全文获取类型
收费全文 | 315749篇 |
免费 | 4663篇 |
国内免费 | 1600篇 |
专业分类
化学 | 176285篇 |
晶体学 | 3946篇 |
力学 | 12775篇 |
综合类 | 67篇 |
数学 | 31752篇 |
物理学 | 97187篇 |
出版年
2019年 | 2779篇 |
2018年 | 3040篇 |
2017年 | 3094篇 |
2016年 | 4999篇 |
2015年 | 3461篇 |
2014年 | 5156篇 |
2013年 | 13955篇 |
2012年 | 10206篇 |
2011年 | 12707篇 |
2010年 | 8623篇 |
2009年 | 8402篇 |
2008年 | 11146篇 |
2007年 | 11026篇 |
2006年 | 10592篇 |
2005年 | 9828篇 |
2004年 | 8879篇 |
2003年 | 8115篇 |
2002年 | 7773篇 |
2001年 | 9224篇 |
2000年 | 7021篇 |
1999年 | 5554篇 |
1998年 | 4472篇 |
1997年 | 4267篇 |
1996年 | 3926篇 |
1995年 | 3926篇 |
1994年 | 3642篇 |
1993年 | 3463篇 |
1992年 | 4262篇 |
1991年 | 4119篇 |
1990年 | 4026篇 |
1989年 | 4028篇 |
1988年 | 4058篇 |
1987年 | 4071篇 |
1986年 | 3847篇 |
1985年 | 5128篇 |
1984年 | 5171篇 |
1983年 | 4160篇 |
1982年 | 4501篇 |
1981年 | 4437篇 |
1980年 | 4245篇 |
1979年 | 4589篇 |
1978年 | 4692篇 |
1977年 | 4714篇 |
1976年 | 4610篇 |
1975年 | 4308篇 |
1974年 | 4122篇 |
1973年 | 4318篇 |
1972年 | 2828篇 |
1968年 | 2653篇 |
1967年 | 2604篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
971.
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
972.
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
973.
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
974.
975.
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
976.
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
977.
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
978.
We have given design of a very small residual dispersion fiber system consisting of a small dispersion fiber(SDF) with flat modal field and a corresponding dual core coaxial dispersion compensating fiber (DCF). 相似文献
979.
提出一种单光子探测器量子效率的绝对自身标定方案,利用光参量下转换过程中产生的光子对在时间上的相关性,先将参量光束分为两路,然后引入相对延时,使同时产生的孪生光子先后进入单光子探测器,然后将探测器之后的电路分为三路,其中一路直接进入计数器得到探测器所探测到的光子的总计数率,另两路用电路方法引入和光路相当的相对延时,经符合电路后进入计数器,得到前后到达探测器的光子对之间的符合计数率.这样,从符合计数率与总光子计数率之比即可在不需要任何其他探测器或者参照标准的情况下获得探测器的量子效率.文中给出两种方案,分别适 相似文献
980.
We have observed three-dimensional sponge-like structures as well as strips of connecting pits on the surface of the LR 115 detector after etching, which can be confused with the small tracks formed after short etching time. We have employed an atomic force microscope (AFM) to study these “damages” as well as genuine alpha tracks for short etching time. It was found that while the track and damage openings could be similar in size and shape, the depths for the damages were consistently smaller. Therefore, the depth of the pits will serve as a clear criterion to differentiate between tracks and other damages. The ability to discriminate between genuine tracks from other damages is most important for etching for short time intervals. 相似文献