全文获取类型
收费全文 | 14580篇 |
免费 | 2366篇 |
国内免费 | 2378篇 |
专业分类
化学 | 11246篇 |
晶体学 | 192篇 |
力学 | 754篇 |
综合类 | 230篇 |
数学 | 1831篇 |
物理学 | 5071篇 |
出版年
2024年 | 16篇 |
2023年 | 200篇 |
2022年 | 318篇 |
2021年 | 388篇 |
2020年 | 442篇 |
2019年 | 503篇 |
2018年 | 394篇 |
2017年 | 375篇 |
2016年 | 594篇 |
2015年 | 651篇 |
2014年 | 776篇 |
2013年 | 1014篇 |
2012年 | 1192篇 |
2011年 | 1335篇 |
2010年 | 1073篇 |
2009年 | 1040篇 |
2008年 | 1189篇 |
2007年 | 1136篇 |
2006年 | 1065篇 |
2005年 | 846篇 |
2004年 | 726篇 |
2003年 | 657篇 |
2002年 | 614篇 |
2001年 | 483篇 |
2000年 | 368篇 |
1999年 | 323篇 |
1998年 | 260篇 |
1997年 | 201篇 |
1996年 | 198篇 |
1995年 | 167篇 |
1994年 | 134篇 |
1993年 | 100篇 |
1992年 | 99篇 |
1991年 | 83篇 |
1990年 | 66篇 |
1989年 | 42篇 |
1988年 | 45篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
超子中子星性质的温度效应 总被引:2,自引:0,他引:2
从相对论平均场理论出发,考虑核子、超子和介子的相互作用,研究了温度对中子星组成粒子、状态方程和中子星质量等的影响.发现温度越高,超子在中子星内部出现时的重子数密度越低.当密度较高时,中子星的核心区主要由超子组成,即中子星转变成以奇异粒子为主要成分的超子星,并且这种转变受到温度的影响,温度越高,转变密度越低.由于超子的出现,中子星核心高密度区域的状态方程,对于不同温度,差别不大,所以有限温度中子星的最大质量都在1.8M⊙附近.这与观测结果相符. 相似文献
72.
本文得到关于全纯扩充的BHW定理的一个全新的证明,同时也对BHW定 理做出了更一般的推广,并且给出了推广后的BHW定理的两种不同的证明方法. 相似文献
73.
74.
Wei Jun Liao Xianfeng Chen Fucheng Chen Yuping Chen Yuxing Xia Yingli Chen 《Optics & Laser Technology》2004,36(8):603-606
In this paper, we first report that a new proton source, glutaric acid, has been used to fabricate optical waveguides in Z-cut lithium niobate crystals. The relationship was experimentally established between proton-exchanged (PE) waveguide parameters and fabrication conditions. It is shown that this new organic acid can be used to obtain deep PE waveguides in fast diffusion speed (0.275 μm2/h at 221°C) and with low loss (0.2 dB/cm). It provides an alternative approach for fabricating PE waveguides in lithium niobate substrate. 相似文献
75.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
76.
77.
在超高真空分子束外延(MBE)生长技术中,反射式高能电子衍射仪(RHEED)能实时显示半导体和金属外延生长过程,给出薄膜表面结构和平整度的信息,成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导(YBa2Cu3O7) 、铁电薄膜(Sr1-xBax TiO3)及它们的同质和异质外延结构的生长机理,获得高质量的符合各种应用 需要的氧化 物多层薄膜结构,在常规的制备氧化
关键词:
高温超导薄膜
RHEED 相似文献
78.
A novel Y-branch waveguide with two reflectors is proposed. The normalized transmitted power for the branching angle of 50°is greater than 70%, which is higher than conventional Y-branch with such wide angle. 相似文献
79.
Tm3+/Yb3+-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G4→3H6 and 1G4→3H4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency. 相似文献
80.
Properties of excitons in vertically coupled GaAs/AlGaAs quantum dots were investigated using the variational method within the envelope function and effective mass approximations. It was found that when the thickness of the spacer layer becomes less than about one exciton Bohr radius, both the exciton binding energy and the fundamental optical transition energy are reduced compared to those in isolated quantum dots. This is a result of increased space extension of exciton due to the penetration of carrier wave functions into the spacer layer and corresponding reduction in confinement energy which dominates over the Coulomb interaction between the electron and the hole. 相似文献