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71.
Krati Joshi 《Molecular physics》2015,113(19-20):2980-2991
Finite-temperature behaviour of a hollow golden cage (HGC) plays a crucialrole in its potential applications as a catalyst, drug delivery agent, contrasting agent and so on. This physico-chemical property of HGCs is not well understood so far. In that context, Born–Oppenheimer molecular dynamics (BOMD) simulations are performed on a well-known ‘free-standing’ HGC. The cluster considered in this study is the ground state Au18 cluster (a cage with a diameter of about >5.5 Å). The results thus obtained are compared with the BOMD simulation results reported earlier on Au32 icosahedron cage, a conformation with a diameter of nearly. The sphericity of both the clusters is studied using a shape deformation parameter as a function of time and temperature. These results are supplemented by radial distribution function at various temperatures. The observations and analysis of results indicate that, both the clusters retain an HGC conformation from 300 to 400 K, admitting structural fluxionality by the Au18 cluster. Remarkably, the Au18 cluster is able to maintain its hollowness and sphericity up to a high temperature of 1000 K. Underlying structural and electronic properties influencing the individualistic behaviour of cages are highlighted. Composition of the frontier molecular orbitals and the charge distribution play a crucial role in the finite-temperature behaviour of the Au cages. The conclusions are supplemented by supporting calculations on another degenerate ground state Au18 hollow cage and a well-known pyramidal Au18 cage at 300 and 400 K. 相似文献
72.
Vinyl acetate radical emulsion polymerization in water with GF51 silane co-monomer was performed by semi continuous way. The GF51 impacts on dispersion rheology as well on films and bonding strength properties were determined. It should be stated that even low quantities of GF51 (up to 6% from VAc) determined high viscosity of dispersions. The GF51 modified films have low water absorption and high affinity to glass. Molecular mass and thermal properties of GF51 modified polymers were determined accordingly. 相似文献
73.
The synthesis of new chiral monomers (M1 ?M3 ) based on menthol and the corresponding polyacrylates (P1 ?P3 ) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, 1H-NMR, elemental analyses, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The effect of the mesogenic core rigidity, spacer length and menthyl steric effect on the phase behaviour of M1 ?M3 and P1 ?P3 is discussed. The expected mesophase of the compounds based on menthol can be obtained by inserting a flexible spacer between the mesogenic core and the terminal groups. For the chiral monomers and polyacrylates, their corresponding melting temperature (T m), glass transition temperature (T g) and clearing temperature (T i) increased with an increase of the mesogenic core rigidity; while the T m, T g and T i decreased with increasing the spacer length. M1 and P1 showed no mesophase, while M2 and M3 all revealed a SmC* and cholesteric phases. P2 and P3 only showed a cholesteric phase. 相似文献
74.
Chiral side-chain liquid-crystalline (LC) polysiloxanes containing isosorbide groups were graft copolymerised with poly(methylhydrogeno)siloxane, a chiral LC monomer 6-(4-methoxy-benzoyloxy)-hexahydro-furo[3,2-b]furan-3-yl 4'-(4-undec-10-enoyloxy-benzoyloxy)-biphenyl-4-yl adipate and a nematic LC monomer 4'-(4-methoxy-benzoyloxy)-biphenyl-4-yl 4-(2-undec-10-enoyloxy-ethoxy)-benzoate. The chemical structures and LC properties of the monomers and polymers were characterised by use of various experimental techniques including Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance (NMR), element analyses (EA), differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). All the chiral LC polymers showed LC properties with very wide mesophase temperature ranges and the chiral component in the LC polymer systems lead to the appearance of a cholesteric phase. The polymers bearing most chiral LC monomer component showed smectic phases by reason of regular structures in the polymer systems. With the increase of another nematic LC monomer in the polymers, the regular polymer structures were destroyed because of different chemical structures between the two kinds of LC monomers, leading to the disappearance of the smectic arrangement. 相似文献
75.
Chiral monomer (M1 ), mesogenic and non-mesogenic crosslinking agents (C1 and C2 ), and the corresponding liquid crystalline elastomers (P1 and P2 series), have been synthesised. Their chemical structures have been characterised by Fourier transform infrared or 1H nuclear magnetic resonance and their phase behaviour investigated by differential scanning calorimetry, polarising optical miscoscopy, thermo-gravimetric analysis (TGA) and X-ray diffraction. The effect of the crosslinking unit on the phase behaviour of the elastomers has been studied. M1 showed a cholesteric oily streak and focal conic texture. C2 exhibited a nematic enantiotropic thread-like and schlieren texture, and a monotropic fan-shaped texture in the SA phase. Due to the introduction of the mesogenic crosslinking unit, elastomers, P2-1 ?P2-5 , exhibited a cholesteric phase, while elastomers, P1-1 ?P1-4 , derived from a non-mesogenic crosslinking unit, exhibit a SA phase. As the content of the crosslinking unit increased, the T g of the P1 series initially decreased and then increased, and the T i of the series decreased. In the P2 series the T g increased, but the T i initially increased and then decreased. TGA confirmed that all the elastomers had improved thermal stability. 相似文献
76.
Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase temperature range. The type and stability of the mesophase depends on the length of the terminal alkoxy chain and the position the two fluoro substituents. A comparison between these investigated compounds with their corresponding three-ring analogues was discussed. 相似文献
77.
Mohammad Mydul Alam 《Liquid crystals》2013,40(12):1427-1434
The effect of ethanol on the phase behaviour and micro-rheology of lyotropic liquid crystals (LC) has been studied using a binary mixture of monoglyceride (MG) and aqueous ethanol. The phase behaviour study reveals the structural modulation of surfactant aggregates with increasing ethanol concentration, namely a bicontinuous cubic phase (Ia3d) transitions to the lamellar phase (Lα), at a fixed MG concentration. This behaviour is explained by considering the critical packing parameter (CPP) of the surfactant molecule. Because ethanol dehydrates the surfactant head group (a s), the CPP values increase (decreasing a s) and thus the formation of larger CPP aggregates is favoured (i.e., the Ia3d–Lα transition occurs). Cross-polarised images and X-ray scattering data support this conclusion. The structural modulation of the LC has further been investigated using a diffusing wave spectroscopy technique. The correlation and relaxation times, determined from the intersection point at short and long time scales of the mean square displacement (MSD), decrease with increasing concentrations of ethanol, indicating structural modulation of the LC. The micro-viscoelastic moduli (G′ and G′′) derived from the Laplace transformation of the MSD decrease with increasing ethanol concentrations, due to the LC modulation. The thermal effects on the micro-rheology of the LC have also been studied. 相似文献
78.
Hui‐Ru Chen Wen‐Wen Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1079-1082
The title CdII coordination framework, [Cd(C15H8O5)(H2O)]n or [Cd(bpdc)(H2O)]n [H2bpdc is 2‐(4‐carboxybenzoyl)benzoic acid], has been prepared and characterized using IR spectroscopy, elemental analysis, thermal analysis and single‐crystal X‐ray diffraction. Each CdII centre is six‐coordinated by two O atoms from one 2‐(4‐carboxylatobenzoyl)benzoate (bpdc2−) ligand in chelating mode, three O‐donor atoms from three other bpdc2− anions and one O atom from a coordinated water molecule in an octahedral coordination environment. Two crystallographically equivalent CdII cations are bridged by one O atom of the 2‐carboxylate group of one bpdc2− ligand and by both O atoms of the 4‐carboxylate group of a second bpdc2− ligand to form a binuclear [(Cd)2(O)(OCO)] secondary building unit. Adjacent secondary building units are interlinked to form a one‐dimensional [Cd(OCO)2]n chain. The bpdc2− ligands link these rod‐shaped chains to give rise to a complex two‐dimensional [Cd(bpdc)]n framework with a 4,4‐connected binodal net topology of point symbol {43.62.8}. The compound exhibits a strong fluorescence emission and typical ferroelectric behaviour in the solid state at room temperature. 相似文献
79.
Co0.5Ni0.5(Gd/Nd)xFe2-xO4 (x ?= ?0.0 and 0.06) ferrites were prepared by the solid-state reaction method. These materials were characterized by XRD, FT-IR spectroscopy, and VSM techniques. The XRD analysis revealed the phase formation of all samples and their cubic spinel structure with the Fd-3m space group. Lattice constant was found to increase due to Gd and Nd ions substitution. However, the crystallite size was observed to decrease by the substitution effect. The FT-IR spectra showed the two vibrational frequency bands of the tetrahedral and octahedral sites. From the magnetic properties study, it was identified that the pure and Gd substituted Co0.5Ni0.5Fe2O4 ferrite showed a ferromagnetic behaviour. While the Nd substituted Co0.5Ni0.5Fe2O4 ferrite delivered a superparamagnetic behaviour. The substitution of Gd and Nd changed the values of the magnetic parameters of Co0.5Ni0.5Fe2O4 ferrite. An increase in the saturation magnetization (Ms) value was observed due to substitution of Gd and Nd in Co0.5Ni0.5Fe2O4 ferrite, indicating that Gd and Nd substitution strengthen the supermagnetic interactions in Co0.5Ni0.5Fe2O4 ferrite. The highest value of Ms was observed in Gd doped sample. 相似文献
80.
A fluorescent Ni(II) complex 1, [Ni(OH-H2Bdc)(Bibimp)]n·nH2O, constructed with 5-hydroxyisophthalic acid(OH-H2Bdc) and 2,6-bis(2-benzimidazolyl)pyridine)(Bibimp) has been synthesized by hydrothermal methods and structurally characterized by elemental analysis, IR spectroscopy, TG/DTG, fluorescence spectrum and single-crystal X-ray diffraction. The title complex crystallizes in triclinic system, space group P1 with a = 10.187(2), b = 10.273(2), c = 13.401(3), α = 69.65(3), β = 69.66(3), γ = 70.61(3)o, V = 1196.8(4) 3, and Z = 2. The adjacent chains of complex 1 are stacked offset with respect to each other in an ABAB fashion by van der Waals interactions, and only a weak interlayer nonclassical C–H···O hydrogen bond has been observed. Complex 1 displays strong blue fluorescent emissions at 483 nm in the solid state upon photo-excitation at 365 nm at room temperature. 相似文献