全文获取类型
收费全文 | 454432篇 |
免费 | 3766篇 |
国内免费 | 1372篇 |
专业分类
化学 | 226951篇 |
晶体学 | 7064篇 |
力学 | 24028篇 |
综合类 | 14篇 |
数学 | 70037篇 |
物理学 | 131476篇 |
出版年
2019年 | 3551篇 |
2018年 | 14785篇 |
2017年 | 14549篇 |
2016年 | 12652篇 |
2015年 | 4623篇 |
2014年 | 6687篇 |
2013年 | 15994篇 |
2012年 | 15056篇 |
2011年 | 23857篇 |
2010年 | 15782篇 |
2009年 | 16229篇 |
2008年 | 19160篇 |
2007年 | 21269篇 |
2006年 | 12074篇 |
2005年 | 11848篇 |
2004年 | 11376篇 |
2003年 | 10922篇 |
2002年 | 9889篇 |
2001年 | 10913篇 |
2000年 | 8312篇 |
1999年 | 6384篇 |
1998年 | 5323篇 |
1997年 | 5360篇 |
1996年 | 5191篇 |
1995年 | 4644篇 |
1994年 | 4590篇 |
1993年 | 4393篇 |
1992年 | 5100篇 |
1991年 | 5121篇 |
1990年 | 4997篇 |
1989年 | 5081篇 |
1988年 | 4966篇 |
1987年 | 4984篇 |
1986年 | 4634篇 |
1985年 | 6097篇 |
1984年 | 6158篇 |
1983年 | 5156篇 |
1982年 | 5319篇 |
1981年 | 5223篇 |
1980年 | 4965篇 |
1979年 | 5448篇 |
1978年 | 5653篇 |
1977年 | 5670篇 |
1976年 | 5611篇 |
1975年 | 5301篇 |
1974年 | 5130篇 |
1973年 | 5284篇 |
1972年 | 3776篇 |
1968年 | 3376篇 |
1967年 | 3450篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
林诒勋 《高校应用数学学报(英文版)》2003,18(3):361-369
§ 1 IntroductionThe cutwidth problem for graphs,as well as a class of optimal labeling and embed-ding problems,have significant applications in VLSI designs,network communicationsand other areas (see [2 ] ) .We shall follow the graph-theoretic terminology and notation of [1 ] .Let G=(V,E)be a simple graph with vertex set V,| V| =n,and edge set E.A labeling of G is a bijec-tion f:V→ { 1 ,2 ,...,n} ,which can by regarded as an embedding of G into a path Pn.Fora given labeling f of G,th… 相似文献
952.
Lancaster G.P.T. Häffner H. Wilson M.A. Becher C. Eschner J. Schmidt-Kaler F. Blatt R. 《Applied physics. B, Lasers and optics》2003,76(8):805-808
We present a scheme for employing a violet extended-cavity diode laser in experiments with single, trapped ions. For this the grating-stabilised laser is spatially and spectrally filtered and referenced to a Fabry–Pérot cavity. We measure an upper limit to the line width by observing a 305-kHz FWHM beat note with the second harmonic of a titanium sapphire laser. The laser is subsequently used to optically cool a single 40Ca+ ion close to the Doppler limit. PACS 03.67.Lx; 32.80.Pj; 42.55.Px 相似文献
953.
A hybrid analytical/numerical method is proposed that permits the efficient dynamic analysis of planar serial-frame structures. The method utilizes a numerical implementation of a transfer matrix solution to the equation of motion. By analyzing the transverse and longitudinal motions of each segment simultaneously and considering the compatibility requirements across each frame angle, the undetermined variables of the entire frame structure system can be reduced to six which can be determined by application of the boundary conditions. The main feature of this method is to decrease the dimensions of the matrix involved in the finite element methods and certain other analytical methods. 相似文献
954.
Maria G. Semenova Larisa E. Belyakova Anna S. Antipova Yu. N. Polikarpov Lida Klouda Anna Markovic Michael M. Il'in 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):47-54
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed. 相似文献
955.
956.
J. Wang J. Kono A. Oiwa H. Munekata C. J. Stanton 《Superlattices and Microstructures》2003,34(3-6):563
We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons. 相似文献
957.
The logarithmic decrement and shear modulus of a bulk amorphous Zr52.5Ti5Cu17.9Ni14.6Al10 alloy were studied with an inverse torsion pendulum in the range from room temperature to the crystallization temperature and in the frequency range 5–40 Hz. The activation energy spectra of reversible and irreversible structural relaxation were estimated. The results obtained are discussed in the context of a two-energy-level model. 相似文献
958.
In this paper a tripartite qualitative design combining abservation, stimulated recall and interview is presented and discussed. This three-step-design makes it possible to get insight into the interaction of internal and external processes when solving mathematical tasks. The data analysis depends on the research question and the methodological approach. In the light of two research projects in mathematics education two different methods of data analysis are presented and methodologically reflected. 相似文献
959.
960.
T. M. Shneidman G. G. Adamian N. V. Antonenko S. P. Ivanova R. V. Jolos W. Scheid 《Physics of Atomic Nuclei》2003,66(2):206-217
Based on the dinuclear system concept, the role of bending vibrations in creation of the angular momentum of primary fission fragments is investigated. For 252Cf spontaneous fission, the angular momenta of the fragments are calculated as a function of the neutron multiplicity and compared with available experimental data. Different cluster compositions of the 252Cf fission modes at the scission point are considered. 相似文献