全文获取类型
收费全文 | 262066篇 |
免费 | 25138篇 |
国内免费 | 17590篇 |
专业分类
化学 | 150577篇 |
晶体学 | 4094篇 |
力学 | 12554篇 |
综合类 | 24篇 |
数学 | 27591篇 |
物理学 | 109954篇 |
出版年
2019年 | 2420篇 |
2018年 | 2552篇 |
2017年 | 3135篇 |
2016年 | 4295篇 |
2015年 | 3925篇 |
2014年 | 4454篇 |
2013年 | 11604篇 |
2012年 | 9234篇 |
2011年 | 12050篇 |
2010年 | 13096篇 |
2009年 | 13190篇 |
2008年 | 9070篇 |
2007年 | 8734篇 |
2006年 | 8219篇 |
2005年 | 8096篇 |
2004年 | 8524篇 |
2003年 | 7287篇 |
2002年 | 6984篇 |
2001年 | 8686篇 |
2000年 | 6512篇 |
1999年 | 5822篇 |
1998年 | 4738篇 |
1997年 | 4589篇 |
1996年 | 4835篇 |
1995年 | 4973篇 |
1994年 | 4973篇 |
1993年 | 4942篇 |
1992年 | 5014篇 |
1991年 | 4551篇 |
1990年 | 4200篇 |
1989年 | 4292篇 |
1988年 | 4258篇 |
1987年 | 3621篇 |
1986年 | 3485篇 |
1985年 | 4055篇 |
1984年 | 4161篇 |
1983年 | 3054篇 |
1982年 | 3705篇 |
1981年 | 3501篇 |
1980年 | 3452篇 |
1979年 | 3381篇 |
1978年 | 3612篇 |
1977年 | 3556篇 |
1976年 | 3830篇 |
1975年 | 2928篇 |
1974年 | 2880篇 |
1973年 | 3135篇 |
1972年 | 2247篇 |
1968年 | 2242篇 |
1967年 | 2306篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We have recently demonstrated that polarization transfer using an adiabatic passage through the Hartmann-Hahn condition (APHH-CP) by a variation of the radio-frequency amplitude can substantially improve the transfer efficiency over Hartmann-Hahn cross polarization. Here we show that APHH-CP can be combined with fast magic angle sample spinning (MAS). The heteronuclear dipolar order, established in the course of the transfer, can indeed be created and preserved. 相似文献
42.
Alloys of the systems Fe–Al (mixable over the whole concentration range) and Fe–Mg (insoluble with each other) were produced by implantation of Fe ions into Al and Mg, respectively. The implantation energy was 200 keV and the ion doses ranged from 1 × 1014 to 9 × 1017cm-2The obtained implantation profiles were determined by Auger electron spectroscopy depth profiling. Maximum iron concentrations reached were up to 60 at.% for implantation into Al and 94 at.% for implantation into Mg. Phase analysis of the implanted layers was performed by conversion electron Mössbauer spectroscopy and X‐ray diffraction. For implantation into Mg, two different kinds of Mössbauer spectra were obtained: at low doses paramagnetic doublets indicating at least two different iron sites and at high doses a dominant ferromagnetic six‐line‐pattern with a small paramagnetic fraction. The X‐ray diffraction pattern concluded that in the latter case a dilated αiron lattice is formed. For implantation into Al, the Mössbauer spectra were doublet structures very similar to those obtained at amorphous Fe–Al alloys produced by rapid quenching methods. They also indicated at least two different main iron environments. For the highest implanted sample a ferromagnetic six‐line‐pattern with magnetic field values close to those of Fe3Al appeared. 相似文献
43.
44.
45.
46.
47.
Whittum D.H. Ebihara K. Hiramatsu S. Kishiro J.-i. Monaka T. Ozaki T. Takayama K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):136-141
Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed 相似文献
48.
Yoshiaki Murata Cheng-Huang Lin Totaro Imasaka 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):543-544
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
49.
50.