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1.
《Physics letters. A》2020,384(27):126674
A nonlinear molecular structural mechanics (MSM) model is proposed in this paper for studying the tensile properties of microtubules (MTs). In the nonlinear MSM models, the interactions between tubulin monomers in MTs are treated as nonlinear axial and torsional springs, whose stiffness coefficients are extracted from all-atom molecular dynamics simulations. The Young's modulus and fracture properties of MTs under tension extracted from the present nonlinear MSM models are found to agree well with the existing simulation and experiment results, which shows the efficiency and accuracy of the proposed nonlinear MSM models. In addition, the nonlinear MSM models are also extended to investigate the tensile properties including Young's modulus and fracture strain of MTs possessing lattice defects. The results obtained from nonlinear MSM models are utilized to develop a predictive equation for quickly predicting the tensile properties of MTs with different lattice defect levels. 相似文献
2.
3.
ABSTRACT The present work describes a phenomenological approach to explain the instantaneous behaviour of tungsten heavy alloys (WHAs) in heat-treated and swaged conditions. The strengths and elongation values of heat-treated materials are lower and higher than those of the swaged samples respectively. The heat-treated materials exhibit two slopes in true stress–true plastic strain curves and follow the Ludwigson constitutive equation. On the other hand, swaged materials display a single slope and adhere to typical Swift constitutive equation. The latter reflect the presence of pre-strain in the materials due to swaging deformation. The fracture surfaces in heat-treated materials consist of W-W decohesion along with matrix rupture and W-cleavage, while swaged samples consist of mainly W-cleavage. Both the materials display three typical stages (I, II and III) of work hardening. The second derivatives of true stress–true plastic strain curves of these alloys exhibit a perfect parabola although the nature of true stress–true strain as well as true stress–true plastic strain curves is quite different in heat-treated and swaged materials. This has been observed for the first time in WHAs consisting of matrix and W-grains. The shape of the parabola is simple and easy to fit. The fitting parameters of parabolas have been successfully employed to explain the flow behaviour of a large number of tungsten heavy alloys having two-phase microstructure in different processing conditions. 相似文献
4.
N-acetyl-3,3-dinitroazetidine (ADNAZ) is an important precursor for synthesizing new multinitroazetidine energetic compounds. Its thermal behaviour was studied under a non-isothermal condition by DSC and TG/DTG methods, the results show that there are one melting process and one endothermic decomposition process. The specific molar heat capacity (Cp,m) of ADNAZ was determined by a continuous Cp mode of micro-calorimeter and theoretical calculation, and the Cp,m of ADNAZ was 240.37 J · K−1 · mol−1 at T = 298.15 K. The detonation velocity (D) and detonation pressure (P) of ADNAZ were estimated using the nitrogen equivalent equation according to the experimental density, the value of D and P are (6685.83 ± 3.12) m · s−1 and (18.36 ± 0.02) GPa, respectively. The free radical signals of ADNAZ were detected by electron spin resonance (ESR) technique, which is used to estimate its sensitivity. 相似文献
5.
Qiu‐Ying Huang Ming‐Yang Su Xiang‐Ru Meng 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(6):474-478
The combination of N‐heterocyclic and multicarboxylate ligands is a good choice for the construction of metal–organic frameworks. In the title coordination polymer, poly[bis{μ2‐1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole‐κ2N3:N4}(μ4‐butanedioato‐κ4O1:O1′:O4:O4′)(μ2‐butanedioato‐κ2O1:O4)dicadmium], [Cd(C4H4O4)(C9H8N6)]n, each CdII ion exhibits an irregular octahedral CdO4N2 coordination geometry and is coordinated by four O atoms from three carboxylate groups of three succinate (butanedioate) ligands and two N atoms from two 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) ligands. CdII ions are connected by two kinds of crystallographically independent succinate ligands to generate a two‐dimensional layered structure with bimt ligands located on each side of the layer. Adjacent layers are further connected by hydrogen bonding, leading to a three‐dimensional supramolecular architecture in the solid state. Thermogravimetric analysis of the title polymer shows that it is stable up to 529 K and then loses weight from 529 to 918 K, corresponding to the decomposition of the bimt ligands and succinate groups. The polymer exhibits a strong fluorescence emission in the solid state at room temperature. 相似文献
6.
ABSTRACTHigh sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties.The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated. 相似文献
7.
Main-chain biodegradable liquid crystal (LC) based on cholesteryl end-capped polycarbonate copolymers was investigated. The novel LC was synthesised through ring-opening copolymerisation of trimethylene carbonate with ε-caprolactone (CL) initiated by cholesterol, without adding any catalyst. The chemical structure of the resulting polymers was confirmed by 1H NMR. The liquid crystalline properties were validated by X-ray diffraction, differential scanning calorimetry and polarising optical microscopy. The results showed that the synthesised polycarbonate copolymers Chol-(TMCL)x + y exhibited liquid crystallinity in particular temperature ranges because of the incorporation of the cholesterol moieties. Furthermore, the effect of CL content on the mesomorphism properties of Chol-(TMCL)x+y was also investigated; the higher the CL content, the lower the mesomorphism properties. It might be attributed to the hindered orientation of LC caused by the crystallinity of the poly(ε-caprolactone) (PCL) segments in the polymer chain. 相似文献
8.
In this paper, we study the stationary problem for the Lotka–Volterra competition system with cross-diffusion in a spatially heterogeneous environment. Although some sufficient conditions for the existence of positive solutions are obtained by using global bifurcation theory, the information for their structure is far from complete. In order to get better understanding of the competition system with cross-diffusion, we focus on the asymptotic behaviour of positive solutions and derive two shadow systems as the cross-diffusion coefficient tends to infinity, moreover, the structure of positive solutions of the limiting system is analysed. The result of asymptotic behaviour also reveals different phenomena from that studied in Wang and Li (2013). 相似文献
9.
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
10.
C.P. Buckley J. Harding C. Ruiz 《Journal of the mechanics and physics of solids》2004,52(10):2355-2377
The constitutive responses of three glassy thermoset polymers at impact rates of strain and slower, together with measurements of adiabatic heating, were reported earlier by the authors. The results are interpreted here in the context of a constitutive model proposed previously for amorphous polymers, expanded to incorporate strain-softening and the adiabatic heating deficit. In terms of the model, both features are a natural consequence of strain-induced evolution of the glass structure, as represented by Tool's “fictive temperature”—the phenomenon of structural rejuvenation. A representation is proposed for the evolution of fictive temperature with plastic strain, motivated by an approximate treatment of the kinetics of physical ageing/rejuvenation. Formulated in this manner, the model agrees reasonably well with experimental results across the wide range of strain rates of the previous experiments, 10−3 to , and across most of the range of strain to failure in compression. At the highest strains, however, an additional adiabatic heating deficit appears that is not predicted by the model, either suggesting the onset of structural breakdown possibly associated with the appearance of cracks or reflecting a need for better physical understanding of large deformations in glassy polymers. 相似文献