全文获取类型
收费全文 | 1917篇 |
免费 | 293篇 |
国内免费 | 215篇 |
专业分类
化学 | 722篇 |
晶体学 | 17篇 |
力学 | 143篇 |
综合类 | 83篇 |
数学 | 768篇 |
物理学 | 692篇 |
出版年
2024年 | 12篇 |
2023年 | 56篇 |
2022年 | 101篇 |
2021年 | 113篇 |
2020年 | 96篇 |
2019年 | 67篇 |
2018年 | 47篇 |
2017年 | 68篇 |
2016年 | 81篇 |
2015年 | 110篇 |
2014年 | 159篇 |
2013年 | 163篇 |
2012年 | 230篇 |
2011年 | 165篇 |
2010年 | 172篇 |
2009年 | 159篇 |
2008年 | 147篇 |
2007年 | 112篇 |
2006年 | 107篇 |
2005年 | 56篇 |
2004年 | 31篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 28篇 |
2000年 | 5篇 |
1999年 | 23篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 26篇 |
1987年 | 13篇 |
1959年 | 3篇 |
排序方式: 共有2425条查询结果,搜索用时 15 毫秒
91.
A field method for integrating the equations of motion of mechanico--electrical coupling dynamical systems 下载免费PDF全文
A field method for integrating the equations of motion for mechanico-electrical coupling dynamical systems is studied. Two examples in mechanico-electrical engineering are given to illustrate this method. 相似文献
92.
DNA is a nucleic acid molecule with double-helical structures that are special symmetrical structures attracting great attention of numerous researchers. The super-long elastic slender rod, an important structural model of DNA and other long-train molecules, is a useful tool in analysing the symmetrical properties and the stabilities of DNA. This paper studies the structural properties of a super-long elastic slender rod as a structural model of DNA by using Kirchhoff's analogue technique and presents the Noether symmetries of the model by using the method of infinitesimal transformation. Baaed on Kirchhoff's analogue it analyses the generalized Hamilton canonical equations. The infinitesimal transfornaationa with rcspect to the radial coordinnte, the gonarnlizod coordinates, and the Cluasi-momenta of 5he model are introduced. The Noether gymmetries and conserved qugntities of the model are obtained. 相似文献
93.
Effect of the stoichiometry on the electronic structure of the Ni(111)/α-Al2O3(0001) interface: a first-principles investigation 下载免费PDF全文
In this paper first-principles calculations of Ni(111)/α-Al2O3(0001) interfaces have been performed, and are compared with the preceding results of the Cu (111)/α-Al2O3(0001) interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu(111)/α Al2O3(0001) interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni(111)/α-A1203(0001) interfaces is similar to that in the corresponding Cu(111)/α- Al2O3(0001) interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively. 相似文献
94.
Anomalous magnetic properties of an iron film system deposited on fracture surfaces of α-Al2O3 ceramics 下载免费PDF全文
An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of α-Al2O3 ceramics. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field He of the iron film exhibits a minimum peak around the temperature T=5 K, which is independent of the magnitude of the cooling field Hcf. However, for T 〉 10K, (1) He is always negative when Hcf=2kOe and (2) for Hcf= 20 kOe (1Oe≈80 A/m), He changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase. 相似文献
95.
考虑随机系数自回归模型Yt =Φtyt-1+ ut,其中 Φt为随机系数,ut为随机误差。在允许Φt与ut相依以及Eut无穷的条件下,构造了误差方差的自加权估计,并证明了该估计的渐近正态性。最后通过数值模拟,说明
自加权估计的稳健和有效性。 相似文献
96.
研究了Lagrange系统的Lie对称性摄动与新型的非Noether绝热不变量. 列出了未受扰Lagrange系统的Lie对称性导致的Lutzky型精确不变量;基于力学系统的高阶绝热不变量的定义,研究在小扰动作用下Lagrange系统Lie对称性的摄动,得到了系统的一类Lutzky形式的绝热不变量.举例说明方法和结果的应用. 相似文献
97.
The electronic structures of doped Sb2O5 by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results
showed that the substituted IV-family elements act as acceptors in Sb2O5. Partial DOSs indicates that by substituting Ge(Ge
Sb
) or Sn(Sn
Sb
), there may be a larger contribution to the total DOSs near E
F
than by substituting Si, which suggests that doping Ge or Sn in Sb2O5 produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely
to exist in the substituted position rather than in the interstitial position in Sb2O5, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb2O5. Ionization energy results show that Ge
Sb
or SnSb, two among the three impurities considered, act as shallow acceptors in Sb2O5, thus producing a higher concentration of holes.
相似文献
98.
Shot noise for entangled and spin-polarized states in a four-probe geometric setup has been studied by adding two rotating magnetic fields in an incoming channel. Our results show that the noise power oscillates as the magnetic fields vary. The singlet, entangled triplet and polarized states can be distinguished by adjusting the magnetic fields. The Berry phase can be derived by measuring the shot noise power. 相似文献
99.
蒙特卡罗方法计算定积分的进一步讨论 总被引:3,自引:0,他引:3
介绍了蒙特卡罗方法计算定积分的原理和方法.给出了用蒙特卡罗方法计算定积分的一个简单证明,从而揭示了蒙特卡罗方法和定积分定义间的内在联系.针对蒙特卡罗方法收敛慢的特点,提出将蒙特卡罗方法与相应的数值计算方法相结合,提高计算结果的精度.此外,将蒙特卡罗方法推广到反常积分上去. 相似文献
100.
该文给出了正弦级数和余弦级数在系数满足NBV条件时属于Ba空间的充分必要条件,所得结论 为Ba空间中的首个此类结果,同时也是对Lp空间中已有结论的本质性推广. 相似文献