全文获取类型
收费全文 | 19447篇 |
免费 | 2045篇 |
国内免费 | 2015篇 |
专业分类
化学 | 8999篇 |
晶体学 | 171篇 |
力学 | 639篇 |
综合类 | 180篇 |
数学 | 1285篇 |
物理学 | 3874篇 |
综合类 | 8359篇 |
出版年
2024年 | 61篇 |
2023年 | 285篇 |
2022年 | 518篇 |
2021年 | 505篇 |
2020年 | 579篇 |
2019年 | 483篇 |
2018年 | 431篇 |
2017年 | 421篇 |
2016年 | 665篇 |
2015年 | 737篇 |
2014年 | 1035篇 |
2013年 | 1159篇 |
2012年 | 1381篇 |
2011年 | 1414篇 |
2010年 | 1217篇 |
2009年 | 1216篇 |
2008年 | 1368篇 |
2007年 | 1363篇 |
2006年 | 1272篇 |
2005年 | 981篇 |
2004年 | 804篇 |
2003年 | 661篇 |
2002年 | 713篇 |
2001年 | 593篇 |
2000年 | 504篇 |
1999年 | 468篇 |
1998年 | 382篇 |
1997年 | 344篇 |
1996年 | 308篇 |
1995年 | 273篇 |
1994年 | 231篇 |
1993年 | 203篇 |
1992年 | 186篇 |
1991年 | 163篇 |
1990年 | 151篇 |
1989年 | 113篇 |
1988年 | 82篇 |
1987年 | 59篇 |
1986年 | 41篇 |
1985年 | 36篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1969年 | 6篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The strategy of expert system for high performance liquid chromatography was discussed, the attentions are mainly placed on the knowledge base for selection of column system, separation modes and detection modes in the analysis of amino acids, peptides and proteins. 相似文献
72.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献
73.
邹仁鋆 《河北省科学院学报》1986,(1)
In this paper, the author analyzes distinguishing features of complex reaction systems and single reversible reaction, and optimizes complex reaction systems starting from set theory.The method of constructing the optimal reactions assemblage and calculating the potential maximum equilibrium yield (PMEY) of objective products is proposed here. This paper points out clearly that the euqilibrium yield of objective products calculated by means of conventional method is the global equilibrium yield (GEY).It is not the thermodynamic constraint, and could be exceeded by observed yield of objective products; only PMEY is the thermodynamic constraint. It gives information on potential and possible optimal yield and thereby improving production. This paper also points out the way in which the real complex reaction system approached the optimal reactions assemblage. The new concept of PMEY and optimal reaction assemblage proposed by this Paper is universally applicable for the important complex reaction systems, such as the pyrolysis of alkane to produce ethylene, steam reforming of methane to produce syngas, production of formaldehyde from methanol, epoxidation of ethylene to produce ethylene oxide, hydrogenation of benzene to produce cyclohexane. 相似文献
74.
建立了一种可积的无穷维系统——时延范德波尔电磁系统,采用Poincaré映射分析了系统随参数E和λ变化发生的分岔与混沌现象,发现这种时延系统具有复杂的非线性动力学特性,例如吸引子共存、间歇性混沌、类似边界碰撞分岔通向混沌以及周期增加的现象.在研究系统时间混沌行为的同时,还对空间混沌行为进行了初步分析,通过描绘空间分布图发现时延范德波尔电磁系统随参数E和λ变化时,在空间中会呈现出周期和混沌等不同的图案.
关键词:
分岔
混沌
无穷维系统
时延范德波尔电磁系统 相似文献
75.
76.
77.
J. Jiang B.Y. Jiang C.X. Ren F.M. Zhang T. Feng X. Wang X.H. Liu S.C. Zou 《Applied Surface Science》2006,252(10):3642-3646
Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO3 compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested. 相似文献
78.
采用从头算CCSD(T)/6-311 G(2d,2p)//B3LYP/6-311G(d,p)方法,研究了自由基-分子反应F CH2CHCH3的各种不同的反应通道.该反应主要是通过复合物形成机制进行,即F分别加到碳碳双键的两端形成自由基复合物1和2.这两种亚稳态自由基会解离成三种产物:H C3H5F、CH3 C2H3F和HF C3H5.理论计算结果表明,生成CH3 C2H3F是反应的主要通道,而生成H C3H5F和HF C3H5对产物也有一定的贡献.这一结果和实验符合得很好. 相似文献
79.
80.
用密度泛函B3LYP/6-311++G(d,p)方法和相对论有效实势(Lanl2dz基组)对VOn±(n=0,1,2)分子离子的势能函数及光谱常数进行了分析. 结果表明它们都能稳定存在, 其基态电子状态分别是:4Σ(VO2-), 3Σ(VO-), 4Σ(VO), 3Σ(VO+)和2Σ(VO2+). 其中VO2-和VO2+的势能函数曲线呈“火山口”型, 属于亚稳态分子离子. 用七参数Murell-Sorbie势拟合VO2-和VO2+分子亚稳态双原子分子离子势能函数, 发现其拟合曲线与势能函数曲线符合得很好. 同时,讨论了电荷对势能函数和能级的影响.
关键词:
分子离子
密度泛函理论
势能函数
能级 相似文献