全文获取类型
收费全文 | 35716篇 |
免费 | 4597篇 |
国内免费 | 4150篇 |
专业分类
化学 | 14038篇 |
晶体学 | 242篇 |
力学 | 2671篇 |
综合类 | 243篇 |
数学 | 9407篇 |
物理学 | 17862篇 |
出版年
2024年 | 82篇 |
2023年 | 333篇 |
2022年 | 695篇 |
2021年 | 804篇 |
2020年 | 998篇 |
2019年 | 933篇 |
2018年 | 941篇 |
2017年 | 1160篇 |
2016年 | 1366篇 |
2015年 | 1196篇 |
2014年 | 1738篇 |
2013年 | 2990篇 |
2012年 | 1911篇 |
2011年 | 2324篇 |
2010年 | 1816篇 |
2009年 | 2332篇 |
2008年 | 2399篇 |
2007年 | 2520篇 |
2006年 | 2136篇 |
2005年 | 1792篇 |
2004年 | 1532篇 |
2003年 | 1462篇 |
2002年 | 1414篇 |
2001年 | 1130篇 |
2000年 | 1154篇 |
1999年 | 948篇 |
1998年 | 846篇 |
1997年 | 614篇 |
1996年 | 515篇 |
1995年 | 463篇 |
1994年 | 375篇 |
1993年 | 355篇 |
1992年 | 347篇 |
1991年 | 262篇 |
1990年 | 262篇 |
1989年 | 238篇 |
1988年 | 229篇 |
1987年 | 208篇 |
1986年 | 178篇 |
1985年 | 196篇 |
1984年 | 177篇 |
1983年 | 101篇 |
1982年 | 139篇 |
1981年 | 136篇 |
1980年 | 103篇 |
1979年 | 108篇 |
1978年 | 89篇 |
1977年 | 88篇 |
1976年 | 83篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
91.
Mats Gyllenberg 《Journal of Differential Equations》2004,205(1):50-76
For time-periodic dissipative and irreducible type-K competitive Kolmogorov systems, it is proved that there is a canonically defined countable family F of unordered, disjoint invariant sets with the property that, for every persistent trajectory whose ω-limit set is not a cycle, there exists a unique trajectory in some element of F such that these two trajectories are asymptotic and the corresponding points in these two trajectories are K-related. 相似文献
92.
Density functional method (DFT) (B3p86) of Gaussian98 has been used to optimize the structure of the Tc_2 molecule. The result shows that the ground state for Tc_2 molecule is an 11-multiple state and its electronic configuration is {}^{11}Σ_g^-, which shows the spin polarization effect of Tc_2 molecule of a transition metal element for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher energy states. So, that the ground state for Tc_2 molecule is an 11-multiple state is indicative of the spin polarization effect of Tc_2 molecule of a transition metal element: that is, there exist 10 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Tc_2 molecule is minimized. It can be concluded that the effect of parallel spin of the Tc_2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state {}^{11}Σ_g^- and other states of Tc_2 molecule are derived. Dissociation energy D_e for the ground state of T_{c2} molecule is 2.266eV, equilibrium bond length R_e is 0.2841nm, vibration frequency ω_e is 178.52cm^{-1}. Its force constants f_2, f_3, and f_4 are 0.9200aJ·nm^{-2}, --3.5700aJ·nm^{-3}, 11.2748aJ·nm^{-4} respectively. The other spectroscopic data for the ground state of Tc_2 molecule ω_eχ_e, B_e, α_e are 0.5523cm^{-1}, 0.0426cm^{-1}, 1.6331×10^{-4}cm^{-1} respectively. 相似文献
93.
Ray Leslie Withers Carlos Otero-Diaz Adrian Gómez-Herrero Albert Prodan Lasse Norén 《Journal of solid state chemistry》2005,178(10):3159-3168
Ternary derivatives of 1T-TaS2 have been synthesized and the variation in the highly structured diffuse intensity distributions characteristic of such materials carefully monitored to investigate the effect that such substitution has upon the band structures and Fermi surfaces (FSs) of the materials. Removal of d electrons via the replacement of Ta ions with lower valent transition metal ions leads to a systematic increase in the radii of the characteristic structured diffuse intensity distribution. Extended Hückel tight binding calculations of the FSs of the doped samples are carried out and used to predict possible nesting wave-vectors. The results are in reasonably good agreement with the radii of the experimentally observed diffuse intensity distributions. 相似文献
94.
A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. We show that
full polarization analysis is the only tool allowing to discriminate unambiguously between different magnetic modes in various
magnetic materials. We show by means of recent results in the Heisenberg ferromagnet EuS that the effects of dipolar interactions
can be studied on a microscopic scale. Moreover, we have found for the first time indications for the divergence of the longitudinal
fluctuations belowT
c. In the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations
are very different, resolving a long standing puzzle concerning the slope of their dispersion. Finally, we show that a measurement
of the polarization-dependent part of the cross section of non-centrosymmetric MnSi proves directly that the chirality of
the magnetic fluctuations is left-handed. 相似文献
95.
从决策有限理性角度,引入行为金融理论于机构投资风险优化系统,对多心理账户条件下机构投资的风险优化设计进行了研究。以Friedman和Savage之谜为释例,对机构投资风险优化中的诸多非标准金融异像进行了解释。以Shefrin和Statman行为证券组合理论为核心,建立了多心理账户条件下机构投资的风险优化模型,为机构投资的风险优化实践提供了一种量化分析工具。 相似文献
96.
97.
98.
99.
估计死亡率分布的一个最大熵模型 总被引:1,自引:0,他引:1
本文提出了一种估计死亡率分布的新模型一最大熵模型。该模型直接从样本信息出发,不需要对待估分布的概率密度函数或先验分布作任何假定,从而克服了极大似然估计和贝叶斯估计的不足。而且通过两个例子的计算结果,表明该方法与样本数据的拟合效果要好于其它两种方法。 相似文献
100.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given. 相似文献