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961.
B. ChoudhuryA. Choudhury A.K.M. Maidul IslamP. Alagarsamy M. Mukherjee 《Journal of magnetism and magnetic materials》2011,323(5):440-446
Co doped TiO2 nanoparticles have been synthesized by a simple sol-gel route taking 7.5, 9.5 and 10.5 mol% of cobalt concentration. Formation of nanoparticles is confirmed by XRD and TEM. Increase in d-spacing occurs for (0 0 4) and (2 0 0) peak with increase in impurity content. Valence states of Co and its presence in the doped material is confirmed by XPS and EDX. The entire vacuum annealed samples show weak ferromagnetism. Increased magnetization is found for 9.5 mol% but this value again decreases for 10.5 mol% due to antiferromagnetic interactions. A blocking temperature of 37.9 K is obtained, which shows shifting to high temperature as the dopant concentration is increased. The air annealed sample shows only paramagnetic behavior. Temperature dependent magnetic measurements for the air annealed sample shows antiferromagnetic behavior with a Curie-Weiss temperature of −16 K. Here we report that oxygen vacancy and cobalt aggregates are a key factor for inducing ferromagnetism-superparamagnetism in the vacuum annealed sample. Appearance of negative Curie-Weiss temperature reveals the presence of antiferromagnetic Co3O4, which is the oxidation result of metallic Co or cobalt clusters present on the host TiO2. 相似文献
962.
Saeed Jameh-Bozorghi 《Journal of fluorine chemistry》2011,132(3):190-195
Electrical and structural properties of mono-, di-, tri- and tetrafluorothiophenes and their radical cations have been studied using density functional theory and B3LYP method with 6-311++G** basis set. The effects of the number and position of the substituent of fluorine atoms on the properties of the thiophene ring have been studied using optimized structures obtained for these molecules and their radical cations. Vibrational frequencies, spin-density distribution, size and direction of dipole moment vector, ionization potential, electric polarizability, HOMO-LUMO gaps and NICS values of these compounds have been calculated as well. The analysis of these data showed that double bonds in 3-fluorothiophene are more delocalized and it is the best possible candidate monomer among all fluorothiophenes for the synthesis of corresponding conducting polymers with modified characteristics. 相似文献
963.
964.
S. Peyman Shariatpanahi Daniel Bonn Mohammad R. Ejtehadi Azam Iraji Zad 《Journal of Polymer Science.Polymer Physics》2016,54(11):1036-1042
The electrical bending instability in charged liquid jets is the phenomenon determining the process of electrospinning. A model of this phenomenon is lacking however, mostly due to the complicated interplay between the viscosity and elasticity of the solution. To investigate the bending instability, we performed electrospinning experiments with a solution of polyethylene oxide in water/ethanol. Using a fast camera and sensitive multimeter, we deduced an experimental dispersion relation describing the helix pitch length as a function of surface charge. To understand this relation, we developed a theoretical model for the instability for a wide range of visco‐elastic materials, from conducting to nonconducting. The theoretical dispersion relation shows good agreement with the experimental results. Using the new model, we find that the elastic tension in the visco‐elastic threads plays an important role in triggering the instability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1036–1042 相似文献
965.
New dimeric Schiff base quinoline complexes: Synthesis,spectral characterization,electrochemistry and cytotoxicity 下载免费PDF全文
A novel Schiff base ligand (H‐DPPMHQ) derived from 2‐hydrazineylquinoline and 1,3‐diphenyl‐1H‐pyrazole‐5‐carbaldehyde and its dimeric complexes with compositions [Cr(DPPMHQ)Cl]2?2Cl and [M(DPPMHQ)Cl]2 (where M = Cu(II), Co(II), Ni(II) and Zn(II)) have been synthesized and characterized using physicochemical methods like elemental analysis, magnetic susceptibility and molar conductivity measurements, multispectral techniques and electrochemical studies. The molar conductance data reveal that all metal chelates are non‐electrolytes, except the Cr(III) complex which shows a ΛM value of 146.82 Ω?1 cm2 mol?1, indicating that it is a 1:2 electrolyte. Infrared spectral results show that the metal is organized through four nitrogen atoms (azomethine and deprotonated imine groups, pyrazole and quinoline rings) besides chlorine atoms. The NH proton is also displaced during complexation, as indicated by 1H NMR spectral data. Based on the electron spin resonance and ligand field parameter data, the bonding parameters of these complexes have been calculated. Using Coats–Redfern and Horowitz–Metzger equations, thermodynamic parameters were determined. The spectral data indicate that the dimeric complexes have octahedral geometry around the central metal ions. The cytotoxic activities of all compounds were evaluated towards human breast cancer (MCF‐7) and lung cancer (A549) cell lines. 相似文献
966.
