全文获取类型
收费全文 | 2393篇 |
免费 | 321篇 |
国内免费 | 279篇 |
专业分类
化学 | 1290篇 |
晶体学 | 132篇 |
力学 | 250篇 |
综合类 | 86篇 |
数学 | 290篇 |
物理学 | 945篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 72篇 |
2021年 | 66篇 |
2020年 | 84篇 |
2019年 | 67篇 |
2018年 | 70篇 |
2017年 | 81篇 |
2016年 | 86篇 |
2015年 | 90篇 |
2014年 | 140篇 |
2013年 | 220篇 |
2012年 | 101篇 |
2011年 | 146篇 |
2010年 | 123篇 |
2009年 | 161篇 |
2008年 | 140篇 |
2007年 | 175篇 |
2006年 | 152篇 |
2005年 | 111篇 |
2004年 | 114篇 |
2003年 | 101篇 |
2002年 | 105篇 |
2001年 | 77篇 |
2000年 | 62篇 |
1999年 | 49篇 |
1998年 | 60篇 |
1997年 | 41篇 |
1996年 | 50篇 |
1995年 | 27篇 |
1994年 | 38篇 |
1993年 | 30篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有2993条查询结果,搜索用时 0 毫秒
31.
Natalini B Marinozzi M Sardella R Macchiarulo A Pellicciari R 《Journal of chromatography. A》2004,1033(2):363-367
The chromatographic resolution of enantiomeric amino acids is accomplished on a reversed phase column using aqueous mobile phase containing the chiral reagent N,N-dimethyl-S-phenylalanine-Cu(II). The separation is a result of the whole interaction between the diastereomeric complex surface and the mixed stationary phase realized by the dynamic coating of the RP-18 carbon chains layer. The elution order seems to be related to the different water coordination capability on copper ion in the formation of the mixed ternary complexes. 相似文献
32.
33.
Theodora Zapryanova Antoaneta Hrussanova Alexander Milchev 《Journal of Electroanalytical Chemistry》2007,600(2):311-317
The nucleation and growth of copper crystals on a glassy carbon electrode are investigated at different constant overpotentials. Current transients are recorded and the number of copper nuclei is microscopically registered. The experimental data for the growth current are interpreted according to the theories of progressive and instantaneous nucleation and information is obtained on the stationary nucleation rate, the saturation nucleus number density and the exchange current density at the crystals–solution interface boundary. 相似文献
34.
35.
Fogolari F Esposito G Viglino P Molinari H 《Journal of computational chemistry》2001,22(15):1830-1842
An easy implementation of molecular mechanics and molecular dynamics simulation using a continuum solvent model is presented that is particularly suitable for biomolecular simulations. The computation of solvation forces is made using the linear Poisson-Boltzmann equation (polar contribution) and the solvent-accessible surface area approach (nonpolar contribution). The feasibility of the methodology is demonstrated on a small protein and a small DNA hairpin. Although the parameters employed in this model must be refined to gain reliability, the performance of the method, with a standard choice of parameters, is comparable with results obtained by explicit water simulations. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1830-1842, 2001 相似文献
36.
We describe and interpret computer simulations of the time evolution of a binary alloy on a cubic lattice, with nearest neighbor interactions favoring like pairs of atoms. Initially the atoms are arranged at random; the time evolution proceeds by random interchanges of nearest neighbor pairs, using probabilities compatible with the equilibrium Gibbs distribution at temperatureT. For temperatures 0.59Tc, 0.81 Tc, and 0.89T
c, with density of A atoms equal to that in the B-rich phase at coexistence, the density C1 of clusters ofl A atoms approximately satisfies the following empirical formulas: C1 w(1 –)3 andC
1, (1 –)4Q1w1 (2 l 10). Herew is a parameter and we defineQ
l
=
K
e
–E(K)
, where the sum goes over all translationally nonequivalentl-particle clusters andE(K) is the energy of formation of the clusterK. Forl > 10,Q
1 is not known exactly; so we use an extrapolation formulaQ
l
Aw
s
–l
l
– exp(–bl
), wherew
s is the value ofw at coexistence. The same formula (withw > w
s) also fits the observed values of C, (for small values ofl) at densities greater than the coexistence density (forT=0.59Tc): When the supersaturation is small, the simulations show apparently metastable states, a theoretical estimate of whose lifetime is compatible with the observations. For higher supersaturation the system is observed to undergo a slow process of segregation into two coexisting phases (andw therefore changes slowly with time). These results may be interpreted as a more quantitative formulation (and confirmation) of ideas used in standard nucleation theory. No evidence for a spinodal transition is found.Supported by AFOSR Grant No. 73-2430D and by ERDA Contract No. EY-76-C-02-3077*000. 相似文献
37.
