全文获取类型
收费全文 | 12110篇 |
免费 | 2466篇 |
国内免费 | 2833篇 |
专业分类
化学 | 8776篇 |
晶体学 | 363篇 |
力学 | 927篇 |
综合类 | 323篇 |
数学 | 1324篇 |
物理学 | 5696篇 |
出版年
2024年 | 38篇 |
2023年 | 156篇 |
2022年 | 425篇 |
2021年 | 503篇 |
2020年 | 523篇 |
2019年 | 457篇 |
2018年 | 482篇 |
2017年 | 532篇 |
2016年 | 575篇 |
2015年 | 685篇 |
2014年 | 870篇 |
2013年 | 1035篇 |
2012年 | 1009篇 |
2011年 | 1070篇 |
2010年 | 922篇 |
2009年 | 941篇 |
2008年 | 1044篇 |
2007年 | 958篇 |
2006年 | 882篇 |
2005年 | 750篇 |
2004年 | 576篇 |
2003年 | 443篇 |
2002年 | 441篇 |
2001年 | 463篇 |
2000年 | 370篇 |
1999年 | 240篇 |
1998年 | 160篇 |
1997年 | 124篇 |
1996年 | 114篇 |
1995年 | 95篇 |
1994年 | 68篇 |
1993年 | 97篇 |
1992年 | 65篇 |
1991年 | 51篇 |
1990年 | 43篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1964年 | 2篇 |
1962年 | 2篇 |
1960年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
41.
42.
Shneor R Monaghan P Subedi R Anderson BD Aniol K Annand J Arrington J Benaoum H Benmokhtar F Bertin P Bertozzi W Boeglin W Chen JP Choi S Chudakov E Cisbani E Craver B de Jager CW Feuerbach RJ Frullani S Garibaldi F Gayou O Gilad S Gilman R Glamazdin O Gomez J Hansen JO Higinbotham DW Holmstrom T Ibrahim H Igarashi R Jans E Jiang X Jiang Y Kaufman L Kelleher A Kolarkar A Kuchina E Kumbartzki G LeRose JJ Lindgren R Liyanage N Margaziotis DJ Markowitz P Marrone S Mazouz M Meekins D Michaels R 《Physical review letters》2007,99(7):072501
We investigated simultaneously the 12C(e,e'p) and 12C(e,e'pp) reactions at Q2=2 (GeV/c)2, xB=1.2, and in an (e, e'p) missing-momentum range from 300 to 600 MeV/c. At these kinematics, with a missing momentum greater than the Fermi momentum of nucleons in a nucleus and far from the delta excitation, short-range nucleon-nucleon correlations are predicted to dominate the reaction. For (9.5+/-2)% of the 12C(e,e'p) events, a recoiling partner proton was observed back-to-back to the 12C(e,e'p) missing-momentum vector, an experimental signature of correlations. 相似文献
43.
文中提出了一个新的、稳定的光谱导数Kalman滤波紫外分光光度法同时定量分析方法,并且成功地将其应用于极难分辨的苯酚-邻氯苯酚和2,4二氯苯酚三组分混合体系的同时测量.选择分析光谱导数的原因是其不仅包含着吸光度,还包括在指定波长位置变化趋向等更多的信息量,这样更利于在吸收峰重叠的位置捕捉有较大差异的信号.利用Kalman滤波可以解决由光谱导数而引起的噪声放大问题,也可以过滤源于实验的噪声以及来自传递模型误差.在260~290 nm区间测量了30组浓度各自在1~10 mg·L-1范围的苯酚-邻氯苯酚和2,4二氯苯酚标准混合溶液紫外吸收光谱图.利用分段延伸高次多项式回归模拟求导准确获得吸光度导数,并且利用偏最小二乘法将其制作成Kalman滤波标准工作系数矩阵.通过随机线性离散系统的Kalman滤波器最优平滑计算,对混合体系中的各组分进行定量分析.回收实验显示出,光谱导数Kalman滤波分析法应用于本实验的极难分辨的三组分体系,得到了非常高的回收率,并且在整个实验范围内光谱导数Kalman滤波分析法具有非常好的稳定性. 相似文献
44.
