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971.
Recent non-contact atomic force microscopy studies have demonstrated that imaging of single atom defects is possible. However, the imaging mechanism was unclear. Long-range forces of attraction, which are normally associated with non-contact mode, are not known to produce sufficient lateral resolution to image atoms. In this study, we suggest a mechanism that could be responsible for the resolution achieved. We use realistic interatomic interaction parameters to do numerical simulations. These simulations are in good agreement with experimental data. As a result, we are able to ‘separate' the attractive and repulsive forces acting between the AFM tip and the sample surface. Calculations indicate that the force responsible for image contrast in the experimental studies mentioned above, is in most cases the repulsive contact force, and not the long-range attractive force. We check our conclusions against a variety of interatomic interaction parameters and our results remain valid for any reasonable set of such parameters, including the power law of the attractive potential N<9. 相似文献
972.
Two-dimensional particle simulation is carried out to study the interaction between a high-intensity finite-size spot laser beam and a plasma with linear density profile. The laser is allowed to propagate in underdense corona until it is cut off near the critical surface. The intense laser can drive various instabilities through particle collective motion and result in electron heating,while relativistic effect and ponderomotive force can bring strong energy absorption and electron heating in the overdense region. As the laser beam is nonuniform in the transverse direction,a density channel forms and hole boring effect occurs as a result of strong ponderomotive force pushing particle outwards. These processes can be investigated well by particle simulation. 相似文献
973.
974.
Concentration dependent morphology of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) copolymer aggregates in aqueous system was investigated by atomic force microscopy (AFM). The AFM results show that, at a low concentration, 4 × 10?5 g/mL, spherical micelles occur, and unmicellized molecules are not distributed homogeneously in the copolymer aqueous solution. Unequal outspread clusters composed of wormlike aggregates are formed at a moderate copolymer concentration, 4 × 10?4 g/mL, those wormlike aggregates are orderly packed in the clusters. At a high concentration of 0.05 g/mL, the copolymer aqueous system is indeed a gel at room temperature, outspread clusters of wormlike aggregates join together to forma network structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1412–1418, 2008 相似文献
975.
976.
977.
力调制显微术被用于观测铜基碳化硅样品,实验中发现在样品表面台阶边缘处出现一些异常信息。为此,文章作者通过测试一种表面同样有台阶但却是由同一种材料组成的样品来通信验证这些异常主要是由台阶的边界引起的,并对引起的异常作了半定量的估算。 相似文献
978.
B~(4 )和H相互作用过程中径向偶合的理论计算 总被引:1,自引:1,他引:0
王利光 《原子与分子物理学报》2001,(2)
利用原子轨道展开的方法 ,对B4 和H碰撞过程中的径向偶合进行了理论计算。为了使计算结果精确并保持连续性 ,在波函数中加入了电子转移因子 ,并在中低能量范围内计算时对所使用的量子力学方程做了半经典近似。所得结果以曲线形式给出 ,是研究离子和原子相互作用的较直观的方法。 相似文献
979.
The effect of lattice anharmonicity on the resonant modes of dilute impurities for Au-Cu, Au-Ag and W-Cr metallic systems
are studied from the poles of the double time temperature dependent impure Green’s function of these crystals. The third order
force constants used in the present work are derived assuming the systems to obey the Lennard-Jones potential. The inclusion
of lattice anharmonicity has been found to increase the resonant frequency which depends upon the mass defect, force constant
change parameter and the impurity concentration terms. Some interesting features about the phase shift and the change in width
of the vibrational spectrum are reported at room temperature for the isotopic defects and the defects interacting with host
atoms. The results are found to be in qualitative agreement with the experiments on the systems considered. 相似文献
980.
A new, fast and convenient method based on coupled thin-layer chromatography (TLC) and Fourier transform-infrared (FT-IR) microscopy is developed to separate, detect and identify the additives in polymers. After the TLC development, the analytes were transferred on to a barium fluoride (BaF2) salt plate via a special capillary technique and analysed by FT-IR microscopy. The additives used for stabilization of polypropylene and the plasticisers used for poly(vinyl chloride) were analysed as examples to illustrate this technique. The overall time taken for the experiment including transferring three marked spots and then identifying them was about 20 min. An amount as small as 0.5 μg can be easily detected and identified. It was a very convenient and reliable method to separate and evaluate complex additives for polymers without the interference from TLC adsorbent, because of a special transferring and identifying method, which is suitable to FT-IR microscopy. 相似文献