全文获取类型
收费全文 | 133946篇 |
免费 | 33715篇 |
国内免费 | 35749篇 |
专业分类
化学 | 88518篇 |
晶体学 | 3667篇 |
力学 | 8822篇 |
综合类 | 2624篇 |
数学 | 19089篇 |
物理学 | 80690篇 |
出版年
2024年 | 500篇 |
2023年 | 1240篇 |
2022年 | 2794篇 |
2021年 | 2712篇 |
2020年 | 2847篇 |
2019年 | 3285篇 |
2018年 | 3166篇 |
2017年 | 4775篇 |
2016年 | 4043篇 |
2015年 | 5261篇 |
2014年 | 5758篇 |
2013年 | 8247篇 |
2012年 | 8991篇 |
2011年 | 10943篇 |
2010年 | 14417篇 |
2009年 | 14866篇 |
2008年 | 9492篇 |
2007年 | 8262篇 |
2006年 | 7736篇 |
2005年 | 7353篇 |
2004年 | 7035篇 |
2003年 | 5451篇 |
2002年 | 5352篇 |
2001年 | 5569篇 |
2000年 | 4915篇 |
1999年 | 3940篇 |
1998年 | 2844篇 |
1997年 | 2496篇 |
1996年 | 2765篇 |
1995年 | 3159篇 |
1994年 | 3217篇 |
1993年 | 3264篇 |
1992年 | 2813篇 |
1991年 | 2363篇 |
1990年 | 2012篇 |
1989年 | 2125篇 |
1988年 | 2066篇 |
1987年 | 1342篇 |
1986年 | 1345篇 |
1985年 | 956篇 |
1984年 | 1067篇 |
1983年 | 466篇 |
1982年 | 975篇 |
1981年 | 797篇 |
1980年 | 822篇 |
1979年 | 597篇 |
1978年 | 557篇 |
1977年 | 643篇 |
1976年 | 1056篇 |
1972年 | 535篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
91.
S. Sabchevski T. Idehara I. Ogawa M. Glyavin K. Ohashi 《International Journal of Infrared and Millimeter Waves》2002,23(5):675-692
A computer code for simulation of beam-field interaction in a resonant cavity of a gyrotron has been developed. It is based on a self-consistent, time-independent, single-mode physical model. The code has been applied to the analysis of the electrodynamical system of a novel high-harmonic gyrotron with axis-encircling beam and a permanent magnet. In this paper both the physical model and numerical techniques used are outlined. Some results of the numerical experiments are presented and discussed. 相似文献
92.
The object of this note is to prove the followingTheorem Let{a_n}and{b_n}be sequences of real numbers such that0<∑∑a_n~2<+∞and0<∑b_n~2<+∞.Then we have the inequalitysum from m=1 to∞sum from n=1 to∞a_mb_n/m+n<{sum from n=1 to∞(π-θ/n~(1/2)a_n~2}~1/2{sum from n=1 to∞(π-θ/n~(1/2)b_n~2}~1/2 (1)whereθ=3/2~(1/2)-1=1.121320343. 相似文献
93.
LI Yu-qiong SUN Zhen-rong ZHANG Shi-an YANG Xi-hua WANG Zu-geng. Key Laboratory of Optical Magnetic Resonance Spectroscopy 《光谱学与光谱分析》2006,26(8):1395-1395
The authors achieved the temporal coherent control in an Er^3+ doped telluride glass, one kind of disordered solids. The upconversion at 670 nm was modulated and the dephasing time was simulated as 300 fs. Moreover, the photon echo signal gave the dephasing time due to the phonon interaction. The agreement between the two data indicates that the interaction between the wavepacket and the phonon leads to the fast disappearance of wavepackets interference, which is helpful for the tech- nique to be applied to the disordered solids. 相似文献
94.
应用不可约张量理论构造了三角对称晶场中3d2/3d8态离子的45阶可完全对角化的微扰哈密顿矩阵,研究了CsNiCl3晶体的光谱精细结构、晶体结构、零场分裂参量、Jahn-Telller效应以及自旋单重态对Ni2+离子基态能级的影响,理论与实验相符合.在此基础上,进一步研究了以前工作中被忽略的自旋-自旋耦合作用和Trees修正对CsNiCl3晶体的光谱精细结构和零场分裂参量的影响,发现有四种机理会影响零场分裂参量:1)自旋-轨道耦合机理,2)自旋-自旋耦合机理;3)自旋-轨道与自旋-自旋联合耦合机理;4)自旋-轨道与Trees修正联合耦合机理,其中自旋-轨道耦合机理是最主要的,其他三种机理也是不可忽略的.
关键词:
基态能级
精细结构
零场分裂
自旋-自旋耦合 相似文献
95.
96.
97.
在长距离无线光通信中,接收点光功率密度与光束发散角平方呈反比关系,为了获得小的发散角和大的功率耦合效率,要求准直系统有较大的数值孔径(NA),但数值孔径过大会增加像差,因此合理设计功率耦合效率与准直系统的数值孔径就非常重要。该文对半导体激光器光束准直系统中功率耦合效率进行了研究,给出了半导体激光器光束功率耦合效率与k(孔径半径与孔径处等效光束半径之比)的关系表达式,并结合激光器光束准直系统,给出了半导体激光器光束功率耦合效率与准直系统数值孔径的关系表达式。该研究结论对于半导体激光器光束准直系统设计具有参考作用。 相似文献
98.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献
99.
Maria Kordaki Athanasia Balomenou 《International Journal of Computers for Mathematical Learning》2006,11(1):99-135
This study focuses on the constructions in terms of area and perimeter in equivalent triangles developed by students aged 12–15 years-old, using the tools provided by Cabri-Geometry II [Labore (1990). Cabri-Geometry (software), Université de Grenoble]. Twenty-five students participated in a learning experiment where they were asked to construct: (a) pairs of equivalent triangles “in as many ways as possible” and to study their area and their perimeter using any of the tools provided and (b) “any possible sequence of modifications of an original triangle into other equivalent ones”. As regards the concept of area and in contrast to a paper and pencil environment, Cabri provided students with different and potential opportunities in terms of: (a) means of construction, (b) control, (c) variety of representations and (d) linking representations, by exploiting its capability for continuous modifications. By exploiting these opportunities in the context of the given open tasks, students were helped by the tools provided to develop a broader view of the concept of area than the typical view they would construct in a typical paper and pencil environment. 相似文献
100.