全文获取类型
收费全文 | 851篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 496篇 |
晶体学 | 12篇 |
力学 | 79篇 |
数学 | 103篇 |
物理学 | 175篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 25篇 |
2013年 | 61篇 |
2012年 | 54篇 |
2011年 | 48篇 |
2010年 | 31篇 |
2009年 | 17篇 |
2008年 | 29篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 31篇 |
2002年 | 30篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1998年 | 6篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 8篇 |
1973年 | 12篇 |
1963年 | 5篇 |
1945年 | 6篇 |
1941年 | 11篇 |
1936年 | 9篇 |
排序方式: 共有865条查询结果,搜索用时 15 毫秒
11.
N.V. Rama Rao R. Gopalan M. Manivel Raja V. Chandrasekaran D. Chakravarty R. Sundaresan R. Ranganathan K. Hono 《Journal of magnetism and magnetic materials》2007
SmCo5+x wt% Fe (x=0, 5 and 10) nanocomposite powders were synthesized by mechanical milling and were consolidated into bulk shape by spark plasma sintering (SPS) technique. The evolution of structure and magnetic properties were systematically investigated in milled powders as well as in SPS samples. A maximum coercivity of 8.9 kOe was achieved in spark plasma sintered SmCo5+5 wt% Fe sample. The exchange spring interaction between the hard and soft magnetic phases was evaluated using δM–H measurements and the analysis revealed that the SPS sample containing 5 wt% Fe had a stronger exchange coupling between the magnetic phases than that of the sample with10 wt% Fe. 相似文献
12.
J. Rama Rao H. Machner G. Buhr M. Nolte M. Palarczyk 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):35-42
Correlations between pairs of projectile-like fragments, emitted by the system 16O$ + $197Au at the laboratory bombarding energy of 515MeV, have been studied under two stipulated conditions: 1) at least one member
of the pair is emitted at an angle less than the grazing angle for the system, 2) both the members of the pair are emitted
at angles larger than the grazing angle. A surprisingly large difference, by more than an order of magnitude, is found between
the correlations for the two cases. This observation could be explained on the basis of a simple semi-classical break-up model.
Further analysis of the variation of the charge correlation function with the difference in the nuclear charges of the correlated
pair showed trends which are consistent with an “inelastic break-up process”, in which the projectile breaks up at the radius
of contact, in such a way that, one fragment (preferably the lighter) is emitted to one side within the grazing angle, while
the other orbits around the target nucleus for a while and emerges on the other side, at a negative scattering angle, much
like in a deep inelastic scattering. 相似文献
13.
The transmitted photon spectra of133Ba,22Na,137Cs,54Mn and60Co point sources are measured through different thicknesses of water, concrete and sand. The multiple-scatter peaks observed
in these materials at 60, 90 and 100 keV energies respectively are found to be independent of incident photon energy and thickness
of the medium. 相似文献
14.
Y. Rama Krishna Sarma 《Annals of the Institute of Statistical Mathematics》1987,39(1):497-512
Summary In this note some asymptotically optimum tests for testing hypotheses concerning parameters when the observations are dependent
are obtained. Test statistics based on the score functions, similar to the one proposed by Rao in the case when the observations
are i.i.d. are proposed. Asymptotically UMP tests for one sided hypotheses against one sided alternatives and asymptotically
UMP unbiased test for a simple hypothesis against two sided alternatives are derived. In the multiparameter case tests for
simple hypotheses that have asymptotically best constant power on some family of surfaces in the parameter space are derived. 相似文献
15.
The transport coefficients for the nine point groups
—which represent the symmetry groups of the quasicrystals in two and three dimensions—have been evaluated and tabulated in
this work, employing group-theoretical methods. 相似文献
16.
The maximum number of non-vanishing and independent second order photoelastic coefficients required by the seven pentagonal
and the two icosahedral point groups 5(C5),
(S10),
(C5h
),
m2(D5h
), 52(D5), 5m(C5v
),
2m(D5d
); 235(I), 2/m
(I
h
)—that describe the quasicrystals symmetry groups in two and three dimensions—is obtained. The schemes of non-vanishing and
independent coefficients have been calculated and listed. Finally the results of this group-theoretical study are briefly
discussed. 相似文献
17.
G A V Ramanamurthy K Ramachandra Rao Y Rama Krishna P Venkateswarlu K Bhaskara Rao P V Ramana Rao S Venkata Ratnam V Seshagiri Rao G J Nagaraju S Bhuloka Reddy 《Pramana》2001,56(5):697-703
The Measurement of K
β
K
/α
intensity ratios are measured in some 3d shell elements by using a 2 MeV proton beam along with a high resolution Si(Li) detector. The present Measurement of K
β
K
/α
intensity ratios are in good agreement with Scofield modified theoretical values, thus supporting the basic assumptions in
that theory. From the present Measurement of K
β
K
/α
intensity ratios, it is evident that due to chemical effects, the experimental Measurement of K
β
K
/α
intensity ratios will be increased while they will be decreased due to the presence of simultaneous M-shell vacancies which are produced due to proton excitation. 相似文献
18.
19.
T. Raghavendra RaoCh. Rama Krishna U.S. Udayachandran ThampyCh. Venkata Reddy Y.P. ReddyP. Sambasiva Rao R.V.S.S.N. Ravikumar 《Physica B: Condensed Matter》2011,406(11):2132-2137
The effect of Li2O content in vanadyl doped 20ZnO+xLi2O+(30−x)Na2O+50B2O3 (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO2+ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g⊥-g∥) and Dt reveals that their values vary non-linearly with Li2O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect. 相似文献
20.
D. Madhavi LathaV.G.K.M. Pisipati C. Rama Chandra PrabhuP.V. Datta Prasad 《Journal of Molecular Liquids》2011,164(3):187-190
The thermodynamic parameters like Moelwyn-Hughes parameter (C1), reduced molar volume (V~), isochoric temperature coefficient of internal pressure (X), Huggin's parameter (F), Gruneisen parameter (Γp), isothermal microscopic Gruneisen parameter, Sharma parameter (So), fraction free volume (f) and (A?) a dimensionless thermal parameter, etc and the Beyer's nonlinearity parameter (B/A) were deduced employing the thermal expansion coefficient derived from density data for the homologues series of compounds terephthalyidene-bis-p-n-alkyl anilines, TBnA with n = 5 to 10,12,14,16 and 18. Further, it is found that the variation of molecular radius, Mr increases with the increase of alkyl chain number, with a core radius of 4.78 Å and the increment for methylene unit is 0.086 Å . The results were discussed with the body of the data available. 相似文献