全文获取类型
收费全文 | 8824篇 |
免费 | 1846篇 |
国内免费 | 908篇 |
专业分类
化学 | 2578篇 |
晶体学 | 135篇 |
力学 | 1109篇 |
综合类 | 55篇 |
数学 | 374篇 |
物理学 | 7327篇 |
出版年
2024年 | 14篇 |
2023年 | 121篇 |
2022年 | 136篇 |
2021年 | 141篇 |
2020年 | 198篇 |
2019年 | 178篇 |
2018年 | 186篇 |
2017年 | 226篇 |
2016年 | 281篇 |
2015年 | 257篇 |
2014年 | 498篇 |
2013年 | 566篇 |
2012年 | 461篇 |
2011年 | 733篇 |
2010年 | 550篇 |
2009年 | 686篇 |
2008年 | 689篇 |
2007年 | 720篇 |
2006年 | 703篇 |
2005年 | 517篇 |
2004年 | 504篇 |
2003年 | 393篇 |
2002年 | 354篇 |
2001年 | 364篇 |
2000年 | 316篇 |
1999年 | 271篇 |
1998年 | 264篇 |
1997年 | 206篇 |
1996年 | 142篇 |
1995年 | 147篇 |
1994年 | 116篇 |
1993年 | 110篇 |
1992年 | 84篇 |
1991年 | 76篇 |
1990年 | 62篇 |
1989年 | 42篇 |
1988年 | 39篇 |
1987年 | 40篇 |
1986年 | 32篇 |
1985年 | 29篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
考虑液面波动和液体压缩时一侧受液作用悬臂梁的横振分析 总被引:2,自引:0,他引:2
本文分析一侧部分受有液体作用悬臂梁的横向自由振动,同时考虑了液面波动和液体可压缩性对悬臂梁自振特性的影响。利用一组广义三角级数的正交完备性,求得了悬臂梁与液体耦联振动的振型函数和频率方程的精确解析解,最后给出了几个数值算例。 相似文献
992.
闪光X射线机技术在中国工程物理研究院(下称CAEP)已有三十年的发展历史在爆轰物理学和y射线辐照效应研究中发挥了重要作用。本文总结了CAEP几种类型闪光X射线机的研制概况,阐述了高压脉冲技术、场发射技术、强流束聚焦等的研究进展,并介绍几种装置的主要技术参数。闪光X射线机是研究爆轰物理过程及其它高速瞬变过程的重要工具。国防科学技术研究中,大型闪光X射线机的研制具有很大的意义。文中对开拓强流电了束新的应用领域提出了展望。 相似文献
993.
Steps, ledges and kinks on the surfaces of platinum nanoparticles of different shapes 总被引:1,自引:0,他引:1
Platinum nanoparticles with a high percentage of cubic-, tetrahedral- and octahedral-like shapes, respectively, have been synthesized by a shape-controlling technique that we developed recently [Ahmadi et al., Science 272 (June 1996) 1924]. High resolution transmission electron microscopy (HRTEM) is used here to directly image the atomic scale structures of the surfaces of these particles with different shapes. The truncated shapes of these particles are mainly defined by the {100}, {111}, and {110} facets, on which numerous atom-high surface steps, ledges and kinds have been observed. This atomic-scale fine structure of the surfaces of these particles is expected to play a critical role in their catalytic activity and selectivity. 相似文献
994.
Andrzej Wolkenberg Tomasz Przes?awski Kazimierz Regiński 《Journal of Physics and Chemistry of Solids》2003,64(1):7-14
At low temperatures In0.53Ga0.47As samples show an increase of carrier concentration, which can be explained in terms of a two carriers transport model. This type of problem exists since the beginning of the semiconductor era, dating back to monocrystalline germanium.We propose that in all the investigated layers, there are X atoms or charged dislocations in the region of the first monolayers, which are built in during epitaxial growth. The layers were intentionally undoped. They form an impurity band in which low mobility carriers dominate over the localised electron scattering due to the s-d exchange interaction. These carriers do not freeze out at liquid helium temperature and give rise to two transport media for electrons; a conduction band at higher temperatures and an impurity band at lower temperatures. The electron which fall down onto the previously ionised X atoms, then move by thermally activated hopping. We show that the two carriers model for In0.53Ga0.47As epitaxial layers are confirmed by the carrier concentration-temperature, carrier concentration-magnetic field, resistivity-magnetic field behaviour, and also by YKA theory also. The differences between the two transport models are so distinctive that observed phenomena may exist. This paper presents experimental results, which constitute comprehensive evidence for the complicated structure of the semiconductor epitaxial layers on the sample of n-type In0.53Ga0.47As/InP layer with n=2.2×1015/cm3. 相似文献
995.
D. Onoufriou 《Surface science》2004,573(2):237-252
The evolution of N,N′-dimethylperylene-3,4,9,10-dicarboxyimide (Me-PTCDI) thin films formed by vapour deposition on InSb(1 1 1)A substrates has been studied by X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS) and low energy electron diffraction (LEED). XPS studies of the Me-PTCDI covered surface indicate that no significant interaction occurs at sub-monolayer coverage when compared to multilayer Me-PTCDI films. HREELS studies suggest only a weak interaction as evidenced by very small changes in the frequencies of several molecular vibrational modes. LEED patterns show the Me-PTCDI overlayer adopts a structure commensurate with the underlying InSb(1 1 1)A substrate surface and that can be rationalised by van der Waals intermolecular energy calculations for the Me-PTCDI unit cell. The results are consistent with a weak interaction at the Me-PTCDI/InSb interface, the formation of the commensurate structure being sufficient to overcome the small energetic penalty associated with deviation from the calculated intermolecular interaction energy minimum. 相似文献
996.
空心束虚阴极激励微波的主模式的研究 总被引:4,自引:3,他引:1
把虚阴极振荡激励微波的过程看成是一个时空振荡电流元激励微波的过程,在薄电荷层近似下,求得空心束虚阴极激励微波的主模式关系,并讨论了束几何位形与微波输出功率之间的关系。我们所确定的主模式与实验和粒子模拟的结果相符。 相似文献
997.
高斯光束在任意分布的径向梯度折射率介质中传输的计算方法 总被引:1,自引:0,他引:1
根据弱波导近似,本文建立了处理高斯光束在任意分布的径向梯度折射率介质中传输的计算方法,并具体计算和讨论了高斯光束腰斑在沿径向呈抛物型分布的介质中随传输距离的变化情况,其数值结果与解析近似符合。 相似文献
998.
999.
A population global optimization algorithm to solve the image alignment problem in electron crystallography 总被引:2,自引:0,他引:2
P. M. Ortigosa J. L. Redondo I. García J. J. Fernández 《Journal of Global Optimization》2007,37(4):527-539
Knowledge of the structure of biological specimens is critical to understanding their function. Electron crystallography is
an electron microscopy (EM) approach that derives the 3D structure of specimens at high-resolution, even at atomic detail.
Prior to the tomographic reconstruction, the images taken from the microscope have to be properly aligned. Traditional alignment
methods in electron crystallography are based on a phase residual function to be minimized by inefficient exhaustive search
procedures. This work addresses this minimization problem from an evolutionary perspective. Universal Evolutionary Global
Optimizer (UEGO), an evolutionary multimodal optimization algorithm, has been applied and evaluated for the task of image
alignment in this field. UEGO has turned out to be a promising technique alternative to the standard methodology. The alignments
found out by UEGO show high levels of accuracy, while reducing the number of function evaluations by a significant factor
with respect to the standard method. 相似文献
1000.