全文获取类型
收费全文 | 722篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 437篇 |
晶体学 | 28篇 |
力学 | 3篇 |
数学 | 75篇 |
物理学 | 201篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 15篇 |
2014年 | 46篇 |
2013年 | 54篇 |
2012年 | 56篇 |
2011年 | 45篇 |
2010年 | 31篇 |
2009年 | 31篇 |
2008年 | 35篇 |
2007年 | 22篇 |
2006年 | 30篇 |
2005年 | 28篇 |
2004年 | 30篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有744条查询结果,搜索用时 62 毫秒
81.
Haladhara Naik Guinyun Kim Ashok Goswami Sarbjit Singh Vijay Kumar Manchanda Devesh Raj Srinivasan Ganesan Young Do Oh Hee-Seock Lee Kyung Sook Kim Man-Woo Lee Moo-Hyun Cho In Soo Ko Won Namkung 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(2):439-445
The mass–yield distributions of various fission products have been determined in the 50-, 60- and 70-MeV end point bremsstrahlung induced fission of natPb using off-line γ-ray spectrometric technique in the electron linac at Pohang Accelerator Laboratory, Korea. The mass–yield distributions are symmetric with average mass of 102.34, 102.25 and 102.03 and FWHM of 21, 22 and 23 mass unit, respectively. From the present data and literature data in the 50–85 MeV bremsstrahlung induced fission of 209Bi the following observations were obtained: (i) The average masses of the yield distributions in the 50–85 MeV bremsstrahlung induced fission of natPb and 209Bi are around 102.25 ± 0.25 and 103 ± 0.5, respectively. (ii) The FWHM of the mass–yield distributions increases from about 21 mass units at 50 MeV to 23 mass units at 70–85 MeV, which is explained from the point of increase in multi-chance fission probability with increasing excitation energy. (iii) Within the bremsstrahlung energy range of 50–85 MeV, the role of nuclear structure effect in the mass–yield distribution was observed in the photo-fission of 209Bi, whereas it was not seen in case of natPb. This may be due to the presence of so many isotopes in natPb unlike mono-isotopic 209Bi. 相似文献
82.
H. Naik P. M. Prajapati S. V. Suryanarayana P. N. Pathak D. R. Prabhu V. Chavan D. Raj P. C. Kalsi A. Goswami S. Ganesan V. K. Manchanda 《The European Physical Journal A - Hadrons and Nuclei》2011,47(8):1-5
The νp process is a primary nucleosynthesis process which occurs in core-collapse supernovae. An essential role in this process is being played by electron antineutrinos. They generate, by absorption on protons, a supply of neutrons which, by (n, p) reactions, allow to overcome waiting point nuclei with rather long beta-decay and proton-capture lifetimes. The synthesis of heavy elements by the νp process depends sensitively on the $\bar \nu _e$ luminosity and spectrum. As has been shown recently, the latter are affected by collective neutrino flavor oscillations which can swap the $\bar \nu _e$ and $\bar \nu _{\mu ,\tau }$ spectra above a certain split energy. Assuming such a swap scenario, we have studied the impact of collective neutrino flavor oscillations on the νp-process nucleosynthesis. Our results show that the production of light p-nuclei up to mass number A = 108 is very sensitive to collective neutrino oscillations. 相似文献
83.
84.
Byron P. Brassel Sunil D. Maharaj Rituparno Goswami 《General Relativity and Gravitation》2017,49(8):101
We establish the result that the standard Boulware–Deser spacetime can radiate. This allows us to model the dynamics of a spherically symmetric radiating dynamical star in five-dimensional Einstein–Gauss–Bonnet gravity with three spacetime regions. The local internal region is a two-component system consisting of standard pressure-free, null radiation and an additional string fluid with energy density and nonzero pressure obeying all physically realistic energy conditions. The middle region is purely radiative which matches to a third region which is the vacuum Boulware–Deser exterior. Our approach allows for all three spacetime regions to be modeled by the same class of metric functions. A large family of solutions to the field equations are presented for various realistic equations of state. A comparison of our solutions with earlier well known results is undertaken and we show that Einstein–Gauss–Bonnet analogues of these solutions, including those of Husain, are contained in our family. We also generalise our results to higher dimensions. 相似文献
85.
