全文获取类型
收费全文 | 308090篇 |
免费 | 3612篇 |
国内免费 | 908篇 |
专业分类
化学 | 170218篇 |
晶体学 | 5354篇 |
力学 | 12381篇 |
综合类 | 16篇 |
数学 | 30392篇 |
物理学 | 94249篇 |
出版年
2019年 | 2466篇 |
2018年 | 2796篇 |
2017年 | 2846篇 |
2016年 | 4618篇 |
2015年 | 3068篇 |
2014年 | 4702篇 |
2013年 | 13281篇 |
2012年 | 9392篇 |
2011年 | 11757篇 |
2010年 | 8014篇 |
2009年 | 7778篇 |
2008年 | 10449篇 |
2007年 | 10385篇 |
2006年 | 10016篇 |
2005年 | 9336篇 |
2004年 | 8408篇 |
2003年 | 7723篇 |
2002年 | 7414篇 |
2001年 | 8950篇 |
2000年 | 6788篇 |
1999年 | 5371篇 |
1998年 | 4327篇 |
1997年 | 4254篇 |
1996年 | 4144篇 |
1995年 | 3941篇 |
1994年 | 3619篇 |
1993年 | 3469篇 |
1992年 | 4302篇 |
1991年 | 4195篇 |
1990年 | 4064篇 |
1989年 | 4103篇 |
1988年 | 4113篇 |
1987年 | 4149篇 |
1986年 | 3940篇 |
1985年 | 5163篇 |
1984年 | 5225篇 |
1983年 | 4213篇 |
1982年 | 4585篇 |
1981年 | 4495篇 |
1980年 | 4312篇 |
1979年 | 4643篇 |
1978年 | 4740篇 |
1977年 | 4768篇 |
1976年 | 4644篇 |
1975年 | 4337篇 |
1974年 | 4159篇 |
1973年 | 4334篇 |
1972年 | 2855篇 |
1968年 | 2647篇 |
1967年 | 2601篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
A. M. Yakunin A. Yu. Silov P. M. Koenraad W. Van Roy J. De Boeck J. H. Wolter 《Superlattices and Microstructures》2003,34(3-6):539
An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn2+3d5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state. 相似文献
912.
913.
Mechanisms of ‘environmental decoherence’ such as surface scattering, Elliot–Yafet process and precession mechanisms, as well as their influence on the spin phase relaxation are considered and compared. It is shown that the ‘spin ballistic’ regime is possible, when the phase relaxation length for the spin part of the wave function (L(s)) is much greater than the phase relaxation length for the ‘orbital part’ (L(e)). In the presence of an additional magnetic field, the spin part of the electron's wave function (WF) acquires a phase shift due to additional spin precession about that field. If the structure length L is chosen to be L(s)>L>L(e), it is possible to ‘wash out’ the quantum interference related to the phase coherence of the ‘orbital part’ of the WF, retaining at the same time that related to the phase coherence of the spin part and, hence, to reveal corresponding conductance oscillations. 相似文献
914.
Various problems associated with optimal path planning for mobile observers such as mobile robots equipped with cameras to obtain maximum visual coverage of a surface in the three-dimensional Euclidean space are considered. The existence of solutions to these problems is discussed first. Then, optimality conditions are derived by considering local path perturbations. Numerical algorithms for solving the corresponding approximate problems are proposed. Detailed solutions to the optimal path planning problems for a few examples are given. 相似文献
915.
A pseudopotential depending on an effective core radius is proposed to study the binding energy, equation of state, ion-ion
interaction, phonon dispersion curves (q-space and r-space analysis), mode Grüneisen parameters and dynamical elastic constants
of some fcc f-shell metals La, Yb, Ce and Th. The contribution of the s-like electrons is calculated in the second-order perturbation
theory for the potential while d and f-like electron is taken into account by introducing repulsive short-range Born-Mayer
term. The parameter of the potential is evaluated by zero pressure condition. An excellent agreement between theoretical investigations
and experimental findings is achieved which confirms the present formalism 相似文献
916.
We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems. 相似文献
917.
D. Behera T. Mohanty S. K. Dash T. Banerjee D. Kanjilal N. C. Mishra 《Radiation measurements》2003,36(1-6):125-129
Swift heavy ions (SHI) with electronic energy loss exceeding a value of 14.4 keVnm−1 create amorphized latent tracks in YBCO type superconductors. In the low fluence regime of an ion beam where tracks do not overlap, a decrease of the superconducting transition temperature as probed through resistivity studies, is not expected due to availability of percolating current paths. The present study however shows Tc decrease by about 1–3 K in thin films of YBCO when irradiated by 250 MeVAg ions at 79 K at a fluence of 5×1010–1×1012 ionscm−2. The highest fluence used in the present study is three times less than the fluence where track overlapping becomes significant. The Tc tends to increase towards the preirradiation value on annealing the films at room temperature. To explain this unusual result, we consider the effect of ion irradiation in inducing materials modification not only through creation of amorphized latent tracks along the ion path, but also through creation of atomic disorder in the oxygen sublattice in the Cu–O chains of YBCO by the secondary electrons. These electrons are emitted radially from the tracks during the passage of the SHI. Considering the correlation between the charge state of copper and its oxygen coordination, we show in particular that the latter process is a consequence of the inelastic interaction of the SHI induced low-energy secondary electrons with the YBCO lattice, which result in chain oxygen disorder and Tc decrease. 相似文献
918.
K. L. Janssens B. Partoens F. M. Peeters 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):349
We investigated theoretically the influence of strain on the exciton in both single and three vertically coupled self-assembled quantum dot systems in the presence of a perpendicular magnetic field. For the single disk, we find that the heavy-hole exciton is the ground state, while for the system of three stacked disks, the light hole state was found to be lower in energy. Results for the diamagnetic shift were compared with experimental results. 相似文献
919.
We establish some liminf theorems on the increments of a (N,d)-Gaussian process with the usual Euclidean norm, via estimating upper bounds of large deviation probabilities on the suprema
of the (N,d)-Gaussian process.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
920.
Synchronized whistlers recorded at Varanasi 总被引:1,自引:0,他引:1
Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of
the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Eckersley whistlers having
dispersion 10 s1/2 and 30 s1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources 相似文献