全文获取类型
收费全文 | 61006篇 |
免费 | 5962篇 |
国内免费 | 3671篇 |
专业分类
化学 | 22162篇 |
晶体学 | 365篇 |
力学 | 8085篇 |
综合类 | 1240篇 |
数学 | 19211篇 |
物理学 | 19576篇 |
出版年
2023年 | 472篇 |
2022年 | 772篇 |
2021年 | 1651篇 |
2020年 | 1287篇 |
2019年 | 1387篇 |
2018年 | 1135篇 |
2017年 | 1425篇 |
2016年 | 1801篇 |
2015年 | 1681篇 |
2014年 | 2226篇 |
2013年 | 3799篇 |
2012年 | 2716篇 |
2011年 | 3211篇 |
2010年 | 2906篇 |
2009年 | 3764篇 |
2008年 | 3920篇 |
2007年 | 4214篇 |
2006年 | 3529篇 |
2005年 | 2800篇 |
2004年 | 2467篇 |
2003年 | 2537篇 |
2002年 | 2259篇 |
2001年 | 1961篇 |
2000年 | 1618篇 |
1999年 | 1410篇 |
1998年 | 1292篇 |
1997年 | 1039篇 |
1996年 | 967篇 |
1995年 | 914篇 |
1994年 | 815篇 |
1993年 | 830篇 |
1992年 | 776篇 |
1991年 | 558篇 |
1990年 | 462篇 |
1989年 | 380篇 |
1988年 | 387篇 |
1987年 | 336篇 |
1986年 | 302篇 |
1985年 | 437篇 |
1984年 | 346篇 |
1983年 | 208篇 |
1982年 | 388篇 |
1981年 | 556篇 |
1980年 | 487篇 |
1979年 | 560篇 |
1978年 | 447篇 |
1977年 | 344篇 |
1976年 | 280篇 |
1974年 | 103篇 |
1973年 | 178篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
11.
从量子力学诞生日起,它的经典对应(或类比)一直是物理学家关心的话题.本文以介观电路量子化的框架中,带有互感的两个介观电容-电感(LC)电路为例,首次讨论了量子纠缠的经典类比(或对应)问题.先用有序算符内的积分理论证明其互感是产生量子纠缠的源头;再推导出求解特征频率的公式,就发现它与一个经典系统的小振动频率的表达式有相似之处,该经典系统组成如下:两个墙壁各连一个相同的弹簧,两个弹簧之间接着一个滑动小车可以在光滑的桌面上运动,小车挂有一根单摆.用分析力学求此系统的小振动频率,发现与上述介观电路的特征频率形式类似,单摆的摆动会造成小车来回振动,摆、小车和弹簧的互相牵制效应反映了小车和摆的"纠缠". 相似文献
12.
13.
《中国物理 B》2021,30(5):56501-056501
Thermal expansion control is always an obstructive factor and challenging in high precision engineering field. Here,the negative thermal expansion of Nb F_3 and Nb OF_2 was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation(QHA). We studied the total charge density, thermal vibration, and lattice dynamic to investigate the thermal expansion mechanism. We found that the presence of O induced the relatively strong covalent bond in Nb OF_2, thus weakening the transverse vibration of F and O in Nb OF_2, compared with the case of Nb F_3.In this study, we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms.The present work not only predicts two NTE compounds, but also provides an insight on thermal expansion control by designing chemical bond type. 相似文献
14.
Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect, while it is challenging to achieve asymmetric nonlinear-mode-conversion (NMC) due to the limitations imposed by phase-matching. In this work, we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequency-doubling process and periodic PT symmetric modulation in an optical waveguide. By engineering the one-way momentum from PT symmetric modulation, we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes. Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry, which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics. 相似文献
15.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
16.
Chinese Annals of Mathematics, Series B - In the present article, the authors find and establish stability of multiplier ideal sheaves, which is more general than strong openness. 相似文献
17.
《Journal of Pure and Applied Algebra》2022,226(8):106948
Let be a Henselian discrete valued field with residue field of characteristic , and be the Brauer p-dimension of K. This paper shows that if , for some . It proves that if and only if . 相似文献
18.
Yves Pomeau 《Comptes Rendus Mecanique》2018,346(3):184-197
The equations for a self-similar solution to an inviscid incompressible fluid are mapped into an integral equation that hopefully can be solved by iteration. It is argued that the exponents of the similarity are ruled by Kelvin's theorem of conservation of circulation. The end result is an iteration with a nonlinear term entering a kernel given by a 3D integral for a swirling flow, likely within reach of present-day computational power. Because of the slow decay of the similarity solution at large distances, its kinetic energy diverges, and some mathematical results excluding non-trivial solutions of the Euler equations in the self-similar case do not apply. 相似文献
19.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
20.
Dr. Silvia Castro-Fernández Carlos M. Cruz Dr. Inês F. A. Mariz Dr. Irene R. Márquez Vicente G. Jiménez Lucía Palomino-Ruiz Prof. Juan M. Cuerva Dr. Ermelinda Maçôas Dr. Araceli G. Campaña 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(18):7205-7211
A new family of distorted ribbon-shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between their structural characteristics and the two-photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven-membered-ring-containing nanographene presenting a tropone moiety at the edge, its full-carbon analogue, and a purely hexagonal one. We have found that the TPA cross-sections and the electrochemical band gaps of the seven-membered-ring-containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non-linear optical properties of those ribbons. 相似文献