全文获取类型
收费全文 | 69708篇 |
免费 | 2627篇 |
国内免费 | 183篇 |
专业分类
化学 | 44753篇 |
晶体学 | 397篇 |
力学 | 1930篇 |
综合类 | 7篇 |
数学 | 11611篇 |
物理学 | 13820篇 |
出版年
2023年 | 500篇 |
2022年 | 522篇 |
2021年 | 943篇 |
2020年 | 1009篇 |
2019年 | 1035篇 |
2018年 | 1339篇 |
2017年 | 1142篇 |
2016年 | 2203篇 |
2015年 | 1962篇 |
2014年 | 2066篇 |
2013年 | 4238篇 |
2012年 | 4613篇 |
2011年 | 4841篇 |
2010年 | 2975篇 |
2009年 | 2615篇 |
2008年 | 4192篇 |
2007年 | 4124篇 |
2006年 | 3696篇 |
2005年 | 3533篇 |
2004年 | 3004篇 |
2003年 | 2473篇 |
2002年 | 2166篇 |
2001年 | 1338篇 |
2000年 | 1153篇 |
1999年 | 858篇 |
1998年 | 665篇 |
1997年 | 638篇 |
1996年 | 774篇 |
1995年 | 532篇 |
1994年 | 578篇 |
1993年 | 561篇 |
1992年 | 582篇 |
1991年 | 500篇 |
1990年 | 472篇 |
1989年 | 432篇 |
1988年 | 370篇 |
1987年 | 375篇 |
1986年 | 335篇 |
1985年 | 533篇 |
1984年 | 497篇 |
1983年 | 338篇 |
1982年 | 454篇 |
1981年 | 414篇 |
1980年 | 393篇 |
1979年 | 357篇 |
1978年 | 331篇 |
1976年 | 337篇 |
1975年 | 293篇 |
1974年 | 285篇 |
1973年 | 299篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
In this Note, we study a 2×2 system of evolution equations with some codimension 3 crossing. We derive two conditions of non-degeneracy. We focus on one of them and reduce our system to some Landau–Zener's type system. Using this reduction, we describe the energy transfer at the crossing by Landau–Zener formula for 2-scales semi-classical measures. To cite this article: C. Fermanian Kammerer, P. Gérard, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 915–920. 相似文献
92.
93.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
94.
A. Guzmn E. Luna J. Miguel-Snchez E. Calleja E. Muoz 《Infrared Physics & Technology》2003,44(5-6):377-382
In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed. 相似文献
95.
96.
I. M. Kolthoff S. R. Cooper V. J. Tulane F. Reimers H. A. J. Pieters K. Höppner V. H. Matula C. B. Macek W. N. Skworzow J. S. Schepelewa F. Čuta K. Kámen S. Cohen R. E. Oesper D. S. Narayanamurthi T. R. Seshadri H. M. State A. W. Kirssanow W. M. Tscherkassow D. M. Mukherjee T. Akiyama Y. Mine S. Yabe Y. Volmar M. Déribéré 《Analytical and bioanalytical chemistry》1937,111(5-6):192-197
97.
Andr Voet 《Colloid and polymer science》1937,78(2):201-204
Zusammenfassung Es wird eine Methode angegeben, welche auf Grund von Flockungsversuchen lyophober Sole die numerische Festlegung der lyotropen
Reihe erm?glicht.
Vorl?ufige Mitteilung: Büchner, Voet und Bruins, Proc. Acad. Sci. Amsterdam35, 563 (1932). 相似文献
98.
J.-C. Thomas L. Achouri J. Äystö R. Béraud B. Blank G. Canchel S. Czajkowski P. Dendooven A. Ensallem J. Giovinazzo N. Guillet J. Honkanen A. Jokinen A. Laird M. Lewitowicz C. Longour F. de Oliveira Santos K. Peräjärvi M. Stanoiu 《The European Physical Journal A - Hadrons and Nuclei》2004,21(3):419-435
99.
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
100.
The rational and sustainable exploitation of nature resources is one of the priority objectives of our society. In this article a method is proposed to evaluate and exploit the energetic resources contained in different forest formations. This method is based on the use of a combustion bomb calorimeter to determine the calorific values of the different samples studied. These results were complemented with chemical analysis of the samples and with environmental and geomorphological studies of the zones were samples were taken. The results obtained during the last 3 years for the residual biomass originated from the forest formations existing in Galicia ensure the reliability and usefulness of the method that can be extended to any forest formation all over the world. 相似文献