全文获取类型
收费全文 | 393篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 283篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 30篇 |
物理学 | 69篇 |
出版年
2024年 | 5篇 |
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 17篇 |
2015年 | 7篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 15篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有399条查询结果,搜索用时 15 毫秒
71.
We used variationally improved perturbation theory (VIPT) in calculating the slope and curvature of Isgur-Wise (I-W) function
with the Cornell potential −$
\frac{{4\alpha _s }}
{{3r}}
$
\frac{{4\alpha _s }}
{{3r}}
+br + c instead of the usual stationary state perturbation theory as done earlier. We used −(4α
s
/3r), i.e. the Coulombic potential, as the parent and the linear one, i.e. br+c as the perturbed potential in the theory and calculated the slope and curvature of Isgur-Wise function including three states
in the summation involved in the first-order correction to wave function in the method. 相似文献
72.
Dipak Kumar Roy Kashyap Jyoti Tamuli Manobjyoti Bordoloi 《Journal of heterocyclic chemistry》2019,56(12):3313-3323
Different results were generated under different reaction conditions for the multicomponent reactions. Herein, an efficiently improved and mild protocol for the synthesis of dihydropyrimidine derivatives using cheap silver trifluoromethanesulfonate (CF3SO3Ag) as reusable catalyst is explained. With conventional heating and microwave irradiation method, the synthesis of substituted 3,4‐dihydropyrimidine‐2(1H)‐one and 3,4‐dihydropyrimidine‐2(1H)‐thione was achieved in different solvent environments like acetonitrile, water, and under solvent free neat condition. Moreover, the solvents (CH3CN and H2O) containing the CF3SO3Ag were reused for several times without loss of much catalytic activity after separation from the desired products. Thus, the method provides much improved and efficient alternative pathway to the original Biginelli reaction. 相似文献
73.
74.
Adsorption of basic fuchsin using waste materials--bottom ash and deoiled soya--as adsorbents 总被引:1,自引:0,他引:1
Basic fuchsin, a triaminotriphenylmethane dye, was removed by adsorption utilizing two waste materials--"bottom ash," a power plant waste material, and "deoiled soya," an agriculture waste product. The adsorbents were characterized through IR spectroscopy and differential thermal analysis (DTA). Batch adsorption experiments were carried out by measuring effects of pH, adsorbate concentration, sieve size, amount of adsorbent, contact time, temperature, etc. The results have been verified on the basis of Langmuir and Freundlich adsorption isotherm models and data obtained have been applied to calculate thermodynamic parameters. Specific rate constants for the processes were calculated by kinetic measurements and a pseudo-second-order adsorption kinetics was observed in each case. To identify whether the ongoing process is particle diffusion or film diffusion, the treatment given by Boyd and Reichenberg was employed. To assess the practical utility of the adsorbent, the aqueous adsorbate samples were eluted through fixed-bed columns of respective adsorbents. Attempts were also made to recover the adsorbed dyes by passing suitable solvent through the columns. 相似文献
75.
76.
77.
78.
JPC – Journal of Planar Chromatography – Modern TLC - Inula cappa (family Compositae) is used in the Ayurvedic medicinal system for the treatment of bronchitis, diabetes, fever,... 相似文献
79.
Recently measured inelastic X-ray spectra (IXS) of detailed coherent dynamical structure factor S(κ, ω) and hence the equilibrium collective dynamics, of the lightest liquid alkali metal, lithium at 475 K, have been successfully explained using the modified microscopic theory of the collective dynamics of a simple liquid, in a huge wave-vector, κ, range: 1.4 nm?1 ≤ κ ≤ 110.0 nm?1, ?κ is the linear momentum transfer. The role of single particle motion in the collective dynamics of the liquid changes from diffusive for smaller values of wave-vector, κ < 21 nm?1 to that of a free particle for higher κ-values, 21 nm?1 ≤ κ ≤ 110 nm?1. The quantum correction due to detailed balance condition in S(κ, ω) for liquid Li, whose dynamics, unlike that of quantum liquid 4He, is essentially classical, yields results in better agreement with the corresponding experimental S(κ, ω) and the quantum correction becomes significant for higher values of κ and ω. The wave-vector dependent variation of longitudinal viscosity, ηl, is in good agreement with the corresponding results obtained from memory function approach. The wave-vector dependent variation of single characteristic relaxation time lies in between the variation of two relaxation times of memory function approach. 相似文献
80.
Plaban Jyoti Sarma Debojyoti Bhattacharjee Bhupesh Kumar Mishra 《Molecular physics》2017,115(8):962-970
Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH2CH2)2NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10?10 cm3 molecule?1 s?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10?10 cm3 molecule?1 s?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH2 and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour. 相似文献