全文获取类型
收费全文 | 2307篇 |
免费 | 46篇 |
国内免费 | 10篇 |
专业分类
化学 | 1194篇 |
晶体学 | 44篇 |
力学 | 47篇 |
数学 | 315篇 |
物理学 | 763篇 |
出版年
2022年 | 25篇 |
2021年 | 25篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 46篇 |
2017年 | 49篇 |
2016年 | 58篇 |
2015年 | 43篇 |
2014年 | 78篇 |
2013年 | 158篇 |
2012年 | 103篇 |
2011年 | 122篇 |
2010年 | 94篇 |
2009年 | 80篇 |
2008年 | 101篇 |
2007年 | 80篇 |
2006年 | 57篇 |
2005年 | 62篇 |
2004年 | 49篇 |
2003年 | 46篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 34篇 |
1992年 | 31篇 |
1990年 | 19篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 28篇 |
1981年 | 42篇 |
1980年 | 43篇 |
1979年 | 32篇 |
1978年 | 41篇 |
1977年 | 43篇 |
1976年 | 27篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1973年 | 38篇 |
1972年 | 24篇 |
排序方式: 共有2363条查询结果,搜索用时 15 毫秒
111.
We have theoretically investigated the effect of pressure on the structural stability of GaP?:?InP mixed system. The three-body-potential (TBP) model has been used. The TBP model consists of long-range as well as short-range interactions; the long-range part includes the modified Coulomb force as well as a three-body term; the short-range part in TBP defines the van der Waals and overlap repulsive interactions. We observe a pressure-induced structural phase transformation from ZnS (B3) to NaCl (B1) type phase in Ga 1?x In x P. Our calculated transition pressures for the initial GaP and final InP compound semiconductors are in good agreement with other reported data. 相似文献
112.
S. Bagˇcı H.M. Tütüncü S. Duman E. Bulut M. Özacar G.P. Srivastava 《Journal of Physics and Chemistry of Solids》2014
We have performed an ab initio study of structural, electronic, magnetic, vibrational and thermal properties of the cubic spinel LiMn2O4 by employing the density functional theory, the linear-response formalism, and the plane-wave pseudopotential method. An analysis of the electronic structure with the help of electronic density of states shows that the density of states at the Fermi level (N (EF)) is found to be governed by the Mn 3d electrons with some contributions from the 2p states of O atoms. It is important to note that the contribution of Mn 3d states to N(EF) is as much as 85%. From our phonon calculations, we have obtained that the main contribution to phonon density of states (below 250 cm−1) comes from the coupled motion of Mn and O atoms while phonon modes between 250 cm−1 and 375 cm−1 are characterized by the vibrations of all the three types of atoms. The contribution from Li increases rapidly at higher frequency (above 375 cm−1) due to the light mass of this atom. Finally, the specific heat and the Debye temperature at 300 K are calculated to be 249.29 J/mol K and 820.80 K respectively. 相似文献
113.
F. Ambrosino F. Anulli D. Babusci S. Bianco C. Bini N. Brambilla R. De Sangro P. Gauzzi P.M. Gensini S. Giovannella V. Muccifora M. Negrini F. Nguyen S. Pacetti G. Pancheri M. Passera A. Passeri A.D. Polosa M. Radici Y.N. Srivastava A. Vairo G. Venanzoni G. Violini 《The European Physical Journal C - Particles and Fields》2007,50(3):729-768
We present a detailed study, done in the framework of the INFN 2006 Roadmap, of the prospects for e+e- physics at the Frascati National Laboratories. The physics case for an e+e- collider running at high luminosity at the φ resonance energy and also reaching a maximum center of mass energy of 2.5 GeV
is discussed, together with the specific aspects of a very high luminosity τ-charm factory. Subjects connected to kaon decay
physics are not discussed here, being part of another INFN Roadmap working group. The significance of the project and the
impact on INFN are also discussed. All the documentation related to the activities of the working group can be found in http://www.roma1.infn.it/people/bini/roadmap.html. 相似文献
114.
C. Srivastava D. E. Nikles J. W. Harrell G. B. Thompson 《Journal of nanoparticle research》2010,12(6):2051-2056
Ternary alloy FePt(Au) nanoparticles were prepared by the co-reduction of platinum(II) acetylacetonate and gold(III) acetate and the thermal decomposition of iron pentacarbonyl in hot phenyl ether in the presence of oleic acid and oleylamine ligands. This gave spherical particles with an average diameter of 4.4 nm with a range of diameters from approximately 1.6–9 nm. The as-synthesized particles had a solid solution, face-centered-cubic structure. Though the average composition of the particles was Fe44Pt45Au11, individual particle analysis by Scanning Transmission Electron Microscopy–X-ray Energy Dispersive Spectroscopy showed a broad distribution in composition. In general, smaller-sized particles tended to have a lower amount of Au as compared to larger-sized particles. As the Au content increased, the ratio of Fe/Pt widened. 相似文献
115.
