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151.
Vincent BailliezRenata M. de Figueiredo Alain OleskerJeannine Cleophax 《Tetrahedron letters》2003,44(51):9151-9153
The macrocyclic core of cycloviracin and glucolipsin has been synthesised in ten steps from levoglucosan and (S)-(−)-dimethyl malate. The limited number of steps to obtain this macrolide makes it a valuable procedure for the synthesis of analogues of cycloviracin and glucolipsin. 相似文献
152.
In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models. 相似文献
153.
Claude Lavalle Alain Leborgne Nicolas Spassky Robert E. Prud'homme 《Journal of polymer science. Part A, Polymer chemistry》1987,25(5):1315-1328
β-(trichloromethyl)-β-propiolactone (CCl3-PL), β-(trifluoromethyl,methyl)-β-propiolactone (CF3, Me-PL) and β-(trifluoromethyl,ethyl)-β-propiolactone (CF3,Et-PL) have been obtained by the reaction of ketene with chloral, 1,1,1-trifluoroacetone and 1,1,1-trifluorobutanone, respectively. Chiral catalysis lead to optically active monomers. The enantiomeric excess of the lactones has been measured by 1H-NMR spectroscopy, in the presence of 2,2,2-trifluoro-1-(9-anthryl)ethanol or an europium chiral shift reagent. Polymerizations have been carried out in bulk or in toluene, at 60°C or 80°C, using mainly organometallic initiators. The Polymers become insoluble and crystalline at enantiomeric excesses over 80% for CCl3-PL and 70% for CF3,Me-PL. Melting temperatures were recorded from 238 to 268°C for poly(CCl3-PL) and from 78 to 100°C for poly(CF3,Me-PL), depending upon the molecular weight and the enantiomeric excess. The 13C-NMR specroscopy of poly(CCL3-PL) indicates that the polymerization of the corresponding lactone leads to polymers of increasing degrees of isotacticity with the enantiomeric excess of the monomer. 相似文献
154.
Ranveer Singh Maxime Vallet Vijay Singh Sanjeev K. Srivastava Alain Claverie Tapobrata Som 《Surface and interface analysis : SIA》2023,55(2):151-161
Due to its outstanding physical properties, CdTe is used to fabricate high efficiency solar cells. However, its high work function poses a challenge, and hence, to fabricate an efficient CdTe-based solar cell, Cu-doping may be useful. Here, we present the role of temperature-dependent Cu-doping in radio frequency sputter-deposited CdTe films and the related changes occurring in their optical, electrical, structural and microstructural properties. For instance, Cu-doping at different temperatures leads to an increase in the grain size and a reduction in the optical reflectance with increasing temperature. In addition, Kelvin probe force microscopy measurements reveal that the work function is found to be smaller corresponding to the annealing temperature of 473 K, whereas resistivity measurements show that it decreases with increasing temperature (the lowest value of resistivity is found to be 1.8 × 10−2 Ω-cm). To understand the electronic structure of CdTe before and after Cu-doping, we have carried out first-principles density functional theory (DFT) simulation, which reveals a strong hybridization among Cu, Cd and Te atoms. This study paves the way to fabricate efficient Cu-doped CdTe-based solar cells. 相似文献
155.
Diana Cruz-Garritz Juventino Garcia-Alejandre Hugo Torrens Cecilio Alvarez Raul A. Toscano Rene Poilblanc Alain Thorez 《Transition Metal Chemistry》1991,16(1):130-135
Summary The thiolato-bridged dinuclear compounds [Rh(-SR)-(COD)]2, where R=p-C6HF4 (1),p-C6H4F (2) and CF3 (3), are obtained from the chloro-bridged analogue by ligand exchange.Compound (1) crystallizes in the space group P1 with a=9.740(3)Å, b=11.642(4)Å, c=13.997(6)Å, =103.87(3)°, =106.98(3)° and =105.10(2)°; z=2. In this dinuclear molecule both Rh atoms have a square planar coordination sharing one edge, namely the two sulphur bridging atoms. The Rh—Rh separation of 2.96 Å is consistent with at most a very weak metal-metal interaction. Upon addition of CO the dimeric [Rh(-SR)(CO)2]2 (4), (5) and (6) are obtained, but addition of PPh3 affords the monomeric species [Rh(SR)(PPh3)-(COD)] (7), (8) and (9). Reactions of the dimeric tetracarbonyl derivatives with PPh3 vary with the nature of R; [Rh(-SR)(PPh3)(CO)]2 is obtained when R=p-C6H4F (10) and CF3 (11) but monomeric [Rh(SR)-(PPh3)(CO)2] (12) is produced when R=p-C6HF4. The latter mononuclear compounds, with R=p-C6H4F (13) and CF3 (14), are also formed by reaction of [Rh(SR)-(PPh3)(COD)] with CO. 相似文献
156.
