全文获取类型
收费全文 | 24175篇 |
免费 | 4726篇 |
国内免费 | 3485篇 |
专业分类
化学 | 14526篇 |
晶体学 | 630篇 |
力学 | 2698篇 |
综合类 | 289篇 |
数学 | 2222篇 |
物理学 | 12021篇 |
出版年
2024年 | 21篇 |
2023年 | 241篇 |
2022年 | 535篇 |
2021年 | 692篇 |
2020年 | 847篇 |
2019年 | 749篇 |
2018年 | 787篇 |
2017年 | 968篇 |
2016年 | 1209篇 |
2015年 | 995篇 |
2014年 | 1406篇 |
2013年 | 2405篇 |
2012年 | 1700篇 |
2011年 | 1617篇 |
2010年 | 1409篇 |
2009年 | 1522篇 |
2008年 | 1534篇 |
2007年 | 1644篇 |
2006年 | 1452篇 |
2005年 | 1301篇 |
2004年 | 1188篇 |
2003年 | 1077篇 |
2002年 | 876篇 |
2001年 | 794篇 |
2000年 | 793篇 |
1999年 | 688篇 |
1998年 | 611篇 |
1997年 | 467篇 |
1996年 | 396篇 |
1995年 | 375篇 |
1994年 | 345篇 |
1993年 | 308篇 |
1992年 | 261篇 |
1991年 | 166篇 |
1990年 | 142篇 |
1989年 | 135篇 |
1988年 | 150篇 |
1987年 | 94篇 |
1986年 | 87篇 |
1985年 | 65篇 |
1984年 | 54篇 |
1983年 | 24篇 |
1982年 | 58篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 36篇 |
1978年 | 28篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
31.
32.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
33.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
34.
理想气体在热力学中的作用 总被引:1,自引:1,他引:0
指出热力学理论是普遍的,不依赖于理想气体.理想气体为热力学理论提供了一个简单的实例,为测量热力学温度提供了一种简单的温度计. 相似文献
35.
利用再沉淀法分别制备出了小尺寸(~10nm)纯相和杂相的Eu3+配合物荧光纳米颗粒。所制备的纯相的荧光纳米颗粒在水溶液中容易聚集,并且荧光猝灭严重。相比较而言,掺有适量疏水性硅烷的杂相纳米颗粒则具有较强的荧光、均匀的尺寸和良好的分散性。硅烷在碱性环境下(pH=9)迅速地水解,而后在纳米微粒的表面形成二氧化硅薄层。亲水的二氧化硅薄层消除了Eu3+配合物纳米颗粒间的疏水相互作用,进而防止了纳米颗粒的聚集,从而导致了杂相荧光纳米颗粒发光性能的提高。 相似文献
36.
从点电荷的电势计算公式出发推导出了瓣形均匀带电面在其直径处的电势分布.进一步讨论了均匀带电半球面在其底面以及均匀带电球面内部和外部的电势分布. 相似文献
37.
38.
C M Srivastava 《Pramana》1989,32(3):251-267
A theory of high temperature superconductivity in YBa2Cu3O7_δ compound has been developed on the basis of the momentum pairing of electrons through the relativistic Darwin interaction.
The transport behaviour of electrons is explained in terms of a mechanism of correlated electron transfer arising from the
electron-phonon coupling. A model Hamiltonian has been developed to describe the superconducting properties of the system.
This gives an energy gap which is higher than the BCS value. Attempts have been made to explain the absence of isotope effect,
the linear dependence of specific heat, the presence of larger temperature-independent paramagnetism in the normal phase and
the softening of some of the optic phonon modes observed in this system. 相似文献
39.
对红外热像仪参数双黑体测量装置的工作原理进行了介绍。装置采用双黑体及反射型靶标为温差辐射源,可实现黑体温度温差准直辐射的定期校准和红外热像仪参数测量量值的溯源,也可实现红外热像仪参数的可控性,以及对它进行稳定的、可复现的精确测量。推导出利用红外热像仪参数双黑体测量装置测量信号传递函数SiTF数学模型,分析了红外热像仪参数测量装置的客观因素——仪器常数,针对仪器常数对SiTF测量的影响进行了试验。试验结果表明,仪器常数对红外热像仪SiTF参数测量精度影响较大,并同时影响时域与空域NETD及3D噪声的准确测量。 相似文献
40.
Th. Seyller K.V. Emtsev F. Speck A. Tadich J.D. Riley O. Rader A.M. Shikin 《Surface science》2006,600(18):3906-3911
Photoelectron spectroscopy, low-energy electron diffraction, and scanning probe microscopy were used to investigate the electronic and structural properties of graphite layers grown by solid state graphitization of SiC(0 0 0 1) surfaces. The process leads to well-ordered graphite layers which are rotated against the substrate lattice by 30°. On on-axis 6H-SiC(0 0 0 1) substrates we observe graphitic layers with up to several 100 nm wide terraces. ARUPS spectra of the graphite layers grown on on-axis 6H-SiC(0 0 0 1) surfaces are indicative of a well-developed band structure. For the graphite/n-type 6H-SiC(0 0 0 1) layer system we observe a Schottky barrier height of ?B,n = 0.3 ± 0.1 eV. ARUPS spectra of graphite layers grown on 8° off-axis oriented 4H-SiC(0 0 0 1) show unique replicas which are explained by a carpet-like growth mode combined with a step bunching of the substrate. 相似文献