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971.
We propose a technique aimed at cooling a harmonically oscillating mirror to its quantum mechanical ground state starting from room temperature. Our method, which involves the two-sided irradiation of the vibrating mirror inside an optical cavity, combines several advantages over the two-mirror arrangements being used currently. For comparable parameters the three-mirror configuration provides a stiffer trap for the oscillating mirror. Furthermore, it prevents bistability from limiting the use of higher laser powers for mirror trapping, and also partially does so for mirror cooling. Lastly, it improves the isolation of the mirror from classical noise so that the quantum mechanical dynamics of the mirror become easier to observe. These improvements are expected to bring the task of achieving and detecting ground state occupation for the mirror closer to completion. 相似文献
972.
We show theoretically that it is possible to trap and cool the rotational motion of a macroscopic mirror made of a perfectly reflecting spiral phase element using orbital angular momentum transfer from a Laguerre-Gaussian optical field. This technique offers a promising route to the placement of the rotor in its quantum mechanical ground state in the presence of thermal noise. It also opens up the possibility of simultaneously cooling a vibrational mode of the same mirror. Lastly, the proposed design may serve as a sensitive torsional balance in the quantum regime. 相似文献
973.
Sarkar C Bhattacharya R Bhattacharyya SS Saha S 《The Journal of chemical physics》2007,127(10):104304
We have theoretically investigated the population transfer from the initial ground rovibrational level v(g)=0, J(g)=0 to the final rovibrational levels v(f)=1,2, J(f)=0 of the ground electronic state X (1)Sigma(g) (+) via the resonant intermediate level v(i)=6, J(i)=0 of the excited electronic state EF (1)Sigma(g) (+) of H(2) molecule by (2+2)-photon stimulated hyper-Raman passage (STIHRP). The density matrix technique has been employed to evaluate the population transfer to the final target levels using linearly chirped pump and Stokes laser pulses with different chirp rates. Both the pulses are considered to have the same temporal shape, pulse width, and linear parallel polarizations. We have studied in detail the dependence of the population transfer on the set of laser parameters for pulse (peak) intensities in the ranges of 1.5 x 10(11)-1.0 x 10(12) and 1.0 x 10(12)-7.0 x 10(12) W/cm(2). The corresponding pulse widths (full width at half maximum) are of the order of 115-200 and 15-30 ps. We have found that the chirp rate parameters can be optimized to achieve almost complete population transfer from the ground (g) to the final (f) target levels. This, to our knowledge, is the first application of a (2+2)-photon STIHRP process with chirpings to a model molecular system (H(2)). The study demonstrates the suitability of the chirped (2+2)-photon STIHRP technique for selective and almost total inversion of vibrational population in a diatomic molecule. 相似文献
974.
Membrane-forming properties of five new gemini cationic lipids possessing an aromatic backbone between the headgroup and hydrocarbon chains have been presented. These gemini lipids differ by the number of polymethylene units [-(CH(2))(n)-] between the cationic ammonium -[N(+)(CH(3))(2)]- headgroups. The membrane-forming properties of these gemini lipids have been studied in detail by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), high-sensitivity differential scanning calorimetry (DSC), Paldan fluorescence studies, and UV-vis absorption spectroscopy. The electron micrographs and dynamic light scattering of their aqueous suspensions confirmed the formation of vesicular-type aggregates. The vesicle sizes and morphologies were found to depend strongly on the n-value of the spacer. Information on the thermotropic and hydration properties of the resulting vesicles was obtained from differential scanning calorimetry and temperature-dependent Paldan fluorescence studies, respectively. Examination of the thermotropic phase-transition properties of the lipid aggregates revealed interesting features of these lipids, which were found to depend on the length of the spacer chain. Paldan fluorescence studies indicate that the membranes of the gemini lipids are less hydrated as compared to that of the monomeric counterpart in their solid-gel state. In contrast in their fluid, liquid-crystalline phase, the hydration of gemini lipid aggregates was found to depend strongly on the length of the spacer. UV-vis absorption studies suggest an apparent H-type aggregate formation in the gemini lipid membranes in the gel states. In fluid state of the lipid membranes, H-aggregate formation was found to be enhanced depending on the length of the spacer. Such an understanding of the properties upon membrane formation from this new class of gemini lipids will be useful for further development of related gene delivery systems. 相似文献
975.
The methanol extract of the flowers of Lagerstroemia parviflora Roxb (Family: Lythraceae) was investigated for its effect on a cough model induced by sulphur dioxide gas in mice. It exhibited significant antitussive activity when compared with the control in a dose-dependent manner. The extract (100, 200, 300 mg kg(-1)) showed maximum inhibition of cough reflex at 90 min after drug administration and the antitussive activity was comparable to that of codeine phosphate, a standard antitussive agent. 相似文献
976.
