全文获取类型
收费全文 | 41100篇 |
免费 | 3501篇 |
国内免费 | 2007篇 |
专业分类
化学 | 28749篇 |
晶体学 | 433篇 |
力学 | 1675篇 |
综合类 | 98篇 |
数学 | 3709篇 |
物理学 | 11944篇 |
出版年
2023年 | 403篇 |
2022年 | 566篇 |
2021年 | 962篇 |
2020年 | 1052篇 |
2019年 | 1049篇 |
2018年 | 867篇 |
2017年 | 769篇 |
2016年 | 1427篇 |
2015年 | 1307篇 |
2014年 | 1609篇 |
2013年 | 2602篇 |
2012年 | 3238篇 |
2011年 | 3409篇 |
2010年 | 2185篇 |
2009年 | 2034篇 |
2008年 | 2741篇 |
2007年 | 2544篇 |
2006年 | 2345篇 |
2005年 | 2149篇 |
2004年 | 1831篇 |
2003年 | 1480篇 |
2002年 | 1501篇 |
2001年 | 1066篇 |
2000年 | 857篇 |
1999年 | 637篇 |
1998年 | 494篇 |
1997年 | 505篇 |
1996年 | 534篇 |
1995年 | 419篇 |
1994年 | 413篇 |
1993年 | 384篇 |
1992年 | 368篇 |
1991年 | 304篇 |
1990年 | 225篇 |
1989年 | 195篇 |
1988年 | 179篇 |
1987年 | 148篇 |
1986年 | 128篇 |
1985年 | 202篇 |
1984年 | 130篇 |
1983年 | 112篇 |
1982年 | 136篇 |
1981年 | 105篇 |
1980年 | 88篇 |
1978年 | 82篇 |
1977年 | 85篇 |
1976年 | 98篇 |
1975年 | 107篇 |
1974年 | 85篇 |
1973年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
91.
非负矩阵与有向图的谱半径 总被引:2,自引:0,他引:2
本文给出非负矩阵的谱半径的上界、下界,由此给出有向图的谱半径的界. 相似文献
92.
93.
Yu. A. Mitropol’skii Nguyen Dong Anh Nguyen Dyk Tynh 《Ukrainian Mathematical Journal》1998,50(11):1731-1737
We construct the second approximation for random oscillations described by the Van der Pol equation which are under the action
of a broadband random process.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 11, pp. 1517–1521, November, 1998. 相似文献
94.
95.
96.
97.
A general formula for the discrete states (NeveuSchwarz sector) in N = 1 2D super-Liouville theory is written down in the world-sheet supersymmetric form. We then derive a set of gauge states at the discrete momenta. These discrete gauge states are shown to carry the ω∞ charges and serve as the symmetry parameters in the old covariant quantization of the theory. 相似文献
98.
Yong Nam Choi Shin Ae Kim Sung Kyu Kim Sung Baek Kim Chang-Hee Lee Pavel Mikula 《Pramana》2004,63(1):175-181
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction
experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However,
a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution
property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction
experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that
the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved. 相似文献
99.
J.H. Sung J.Y. Park T. Imran Y.S. Lee C.H. Nam 《Applied physics. B, Lasers and optics》2006,82(1):5-8
Optical pulses with 1.1-mJ energy and 5.5-fs duration have been generated at 1-kHz repetition rate from a chirped pulse amplification
Ti:Sapphire laser incorporating a differentially pumped hollow-fiber chirped-mirror compressor. The effects of self-focusing
and multi-photon ionization during the beam propagation were minimized by differentially pumping the hollow fiber filled with
neon. The spectral broadening at the hollow-fiber compressor was optimized by adjusting gas pressure, laser intensity, and
laser chirp, covering from 540 nm to 950 nm.
PACS 42.65.Jx; 42.65.Re 相似文献
100.
Jae-Yeon Lee Eugene Lubarsky Ben T. Zinn 《Proceedings of the Combustion Institute》2005,30(2):1757-1764
This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (NanomiserTM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities. 相似文献