全文获取类型
收费全文 | 48884篇 |
免费 | 2473篇 |
国内免费 | 1896篇 |
专业分类
化学 | 27138篇 |
晶体学 | 835篇 |
力学 | 2360篇 |
综合类 | 129篇 |
数学 | 5171篇 |
物理学 | 17620篇 |
出版年
2022年 | 681篇 |
2021年 | 756篇 |
2020年 | 748篇 |
2019年 | 759篇 |
2018年 | 915篇 |
2017年 | 829篇 |
2016年 | 1249篇 |
2015年 | 979篇 |
2014年 | 1443篇 |
2013年 | 2488篇 |
2012年 | 2543篇 |
2011年 | 3029篇 |
2010年 | 2193篇 |
2009年 | 2213篇 |
2008年 | 2516篇 |
2007年 | 2362篇 |
2006年 | 2165篇 |
2005年 | 1781篇 |
2004年 | 1579篇 |
2003年 | 1345篇 |
2002年 | 1339篇 |
2001年 | 1680篇 |
2000年 | 1275篇 |
1999年 | 1061篇 |
1998年 | 802篇 |
1997年 | 750篇 |
1996年 | 707篇 |
1995年 | 635篇 |
1994年 | 543篇 |
1993年 | 492篇 |
1992年 | 547篇 |
1991年 | 547篇 |
1990年 | 525篇 |
1989年 | 487篇 |
1988年 | 483篇 |
1987年 | 468篇 |
1986年 | 410篇 |
1985年 | 464篇 |
1984年 | 488篇 |
1983年 | 364篇 |
1982年 | 400篇 |
1981年 | 384篇 |
1980年 | 322篇 |
1979年 | 404篇 |
1978年 | 380篇 |
1977年 | 395篇 |
1976年 | 392篇 |
1975年 | 343篇 |
1974年 | 325篇 |
1973年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The revival of the nondiffracting vortex beam after its interaction with the 2D on axis obstacle is examined. We show that the phase topology and the spatial distribution of the orbital angular momentum of the beam transmitted through the obstacle regenerate to the initial form during further free propagation. We verify that the healing effect appears even if the interaction is accompanied by the exchange of the orbital angular momentum. 相似文献
43.
44.
45.
以均苯三甲酸为配体,水热条件下合成了均苯三甲酸铕及铕镧系列发光配合物LaxEu1-x(BTC)·nH2O(x=0,0.1,0.3,0.5,0.7,0.9),通过元素分析及化学滴定法测定了配合物的组成。用红外光谱对其进行了表征,确定了该系列配合物的组成为LaxEu1-x(BTC)·nH2O。研究了系列配合物的荧光性质,荧光光谱表明:该类配合物均能发出强的铕离子的特征荧光,并且镧元素的掺入能增强铕配合物的发光强度,但发射峰的位置基本上没有变化;其中5D0→7F1和5D0→7F2的跃迁发射较强,且均劈裂为两个峰(587,593nm)和(611,618nm),这是由于铕离子所处的配位环境引起的。 相似文献
46.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献
47.
An experimental study of the aerodynamic damping of oscillating plates has been undertaken. Plates of various shapes were placed into an air flow normal to the plate and excited to oscillate parallel to the flow direction by electromagnetic forces of equal amplitudes and random frequencies. The aerodynamic damping of oscillating plates, evaluated in terms of a quality Q-factor from a frequency response resonance curve, was found to vary linearly with the absolute pressure in stationary surrounding air and with the air flow velocity in moving air. The flow velocity was also found to affect the aerodynamic damping more than the absolute pressure. A simple empirical model has been developed to predict the variation of the aerodynamic damping with the flow velocity. 相似文献
48.
High-temperature series expansions of the susceptibility and second moment to 15th order are calculated for zero external field on the linear chain (LC), plane square (PSQ), simple cubic (SC), and body-centered cubic (BCC) lattices. Checks for specific models against pertinent work in the literature are detailed. 相似文献
49.
50.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献