全文获取类型
收费全文 | 7104篇 |
免费 | 1295篇 |
国内免费 | 1093篇 |
专业分类
化学 | 3430篇 |
晶体学 | 36篇 |
力学 | 549篇 |
综合类 | 73篇 |
数学 | 1065篇 |
物理学 | 4339篇 |
出版年
2024年 | 7篇 |
2023年 | 92篇 |
2022年 | 181篇 |
2021年 | 181篇 |
2020年 | 250篇 |
2019年 | 232篇 |
2018年 | 193篇 |
2017年 | 213篇 |
2016年 | 243篇 |
2015年 | 243篇 |
2014年 | 349篇 |
2013年 | 615篇 |
2012年 | 440篇 |
2011年 | 441篇 |
2010年 | 348篇 |
2009年 | 451篇 |
2008年 | 491篇 |
2007年 | 497篇 |
2006年 | 486篇 |
2005年 | 424篇 |
2004年 | 390篇 |
2003年 | 355篇 |
2002年 | 316篇 |
2001年 | 246篇 |
2000年 | 278篇 |
1999年 | 207篇 |
1998年 | 207篇 |
1997年 | 176篇 |
1996年 | 117篇 |
1995年 | 110篇 |
1994年 | 93篇 |
1993年 | 80篇 |
1992年 | 85篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 38篇 |
1988年 | 37篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 34篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1974年 | 6篇 |
排序方式: 共有9492条查询结果,搜索用时 15 毫秒
171.
The intermolecular potential function of Smith–Thakkar type for C60 has been proposed, and its expression is as followsThe unit of u(r) is J/mol, r is the distance between two C60 molecules center and the unit is nm. Some properties of C60 in the gas and crystal have been studied using the interaction potential of Smith–Thakkar type, such as stability of C60 crystals, virial coefficient and lattice dynamics. 相似文献
172.
173.
O. V. Prokuda V. R. Belosludov I. K. Igumenov P. A. Stabnikov 《Journal of Structural Chemistry》2006,47(6):1032-1041
Experimental data have been analyzed and interpreted for four volatile acetylacetonates of trivalent metals Al, Cr, Fe, and Ir. The crystal lattice energies were calculated by the atom-atom potential method. The lattice energies obtained by using the Buckingham potential are in better agreement with the sublimation heats of these metal complexes than those calculated from the Lennard-Jones potential. The experimental dependences of vapor pressure for the complexes are in satisfactory agreement with the values obtained from the calculated lattice energies and entropies of crystal-gas transitions. 相似文献
174.
Vanadium Doped Sol-Gel TiO2 Coatings 总被引:1,自引:0,他引:1
Maria Crisan Maria Zaharescu D. Crisan Rodica Ion Mihaela Manolache 《Journal of Sol-Gel Science and Technology》1998,13(1-3):775-778
A study of the experimental conditions required to obtain vanadium doped sol-gel TiO2 coatings is presented. Tetraethyl orthotitanate was employed as the TiO2 source and VCl3, VOSO4 · H2O and VOSO4 dissolved H2SO4 where employed as vanadium sources.Dip coating has been used to produce coatings on silicon wafers, spectral carbon electrodes and titanium electrodes. Both supported and unsupported films have been studied by UV-Vis spectra, IR spectroscopy and X-ray diffraction (XRD). The measurements have been made on samples as prepared and treated thermally at temperatures between 100°C and 300°C. The thermal treatment temperatures have been established from DTA/TGA measurements.The vanadium doped sol-gel TiO2 coatings have been tested as sensors for redox potential measurements in electrochemical processes. The influence of both the thickness of films and the nature of substrate has been investigated. 相似文献
175.
