全文获取类型
收费全文 | 735745篇 |
免费 | 6103篇 |
国内免费 | 1879篇 |
专业分类
化学 | 348141篇 |
晶体学 | 10241篇 |
力学 | 41807篇 |
综合类 | 19篇 |
数学 | 125397篇 |
物理学 | 218122篇 |
出版年
2021年 | 6183篇 |
2020年 | 6719篇 |
2019年 | 7688篇 |
2018年 | 20112篇 |
2017年 | 20023篇 |
2016年 | 20191篇 |
2015年 | 8465篇 |
2014年 | 13553篇 |
2013年 | 29336篇 |
2012年 | 26196篇 |
2011年 | 36434篇 |
2010年 | 25779篇 |
2009年 | 26121篇 |
2008年 | 31628篇 |
2007年 | 33341篇 |
2006年 | 23466篇 |
2005年 | 21866篇 |
2004年 | 20717篇 |
2003年 | 19381篇 |
2002年 | 18438篇 |
2001年 | 18414篇 |
2000年 | 14445篇 |
1999年 | 11111篇 |
1998年 | 9891篇 |
1997年 | 9639篇 |
1996年 | 9066篇 |
1995年 | 8039篇 |
1994年 | 8087篇 |
1993年 | 7893篇 |
1992年 | 8159篇 |
1991年 | 8713篇 |
1990年 | 8420篇 |
1989年 | 8321篇 |
1988年 | 8026篇 |
1987年 | 7872篇 |
1986年 | 7456篇 |
1985年 | 9351篇 |
1984年 | 9874篇 |
1983年 | 8327篇 |
1982年 | 8684篇 |
1981年 | 8125篇 |
1980年 | 7667篇 |
1979年 | 8422篇 |
1978年 | 8617篇 |
1977年 | 8645篇 |
1976年 | 8642篇 |
1975年 | 8244篇 |
1974年 | 8053篇 |
1973年 | 8294篇 |
1972年 | 6365篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
921.
A. Guzmn E. Luna J. Miguel-Snchez E. Calleja E. Muoz 《Infrared Physics & Technology》2003,44(5-6):377-382
In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed. 相似文献
922.
A. D. Matveev 《Journal of Applied Mechanics and Technical Physics》2003,44(5):721-726
Modified three-dimensional formulations of bending problems of homogeneous elastic plates and beams are considered. Modification of the known three-dimensional formulations reduces to using additional constraints imposed on displacement functions. An advantage of the formulations proposed is that complex fixing conditions of plates and beams can be taken into account. 相似文献
923.
924.
A. N. Bandura V. V. Chebotarev I. E. Garkusha V. A. Makhlay A. K. Marchenko D. G. Solyakov V. I. Tereshin S. A. Trubchaninov A. V. Tsarenko I. Landman 《Czechoslovak Journal of Physics》2004,54(3):C53
The paper presents experimental investigation of energy characteristics of the plasma streams generated with quasi—steady—state plasma accelerator QSPA Kh-50 and adjustment of plasma paramenters from the point of view its applicability for simulation of transient plasma heat loads expected for ITER disruptions and type I ELMs. Possibility of generation of high-power magnetized plasma streams with ion impact energy up to 0.6 keV, pulse length 0.25 ms and heat loads varied in wide range from 0.5 to 30 MJ/m2 has been demonstrated and some features of plasma interaction with tungsten targets in dependence on plasma heat loads are discussed. 相似文献
925.
V. A. Alekseev 《Optics and Spectroscopy》2004,96(4):492-496
The absorption spectra of Xe + CF4 and Kr + CF4 mixtures in the vacuum ultraviolet region are presented. A considerable broadening of the short-wavelength wings of the atomic absorption lines is explained by a repulsive character of the Rg*-CF4 interaction potential. This repulsive character is also considered to be the most probable reason for the anomalously small cross sections of the quenching of electronically excited atoms of rare gases by CF4 molecules. The influence of CF4 on the emission rate of the trapped resonance radiation of Xe from the cell is discussed. 相似文献
926.
927.
The pure state space of Quantum Mechanics is investigated as Hermitian Symmetric Kähler manifold. The classical principles of quantum mechanics (Quantum Superposition Principle, Heisenberg Uncertainty Principle, Quantum Probability Principle) and Spectral Theory of observables are discussed in this non-linear geometrical context. 相似文献
928.
M. A. Nikitina 《Russian Physics Journal》2003,46(3):296-304
The h
2-persistent multiple-access communication networks with discrete and continuous strategy of control of conflict messages are investigated. 相似文献
929.
930.
For more than 25 yearsJΨ production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood
while others are still unclear. The current status of the theory ofJΨ production will be sketched, paying special attention to the issues of formation time andJΨ re-interaction in a nuclear medium. 相似文献