全文获取类型
收费全文 | 474954篇 |
免费 | 5436篇 |
国内免费 | 1452篇 |
专业分类
化学 | 251823篇 |
晶体学 | 7143篇 |
力学 | 21223篇 |
综合类 | 19篇 |
数学 | 53769篇 |
物理学 | 147865篇 |
出版年
2021年 | 4070篇 |
2020年 | 4485篇 |
2019年 | 4791篇 |
2018年 | 6217篇 |
2017年 | 6073篇 |
2016年 | 9437篇 |
2015年 | 6004篇 |
2014年 | 9190篇 |
2013年 | 21934篇 |
2012年 | 17233篇 |
2011年 | 21288篇 |
2010年 | 14985篇 |
2009年 | 14852篇 |
2008年 | 19419篇 |
2007年 | 19191篇 |
2006年 | 17864篇 |
2005年 | 15903篇 |
2004年 | 14777篇 |
2003年 | 13012篇 |
2002年 | 12788篇 |
2001年 | 15269篇 |
2000年 | 11446篇 |
1999年 | 8917篇 |
1998年 | 7307篇 |
1997年 | 7044篇 |
1996年 | 6691篇 |
1995年 | 6014篇 |
1994年 | 5854篇 |
1993年 | 5627篇 |
1992年 | 6421篇 |
1991年 | 6537篇 |
1990年 | 6195篇 |
1989年 | 5940篇 |
1988年 | 5939篇 |
1987年 | 5852篇 |
1986年 | 5494篇 |
1985年 | 7125篇 |
1984年 | 7247篇 |
1983年 | 5697篇 |
1982年 | 5760篇 |
1981年 | 5728篇 |
1980年 | 5304篇 |
1979年 | 5788篇 |
1978年 | 5940篇 |
1977年 | 5857篇 |
1976年 | 5725篇 |
1975年 | 5260篇 |
1974年 | 5262篇 |
1973年 | 5208篇 |
1972年 | 3637篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
M Lepère R Gobeille V.Malathy Devi M.A.H Smith B Aoaeh A.W Mantz 《Journal of Molecular Spectroscopy》2004,224(1):7-12
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. 相似文献
133.
M. Castagnino R. Id Betan R. Laura 《International Journal of Theoretical Physics》2003,42(10):2423-2439
By extending the notion of mixed states to functionals acting on the space of observables with diagonal singularity we obtain a well-defined complex spectral decomposition of the time evolution for a quantum decaying system. In this formalism, generalized Gamow states are obtained with well-defined physical properties. 相似文献
134.
Dikandé A. M. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,42(2):247-253
Small and large-amplitude elastic deformations of the armchair structure of single-walled carbon nanotubes are investigated with emphasis on the cylindrical geometry. As starting model, we consider a discrete one-dimensional lattice of atoms interacting via a Lennard-Jones type two-body potential. In an expansion scheme using cylindrical coordinates where radial displacements are assumed negligible compared to the angular motions, a sine-lattice Hamiltonian is derived. In the limit of small-amplitude angular displacements, the dispersion spectrum of acoustic phonons is derived and the associate characteristic frequency is given as a function of parameters of the model. In the large-amplitude regime, lattice vibrations give rise to kink-type deformations which move undergoing lattice dispersion and lattice discreteness effects. The dispersion law of the kink motion is obtained and shown to lower the effect of lattice discreteness, giving rise to a vanishing Peierls stress for kink sizes of the order of a few lattice spacings. Implications of the coupling of two armchair structures on the stability of vibrational modes of an individual armchair nanotube are also discussed. A gap of forbidden modes is predicted in the phonon spectrum while the energy needed to create a kink deformation in individual nanotubes is shifted in the presence of a wall-to-wall interaction.Received: 2 August 2004, Published online: 14 December 2004PACS:
81.07.De Nanotubes - 62.30. + d Mechanical and elastic waves-vibrations - 63.22. + m Phonons in low-dimensional nanoscale materials - 63.20.Ry Anharmonic lattices modes 相似文献
135.
In a recent paper to this journal (Whitman A M et al 2003 Waves Random Media 13 269-86) we derived a set of coupled equations that describe the intermodal scattering of acoustic radiation in a duct whose speed of sound varies randomly in space and time. In the paper we were mainly interested in modes that were not near cutoff. Here we study the solution of these equations in the vicinity of the cutoff. We find that near cutoff almost all the energy is reflected back independent of the other duct parameters. In addition to presenting these results, we analyse the mathematical structure of the equations in these regions in order to elucidate the reason for this behaviour. 相似文献
136.
We show that there are close relations between extremal problems in dual Brunn-Minkowski theory and isotropic-type properties for some Borel measures on the sphere. The methods we use allow us to obtain similar results in the context of Firey-Brunn-Minkowski theory. We also study reverse inequalities for dual mixed volumes which are related with classical positions, such as ?-position or isotropic position. 相似文献
137.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
138.
Yu. M. Dyukarev 《Mathematical Notes》2004,75(1-2):66-82
In this paper, we obtain criteria for the indeterminacy of the Stieltjes matrix moment problem. We obtain explicit formulas for Stieltjes parameters and study the multiplicative structure of the resolvent matrix. In the indeterminate case, we study the analytic properties of the resolvent matrix of the moment problem. We describe the set of all matrix functions associated with the indeterminate Stieltjes moment problem in terms of linear fractional transformations over Stieltjes pairs. 相似文献
139.
140.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献