S.K. Srivastava 《Journal of Physics and Chemistry of Solids》1977,38(5):451-462
In this communication, the pseudopotential investigation of, the various properties of non-transition metals and alloys, is discussed. Various one parametric model pseudopotentials, derived from well known spherical functions sl(x), are employed in the calculations. Many recurrence relations of the sl(x) function have been described. The effects of exchange and correlation on conduction electrons are also considered separately by using different dielectric screenings in various properties. The ion-ion interaction, force constants, phonon spectrum, temperature coefficient of Knight shift and electronic transport coefficients of certain metals and alloys are evaluated. The results are compared with available experimental values. Generally good agreement is achieved. The screening charge density of certain metals in low and high density region are also determined. 相似文献
116.
S. K. Srivastava Shailja Tomar Rupali Rastogi Richa Saxena 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):634-640
Six new substituted diphenyltin(IV) O,O′-alkylene dithiophosphates, (C6H5)2Sn(X)S(S) POGO [G = —CH2C(CH3)2CH2—, X = Cl (1), SCN (3), ClO4 (5); G = —CH2C (C4H9)(C2H5)CH2—, X = Cl (2), SCN (4), ClO4 (6)], were synthesized by the reaction of the corresponding ammonium salts of the O,O’-alkylene dithiophosphates with an appropriate organotin(IV) chloride. The compounds were characterized on the basis of elemental and spectral analyses (ESI mass spectrometry, IR, 1H, 13C, 31P, and 119Sn NMR). The presence of a four-coordinated Sn atom and monodentate O,O’-alkylene dithiophosphate moiety in compounds 1–4 as well as bidentate O,O’-alkylene dithiophosphate unit in compounds 5,6 is established. 相似文献
117.
A. Srivastava S. Chhillar D. Singh R. Acharya P. K. Pujari 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(3):1461-1464
A non-destructive, in situ current normalized particle induced gamma-ray emission methodology has been standardized for quantification of fluorine (F) in soil samples from Punjab state, India. The samples were irradiated using 4 MeV proton beam from the Folded Tandem Ion Accelerator at BARC, Mumbai. The gamma rays of energies 197 and 478 keV arising from 19F(p, p′γ)19F and 7Li(p, p′γ)7Li nuclear reactions were measured using high resolution gamma-ray spectrometry. The concentration of fluorine in soil samples was found to vary between 414 and 5,746 mg kg?1. 相似文献
118.
Cadmium telluride thin films have been found to exhibit polytypism. The polytypes are formed when the as grown amorphous CdTe thin films undergo amorphous to crystalline transformation. The transformed single crystal regions correspond to different polytypes. Besides the well known zinc blende type 3 C cubic phase and less often found wurtzite type 2 H phase, four new polytypes (5 H, 6 H, 6 R and 15 R) the only ones known to-date have been found in the present investigation. In addition to the new polytypes, a new structural variant has also been found. This has the same ‘c’ parameter as that of the 2 H phase but has its ‘a’ lattice parameter as ‘a0 \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm o} \sqrt {3} $\end{document}’ (a0 being the common lattice parameter of the polytypes). A feasible mechanism making the formation of polytypes intelligible has been suggested. 相似文献
119.
120.
Himanshu Srivastava Pragya TiwariA.K. Srivastava Sanjay RaiTapas Ganguli S.K. Deb 《Applied Surface Science》2011,258(1):494-500
The effect of texture of iron foil substrate on the growth of hematite nanowires by annealing method has been investigated in detail. Three substrates of different textures were prepared from a [2 0 0] oriented iron foil by some simple processes. The hematite nanowires on these substrates were synthesized by annealing iron foil at 700 °C in moist oxygen. The growth pattern of nanowires on these substrates showed that the growth of hematite nanowires depends strongly on the iron substrate texture and [1 1 0] oriented iron grains are necessary for their growth. The samples were characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD), Electron Back Scatter Diffraction (EBSD) and Raman Spectroscopy. We have also tried to explain the various observations on the mechanism of growth. Mainly, the presence of water vapor significantly enhanced the formation of hematite nanowires which resulted in a very dense and aligned growth of nanowires on the substrate areas of favorable texture. Finally, the study proved the substrate texture to be a powerful tool to control growth of nanowires and can be used efficiently for patterning and large scale synthesis of the nanowires. 相似文献