全文获取类型
收费全文 | 12229篇 |
免费 | 1962篇 |
国内免费 | 1096篇 |
专业分类
化学 | 8816篇 |
晶体学 | 478篇 |
力学 | 1414篇 |
综合类 | 51篇 |
数学 | 301篇 |
物理学 | 4227篇 |
出版年
2024年 | 38篇 |
2023年 | 155篇 |
2022年 | 329篇 |
2021年 | 418篇 |
2020年 | 709篇 |
2019年 | 479篇 |
2018年 | 425篇 |
2017年 | 451篇 |
2016年 | 711篇 |
2015年 | 702篇 |
2014年 | 748篇 |
2013年 | 966篇 |
2012年 | 666篇 |
2011年 | 835篇 |
2010年 | 732篇 |
2009年 | 741篇 |
2008年 | 809篇 |
2007年 | 826篇 |
2006年 | 728篇 |
2005年 | 580篇 |
2004年 | 574篇 |
2003年 | 573篇 |
2002年 | 386篇 |
2001年 | 328篇 |
2000年 | 259篇 |
1999年 | 193篇 |
1998年 | 170篇 |
1997年 | 120篇 |
1996年 | 115篇 |
1995年 | 70篇 |
1994年 | 75篇 |
1993年 | 56篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 31篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1971年 | 6篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
应用深能级瞬态谱(DLTS)技术研究分子束外延(MBE)生长的highelectronmobilitytransistors(HEMT)和Pseudomorphichighelectronmobilitytransistors(PHEMT)结构深中心行为.样品的DLTS谱表明,在HEMT和PHEMT结构的nAlGaAs层里存在着较大浓度(1015-1017cm-3)和俘获截面(10-16cm2)的近禁带中部电子陷阱.它们可能与AlGaAs层的氧含量有关.同时还观察到PHEMT结构晶格不匹配的AlGaAsInGaAsGaAs系统在AlGaAs里产生的应力引起DX中心(与硅有关)能级位置的有序移动.其移动量可作为应力大小的一个判据,表明DLTS技术是定性识别此应力的可靠和简便的工具.
关键词:
分子束外延生长
高电子迁移率超高速微结构功能材料
深中心 相似文献
82.
83.
84.
A. Konjhodzic A. Adamczyk F. Vagizov Z. Hasan E E. Alp W. Sturhahn Jiyong Zhao J J. Carroll 《Hyperfine Interactions》2006,170(1-3):83-89
With the decrease in size of devices, rapid characterization of nano-devices is an inevitable necessity. It is shown that Mössbauer spectroscopy using synchrotron radiation from the advanced photon source provides such a tool of investigation. Results are presented and compared for conventional Mössbauer and Nuclear Forward Scattering for 151Eu-doped magnesium sulfide as an example, especially at low concentrations. 相似文献
85.
Leszek Wachowski Antoni Grodzicki Piotr Piszczek Monika Richert Magdalena Hofman 《Reaction Kinetics and Catalysis Letters》2007,91(1):93-99
Hydrogenation of styrene has been applied as a test reaction to study the catalytic activity of TiO2 deposited by the CVD (chemical vapour deposition) method on the surface of a carbonaceous material enriched in nitrogen (CN). 相似文献
86.
87.
Jin Kyu Park Dong Hun Lee Bok Ju Song Jae Buem Oh Hwan Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1326-1342
We have designed and synthesized novel perfluorinated polyimides with 3D controlled structure. At first, we successfully developed the new synthetic routes to diamines with pendant bulky perfluorinated aromatic units in a multi‐step synthetic procedure. Novel perfluorinated polyimides were prepared in a two‐step reaction in N‐methyl‐2‐pyrrolidinone (NMP) solution: The first step was for the synthesis of polyamic acids (PAAs) and the second reaction was for the imidization of PAA. The polymer yield was over 89% and the inherent viscosity of PAAs was in the range of 0.24–0.36 dL/g. The thin films were prepared by spin‐coating the PAA solution in NMP onto various substrates such as a Si wafer or a KBr pellet, dried at 80 °C and further cured at 230 °C. The resultant polyimides are thermally stable over 400 °C. The refractive index and birefringence of the resultant polyimides are 1.5858–1.6452 and 0.01–0.005, respectively. The refractive index of polyimide decreases with increasing the fluorine content. The copolymerization and the ether linkages into the backbone reduce the birefringence of polyimides. Surprisingly, the pendant ether linkage is not a crucial factor in reducing the polyimide birefringence. Their birefringence is comparatively very low, compared with that of previous polyimides. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1326–1342, 2006 相似文献
88.
Summary Equilibrium equations and stability conditions for the simple deformable elastic body are derived by means of considering
a minimum of the static energy principle. The energy is supposed to be sum of the volume (elastic) and the surface terms.
The ability to change relative positions of different material particles is taken into account, and appropriate natural definitions
of the first and second variations of the energy are introduced and calculated explicitly. Considering the case of negligible
magnitude of the surface tension, we establish that an equilibrium state of a nonhydrostatically stressed simple elastic body
(of any physically reasonable elastic energy potential and of any symmetry) possessing any small smooth part of free surface
is always unstable with respect to relative transfer of the material particles along the surface. Surface tension suppresses
the mentioned instability with respect to sufficiently short disturbances of the boundary surface and thus can probably provide
local smoothness of the equilibrium shape of the crystal. We derive explicit formulas for critical wavelength for the simplest
models of the internal and surface energies and for the simplest equilibrium configurations. We also formulate the simplest
problem of mathematical physics, revealing peculiarities and difficulties of the problem of equilibrium shape of elastic crystals,
and discuss possible manifestations of the above-mentioned instability in the problems of crystal growth, materials science,
fracture, physical chemistry, and low-temperature physics. 相似文献
89.
90.
纳秒级激光闪光光解装置可用于有机光化学、光物理过程,瞬态发光和吸收的动力学过程的研究,在不改变原装置整体布局和结构的基础上,建立了有机非线性光学材料的二阶非线性系数测定方法,并为国家863专家委员会承担过仲裁测定。 相似文献