单个鼻咽癌细胞的拉曼光谱分析的研究 总被引:3,自引:0,他引:3
利用激光镊子拉曼光谱系统研究了鼻咽癌细胞株和正常人鼻咽部气道上皮细胞株的单个细胞的拉曼光谱,对于每个细胞在不同部位测3个点。结果显示:正常细胞和癌细胞的平均拉曼光谱有显著差异:正常的细胞光谱强度比癌细胞的明显要高;正常细胞的1304和1336 cm-1处峰的强度比值为1.05,癌细胞的为1.22。用PCA主成分分析和DFA判别分析分别对单个细胞的平均光谱和不同位置所取得的单独光谱进行分析,结果发现:PCA和DFA均可以把癌细胞和正常细胞正确区分,对于单独光谱,DFA的效果更好一些。同时还发现同一个细胞中不同的光谱位置对PCA和DFA的区分度影响不是很大;PCA和DFA的图中还表明癌细胞的均匀度要比正常细胞的差。以上的研究均表明:激光镊子拉曼光谱可以成为区别正常鼻咽细胞和鼻咽癌细胞的有效手段。 相似文献
45.
Evaluation of Optical Properties of Self-Frequency-Doubling Crystal Yb:GdYAl3(BO3)4 for Laser Applications 下载免费PDF全文
Yb:GdYAl3 (B03)4 (Yb:GdYAB) is investigated as a new laser crystal for potential applications in self-frequency doubling. The emission and absorption properties of Yb:GdYAB crystal are studied, and the emission decay times of the upper laser level are measured. The emission cross sections are evaluated using the absorption cross section and principle of reciprocity. The other laser performance parameters, such as the minimum inversion fraction βmin, pump saturation intensity Isat and minimum pump intensity 1rain, are also calculated. The results are discussed in the framework of requirements for an effective diode-pumped Yb^3+ laser system. Yb:GdYAB is expected to exhibit the most useful laser properties and to be superior to Yb:YAB crystal that has been excellent self-frequency-doubling crystal at present in many key spectroscopic parameter values. 相似文献
46.
Investigation on improving characteristics of two-cell SBS system with CCl4/C2H5OH liquid mixture 下载免费PDF全文
In order to improve the performance of the two-cell stimulated Brillouin scattering (SBS) system, this paper proposes the methods of using mixtures, which require amplifier media to have small absorption rate, and generator media to have high optical breakdown threshold and Brillouin frequency shift equal to that of the amplification media. The characteristics of the two-cell SBS system are studied experimentally by using CCl4 as amplifier medium and CCl4, C2H5OH and CCl4/C2H5OH liquid mixture as generator medium pumped by Nd:YAG Q-switched laser. The obtained results show that liquid mixture in generator cell improves the power load ability, phase conjugation fidelity, energy reflectivity (ER) and ER stability. 相似文献
47.
In this paper, we study the Lie symmetrical Hojman conserved quantity of a relativistic mechanical system under general infinitesimal transformations of groups in which the time parameter is variable. The determining equation of Lie symmetry of the system is established. The theorem of the Lie symmetrical Hojman conserved quantity of the system is presented. The above results are generalization to
Hojman's conclusions, in which the time parameter is not variable and the system is non-relativistic. An example is given to illustrate the application of the results in the last. 相似文献
48.
A fractional order hyperchaotic system derived from Liu system and its circuit realization 下载免费PDF全文
In this paper we propose a novel four-dimensional fractional order hyperchaotic system derived from Liu system. Electronics workbench (EWB) and Matlab simulations show the dynamical behavior of the proposed four-dimensional fractional order hyperchaotic system. Finally, after separately using EWB and Matlab, an electronic circuit is designed to realize the novel four-dimensional fractional order hyperchaotic system and the experimental circuit results are obtained which are identical to software simulations. 相似文献
49.
Transport through artificial single-molecule magnets: Spin-pair state sequential tunneling and Kondo effects 下载免费PDF全文
The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn+2 ion(S=5/2) are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with(2S+1) sublevels.In the sequential tunneling regime,the differential conductance exhibits(2S+1) possible peaks,corresponding to resonance tunneling via(2S+1) sublevels.At low temperature,Kondo physics dominates transport and(2S+1) Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states. 相似文献
50.
In a view to balancing cost and lithium ion conductivity, Li6BaLa2Nb x Ta2???x O12 (x?=?0–2) was prepared by solid-state reaction, and its corresponding AC impedances were tested at temperatures ranging from 20 to 250 °C in air. Li6BaLa2Ta2O12 exhibits the highest conductivity, 8.77?×?10?6?S/cm, and the second highest is Li6BaLa2Nb2O12 with 6.69?×?10?6?S/cm. Partial replacement of Ta with Nb cannot bestow the advantages of cost saving or the enhancement of lithium ion conductivity. X-ray diffraction patterns revealed a gradual change as an increasing amount of Nb replaces Ta in Li6BaLa2Nb x Ta2???x O12 (x?=?0–2), and it is thought that the trending of Nb and Ta to rest on the crystallographic planes is different. 相似文献