全文获取类型
收费全文 | 10027篇 |
免费 | 2556篇 |
国内免费 | 1098篇 |
专业分类
化学 | 2932篇 |
晶体学 | 178篇 |
力学 | 1664篇 |
综合类 | 91篇 |
数学 | 1132篇 |
物理学 | 7684篇 |
出版年
2024年 | 22篇 |
2023年 | 119篇 |
2022年 | 257篇 |
2021年 | 231篇 |
2020年 | 369篇 |
2019年 | 302篇 |
2018年 | 272篇 |
2017年 | 329篇 |
2016年 | 439篇 |
2015年 | 397篇 |
2014年 | 678篇 |
2013年 | 743篇 |
2012年 | 630篇 |
2011年 | 819篇 |
2010年 | 619篇 |
2009年 | 752篇 |
2008年 | 777篇 |
2007年 | 727篇 |
2006年 | 733篇 |
2005年 | 549篇 |
2004年 | 556篇 |
2003年 | 420篇 |
2002年 | 413篇 |
2001年 | 399篇 |
2000年 | 338篇 |
1999年 | 269篇 |
1998年 | 269篇 |
1997年 | 213篇 |
1996年 | 167篇 |
1995年 | 158篇 |
1994年 | 116篇 |
1993年 | 106篇 |
1992年 | 100篇 |
1991年 | 66篇 |
1990年 | 63篇 |
1989年 | 55篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Corrosion-related defects of pure iron were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation and positron annihilation lifetime (PAL). Defect profiles of the S-parameter from DBES as a function of positron incident energy up to 30 keV (i.e. ∼1 μm depth) were analyzed. The DBES data show that S-parameter increases as a function of positron incident energy (mean depth) after corrosion, and the increase in the S-parameter is larger near the surface than in the bulk due to corrosion. Furthermore, information on defect size from PAL data as a function of positron incident energy up to 10 keV (i.e. ∼0.2 μm depth) was analyzed. In the two-state trapping model, the lifetime τ2 = 500 ps is ascribed to annihilation of positrons in voids with a size of the order of nanometer. τ1, which decreases with depth from the surface to the bulk, is ascribed to the annihilation of positrons in dislocations and three-dimensional vacancy clusters. The corroded samples show a significant increase in τ1 and the intensity I2, and near the surface the corroded iron introduces both voids and large-size three-dimensional vacancy clusters. The size of vacancy clusters decreases with depth. 相似文献
122.
Surface reconstructions of InGaAs alloys 总被引:1,自引:0,他引:1
The surface reconstructions of InxGa1−xAs alloys grown by molecular beam epitaxy on the (0 0 1) surfaces of GaAs and InAs have been studied by reflection high-energy electron diffraction and scanning tunnelling microscopy. A surface phase diagram is presented for the nominally strain-free alloy as a function of substrate temperature and alloy composition, and structural models for the commonly observed 3× reconstructions are discussed. Two new, electronically stable structural models are described that account for the transition of the InxGa1−xAs surface alloy from a c(4 × 4) to an asymmetric 3× reconstruction and that are fully consistent with all current experimental evidence. 相似文献
123.
通过求解BogoliubovedeGennes(BdG)方程,利用推广的BlonderTinkhamKlapwijk(BTK)理论,计算铁磁绝缘层铁磁d波超导结中的微分电导、平均电流和散粒噪声功率.研究表明,系统的微分电导和散粒噪声与平均电流的比值都随中间铁磁层厚度作周期性振荡,振荡的幅度随绝缘层势垒增高而变大,随铁磁层中磁交换劈裂的增强而变小.
关键词:
微分电导 散粒噪声 磁交换劈裂 相似文献
124.
A. Pompei 《Applied Acoustics》2006,67(5):420-431
In the present paper, we simulate focused wave fields generated by a system of plane transducers used in an immersion ultrasonic technique. The ultrasonic beam penetrates into the elastic medium through the fluid-solid boundary. A real-time computer algorithm is proposed to calculate stress components in the solid medium. It is shown that a good focusing wave structure can be provided by a pair of plane rectangular transducers, inclined with respect to each other and to the beam acoustic axis. 相似文献
125.
126.
127.
Based on scalar diffraction theory, 8-phase-level 256×256 elements diffractive microlens array with element dimension of 50×33 μm2 have been fabricated on the back-side of PtSi(3~5 μm) infrared CCD. The measurement results indicated that the ratio of the signal-to-noise of the infrared CCD with microlens was increased by a factor of 2.8. 相似文献
128.
129.
130.