The composition of the essential oil of Bifora radians, an aldehyde-producing weed, has been investigated by capillary gas chromatography, coupled gas chromatography – mass spectrometry, on-line catalytic hydrogenation and coupled gas chromatography – infrared spectrometry. The nineteen compounds identified included eighteen aldehydes: seven alkanals (C6, C9, C10, C11, C12, C13, and C14), ten alkenals, including five (E)-2-alkenals (C12, C13, C14, C15, and C16), and one (E,E)-2,4-alkadienal (C13). Typical Bifora odors were attributed to three major (E)-2-alkenals, C12, C13, and C14. 相似文献
157.
Rolle Rahikainen Pramila Rijal Tiong Kit Tan Hung‐Jen Wu Anne‐Marie C. Andersson Jordan R. Barrett Thomas A. Bowden Simon J. Draper Alain R. Townsend Mark Howarth 《Angewandte Chemie (International ed. in English)》2021,60(1):321-330
Matching of symmetry at interfaces is a fundamental obstacle in molecular assembly. Virus‐like particles (VLPs) are important vaccine platforms against pathogenic threats, including Covid‐19. However, symmetry mismatch can prohibit vaccine nanoassembly. We established an approach for coupling VLPs to diverse antigen symmetries. SpyCatcher003 enabled efficient VLP conjugation and extreme thermal resilience. Many people had pre‐existing antibodies to SpyTag:SpyCatcher but less to the 003 variants. We coupled the computer‐designed VLP not only to monomers (SARS‐CoV‐2) but also to cyclic dimers (Newcastle disease, Lyme disease), trimers (influenza hemagglutinins), and tetramers (influenza neuraminidases). Even an antigen with dihedral symmetry could be displayed. For the global challenge of influenza, SpyTag‐mediated display of trimer and tetramer antigens strongly induced neutralizing antibodies. SpyCatcher003 conjugation enables nanodisplay of diverse symmetries towards generation of potent vaccines. 相似文献
158.
Magali Cassebras Sagrario Pascual Alain Polton Michel Tardi Jean‐Pierre Vairon 《Macromolecular rapid communications》1999,20(5):261-264
Di‐ and triblock copolymers of styrene and butyl acrylate with controlled molar masses (Mn up to ≈ 105) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers as initiators and the copper(I) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene‐co‐butyl acrylate) was synthesized and the cross‐over reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined. 相似文献
159.
The adsorption of one or many silver atoms on a (111) silicon face (reduced to 61 dangling atomic orbitals) is investigated by means of a self-consistent Hartree–Fock method parametrized from atomic and thermodynamical data. The valley sites (above three Si atoms) are favored over the top sites (above one Si atom). The extrapolation of the results obtained for several structures corresponding to the adsorption of n = 1, 2, 3, 4, 6, and 7 Ag atoms allows us to conclude that the most stable structures correspond: for \documentclass{article}\pagestyle{empty}\begin{document}$ \theta = \frac{1}{3} $\end{document} to linear Ag chains (3 × 1 phase), for \documentclass{article}\pagestyle{empty}\begin{document}$ \theta = \frac{2}{3} $\end{document} to an honeycomb lattice (\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 3 \times \sqrt 3 $\end{document} phase), and for θ = 1 to a centred hexagonal lattice (\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 3 \times \sqrt 3 $\end{document} phase), the Ag atoms located at the centers of the hexagons being beneath the plan of the hexagons. The adsorption energies corresponding to the various θ are practically equal (ca. 3 eV/Ag). The net charges of Ag atoms are equal to 0.35. 相似文献
160.
The silver nitrate assisted cyclization of the entitled diols leads, depending on the substitution of the allenic linkage, specifically to dihydropyranes , when R is alkyl or to an equimolecular mixture of and its tetrahydrofuranyl isomer when R is hydrogen. 相似文献