引:1
Parthasarathi R Padmanabhan J Elango M Chitra K Subramanian V Chattaraj PK 《The journal of physical chemistry. A》2006,110(20):6540-6544
996.
Parthasarathi R Subramanian V Sathyamurthy N 《The journal of physical chemistry. A》2006,110(10):3349-3351
It is shown that the electron density at the hydrogen bond critical point increases approximately linearly with increasing stabilization energy in going from weak hydrogen bonds to moderate and strong hydrogen bonds, thus serving as an indicator of the nature and gradual change of strength of the hydrogen bond for a large number of test intermolecular complexes. 相似文献
997.
Quantum mechanical calculations of energies, geometries and vibrational wave numbers of 7-amino-4-trifluoromethyl coumarin
(7A4TFMC) were carried out using Hartree-Fock (HF) and density functional theory (DFT) using hybrid functional BLYP and B3LYP
with 6–31G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement
with the experimental X-ray data. The best method to reproduce the experimental wave numbers is B3LYP method with the 6–31G(d,p)
basis set. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A
detailed interpretation of the infrared spectra of 7A4TFMC was also reported. The entropy of the title compound was also performed
at HF using the hybrid functional BLYP and B3LYP with 6–31 G(d,p) as basis set levels of theory. Natural bond orbital (NBO)
analysis of the title molecule is also carried out. The theoretical spectrogram for FTIR spectra of the title molecule has
been constructed. 相似文献
998.
Quantum well devices feature heterostructures of very thin epitaxial layers of group III-V and II-VI semiconductor materials.
Quantum well devices are integrated monolithically with various optoelectronics devices to provide photonic integrated circuits.
The representative structure could be realized with GaAs wells with GaAlAs barriers for wavelengths around 0.9 μm and InGaAsP
are used for longer wavelengths. Together with quantum well, superlattice structure is another popular design for InGaAs Avalanche
Photo Diode (APD). Quantum well structures find their applications in improved lasers, superlattice for photodiodes, modulators
and switches. Consequences of quantum well theory are available today in terms of quantum wires and quantum dots. Upon the
application of the normal electric field to quantum well structures, exciton pairs becomes more and more confined and the
sharp exciton absorption peaks are observed. The effect is termed as “Quantum Confined Stark Effect”. The electro-absorption effect is approximately 50 times larger in multiple quantum well structures than it is in bulk semiconductors.
Another electro-absorption effect known as “Franz Keldysh Effect” has been employed in monolithic waveguide detector. These effects lead to electro-absorption lasers (EAL) as well as electro-absorption
laser modulators (EML). 相似文献
999.
Nonafluorobutanesulfonyl-1H-benzotriazole affords phenylazomethylenetriphenylphosphoranes upon treatment with in situ generated alkyl triphenylphosphoranylidenes. Methylenetriphenylphosphorylidene yields the corresponding bis-phenylazomethylene-triphenylphosphorane. 相似文献
1000.