V. Climent N. García-Araez E. Herrero J. Feliu 《Russian Journal of Electrochemistry》2006,42(11):1145-1160
The electrochemical behavior of platinum single-crystal electrodes is revisited, with special emphasis on the determination
of the potential of zero charge. We show that the measure of the charge displaced during CO adsorption allows the determination
of the potential of zero total charge (PZTC). The estimation of the potential of zero free charge (PZFC) is discussed, with
different degrees of approximation. The application of this methodology to the study of the PZTC of platinum stepped surfaces
vicinal to Pt(111) reveals a marked decrease of the PZTC due to the introduction of surface steps. This effect is interpreted
as the result of the existence of markedly smaller surface potentials localized on step sites. The importance of considering
local aspects of the interface is emphasized with the use of N2O reduction as a sensitive probe to the local structure of the surface. It is proposed that the different local maxima observed
in the absolute value of the reduction current correspond to the local values of PZTC. It is shown that there is, in general,
good agreement between the overall PZTC, obtained from the CO displacement, and that calculated from the local values inferred
from the N2O reduction. Further insight is obtained with the application of the laser-induced temperature jump method. This technique
is useful to calculate the potential of maximum entropy of the double-layer formation. The resulting value of this potential
for Pt(111) is discussed in the light of the PZFC value obtained from different approaches. For stepped surfaces vicinal to
Pt(111), two local maxima in the entropy of the double layer are observed that are close to the local PZTC values estimated
from the N2O reduction. This result suggests the existence of cooperative effects in the organization of the water dipoles close to the
electrode surface.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1275–1292.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
176.
Intramolecular cyclization reactions of 3,4-bis(indol-3-yl)maleimides 1, 3-(indol-1-yl)-4-(indol-3-yl)maleimides 2, and 3,4-bis(indol-1-yl)maleimides 3 under the action of protic acids were studied in order to estimate the parameters of the interaction between protonated and
unprotonated indole moieties. Geometric parameters, charge distributions, energy characteristics, and information concerning
the frontier orbitals of bisindolylmaleimides 1–3 were obtained from density functional B3LYP/6-31G(d) quantum chemical calculations. Alternative pathways of protonation of
bisindolylmaleimides with differently bonded indole and maleimide moieties were studied and pathways of cyclization of corresponding
conjugated acids leading to polyannelated compounds were analyzed. All the key intermediates of the cyclization reactions
correspond to stationary points on the potential energy surfaces (minima and transition states). Analysis of the potential
energy surfaces revealed almost linear dependences of the activation energies of the cyclization reactions under study on
the distances between the reaction centers, on the angle of approach of intramolecular electrophile, and on the energy gap
(energy difference between frontier orbitals). The key role in the cyclization reactions is played by structural similarity
between the starting indoleninium cations and the activated complexes of the reactions under study.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 754–760, May, 2006. 相似文献
177.
178.
本文制备了PANI纳米点阵列, 利用导电原子力显微镜(C-AFM)表征了其形貌和导电性能, 在室温下观察到PANI纳米点的库仑台阶(Coulomb staircase)现象, 并利用库仑阻塞效应的理论进行了初步的分析. 相似文献
179.
Ab initio study of the adiabatic potential energy surface (PES) for 1,2,3-trifluorobenzene cation-radical was carried out by the ROHF, UHF, MCSCF, MP2, and DFT (B3LYP) methods with the 6-31G* basis set. The PES in question is a pseudorotation surface at all calculation levels. The pseudorotation barrier height does not exceed 3.2 kcal/mol, suggesting a possibility for its manifestations in experimental EPR spectra. 相似文献
180.
The crystal habit of fcc metal particles formed on an amorphous carbon film electrode in solution at different electrode
potentials is discussed. The fcc metal particles have different crystallographic habits depending on applied electrode potential;
that is, icosahedral and/or decahedral particles are formed at lower potentials, and fcc single-crystalline or polycrystalline
particles at higher potentials. It was found that decahedra and icosahedra of Cu-Au alloy particles are formed in the potential
region of underpotential deposition (UPD) of Cu at which only fcc Au single-crystalline particles and Au polycrystalline particles
appear. This is attributed to the charge transfer from the UPD Cu ions to the Au overlayer of Cu-Au alloy particles. The formation
of decahedral and icosahedral Cu-Au alloy particles depends on the composition of the Cu-Au alloy. On the basis of these results
it was deduced that the contraction of the surface lattice of the growing particles is responsible for the formation of icosahedral
and decahedral particles.
Received: 25 February 1997 / Accepted: 21 April 1997 相似文献