In this study, a new periodic beam model is introduced. This beam consists of the concentrated rigid masses and tapered beam elements with linearly variable width. The theoretical equations are derived by employing the Euler-Bernoulli beam and the Bloch–Floquet theorem and then solved using the generalized differential quadrature rule method to calculate the first two band gaps. The effects of the mass, mass moment of inertia and taper ratio on the widths and central frequencies of the first two band gaps are investigated. Results show that the wide band gaps at low frequency ranges can be obtained by changing the geometrical parameters. This is of interest for different applications of the band gap phenomenon such as broadband piezoelectric energy harvesting. Finally, the finite element simulation (ANSYS software) is used to validate the analytical method and good agreement is found. 相似文献
967.
A. Gueddouh 《Phase Transitions》2017,90(10):984-1000
In this paper, spin polarization and pressure effects on the structure, magnetic and anisotropic elastic properties of the 3d transition-metal mono-borides TMB (TM = Mn, Fe) have been investigated by using generalized gradient approximation within the framework of density functional theory. It seems that manganese in MnB carries a higher magnetic moment (1.83 μB) than iron in FeB (1.12 μB). Applied pressure ranges from 0 to 150 GPa, these ferromagnetic compounds show at a certain pressure (143 GPa for MnB and 77 GPa for FeB) a pronounced abrupt collapse of the magnetic moment (first-order quantum phase transitions). Furthermore, elastic properties, including bulk, shear and Young moduli as well as the Poisson ratio are obtained by Voigt–Reuss–Hill approximation. By the elastic stability criteria, it is predicted that MnB and FeB are stable up to the selected pressures. In both cases, mechanical anisotropies are discussed by calculating different anisotropic indexes and factors. The three-dimensional surfaces and planar contours of Young, and bulk moduli of compounds are plotted, at several crystallographic planes ((100), (010) and (001)) to reveal their elastic anisotropy. 相似文献
968.
Principal parametric resonances of a slender cantilever beam subject to axial narrow-band random excitation of its base 总被引:1,自引:0,他引:1
The non-linear integro-differential equations of motion for a slender cantilever beam subject to axial narrow-band random excitation are investigated. The method of multiple scales is used to determine a uniform first-order expansion of the solution of equations. According to solvability conditions, the non-linear modulation equations for the principal parametric resonance are obtained. Firstly, The largest Lyapunov exponent which determines the almost sure stability of the trivial solution is quantificationally resolved, in which, the modified Bessel function of the first kind is introduced. Results show that the increase of the bandwidth facilitates the almost sure stability of the trivial response and stabilizes the system for a lower acceleration oscillating amplitude but intensifies the instability of the trivial response for a higher one. Secondly, the first and second order non-trivial steady state response of the system is obtained by perturbation method and the corresponding amplitude–frequency curves are calculated when the bandwidth is very small. Results show that the effective non-linearity of whether the amplitude expectation of the first order steady state response or the amplitude expectation of the second order steady state response is of the hardening type for the first mode, whereas for the second mode the effective non-linearity of whether the amplitude expectation of the first order steady state response or the amplitude expectation of the second order steady state response is of the softening type. Finally, the stochastic jump and bifurcation is investigated for the first and second modal parametric principal resonance. The basic jump phenomena indicate that, under the conditions of system parameters with a smaller bandwidth, the most probable motion is around the non-trivial branch of the amplitude response curve, whereas with a higher bandwidth, the most probable motion is around the trivial one of the amplitude response curve. However, the stochastic jump is sometimes more sensitive to the change of the bandwidth, in other words, a small change of bandwidth may induce a series of stochastic jump and bifurcation. 相似文献
969.
基于广义变分原理得到的磁力计算公式,采用塑性增量理论,Mises屈服准则和有效的增量有限元计算方法,研究了线性强化材料铁磁矩形板的磁弹塑性弯曲行为。在文中定量模拟了铁磁简支矩形板在外加磁场作用下的挠度特征曲线,铁磁板发生塑性变形时的构型图和不同外加磁场下的中截面构型,以及铁磁板在卸载后的残余挠度特征曲线等力学特征,分析了塑性区域随磁场增加而扩展的情况。数值结果表明:当铁磁矩形板上的部分区域发生塑性屈服后,其变形明显大于相同磁场条件下铁磁板发生的弹性变形值;且随着外加磁场倾角的增大(0°<α≤45°),铁磁板进入塑性屈服状态的临界屈服磁场值减小;铁磁板的中截面构形为双半波型,其塑性区域由铁磁板两侧挠度最大的区域向板的中心区域扩展,板的中心最后进入塑性区域等。 相似文献
970.