Maiti K Chakraborty I Bhattacharya SC Panda AK Moulik SP 《The journal of physical chemistry. B》2007,111(51):14175-14185
Octadecyl-trimethyl-ammonium bromide (C18TAB) is a much less studied representative in the alkyltrimethylammonium halide surfactant series. A comprehensive study of its normal and reverse micelle (microemulsion) formation has been herein conducted by the methods of conductometry, tensiometry, fluorimetry, and microcalorimetry. The energetics of its air/liquid interfacial adsorption and self-association in aqueous solution have been examined. The phase behavior of its combinations with water, n-butanol, and n-heptane in the formation of microemulsions have been investigated with identification of a variety of phases. The energetics of formation of water dispersion in oil (w/o) has been evaluated from dilution experiments conducted at different temperatures. From the results, structural parameters of the droplets have been determined at different [water]/[surfactant] mole ratios (omega) and temperatures. The w/o dispersions have evidenced both volume- and temperature-induced conductance percolation. The results have been treated in light of the Scaling equations, and the associated parameters for the process have been determined. The activation energies for the temperature-induced percolation process of the w/o dispersion have been evaluated and assessed. 相似文献
977.
Banerjee P Chatterjee S Pramanik S Hossain SU Bhattacharya S Bhattacharya SC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,66(4-5):1110-1114
Spectroscopic studies of newly synthesized bioactive compound 2-(2-bromo-ethyl)-6-nitro-benzo[de]isoquinolene-1,3-dione (BNBIO) have been carried out in polar aprotic solvent, viz. acetonitrile, tetrahydrofuran, 1,4-dioxan, ethylene glycol, dimethyl formamide, and polar protic solvent, viz. methanol, ethanol, propanol, water. Variation in absorbance of BNBIO in water-methanol, water-ethanol and water-propanol mixtures at their different compositions have been observed. Absorption behaviour of the dye has been studied in poly(oxyethylene) nonylphenol surfactants Igepal CO 630, Igepal CO 720 and Igepal CO 890 containing same hydrophobic tail and different numbers of poly(oxyethylene) groups. Experimental results of the BNBIO nonionic micelles have been explained in terms of 1:1 electron donor-acceptor (EDA) complexation and the complexation equilibrium becomes suppressed with increasing number of poly(oxyethylene) residue on the Igepal surfactant. Variation in binding constant of dye-micelle complexation has been rationalized considering a competitive equilibrium process between the BNBIO-water interactions. 相似文献
978.
Influence of polymer-pore interactions on translocation 总被引:1,自引:0,他引:1
We investigate the influence of polymer-pore interactions on the translocation dynamics using Langevin dynamics simulations. An attractive interaction can greatly improve the translocation probability. At the same time, it also increases the translocation time slowly for a weak attraction while an exponential dependence is observed for a strong attraction. For fixed driving force and chain length the histogram of translocation time has a transition from Gaussian distribution to long-tailed distribution with increasing attraction. Under a weak driving force and a strong attractive force, both the translocation time and the residence time in the pore show a nonmonotonic behavior as a function of the chain length. Our simulations results are in good agreement with recent experimental data. 相似文献
979.
Michael-type addition reactions of planar N-heterocycles at the C-2 positions of vinyl sulfone-modified carbohydrates provide an efficient and general route for the carbon-N-heterocycle bond formation. Therefore, the addition pattern of planar heterocycles, such as imidazole, triazole, thymine, and adenine to 3-C-phenylsulfonyl-hex-2-enopyranosides (1α/1β) and 3-C-p-toluenesulfonyl-pent-2-enofuranosides (2α/2β) was studied for developing a general methodology for the synthesis of new classes of isonucleosides possessing a carbon-N-heterocycle linkage at C-2 positions of furanosyl and pyranosyl sugars. To a great extent, the anomeric configurations of the starting vinyl sulfones play crucial roles in deciding the diastereoselectivity of addition of heterocycles. However, the trityl protected 3-C-p-toluenesulfonyl-hex-2-enopyranosides (33α/33β) were judged to be more practical starting materials for desulfonylation and deprotection for the synthesis of a new class of thymine and adenine deoxyisonucleosides. 相似文献
980.
Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H2L-R, where H2 denotes the two acidic protons and R (R = OCH3, CH3, H, Cl and NO2) the para substituent in the aryl fragment) with [Ru(trpy)Cl3](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt3) affords a group of complexes of the type [RuII(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [RuII(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [RuII(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [RuII(trpy)(L-R)] complexes produces the corresponding [RuIII(trpy)(L-R)]+ complexes, which have been isolated as the perchlorate salts. Structure of the [RuIII(trpy)(L-CH3)]ClO4 complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [RuIII(trpy)(L-R)]ClO4 complexes near 1600 nm. 相似文献