全文获取类型
收费全文 | 543篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 261篇 |
晶体学 | 10篇 |
力学 | 8篇 |
数学 | 27篇 |
物理学 | 255篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 48篇 |
2012年 | 23篇 |
2011年 | 35篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1938年 | 2篇 |
排序方式: 共有561条查询结果,搜索用时 15 毫秒
501.
4-Amino-4-carboxylthiapyran crystallizes in space groupP21/c witha = 10.61,b = 6.55,c= 10.97 Å, =96.3 °, andZ = 4. The structure was solved by the heavy-atom method, with 897 observed reflections, and refined to anR of 0.093. The packing of the structure is found to be very similar to that in the structure of 1-aminocyclohexane carboxylic acid. The conformation of the thiapyran ring exists in the puckered chair form.Contribution No. 410 from the Dept. of Crystallography and Biophysics, Univeristy of Madras, Guindy Campus, Madras-600025, India. 相似文献
502.
503.
Natural coir fibers, subjectd to thermal treatments in the range of 0°C to 200°C and alkali treatment with 5% to 30% concentration
w/w, have been used in the present investigation to determine the interlayer variability of the cellulose planes (020), (110)
and (1$
\bar 1
$
\bar 1
0). Among the equatorial reflections (110), (1$
\bar 1
$
\bar 1
0) and (020), the extent of variability is found to be more with the proportion of such affected planes less for (020) reflection
in the native cellulose at lower temperature while at higher temperature (110) and (1$
\bar 1
$
\bar 1
0) become more affected by variability defect. (110) and (1$
\bar 1
$
\bar 1
0) planes are more affected also with alkali treatment. 相似文献
504.
Ashis Bhattacharjee Karsten Falk Michio Sorai 《Journal of Physics and Chemistry of Solids》2005,66(1):147-154
Heat capacity study was performed, for the first time, for [MnF4TPP][TCNE]·0.5MeOH and [Mn(OC14H29)4TPP][TCNE]·MeOH complexes in the 1.8-100 K temperature range under the 0-9 T magnetic field and disclosed new aspects inherent in such strongly coupled charge-transfer Mn-porphyrin-TCNE linear chain systems, where TPP=5,10,15,20-tetraphenylporphyrinato, TCNE=tetracyanoethylene and MeOH=methanol. Any heat capacity anomaly due to the onset of the magnetic long-range-order was not detected, whereas the magnetic phase transition has clearly been observed around 20 K by previous magnetic studies. As these materials are well approximated by quasi-one-dimensional ferrimagnetic Heisenberg chains with very large intrachain spin-spin interactions, the most part of the magnetic entropy is retained above the phase transition temperature as the dominant short-range order. This is the reason why no magnetic phase transition was detected by calorimetry. On the other hand, the big effect observed in the magnetic susceptibility is well accounted for if the formation of magnetic domains is assumed in the crystal. 相似文献
505.
S. Chakraborty H. P. Sharma S. S. Tiwary C. Majumder P. K. Prajapati S. Rai P. Popli M. Singh S. S. Bhattacharjee R. P. Singh S. Muralithar P. Banerjee S. Ganguly S. Kumar A. Kumar R. Palit 《Brazilian Journal of Physics》2017,47(4):406-410
High spin states in 127Xe have been investigated via 9Be induced fusion-evaporation reaction at 48 MeV. Spin and parity of excited states up to \( \sim \frac {47}{2} \hbar \) have been confirmed from angular correlation and linear polarization results. Rotational alignment of the second pair of h 11/2 neutrons has been observed at \(\hbar \omega \sim \) 0.44 MeV; beyond that, the band is associated with ν[h 11/2]3 configuration. The alignment phenomena has been discussed in comparison with the neighboring 125,129Xe. 相似文献
506.
