全文获取类型
收费全文 | 1218篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
化学 | 929篇 |
晶体学 | 6篇 |
力学 | 23篇 |
数学 | 33篇 |
物理学 | 262篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 23篇 |
2020年 | 24篇 |
2019年 | 30篇 |
2018年 | 36篇 |
2017年 | 38篇 |
2016年 | 50篇 |
2015年 | 33篇 |
2014年 | 47篇 |
2013年 | 111篇 |
2012年 | 82篇 |
2011年 | 82篇 |
2010年 | 58篇 |
2009年 | 61篇 |
2008年 | 72篇 |
2007年 | 68篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 26篇 |
2002年 | 27篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 8篇 |
排序方式: 共有1253条查询结果,搜索用时 15 毫秒
141.
Polypyrrole based solid state electrochemical redox supercapacitors have been fabricated using the polymeric gel electrolytes comprising of poly methyl methacrylate (PMMA)-propylene carbonate (PC)-ethylene carbonate (EC)-perchlorate salts of different cations [Li+, Na+ and (C2H5)4N+ (TEA+)]. A comparative study has been carried out using linear sweep reversal voltammetry, complex impedance spectroscopy and constant current charge-discharge tests. The capacitance values of the cells have been observed to be in the range of 15.3-22.5 mF cm−2 (equivalent to single electrode specific capacitance of 120-178 F g−1 of polypyrrole). This corresponds to the values of energy density 16.7-24.7 Wh kg−1 and power density 1.6-2.8 kW kg−1 calculated for the working voltage of 1.0 V limited for polypyrrole based redox capacitors. Substantial improvements in the coulombic efficiency of the cells have been observed (close to 100%) due to the application of gel electrolytes showing flexible and liquid like behaviour. Further, the types and sizes of the cations in the gel electrolytes do not play any dominant role in the capacitive behaviour of the redox cells. 相似文献
142.
N. Kalaiselvi M. Ashok Kumar M. S. Prasath N. G. Renganathan M. Raghavan N. Muniyandi 《Ionics》2002,8(5-6):447-452
Li2CoMn3O8, a 5 V cathode material used in rechargeable lithium batteries, has been synthesized by adopting a novel technique of using
fuels along with the nitrate reactants. The effect of the fuel on the synthesis of Li2CoMn3O8 has been analyzed in terms of the physical and electrochemical properties of the final product formed by various methods
such as solid-state carbonate fusion and the solution route using acetate and nitrate precursors. Powder X-ray diffraction
FT IR spectrum, particle size, surface area and SEM analysis were carried out. The combustion method, also known as selfpropagating
high temperature (SPHT) method, has been employed in the present study by using nitrate mixtures of the respective salts and
a nitrogeneous fuel (urea or glycine) at a temperature of 300 °C for 3 hrs. The nitrate reactants without the addition of
fuel gave only a deliquescent product even at elevated temperature (600 °C) thus indicating the necessity of fuels. Similar
attempts using acetate reactants with and without the addition of nitrogeneous fuels were made separately in order to find
out the necessity of fuel also in this case. The characterization of the product in terms of purity, single-phase formation
and surface morphology suggested that the fuel played no role in the case of the acetate precursors. A comparative study was
made on the products obtained by the acetate precursor, combustion method and the conventional carbonate method. Among the
three methods, the combustion method with glycine as fuel yielded the spinel phase with high purity Li2CoMn3O8 with superior electrochemical behavior both in terms of high cell voltage and good cycle life behavior. 相似文献
143.
H. Yasuda Ashok K. Sharma Takeshi Yasuda 《Journal of Polymer Science.Polymer Physics》1981,19(9):1285-1291
The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water-swollen three-dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short-range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer-air interface. 相似文献
144.
The high spin yrast states up toJ=20+ in184, 186Pt and190, 192, 194Pt are studied in a microscopic approach of variation with number-conserved projected states. The energy spectra, quadrupole
moments andB(E2) values are calculated by employing the Hamiltonian with quadrupole plus pairing interactions. The results of the calculations
are in fair agreement with the available experimental data. 相似文献
145.
The high spin yrast states uptoJ=22+ in182,184,186Os are studied in a microscopic variational approach with number-conserved projected states. The energy spectra, quadrupole,
moments andB (E2) values are calculated by employing the Hamiltonian with quadrupole plus pairing interactions. The results of the calculations
are in fair agreement with the available experimental data. 相似文献
146.
Quantum chromodynamics based isovector isoscolar particle mixing arising out of isospin violating quark mass differences has been used to construct a new charge-symmetry breaking Λ-N interaction element. It appears that vector meson exchanges between N and a physical Λ rather than pseudoscalar exchanges provide the largest contribution to explain the binding energy difference between the mirror hyper-nuclei ΛHe4 and ΛH4. Prediction of the model to Λn and Λp scattering lengths have been compared with those obtained from the combined analysis of ΛN scattering and s-shell hyperfragment data. We find satisfactory agreement of our results. 相似文献
147.
Sensitivity of Bayes decisions for the success probability for samples from a nonbinomial population
Ashok K. Bansal 《Annals of the Institute of Statistical Mathematics》1982,34(1):143-149
Summary A family of generalised negative binomial distributions is employed to investigate inference robustness of the Bayes estimator
of the unknown parameter of the binomial distribution. A zone of sensitivity for the test of significance is constructed to
forewarn the pro-Jeffreys Bayesians against indiscriminate choice of the probability in favour of the null hypothesis. A few
selected tables are presented to illustrate the effect of relaxation of the ‘binomiality’ assumption. 相似文献
148.
Calculations of the electrical resistivity of several solid noble and transition metals have been carried out using the transition metal model potential proposed by Animalu. It has been found that, except for Cu, Ag and Au, the calculated resistivities of solid transition metals are considerably below the experimental values indicating that the Animalu's model potential fails to account for the electrical resistivities of transition metals. The failure of the Animalu's model potential has been discussed. 相似文献
149.
The equilibrium deformations of tungsten, osmium and platinum nuclei are studied with the self-consistent quadrupole plus
pairing interaction model by considering all the nucleons in nucleus explicitly. It is shown that similar results can be obtained
by performing calculations with or without the assumption of an inert core. The only difference is in the strength of the
quadrupole and pairing interactions to be employed in the respective calculations. The experimental static quadrupole moments
and theB (E2) values are correctly reproduced by performing calculations with bare nucleon charge for all the nucleons. 相似文献
150.