全文获取类型
收费全文 | 17745篇 |
免费 | 325篇 |
国内免费 | 75篇 |
专业分类
化学 | 10218篇 |
晶体学 | 135篇 |
力学 | 608篇 |
数学 | 2393篇 |
物理学 | 4791篇 |
出版年
2022年 | 116篇 |
2021年 | 135篇 |
2020年 | 196篇 |
2019年 | 146篇 |
2018年 | 141篇 |
2017年 | 119篇 |
2016年 | 263篇 |
2015年 | 290篇 |
2014年 | 314篇 |
2013年 | 631篇 |
2012年 | 709篇 |
2011年 | 891篇 |
2010年 | 519篇 |
2009年 | 444篇 |
2008年 | 757篇 |
2007年 | 809篇 |
2006年 | 783篇 |
2005年 | 807篇 |
2004年 | 667篇 |
2003年 | 548篇 |
2002年 | 509篇 |
2001年 | 484篇 |
2000年 | 447篇 |
1999年 | 274篇 |
1998年 | 233篇 |
1997年 | 231篇 |
1996年 | 302篇 |
1995年 | 281篇 |
1994年 | 261篇 |
1993年 | 299篇 |
1992年 | 292篇 |
1991年 | 263篇 |
1990年 | 215篇 |
1989年 | 207篇 |
1988年 | 235篇 |
1987年 | 213篇 |
1986年 | 179篇 |
1985年 | 240篇 |
1984年 | 213篇 |
1983年 | 173篇 |
1982年 | 207篇 |
1981年 | 184篇 |
1980年 | 189篇 |
1979年 | 187篇 |
1978年 | 187篇 |
1977年 | 158篇 |
1976年 | 167篇 |
1975年 | 130篇 |
1974年 | 149篇 |
1973年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
CW diode pumping and FM mode locking of a Nd: KGW laser 总被引:2,自引:0,他引:2
C. J. Flood D. R. Walker H. M. van Driel 《Applied physics. B, Lasers and optics》1995,60(2-3):309-312
We have demonstrated cw diode end pumping of Nd: KGW, a novel solid-state gain medium, with up to 30% conversion efficiency into near-TEM00 (M2 < 1.05) output at = 1.067 µm for a pump level of 2.7 W. The slope efficiency was limited by intracavity reflections to 36%; however, direct comparison to a similar Nd:YAG laser indicates the same intrinsic slope efficiency of 60%. FM mode locking of this laser at 200 MHz has produced 12 ps pulses (compared to 16 ps for Nd: YAG), although an intracavity etalon was required. Considerable reduction in pulse width is possible (the line width limit is 0.5 ps) but different techniques may be necessary. Spatial hole burning was evident in both the 120 GHz free-running spectrum and the etalon-limited mode-locked spectrum. 相似文献
152.
N. V. Shcherbatska A. van Hoek P. I. H. Bastiaens A. J. W. G. Visser 《Journal of fluorescence》1995,5(2):171-177
We have studied the fluorescent properties of a well-defined model flavin compound (3-methyllumiflavin) in a relatively polar solvent like propylene glycol or ethanol. Inhomogeneous spectral broadening effects were directly time-resolved by detection at the extreme blue and red edges of the fluorescence band of 3-methyllumiflavin using excitation in the main absorption band. At the high-energy side of the emission band a rapid decay component (tens of picoseconds) was resolved indicative for the disappearance of the initially prepared, nonequilibrium state with a characteristic dipolar relaxation time. At the low-energy side the rise of a solvent relaxed fluorescent species could be time-resolved. The wavelength-dependent effects on the dipolar relaxation were abolished when excitation was at the low-energy side of the absorption band. The experimental decays of the flavin solvate at different energies of fluorescence and excitation are presented as they represent an easy diagnosis for energy dependent solvation dynamics. Wavelength dependent rotation of 3-methyllumiflavin, examined by fluorescence anisotropy decay, turned out to be absent for 3-methyllumiflavin in propylene glycol between 263 and 293 K, probably because of the small change in dipole moment upon flavin excitation. 相似文献
153.
We formulate general conjectures about the relationship between the A-model connection on the cohomology of ad-dimensional Calabi-Yau complete intersectionV ofr hypersurfacesV
1
,...,V
r
in a toric varietyP
and the system of differential operators annihilating the special generalized hypergeometric series 0 constructed from the fan . Using this generalized hypergeometric series, we propose conjectural mirrorsV ofV and the canonicalq-coordinates on the moduli spaces of Calabi-Yau manifolds.In the second part of the paper we consider some examples of Calabi-Yau 3-folds having Picard number >1 in products of projective spaces. For conjectural mirrors, using the recurrent relation among coefficients of the restriction of the hypergeometric function 0 on a special line in the moduli space, we determine the Picard-Fuchs equation satisfied by periods of this special one-parameter subfamily. This allows to obtain some sequences of integers which can be conjecturally interpreted in terms of Gromov-Witten invariants. Using standard techniques from enumerative geometry, first terms of these sequence of integers are checked to coincide with numbers of rational curves on Calabi-Yau 3-folds. 相似文献
154.
van der Sanden GC Wormer PE van der Avoird A Schmuttenmaer CA Saykally RJ 《Chemical physics letters》1994,226(1-2):22-26
We have calculated state-to-state total cross sections for rotational excitation and inversion of NH3 by collisions with Ar using the close coupling method. The Ar-NH3 interaction potential has been obtained from a fit to the spectrum of this van der Waals molecule. The calculated cross sections agree to within about 30% with the measured values; the estimated error in the latter is 10% to 20%. 相似文献
155.
156.
157.
Makins NC Ent R Chapman MS Hansen J Lee K Milner RG Nelson J Arnold RG Bosted PE Keppel CE Lung A Rock SE Spengos M Szalata ZM Tao LH White JL Coulter KP Geesaman DF Holt RJ Jackson HE Papavassiliou V Potterveld DH Zeidman B Arrington J Beise EJ Belz E Filippone BW Gao H Lorenzon W Mueller B McKeown RD O'Neill TG Epstein M Margaziotis DJ Napolitano J Kinney E Anthony PL van Bibber K Dietrich FS Gearhart RA Patratos GG Kuhn SE van den Brand JF Bulten H Jones CE 《Physical review letters》1994,72(13):1986-1989
158.
159.
160.