全文获取类型
收费全文 | 4552篇 |
免费 | 3498篇 |
国内免费 | 3697篇 |
专业分类
化学 | 3493篇 |
晶体学 | 261篇 |
力学 | 102篇 |
综合类 | 154篇 |
数学 | 198篇 |
物理学 | 7539篇 |
出版年
2024年 | 69篇 |
2023年 | 194篇 |
2022年 | 250篇 |
2021年 | 218篇 |
2020年 | 181篇 |
2019年 | 189篇 |
2018年 | 195篇 |
2017年 | 214篇 |
2016年 | 263篇 |
2015年 | 289篇 |
2014年 | 595篇 |
2013年 | 543篇 |
2012年 | 513篇 |
2011年 | 594篇 |
2010年 | 566篇 |
2009年 | 526篇 |
2008年 | 636篇 |
2007年 | 523篇 |
2006年 | 509篇 |
2005年 | 506篇 |
2004年 | 477篇 |
2003年 | 430篇 |
2002年 | 353篇 |
2001年 | 372篇 |
2000年 | 314篇 |
1999年 | 222篇 |
1998年 | 240篇 |
1997年 | 217篇 |
1996年 | 184篇 |
1995年 | 199篇 |
1994年 | 206篇 |
1993年 | 177篇 |
1992年 | 184篇 |
1991年 | 157篇 |
1990年 | 160篇 |
1989年 | 141篇 |
1988年 | 25篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We have measured lifetimes of △n=0 allowed transitions in beryllium-like sulfur using beam foil spectroscopic techniques. The measured values, derived from analysis of arbitrarily normalized decay curves, are presented and compared with theoretical calculations and previous measurements. Accurate probabilities have been determined by the well-known relationship. 相似文献
22.
By using the measure of von Neumann entropy, we numerically investigate quantum entanglement of an electron moving in the one-dimensional Harper model and in the one-dimensional slowly varying potential model. The delocalized and localized eigenstates can be distinguished by von Neumann entropy of the individual eigenstates.There are drastic decreases in von Neumann entropy of the individual eigenstates at mobility edges. In the curve of the spectrum averaged von Neumann entropy as a function of potential parameter λ, a sharp transition exists at the metal-insulator transition point λc = 2. It is found that the von Neumann entropy is a good quantity to reflect localization and metal-insulator transition. 相似文献
23.
24.
Due to the inherent symmetry structures and the electric properties in the microtubule (MT), we treat the MT as a one-dimensional ferroelectric system and describe the nonlinear dynamics of dimer electric dipoles in one protofilament of the MT by virtue of the double-well potential. Consequently, the physical problem has been mapped onto the pseudo-spin system, and the mean-field approximation has been taken to obtain some physical results, including the expression for the phase transition temperature Tc and the estimated value of Tc (=312 K). 相似文献
25.
富勒烯 (C60 /C70 )与N ,N ,N′ ,N′ 四 (对甲苯基 ) 4,4′ 二胺 1,1′ 二苯硒醚 (TPDASe)间在激光光诱导条件下 ,发生了分子间的电子转移过程 .在可见 -近红外区 ( 60 0~ 12 0 0nm) ,观测到了TPDASe阳离子自由基、富勒烯 (C60 /C70 )激发三线态和阴离子自由基 ,在苯腈溶液中 ,观测瞬态谱测定了电子从TPDASe转移到富勒烯 (C60 /C70 )激发三线态的量子转化产率(ΦTet)和电子转移常数 (Ket) . 相似文献
26.
27.
28.
We analyse the influence of properties of organic/organic interface (OOI) on the characteristics of recombination efficiency of organic double-layer light-emitting diodes. Based on the disordered hopping theory model, spatial and energetic disorder of hopping states are also discussed for the case of space charge limited currents in hole transmitting layers but injection-limited currents in electron transporting layers. The results show that the recombination efficiency increases firstly and then decreases for different OOI parameters, and there is a maximum value changed with different spatial disorder parameters and energetic disorder scale. Different spatial disorder parameters make carrier mobilities change greatly, and the energetic disorder scale causes various localized state densities. Our calculated results are qualitatively in agreement with the experimental data. 相似文献
29.
制作了掺杂rubrene和4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9,enyl)-4H-pyran(DCJTB)两种荧光染料的红光有机电致发光器件。N,N’-diphenyl-N,N’-bis(1-naphthyl)-(1,1’-biphenyl)-4,4’-diamine(NPB)和掺杂的Tri-(8-hydroxyquinoline)aluminum(Alq3)分别作为空穴和电子传输层。我们发现掺rubrene和DCJTB的器件性能与只掺DCJTB的器件性能相比有所提高。器件性能的改善是因为掺入的rubrene能够促进从Alq3到DCJTB的能量转移。根据荧光衰减曲线,计算出从Alq3到DCJTB、从Alq3到rubrene以及从rubrene到DCJTB的能量转移速率分别为1.04×109,3.89×109,2.79×109s-1。可以看出能量通过rubrene从Alq3到DCJTB的转移速率是能量直接从Alq3到DCJTB的2.7倍。 相似文献
30.
We investigate the potential profiles and elemental distribution of barriers in Co/ZrAlOx/Co magnetic tunnel junctions (MTJs) using electron holography (EH) and scanning transmission electron microscopy. The MTJ barriers are introduced by oxidizing a bilayer consisting with a uniform 0.45-nm Al layer and a wedge-shaped Zr layer (0-2 nm). From the scanning transmission electron microscopy, AlOx and ZrOx layers are mixed together, indicating that compact AlOx layer cannot be formed in such a bilayer structure of barriers. The Eli results reveal that there are no sharp interfaces between the barrier and magnetic electrodes, which may be responsible for a smaller tunnelling magnetoresistance compared with the MTJs of Co/AlOx/Co. 相似文献