全文获取类型
收费全文 | 152501篇 |
免费 | 1567篇 |
国内免费 | 382篇 |
专业分类
化学 | 81986篇 |
晶体学 | 2028篇 |
力学 | 6657篇 |
综合类 | 7篇 |
数学 | 15279篇 |
物理学 | 48493篇 |
出版年
2020年 | 1111篇 |
2019年 | 1171篇 |
2018年 | 1475篇 |
2017年 | 1451篇 |
2016年 | 2467篇 |
2015年 | 1545篇 |
2014年 | 2422篇 |
2013年 | 6314篇 |
2012年 | 4925篇 |
2011年 | 6256篇 |
2010年 | 4277篇 |
2009年 | 4289篇 |
2008年 | 5690篇 |
2007年 | 5763篇 |
2006年 | 5403篇 |
2005年 | 4992篇 |
2004年 | 4409篇 |
2003年 | 3852篇 |
2002年 | 3882篇 |
2001年 | 4333篇 |
2000年 | 3316篇 |
1999年 | 2572篇 |
1998年 | 2241篇 |
1997年 | 2184篇 |
1996年 | 1982篇 |
1995年 | 1897篇 |
1994年 | 1886篇 |
1993年 | 1726篇 |
1992年 | 1991篇 |
1991年 | 2119篇 |
1990年 | 1917篇 |
1989年 | 1916篇 |
1988年 | 1856篇 |
1987年 | 1755篇 |
1986年 | 1692篇 |
1985年 | 2192篇 |
1984年 | 2324篇 |
1983年 | 1897篇 |
1982年 | 2079篇 |
1981年 | 1965篇 |
1980年 | 1889篇 |
1979年 | 2032篇 |
1978年 | 2204篇 |
1977年 | 2068篇 |
1976年 | 2113篇 |
1975年 | 2024篇 |
1974年 | 2076篇 |
1973年 | 2063篇 |
1972年 | 1355篇 |
1971年 | 1211篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
F. G. Vagizov 《Hyperfine Interactions》1995,95(1):85-95
We present the results of an experimental investigation of a RF splitting of57Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field. 相似文献
72.
73.
A comparison of steady-state evoked potentials to modulated tones in awake and sleeping humans. 总被引:12,自引:0,他引:12
L T Cohen F W Rickards G M Clark 《The Journal of the Acoustical Society of America》1991,90(5):2467-2479
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation. 相似文献
74.
R. F. Bikbaev 《Theoretical and Mathematical Physics》1989,80(3):1004-1006
Physics and Mathematics Division with Computational Center of the Bashkir Branch of the USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 80, No. 3, pp. 470–473, September, 1989. 相似文献
75.
Zarubitskii O. G. Budnik V. G. Omel'chuk A. A. Melekhin V. T. Opanasyuk V. P. Zakharchenko N. F. 《Russian Journal of Applied Chemistry》2002,75(4):558-561
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry. 相似文献
76.
In this paper, a two-dimensional finite volume unstructured mesh method (FVUM) based on a triangular background interpolation mesh is developed for analysing the evolution of the saltwater intrusion into single and multiple coastal aquifer systems. The model formulation consists of a ground-water flow equation and a salt transport equation. These coupled and non-linear partial differential equations are transformed by FVUM into a system of differential/algebraic equations, which is solved using backward differentiation formulas of order one through five. Simulation results are compared with previously published solutions where good agreement is observed. 相似文献
77.
A.-S. F. Obada M. Darwish H. H. Salah 《International Journal of Theoretical Physics》2002,41(9):1755-1768
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined. 相似文献
78.
79.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
80.
In a twisted nematic liquid crystal cell we report and study the self-transparency effect induced by the creation of an isotropic droplet. A simple theoretical model is presented and good agreement with experimental data is found. In a two beams configuration transistor-like behavior is observed and theoretically discussed. 相似文献