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61.
丝电爆制备纳米粉时, 电流从电极导入金属丝的过程直接影响电极烧损和粉末中微米级大颗粒产生. 分别通过接触和气体放电两种方式导入电流进行电爆试验. 结果表明, 光测量装置检测到的丝端部光电流几乎与回路放电电流同时产生, 而中间位置的光电流则要滞后一段时间; 由探针收集的产物确定, 金属丝端部主要形成熔融粒子, 中间部分主要形成气相粒子. 分析可知, 接触方式导入电流时, 丝端部也存在气体放电现象, 大电流主要通过气体放电形成的等离子体导入. 等离子体对电流的旁路作用会阻碍能量向金属丝沉积, 这是产生微米级大颗粒和"积瘤"主要原因. 通过气体放电方式导入电流时, 电极烧损明显减轻, 并可以避免"积瘤"产生. 相似文献
62.
We carried out molecular dynamics simulations of a Lorentz gas, consisting of a lone hydrogen molecule moving in a sea of stationary argon atoms. A Lennard-Jones form was assumed for the H2-Ar potential. The calculations were performed at a reduced temperatureK
* =kT/H
2–Ar = 4.64 and at reduced densities
*=
Ar
Ar
3
in the range 0.074–0.414. The placement of Ar atoms was assumed to be random rather than dictated by equilibrium considerations. We followed the trajectories of many H2 molecules, each of which is assigned in turn a velocity given by the Maxwell-Boltzmann distribution at the temperature of the simulation. Solving the equations of motion classically, we obtained the translational part of the incoherent dynamic structure factor for the H2 molecule,S
tr(q, ). This was convoluted with the rotational structure factorS
rot(q, ) calculated assuming unhindered rotation to obtain the total structure factorS(q, ). Our results agree well with experimental data on this function obtained by Egelstaffet al. At the highest density (
*=0.414) we studied the dependence ofS(q, ) on system size (number of Ar atoms), number of H2 molecules for which trajectories are generated, and the length of time over which these trajectories are followed. 相似文献
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66.
变量选择是光谱分析领域一个重要的组成部分。为了克服传统区间选择法的缺点与不足,基于无信息变量消除法和岭极限学习机提出一种新型的变量选择与评价方法。首先,利用无信息变量消除法剔除整个光谱区间中无信息的波长点;其次,为了解决传统建模方法(偏最小二乘法、BP神经网络等)存在的共线性问题,采用岭极限学习机方法建立回归模型;最后,最佳的特征光谱波长点组合利用特征选择路径图和稀疏度-误差折中曲线进行确定。CO气体的浓度反演实验结果表明:(1)利用无信息变量消除法可以有效筛选出最能表征CO气体透过光谱的特征波长点;(2)岭极限学习机方法具有快速建模、避免共线性和高精度等优点(CO气体浓度反演模型的决定系数可达0.995);(3)特征选择路径图和稀疏度-误差折中曲线可以直观地帮助用户寻找出最佳的特征波长点组合。 相似文献
67.
S. Ramasamy D. J. Smith P. Thangadurai K. Ravichandran T. Prakash K. PAdmaprasad V. Sabarinathan 《Pramana》2005,65(5):881-891
The ultra high vacuum chamber was developed in the Department of Nuclear Physics, University of Madras with the funding from
DST, India. This UHV chamber is used to prepare nanocrystalline materials by inert gas condensation technique (IGCT). Nanocrystalline
materials such as PbF2, Mn2+-doped PbF2, Sn-doped In2O3 (ITO), ZnO, Al2O3, Ag2O, CdO, CuO, ZnSe:ZnO etc., were prepared by this technique and characterized. Results of some of these materials will be
presented in this paper. In solid-state207Pb NMR on PbF2 a separate signal due to the presence of grain boundary has been observed. The structural phase transition pressure during
the phase transformation from the cubic phase to orthorhombic phase under high pressure shows an increase with the decrease
in grain size. Presence of electronic centres in nanocrystalline PbF2 is observed from Raman studies and the same has been confirmed by photoluminescence studies. Al2O3 was prepared and56Fe ions were implanted. After implantation segregation of56Fe ions was examined by SEM. The oxidation properties of ITO were studied by HRTEM. As against the expectation of oxide coating
on individual nanograins of In-Sn alloy, ITO nanograins grew into faceted nanograins on heat treatment in air and O2 atmosphere. The growth of ITO under O2 atmosphere showed pentagon symmetry. The PMN was initially prepared by solid-state reaction. Further, this PMN relaxor material
will be used to convert into nanocrystalline PMN by IGCT with sputtering and will be studied 相似文献
68.
69.
Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer 下载免费PDF全文
In this paper,two-dimensional electron gas(2DEG) regions in AlGaN/GaN high electron mobility transistors(HEMTs) are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field. 相似文献
70.
利用深能级瞬态谱(DLTS)研究了气源分子束外延(GSMBE)生长的InP1-xBix材料中深能级中心的性质。在未有意掺杂的InP中测量到一个多数载流子深能级中心E1,E1的能级位置为Ec-0.38 e V,俘获截面为1.87×10~(-15)cm~2。在未有意掺杂的InP0.9751Bi0.0249中测量到一个少数载流子深能级中心H1,H1的能级位置为Ev+0.31 eV,俘获截面为2.87×10~(-17)cm~2。深中心E1应该起源于本征反位缺陷PIn,深中心H1可能来源于形成的Bi原子对或者更复杂的与Bi相关的团簇。明确这些缺陷的起源对于InPBi材料在器件应用方面具有重要的意义。 相似文献