全文获取类型
收费全文 | 164239篇 |
免费 | 2134篇 |
国内免费 | 713篇 |
专业分类
化学 | 89048篇 |
晶体学 | 1721篇 |
力学 | 7072篇 |
综合类 | 36篇 |
数学 | 17475篇 |
物理学 | 51734篇 |
出版年
2020年 | 1342篇 |
2019年 | 1420篇 |
2018年 | 1691篇 |
2017年 | 1623篇 |
2016年 | 2874篇 |
2015年 | 1929篇 |
2014年 | 2858篇 |
2013年 | 7171篇 |
2012年 | 5681篇 |
2011年 | 7080篇 |
2010年 | 4858篇 |
2009年 | 4823篇 |
2008年 | 6434篇 |
2007年 | 6505篇 |
2006年 | 6039篇 |
2005年 | 5633篇 |
2004年 | 4992篇 |
2003年 | 4356篇 |
2002年 | 4149篇 |
2001年 | 4535篇 |
2000年 | 3437篇 |
1999年 | 2587篇 |
1998年 | 2213篇 |
1997年 | 2197篇 |
1996年 | 2020篇 |
1995年 | 2038篇 |
1994年 | 2022篇 |
1993年 | 1822篇 |
1992年 | 2080篇 |
1991年 | 2215篇 |
1990年 | 2030篇 |
1989年 | 2001篇 |
1988年 | 1934篇 |
1987年 | 1830篇 |
1986年 | 1753篇 |
1985年 | 2333篇 |
1984年 | 2485篇 |
1983年 | 1998篇 |
1982年 | 2183篇 |
1981年 | 2050篇 |
1980年 | 1974篇 |
1979年 | 2116篇 |
1978年 | 2264篇 |
1977年 | 2182篇 |
1976年 | 2212篇 |
1975年 | 2097篇 |
1974年 | 2146篇 |
1973年 | 2132篇 |
1972年 | 1387篇 |
1971年 | 1227篇 |
排序方式: 共有10000条查询结果,搜索用时 176 毫秒
71.
Abou-Dina M. S. Helal M. A. Ghaleb Ahmed F. Kaoullas George Georgiou Georgios C. 《Meccanica》2020,55(7):1499-1507
Meccanica - The occurrence of slip complicates the estimation of the viscosity in rheometric flows. Thus, special analyses and experimental protocols are needed in order to obtain reliable... 相似文献
72.
Tsuvarev E. S. Kassan-Ogly F. A. Proshkin A. I. 《Journal of Experimental and Theoretical Physics》2020,131(3):447-455
Journal of Experimental and Theoretical Physics - The Ising model on an one-dimensional monoatomic equidistant lattice with different exchange interactions between atomic spins at the sites of... 相似文献
73.
Torsional states caused by vibrations of hydroxyl groups in the methanediol molecule and its two deuterated analogues – DO(CH2)OH and DO(CH2)OD were analysed at MP2/cc-pVTZ and CCSD(T)/cc-pVQZ levels of theory. In the first case, 2D PES and 2D surfaces of kinematic coefficients were calculated with geometry optimisation for all other geometric parameters, and in the second case, only the energy of optimised configurations at the MP2/cc-pVTZ level of theory was determined. Then 2D PES was recounted to the complete basis set (CBS) limit by extrapolating the results of calculations at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory The calculated values were then averaged over four equivalent points on the coordinate plane. Hamiltonian matrices were constructed using DVR and Fourier methods. After their subsequent diagonalization, the energies of the stationary torsional states were computed. Their classification by C2V(M) and CS(M) molecular symmetry groups has been performed. The splitting values due to the tunnelling of the thirty most deeply located torsional states in the three studied molecules were also determined. The torsional states, internal rotation barriers, and tunnelling frequencies in the molecules of methanediol and hydrogen trioxide were compared. 相似文献
74.
Optics and Spectroscopy - We propose an approach to the analysis and interpretation of spectra of photoinduced circular dichroism (PICD) of semiconductor nanocrystals, in particular, quantum dots,... 相似文献
75.
I.F. Mikhailov A.A. Baturin A.I. Mikhailov S.S. Borisova S.V. Surovitskiy 《X射线光谱测定》2020,49(2):284-290
Compton to Rayleigh scattering intensity ratios (IC/IR) have been measured using X-rays with energy 17.44 keV for single-component materials with atomic number Z from 4 (Be) to 31 (Ga) and binary compounds of stoichiometric composition. The measurements have been performed using two optical schemes: an energy-dispersive X-ray fluorescence scheme with a molybdenum secondary target and wavelength-dispersive X-ray fluorescence one. The processing of the spectra was carried out by fitting with Pearson VII functions. For single-component and binary standards, the experimental dependence of the scattering intensity ratio on the atomic number was found to be the same. This confirms the additivity of the contribution of different atoms to the scattering. The dependence has a complex shape but is well described by the theoretical relationship for IC/IR with correction on the difference between Compton and Rayleigh radiation absorption coefficients. Two ranges of atomic number values are defined, in which the effective atomic number Zeff can be determined by the calibration method using this dependence: for Z from 4 to 7 with low error of ΔZeff =±0.15 and for Zeff from 10 to 18 with low error of ΔZeff =±0.69. A change in the shape of the Compton peak and an overestimated value of the of the Compton and Rayleigh peak intensity ratio when passing from a single-component scatterer (Al or Si) to their oxides Al2O3 or SiO2, respectively, have been revealed. 相似文献
76.
Ivanov Yu. F. Petrikova E. A. Teresov A. D. Ivanova O. V. 《Russian Physics Journal》2020,62(11):2081-2085
Russian Physics Journal - The paper presents the results of the structure and properties modification of 20Cr23Ni18 (AISI 310) high chrome austenitic stainless steel after the exposure to the low... 相似文献
77.
Abramova E. S. Balandin S. F. Donchenko V. A. Myshkin V. F. Potekaev A. I. Khan V. A. 《Russian Physics Journal》2020,63(2):332-337
Russian Physics Journal - The paper deals with the propagation of the powerful laser beam in gas-dispersion systems and atmospheric aerosol background, which is accompanied by a wide spectrum of... 相似文献
78.
79.
Zeus A. De los Santos Sean MacAvaney Katina Russell Christian Wolf 《Angewandte Chemie (International ed. in English)》2020,59(6):2440-2448
We have developed an optical method for accurate concentration, er, and dr analysis of amino alcohols based on a simple mix‐and‐measure workflow that is fully adaptable to multiwell plate technology and microscale analysis. The conversion of the four aminoindanol stereoisomers with salicylaldehyde to the corresponding Schiff base allows analysis of the dr based on a change in the UV maximum at 420 nm that is very different for the homo‐ and heterochiral diastereomers and of the concentration of the sample using a hypsochromic shift of another absorption band around 340 nm that is independent of the analyte stereochemistry. Subsequent in situ formation of CuII assemblies in the absence and presence of base enables quantification of the er values for each diastereomeric pair by CD analysis. Applying a linear programming method and a parameter sweep algorithm, we determined the concentration and relative amounts of each of the four stereoisomers in 20 samples of vastly different stereoisomeric compositions with an averaged absolute percent error of 1.7 %. 相似文献
80.
Physics of the Solid State - Phosphate solid solutions based on the whitlockite family Ca9 – xMxDy(PO4)7 (M = Zn2+ or Mg2+) have been obtained. The samples have been... 相似文献