我们利用Born-Mayer-Huggins相互作用势函数对(KF)N(N=108,256,500和864)团簇进行了分子动力学(MD)模拟。为了避免周期性边界条件对相变、成核和重结晶的干扰作用,对体系采用了自由边界。基于MD模拟结果,对团簇的熔化温度、熔化焓、扩散系数、成核速率、固液界面自由能、临界核大小等进行了计算和讨论。在对(KF)864双晶团簇的热退火模拟中,观察到了固态的重结晶和晶粒的生长。经典的成核理论成功地解释了(KF)864双晶团簇的重结晶MD模拟结果。 相似文献
38.
D. Berger C. Matei F. Papa G. Voicu V. Fruth 《Progress in Solid State Chemistry》2007,35(2-4):183-191
We report the synthesis of La1−xSrxCoO3 nanopowders by solution combustion method using metal nitrates and -alanine (alanine method) or urea (urea method) as fuel. The influence of metal nitrates/organic substance molar ratio and the type of fuel was investigated. The isolated complex precursors were characterized by atomic absorption spectroscopy (AAS), FT-IR spectra and DTA–TG analysis. The La1−xSrxCoO3 (x = 0–0.3) powders were characterized by X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray analysis (SEM–EDX), as well as by specific surface area measurements. XRD patterns indicate the formation of single-phase LaCoO3 (rhombohedral) when as-synthesized powders were calcined at 873 K, 3 h in the case of the alanine method and at 1073 K, 3 h for urea-based system. Also, strontium doped lanthanum cobaltites obtained by both methods at 1273 K are single phase with rhombohedral perovskite-like structure as XRD data have proved. SEM investigation of pure and doped lanthanum cobaltites reveal that the samples prepared by both methods have fine particles with tendency of agglomerates formation with different shapes, spongy aspect and high porosity. La1−xSrxCoO3 nanopowders obtained by alanine method have larger specific surface area values than those prepared by urea method. 相似文献
39.
C. Mansilla F. Gracia A. I. Martin‐Concepción J. P. Espinós J. P. Holgado F. Yubero A. R. González‐Elipe 《Surface and interface analysis : SIA》2007,39(4):331-336
The initial steps in the formation of thin films have been investigated by analysis of the peak shape (both inelastic background and elastic contributions) of X‐ray photoelectron spectra. Surface coverage and averaged height of the deposited particles have been estimated for several overlayers (nanometre range) after successive deposition cycles. This study has permitted the assessment of the type of nucleation and growth mechanisms of the films. The experiments have been carried out in situ in the preparation chamber of an XPS spectrometer. To check the performance of the method, several materials (i.e. cerium oxide, vanadium oxide and cadmium sulfide) have been deposited on different substrates using a variety of preparation procedures (i.e. thermal evaporation, ion beam assisted deposition and plasma enhanced chemical vapour deposition). It is shown that the first deposited nuclei of the films are usually formed by three‐dimensional particles whose heights and degree of surface coverage depend on the chemical characteristics of the growing thin film and substrate materials, as well as the deposition procedure. It is concluded that XPS peak shape analysis can be satisfactorily used as a general method to characterize morphologically the first nanometric moieties that nucleate a thin film. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
40.
In order to obtain a catalyst support with a high surface area, ZrO2 and ZrO2-Y2O3 were prepared by the hydrolytic decomposition of the corresponding isopropoxide dissolved in benzene. The hydrolysis was carried out at 80°C using an excess amount of distilled water in flowing dry nitrogen. The precipitates thus obtained were dried at 100°C followed by calcination at 500°C in air or nitrogen for 1 h. The specific surface areas for both of the ZrO2 and ZrO2-Y2O3 increased with increasing amount of water added for hydrolysis, and the surface areas for ZrO2-Y2O3 increased with increasing yttrium content. A ZrO2 having a surface area of 130 m2/g was produced, and a stabilized tetragonal ZrO2 with 15 mol% Y3+ having a surface area of 200 m2/g was produced. Furthermore, despite the difference in the ZrO2 and ZrO2-Y2O3 crystal structures, the lattice-strain of ZrO2 has been unequivocally related to the surface area. 相似文献