P. Majee G. Goswami M. K. Sen B. C. Bag 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(3):435-439
In this paper we have studied the directed motion of a Brownian particle
in a multiplicative noise
driven flashing ratchet system. Our investigation shows
the current (j) is either maximum or minimum
in the super-diffusion (SPD) region depending on the asymmetric character of the ratchet potential.
But the optimum behavior disappears for the symmetric
ratchet potential and there is a current inversion around the normal diffusion (ND). With increase of
half cycle period(tp/2) (which controls the on-off operation
mechanism of the potential), j
passes through a maximum and the peak height is the highest for the SPD. Also
at low asymmetry in the system, the mobility is more dominating for
the normal and the super-diffusion cases than the sub-diffusion.
For large asymmetry in the ratchet potential,
the diffusion control positive current
is larger for the ND compared to the other cases.
Finally, we observe that there is a maximum in the variation of current as a function of noise correlation time for
SPD. But it disappears for the other cases. 相似文献
86.
This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations
are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic
ligands viz. HL1 and HL2 were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL1 has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL1 ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern
due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection
of this work is noted. 相似文献
87.
Watekar P.R. Goswami M.L.N. Biswas J.C. Acharya H.N. 《Optical and Quantum Electronics》2004,36(5):405-411
The Er-doped double-core dispersion compensating fiber (EDDCF) has been fabricated using modified chemical vapor deposition
(MCVD) technique. We have obtained 14 dB gain at 1550 nm (using a diode laser of 980 nm wavelength which provides 100 mW of
pump power) with dispersion of about −165 ps/km nm. It is useful for the optical fiber network where amplification as well
as negative dispersion is necessary. We are the first to report the experimental realization and characterization of the EDDCF. 相似文献
88.
Summary. The objective of this paper is to introduce a fast algorithm for computing the integral wavelet transform (IWT) on a dense
set of points in the time-scale domain. By applying the duality principle and using a compactly supported spline-wavelet as
the analyzing wavelet, this fast integral wavelet transform (FIWT) is realized by applying only FIR (moving average) operations,
and can be implemented in parallel. Since this computational procedure is based on a local optimal-order spline interpolation
scheme and the FIR filters are exact, the IWT values so obtained are guaranteed to have zero moments up to the order of the
cardinal spline functions. The semi-orthogonal (s.o.) spline-wavelets used here cannot be replaced by any other biorthogonal
wavelet (spline or otherwise) which is not s.o., since the duality principle must be applied to some subspace of the multiresolution
analysis under consideration. In contrast with the existing procedures based on direct numerical integration or an FFT-based
multi-voice per octave scheme, the computational complexity of our FIWT algorithm does not increase with the increasing number
of values of the scale parameter.
Received March 3, 1994 相似文献
89.
The problem of the diffraction of surface waves, obliquely incident on a partially immersed fixed vertical barrier in deep water, is solved approximately by reducing it to the solution of an integral equation, for small angle of incidence of the incident wave. The corrections to the reflection and transmission coefficients over their normal incidence values for small angle of incidence are obtained and presented graphically for some intermediate values of wave numbers. 相似文献
90.
Joshi P Ethirajan M Goswami LN Srivatsan A Missert JR Pandey RK 《The Journal of organic chemistry》2011,76(21):8629-8640
In this report, we present a regioselective oxidation of a series bacteriochlorins, which on reacting with either ferric chloride (FeCl(3)) or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) yielded the corresponding ring-B or ring-D reduced chlorins. The effect of the number of electron-withdrawing groups present at the peripheral position, with or without a fused isocyclic ring (ring-E), did not make any significant difference in regioselective oxidation of the pyrrole rings. However, depending on the nature of substituents, the intermediate bis-dihydroxy bacteriochlorins on subjecting to pinacol-pinacolone reaction conditions gave various ketochlorins. The introduction of the keto-group at a particular position in the molecule possibly depends on the stability of the intermediate carbocation species. The newly synthesized bacteriochlorins show strong long-wavelength absorption and produced significant in vitro (Colon26 cells) photosensitizing ability. Among the compounds tested, the bacteriochlorins containing a keto-group at position 7 of ring-B with cleaved five-member isocyclic ring showed the best efficacy. 相似文献