全文获取类型
收费全文 | 73046篇 |
免费 | 6568篇 |
国内免费 | 6637篇 |
专业分类
化学 | 30373篇 |
晶体学 | 521篇 |
力学 | 5682篇 |
综合类 | 685篇 |
数学 | 17847篇 |
物理学 | 31143篇 |
出版年
2024年 | 139篇 |
2023年 | 666篇 |
2022年 | 1437篇 |
2021年 | 1656篇 |
2020年 | 1875篇 |
2019年 | 1858篇 |
2018年 | 1710篇 |
2017年 | 1930篇 |
2016年 | 2224篇 |
2015年 | 1862篇 |
2014年 | 2844篇 |
2013年 | 5063篇 |
2012年 | 3305篇 |
2011年 | 3744篇 |
2010年 | 3000篇 |
2009年 | 4412篇 |
2008年 | 4621篇 |
2007年 | 5058篇 |
2006年 | 4230篇 |
2005年 | 3478篇 |
2004年 | 2905篇 |
2003年 | 3182篇 |
2002年 | 3497篇 |
2001年 | 2664篇 |
2000年 | 2558篇 |
1999年 | 2154篇 |
1998年 | 2076篇 |
1997年 | 1307篇 |
1996年 | 1149篇 |
1995年 | 1001篇 |
1994年 | 1026篇 |
1993年 | 810篇 |
1992年 | 870篇 |
1991年 | 618篇 |
1990年 | 589篇 |
1989年 | 498篇 |
1988年 | 452篇 |
1987年 | 437篇 |
1986年 | 390篇 |
1985年 | 372篇 |
1984年 | 375篇 |
1983年 | 216篇 |
1982年 | 294篇 |
1981年 | 292篇 |
1980年 | 221篇 |
1979年 | 246篇 |
1978年 | 209篇 |
1977年 | 193篇 |
1976年 | 143篇 |
1973年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
101.
According to an induced-matter approach, Liu and Wesson obtained the rest mass of a typical particle from the reduction of a 5D Klein–Gordon equation to a 4D one. Introducing an extra-dimension momentum operator identified with the rest mass eigenvalue operator, we consider a way to generalize the 4D Dirac equation to 5D. An analogous normal Dirac equation is gained when the generalization reduces to 4D. We find the rest mass of a particle in curved space varies with spacetime coordinates and check this for the case of exact solitonic and cosmological solution of the 5D vacuum gravitational field equations. 相似文献
102.
103.
本文利用聚集型状态方程,克拉贝龙方程以及临界条件推出聚集活性参量方程.分析结果表明,医药的药理活性是可以用聚集活性参量予以定量表征.本文给出了某些医药的主要的药物成分,如氧化亚氮 乙醚、氯仿和水杨酸甲酯等嘛醉剂),一氧化氮(硝酸甘油)、乙醇胺(医药活性剂)和多巴胺(神经递质)的生物活性数据.实践经验表明,这些化学品分别在生命体的心血管系统、神经系统和免疫系统中起着重要的药理功能作用.这表明,本文研究的内容在医药学研究领域有其重要意义. 相似文献
104.
A Dirac picture perturbation theory is developed for the time evolution operator in classical dynamics in the spirit of the Schwinger–Feynman–Dyson perturbation expansion and detailed rules are derived for computations. Complexification formalisms are given for the time evolution operator suitable for phase space analyses, and then extended to a two-dimensional setting for a study of the geometrical Berry phase as an example. Finally a direct integration of Hamilton's equations is shown to lead naturally to a path integral expression, as a resolution of the identity, as applied to arbitrary functions of generalized coordinates and momenta. 相似文献
105.
F. S. de Aguiar L. B. Bernardes S. Goulart Rosa Jr. 《Journal of statistical physics》1991,64(3-4):673-682
Metastability in the ferromagneticp-state Potts model defined on the Cayley tree is discussed. It is shown that the sign of the boundary fieldH
s
determines the order of the transition as well as the stability of the low-temperature phase. Lowering the temperature withH
s
>0, a system withp<2 (p>2) will display a second (first)-order transition to a metastable (stable) phase. ForH
s
>0 a second (first)-order transition to a metastable (stable) phase occurs ifp>2 (p<2). In this case the system also has a residual entropy which is negative forp<2. 相似文献
106.
测试了Bi2O3-B2O3-SiO2玻璃中的Er3+离子的吸收光谱、发射光谱、4I13/2的荧光寿命、拉曼光谱,及OH-的傅里叶红外吸收光谱。应用Judd-Ofelt理论计算了该玻璃中的Er3+离子的J-O参数、振子强度、4I13/2能级的寿命,从而利用测得的4I13/2的荧光寿命得出了4I13/2能级的量子效率(15%)。由于较低量子效率可能与OH-有关,所以计算了玻璃中的OH-浓度,发现其浓度较高(1.66×1019cm-1,相当于Er3+浓度的3倍)。应用McCumber理论和四能级模型计算了Er3+离子的受激发射截面和荧光发射光谱的半峰全宽,结果与通过吸收光谱计算所得基本吻合。根据透射率和折射率的关系计算了折射率,发现和测量值相差很大,说明有较大的散射,通过拉曼光谱和显微镜测试,认为是玻璃中的微小气泡造成的。 相似文献
107.
108.
The spin-1 Ising model, which is equivalent to the three-component lattice gas model, is used to study wetting transitions in three-component surfactant systems consisting of an oil, water, and a nonionic surfactant. Phase equilibria, interfacial profiles, and interfacial tensions for three-phase equilibrium are determined in mean field approximation, for a wide range of temperature and interaction parameters. Surfactant interaction parameters are found to strongly influence interfacial tensions, reducing them in some cases to ultralow values. Interfacial tensions are used to determine whether the middle phase, rich in surfactant, wets or does not wet the interface between the oil-rich and water-rich phases. By varying temperature and interaction parameters, a wetting transition is located and found to be of the first order. Comparison is made with recent experimental results on wetting transitions in ternary surfactant systems.This paper is dedicated to J. K. Percus in honor of his 65th birthday. 相似文献
109.
C Premkumar Yesudian 《Pramana》1989,33(6):651-657
An extended technicolour grand unification model based on the gauge groupE
6×SU(7) extended technicolour is presented. The symmetry-breaking based on extended technicolour theory is discussed. It is
shown that the existing phenomenology is well explained by the model. The strangeness changing neutral currents may not be
a problem with this model. 相似文献
110.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献