全文获取类型
收费全文 | 474148篇 |
免费 | 2822篇 |
国内免费 | 734篇 |
专业分类
化学 | 213280篇 |
晶体学 | 7036篇 |
力学 | 28632篇 |
综合类 | 13篇 |
数学 | 75898篇 |
物理学 | 152845篇 |
出版年
2021年 | 4062篇 |
2020年 | 4414篇 |
2019年 | 5347篇 |
2018年 | 12585篇 |
2017年 | 12895篇 |
2016年 | 12641篇 |
2015年 | 5200篇 |
2014年 | 9155篇 |
2013年 | 17477篇 |
2012年 | 16790篇 |
2011年 | 24026篇 |
2010年 | 17538篇 |
2009年 | 18009篇 |
2008年 | 22190篇 |
2007年 | 24270篇 |
2006年 | 14082篇 |
2005年 | 15259篇 |
2004年 | 13262篇 |
2003年 | 12824篇 |
2002年 | 11877篇 |
2001年 | 11261篇 |
2000年 | 8919篇 |
1999年 | 6560篇 |
1998年 | 5967篇 |
1997年 | 5865篇 |
1996年 | 5525篇 |
1995年 | 4792篇 |
1994年 | 4933篇 |
1993年 | 4902篇 |
1992年 | 5099篇 |
1991年 | 5531篇 |
1990年 | 5401篇 |
1989年 | 5420篇 |
1988年 | 5193篇 |
1987年 | 5193篇 |
1986年 | 4867篇 |
1985年 | 5893篇 |
1984年 | 6183篇 |
1983年 | 5230篇 |
1982年 | 5424篇 |
1981年 | 5097篇 |
1980年 | 4716篇 |
1979年 | 5445篇 |
1978年 | 5475篇 |
1977年 | 5655篇 |
1976年 | 5734篇 |
1975年 | 5382篇 |
1974年 | 5211篇 |
1973年 | 5460篇 |
1972年 | 4417篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
C. Sannié V. Poremski G. Miescher F. Almasy und K. Kläui 《Fresenius' Journal of Analytical Chemistry》1938,113(1-2):51-52
Ohne Zusammenfassung 相似文献
842.
843.
844.
N. A. Orlow 《Fresenius' Journal of Analytical Chemistry》1910,49(3-4):226-227
Ohne Zusammenfassung 相似文献
845.
846.
847.
C. Mavroyannis 《Applied physics. B, Lasers and optics》2003,76(8):839-850
We have calculated the spectral functions for a number of induced excitations near the sum-frequency generation of a bichromatic field interacting with a three-level atom in the cascade configuration. Although the two-photon spontaneous emission is electric dipole forbidden, there are induced peaks whose subnatural line widths and spectral heights depend on the intensities of the bichromatic field. At low intensities of both laser fields, the maximum heights of the induced peaks take positive, zero, and negative values, indicating that the physical processes of absorption (attenuation), dark resonance (nonabsorbing state), and stimulated emission (amplification) are likely to occur at the sum-frequency generation of the two laser fields, respectively. The derived results are graphically presented and discussed. PACS 32.80.-t; 42.50.Hz 相似文献
848.
Porous silicon (PS) exhibits several photoluminescence (PL) bands, whose spectral position and intensity depend strongly on the actual conditions of preparation of PS, its treatment, and subsequent use. The PS PL band peaking at about 1.8 eV and usually assigned to the intrinsic emission of silicon nanocrystals was studied. It was shown that the temperature-induced variation of the PL kinetics in the 80 to 300-K interval follows a complex pattern and depends noticeably on the actual point on the band profile. The temperature behavior of PL decay in the 1.8-eV band is determined by the electron-hole recombination rate within a nanocrystal and the cascade carrier transitions from small to large nanocrystals, with an attendant decrease in energy. 相似文献
849.
Vinod Kumar Pragya Das R.P. Singh S. Muralithar R.K. Bhowmik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):153-157
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh
11/2 ⊗ νh
11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies
in the spin assignment of the band head.
Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003 相似文献
850.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector. 相似文献