全文获取类型
收费全文 | 22430篇 |
免费 | 4593篇 |
国内免费 | 5771篇 |
专业分类
化学 | 16974篇 |
晶体学 | 714篇 |
力学 | 1492篇 |
综合类 | 628篇 |
数学 | 2496篇 |
物理学 | 10490篇 |
出版年
2024年 | 77篇 |
2023年 | 408篇 |
2022年 | 888篇 |
2021年 | 965篇 |
2020年 | 1000篇 |
2019年 | 996篇 |
2018年 | 854篇 |
2017年 | 1012篇 |
2016年 | 1067篇 |
2015年 | 1259篇 |
2014年 | 1554篇 |
2013年 | 1944篇 |
2012年 | 2111篇 |
2011年 | 2218篇 |
2010年 | 1777篇 |
2009年 | 1775篇 |
2008年 | 2022篇 |
2007年 | 1666篇 |
2006年 | 1549篇 |
2005年 | 1271篇 |
2004年 | 996篇 |
2003年 | 720篇 |
2002年 | 703篇 |
2001年 | 646篇 |
2000年 | 727篇 |
1999年 | 451篇 |
1998年 | 259篇 |
1997年 | 183篇 |
1996年 | 214篇 |
1995年 | 176篇 |
1994年 | 176篇 |
1993年 | 178篇 |
1992年 | 162篇 |
1991年 | 109篇 |
1990年 | 120篇 |
1989年 | 106篇 |
1988年 | 93篇 |
1987年 | 70篇 |
1986年 | 60篇 |
1985年 | 42篇 |
1984年 | 36篇 |
1983年 | 37篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1974年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
31.
32.
33.
Jianhu Yang Shixun Dai Nengli Dai Lei Wen Lili Hu Zhonghong Jiang 《Journal of luminescence》2004,106(1):9-14
Nonradiative decay of 4I13/2→4I15/2 transition of Er3+ has been investigated in a series of oxide glasses. For Er3+-doped glass samples, the Judd-Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er3+ concentration limit. Infrared spectra were measured in order to investigate the influence of OH− groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH− groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior. 相似文献
34.
The problem of generating a matrix A with specified eigen‐pair, where A is a symmetric and anti‐persymmetric matrix, is presented. An existence theorem is given and proved. A general expression of such a matrix is provided. We denote the set of such matrices by ??????En. The optimal approximation problem associated with ??????En is discussed, that is: to find the nearest matrix to a given matrix A* by A∈??????En. The existence and uniqueness of the optimal approximation problem is proved and the expression is provided for this nearest matrix. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
35.
36.
Lei Liu 《Journal of Mathematical Analysis and Applications》2007,328(2):1484-1486
In this note, we generalize the inequality about the trace of positive semidefinite matrix trk(AB)?k(trA)k(trB) to Hilbert space, and obtain a relevant inequality about positive trace class operator. 相似文献
37.
38.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
39.
蒋忠樟 《数学的实践与认识》2007,37(15):174-179
实对称正定矩阵的复合矩阵正定性的研究已有结论,但对于一般意义下的正定矩阵的复合矩阵是否仍然是正定的研究需要利用一般的正定矩阵的标准形的复合矩阵进行讨论,给出了一般公式及具体算法,为讨论其复合矩阵的正定性提供了基础条件. 相似文献
40.