全文获取类型
收费全文 | 208868篇 |
免费 | 2713篇 |
国内免费 | 621篇 |
专业分类
化学 | 116770篇 |
晶体学 | 3346篇 |
力学 | 8083篇 |
综合类 | 4篇 |
数学 | 20706篇 |
物理学 | 63293篇 |
出版年
2016年 | 2628篇 |
2015年 | 2014篇 |
2014年 | 2689篇 |
2013年 | 8408篇 |
2012年 | 5829篇 |
2011年 | 7351篇 |
2010年 | 4781篇 |
2009年 | 4711篇 |
2008年 | 6655篇 |
2007年 | 6803篇 |
2006年 | 6548篇 |
2005年 | 5927篇 |
2004年 | 5342篇 |
2003年 | 4799篇 |
2002年 | 4653篇 |
2001年 | 6035篇 |
2000年 | 4639篇 |
1999年 | 3702篇 |
1998年 | 2908篇 |
1997年 | 2943篇 |
1996年 | 2917篇 |
1995年 | 2717篇 |
1994年 | 2570篇 |
1993年 | 2490篇 |
1992年 | 3008篇 |
1991年 | 2858篇 |
1990年 | 2774篇 |
1989年 | 2789篇 |
1988年 | 2697篇 |
1987年 | 2725篇 |
1986年 | 2564篇 |
1985年 | 3445篇 |
1984年 | 3490篇 |
1983年 | 2895篇 |
1982年 | 3081篇 |
1981年 | 3056篇 |
1980年 | 2911篇 |
1979年 | 3057篇 |
1978年 | 3304篇 |
1977年 | 3148篇 |
1976年 | 3036篇 |
1975年 | 2910篇 |
1974年 | 2860篇 |
1973年 | 2847篇 |
1972年 | 1837篇 |
1971年 | 1534篇 |
1968年 | 1978篇 |
1967年 | 2198篇 |
1966年 | 1967篇 |
1965年 | 1553篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
C. Waldtmann H.-U. Everts B. Bernu C. Lhuillier P. Sindzingre P. Lecheminant L. Pierre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):501-507
We study the exact low energy spectra of the spin 1/2 Heisenberg antiferromagnet on small samples of the kagomé lattice of up to N=36 sites. In agreement with the conclusions of previous authors, we find that these low energy spectra contradict the hypothesis
of Néel type long range order. Certainly, the ground state of this system is a spin liquid, but its properties are rather
unusual. The magnetic () excitations are separated from the ground state by a gap. However, this gap is filled with nonmagnetic () excitations. In the thermodynamic limit the spectrum of these nonmagnetic excitations will presumably develop into a gapless
continuum adjacent to the ground state. Surprisingly, the eigenstates of samples with an odd number of sites, i.e. samples with an unsaturated spin, exhibit symmetries which could support long range chiral order. We do not know if these
states will be true thermodynamic states or only metastable ones. In any case, the low energy properties of the spin 1/2 Heisenberg
antiferromagnet on the kagomé lattice clearly distinguish this system from either a short range RVB spin liquid or a standard chiral spin liquid. Presumably
they are facets of a generically new state of frustrated two-dimensional quantum antiferromagnets.
Received: 27 November 1997 / Accepted: 29 January 1998 相似文献
72.
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
73.
74.
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
75.
76.
77.
78.
79.
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
80.
Molecular n-v complexes of quinoline N-oxides with BF3 have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994. 相似文献