全文获取类型
收费全文 | 8910篇 |
免费 | 3803篇 |
国内免费 | 3067篇 |
学科分类
数理化 | 15780篇 |
出版年
2024年 | 80篇 |
2023年 | 314篇 |
2022年 | 417篇 |
2021年 | 391篇 |
2020年 | 333篇 |
2019年 | 332篇 |
2018年 | 245篇 |
2017年 | 339篇 |
2016年 | 353篇 |
2015年 | 375篇 |
2014年 | 708篇 |
2013年 | 556篇 |
2012年 | 634篇 |
2011年 | 646篇 |
2010年 | 684篇 |
2009年 | 668篇 |
2008年 | 738篇 |
2007年 | 665篇 |
2006年 | 738篇 |
2005年 | 616篇 |
2004年 | 655篇 |
2003年 | 596篇 |
2002年 | 595篇 |
2001年 | 528篇 |
2000年 | 418篇 |
1999年 | 333篇 |
1998年 | 322篇 |
1997年 | 369篇 |
1996年 | 278篇 |
1995年 | 265篇 |
1994年 | 259篇 |
1993年 | 249篇 |
1992年 | 241篇 |
1991年 | 216篇 |
1990年 | 211篇 |
1989年 | 186篇 |
1988年 | 72篇 |
1987年 | 62篇 |
1986年 | 39篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1979年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
就标准厚度卡片在霍尔传感器的定标方面的应用作了有益的探讨。在纵向测量微小长度时,霍尔片处于磁场边缘位置,其对磁场的梯度更大,即灵敏度更高,且靠中心位置的线性更好。 相似文献
2.
3.
4.
磁化水具有比普通水更小的簇合分子,具有硬度、pH值、含氧浓度均增加的性质.采用傅立叶变换红外光谱技术,测量了大豆与玉米实验组与空白组的叶绿体的红外光谱,发现两者在酰氨键的振动吸峰处存在一定的差异,实验组的吸收明显强于对照组,说明磁化水对作物的生长发育有一定影响,具有一定的生物效应. 相似文献
5.
6.
Ennio Arimondo 《量子光学学报》2006,12(B08):59-60
Cold atoms and, more recently, Bose-Einstein condensates (BEC's) in optical lattices have attracted increasing interest since their first realization. In particular, the formal similarity between the wavefunction of a BEC inside the periodic potential of an optical lattice and of the electrons in a crystal lattice has triggered theoretical and experimental efforts alike. Many phenomena from condensed matter physics, such as Bloch oscillations and Landau-Zener tunneling have been shown to be observable also in optical lattices. An important difference between electrons in a crystal lattice and a BEC inside the periodic potential of an optical lattice is the strength of the self interaction and hence the magnitude of the nonlinearity of the system. Electrons in a metal are almost noninteracting, whereas atoms inside a BEC interact strongly. A' perturbation approach is appropriate in the former case while in the latter the full nonlinearity must be taken into account. From this feature new physics is expected. Most experiments to date have been carried out in the regime of shallow lattice depth, for which the system is well described by the mean field Gross-Pitaevskii equation with a periodic potential. Moreover, the nonlinearity induced by the mean-field of the condensate has been shown, both theoretically and experimentally, to give rise to instabilities in certain regions of the Brillouin zone. These instabilities are not present in the corresponding linear system, i.e. the electron system. Experimental and theoretical results on the subject of nonlinear Landau-Zener tunneling and nonlinearity-induced instabilities in a Bose-Einstein condensate interacting with an external periodic potential will be presented. 相似文献
8.
9.
The electronic structures for three types of PbW04 (PWO) crystals, the perfect PWO, the PWO containing lead vacancy (PWO-Vpb) and fluorine doped PWO crystal (F^-:PWO), are systematically studied within the framework of density functional theory. The computational results show that the Pb 6s state situates below the valence band so that Pb^2 ions are unable to trap holes forming Pb^3 or Pb^4 to compensate for VPb^2-. The hole-trappers in PWO-Vpb are O^2- ions. Two of the longer-bond O^2- ions share a hole forming O2^3-, and four of the longer-bond oxygen ions trap two holes forming an associated color centre [O2^3--Vpb-O2^3-], which may be the origin of the 42Onto absorption band. It is also concluded that the doping of F^- would reduce the band gap and F^- ions substituting for O^2- can effectively restrict the formation of [O2^3--Vpb-O2^3-] and weaken the 42Onm absorption band and hence enhance the scintillation property of PWO. 相似文献
10.
Singlet-Triplet Transition in Quantum Dots Confined by Triangular and Bowl-Like Potentials: the Effect of Electric Fields 下载免费PDF全文
We theoretically investigate the energy spectra of two-electron two-dimensional (2e 2D) quantum dots (QDs) confined by triangular potentials and bowl-like potentials in a magnetic field by exact diagonalization in the framework of effective mass theory. An in-plane electric field is found to contribute to the singlet-triplet transition of the ground state of the 2e 2D QDs confined by triangular or bowl-like potentials in a perpendicular magnetic field. The stronger the in-plane electric field, the smaller the magnetic field for the total spin of the ground states in the dot systems to change from S = 0 to S = 1. However, the influence of an in-plane electric field on the singlettriplet transition of the ground state of two electrons in a triangular QD modulated by a perpendicular magnetic field is quite small because the triangular potential just deviates from the harmonic potential well slightly. We find that the strength of the perpendicular magnetic field needed for the spin singlet-triplet transition of the ground state of the QD confined by a bowl-like potential is reduced drastically by applying an in-plane electric field. 相似文献