Sanket?Chougale Dhammaraj?Rokade Tanushree?Bhattacharjee Harshawardhan?PolEmail author Renu?DhadwalEmail author 《Rheologica Acta》2018,57(6-7):493-503
Extrusion film casting (EFC) is an industrially important process which produces thousands of tons of polymer films, sheets, and coating used for various industrial as well as household applications. In this paper, we focus on an instability which occurs during certain polymer processing operations operating under predominantly elongational flow, such as extrusion film casting and fiber spinning. This instability, called the draw resonance, occurs in the form of sustained periodic fluctuations in the film dimensions. It appears when the process goes beyond the critical line speed of the EFC process. In this work, a conventional linear stability analysis is carried out for nonisothermal EFC process to determine the onset of the draw resonance. The polymer rheology is modeled by the Phan-Thien Tanner (PTT) multi-mode constitutive equation. For the implementation, a conventional shooting method approach is used. Extrusion film casting experiments were also carried out using a conventional linear low-density polyethylene (LLDPE) by varying process parameters such as draw ratio and aspect ratio, to observe the effect on the stability of the process. Linear stability analysis results under non-isothermal conditions are compared and validated with existing results from literature and with our own experimental data. This work displays the effect of multiple relaxation modes as well as the temperature influence on the stability of EFC process. Finally, results also indicate that the temperature highly affects the stability of the EFC process and cannot be ignored from modeling of EFC process. 相似文献
507.
Arnab K. Ray Niladri Sarkar Abhik Basu Jayanta K. Bhattacharjee 《Physics letters. A》2018,382(47):3399-3404
The rotation of polygons in a Type-II hydraulic jump prompts us to look for a rotational feature in the Type-I hydraulic jump. Coupling the radial and azimuthal flows breaks the azimuthal symmetry of the shallow-water circular jump. An unstable rotating wave along the circumference of the jump is possible with a kinematic viscosity of very small order, whose upper threshold value is less than the kinematic viscosity of water. 相似文献
508.
In this paper, we systematically study spacetimes of gravitational plane waves in Einstein-aether theory. Due to the presence of the timelike aether vector field, now the problem in general becomes overdetermined. In particular, for the linearly polarized plane waves, there are five independent vacuum Einstein-aether field equations for three unknown functions. Therefore, solutions exist only for particular choices of the four free parameters \(c_{i}\)’s of the theory. We find that there exist eight cases, in two of which any form of gravitational plane waves can exist, similar to that in general relativity, while in the other six cases, gravitational plane waves exist only in particular forms. Beyond these eight cases, solutions either do not exist or are trivial (simply representing a Minkowski spacetime with a constant or dynamical aether field). 相似文献
509.
Scanning tunneling microscopy (STM) and high resolution cross-sectional transmission electron microscopy (XTEM) studies have been used to investigate the formation of Ge nanocrystals grown on Si(1 0 0)-(2 × 1) surfaces by molecular beam epitaxy (MBE). We observe relatively high density of Ge islands where small ‘pyramids’, small ‘domes’ and facetted ‘domes’ of various sizes co-exist in the film. As revealed from XTEM images, a large fraction of islands, especially dome-shaped Ge islands have been found to have an aspect ratio of ∼1 (diameter):1 (height). Observation of truncated-sphere-shaped Ge islands with a narrow neck contact with the wetting layer is reported. 相似文献
510.
Srinivasa Rao Karumuri Joydeep Choudhury Nirmal Kumar Sarkar Ramendu Bhattacharjee 《Pramana》2009,72(3):517-525
One of the most interesting areas of current research in molecular physics is the study of the vibrationally excitated states
of medium and large molecules. In view of the considerable amount of experimental activity in this area, one needs theoretical
models within which to interpret experimental data. Using Lie algebraic method, the vibrational energy levels of nickel metalloporphyrins
like Ni(OEP), Ni porphyrin and Ni(TPP) are calculated for 16 vibrational modes. The algebraic Hamiltonian
, where A
i
, A
ij
and λ
ij
are the algebraic parameters which vary from molecule to molecule and C
i
, C
ij
and M
ij
are algebraic operators. The vibrational energy levels are calculated using algebraic model Hamiltonian and the results are
compared with the experimental values. The results obtained by this model are very accurate.
相似文献