全文获取类型
收费全文 | 7218篇 |
免费 | 327篇 |
国内免费 | 82篇 |
专业分类
化学 | 4302篇 |
晶体学 | 222篇 |
力学 | 195篇 |
综合类 | 4篇 |
数学 | 1044篇 |
物理学 | 1860篇 |
出版年
2022年 | 82篇 |
2021年 | 78篇 |
2020年 | 96篇 |
2019年 | 145篇 |
2018年 | 102篇 |
2017年 | 100篇 |
2016年 | 147篇 |
2015年 | 122篇 |
2014年 | 190篇 |
2013年 | 565篇 |
2012年 | 315篇 |
2011年 | 359篇 |
2010年 | 240篇 |
2009年 | 211篇 |
2008年 | 247篇 |
2007年 | 254篇 |
2006年 | 219篇 |
2005年 | 176篇 |
2004年 | 173篇 |
2003年 | 203篇 |
2002年 | 172篇 |
2001年 | 102篇 |
2000年 | 97篇 |
1999年 | 67篇 |
1997年 | 70篇 |
1996年 | 79篇 |
1995年 | 86篇 |
1994年 | 82篇 |
1993年 | 84篇 |
1992年 | 98篇 |
1991年 | 88篇 |
1990年 | 76篇 |
1989年 | 110篇 |
1988年 | 76篇 |
1987年 | 70篇 |
1986年 | 81篇 |
1985年 | 126篇 |
1984年 | 119篇 |
1983年 | 93篇 |
1982年 | 98篇 |
1981年 | 101篇 |
1980年 | 85篇 |
1979年 | 99篇 |
1978年 | 74篇 |
1977年 | 101篇 |
1976年 | 79篇 |
1975年 | 87篇 |
1974年 | 92篇 |
1973年 | 97篇 |
1972年 | 57篇 |
排序方式: 共有7627条查询结果,搜索用时 15 毫秒
981.
The feasibility of using homogeneous membrane-type halide ion-selective electrodes in solutions containing cationic surfactant compounds was examined. The results established the applicability of these electrodes for monitoring halide ions in solution without interference by the surfactants. The data also provided a basis for estimation of the surfactant in solution through the halide content. Two typical plating-bath compositions containing CTAB have been successfully analysed for their surfactant content by this procedure. 相似文献
982.
983.
The rotational structure of the ν1, ν3, 2ν2, ν1 + ν2, and ν2 + ν3 bands of water vapor has been recorded using a high resolution vacuum infrared spectrograph. Values for the energy levels of the ground vibrational state and of the upper states of these bands have been determined. Several intensity anomalies have been observed in lines previously assigned to the ν1, ν3, and 2ν2 bands. Experimental results for these intensity anomalies have been presented. 相似文献
984.
The uniqueness of the general harmonic force field of methyl fluoride is analyzed. The analysis is applicable to other methyl halides as well. Through the compliance scheme, it is seen that by supplementing the data employed by Aldous and Mills (i.e., vibrational frequencies ωi, Coriolis coupling constants ζi and the centrifugal stretching constants DJ, DJK of CH3F and CD3F molecules), with the frequencies of A′ or A″ species of either CH2DF or CD2HF, the force field is uniquely determined. The addition of any other extra data including the 12CH3F13CH3F isotopic shifts only makes the determination of the force field parameters more precise. 相似文献
985.
Stephen C. Hurlock K.Narahari Rao Lawrence A. Weller Peter K.L. Yin 《Journal of Molecular Spectroscopy》1973,48(2):372-394
The ν2 band of 14N16O2 near 13.3 μm has been measured under high resolution using a vacuum grating spectrograph equipped with a liquid helium cooled Ge:Cu detector. Over 750 transitions were identified. Analysis of the band, combined with previous work at shorter wavelengths, led to modified constants for the ground state, (0, 0, 0), and new values for the constants of the upper state, (0, 1, 0). The new constants reproduced 272 nonzero-weighted transitions with a standard deviation of 0.011 cm?1 and reproduced 346 ground state combination differences with a standard deviation of 0.010 cm?1. The spin-rotation line splittings which were observed were described satisfactorily using existing formulations. 相似文献
986.
Several characteristics of fission accompanied by long range alpha particles (LRA) have been studied in the thermal neutron
induced fission of235U. The kinetic energies of fission fragments and the LRA were measured with a back-to-back ionization chamber and semiconductor
detectors respectively. The kinetic energies of the two fragments and the LRA in LRA fission, along with the energies of pair
fragments in the normal binary fissions, were recorded event by event on a magnetic tape by means of a four-parameter data
acquisition system. The data were analysed to study the dependence of different quantities in LRA fission on the fragment
mass ratio, LRA energy and the total kinetic energy of the fission fragments. It is seen that the most probable energy of
LRA increases significantly for near symmetric mass divisions. The total kinetic energy for all mass ratios in LRA fission
is found to be (2.6±0.7) MeV larger than that in binary fission. The difference in the total kinetic energies in LRA and binary
fissions is seen to be dependent on mass ratio. This result may suggest that the scission configuration in LRA fission is
different for different mass ratios. Correlations between the fission fragment and LRA energies have been studied for several
mass ratios. It is seen that the most probable fragment kinetic energyĒ
k varies nearly linearly with the LRA energyE
a for various mass divisions but the variation of the most probable LRA energyĒ
a with fragment kinetic energyE
k is found to deviate from linearity for several mass ratios. From a least square fit to the variation ofĒ
k withE
a it is found that the slope (dĒ
k/dEa) increases with the increase in mass ratio. The present results are discussed to arrive at a better understanding of the
scission configuration in the fission accompanied by LRA emission. 相似文献
987.
Several vibration rotation bands of the H12C14N16O molecule have been studied by using high resolution vacuum grating infrared spectrographs. A linear molecular model has been used in establishing the vibrational assignments and evaluating the molecular constants. A value of 224.101 cm?1 has been determined for the band center of the ν5 fundamental by application of the Ritz combination principle. Future efforts will be directed to arriving at a similar result for the ν4 fundamental. 相似文献
988.
P.V.S. Rao 《Journal of Physics and Chemistry of Solids》1974,35(6):669-684
Phonon dispersion relations and effective interionic potential for solid Al are calculated using the nonlocal optimized model potential of Shaw screened with the improved self-consistent dielectric function of Vashishta and Singwi. A very good agreement is obtained between the calculated and experimental phonon frequencies. Comparison is made using three other dielectric functions. It turns out that in Al the interionic potential is very sensitive to the screening function. Also electrical resistivity of liquid Al has been calculated using the model potential when screened with the four different dielectric functions. Influence of the spatial distribution of depletion charge at the ion site is discussed. A comparative study of nonlocal and local potentials by taking two local potentials: (1) modified point-ion, and (2) empty core, screened with the self-consistent dielectric function, is also presented. 相似文献
989.
B. Sreenivasulu V. Sundaramurthy N. V. Subba Rao 《Proceedings Mathematical Sciences》1974,79(1):41-47
A number of 3-(3-pyridyl) coumarins with and without 4-methyl substituent have been prepared following Oglialoro and modified Perkin reactions. These compounds have been tested against fish and bacteria. Of all the compounds tested, 7-bromo-4-methyl-3-(3-pyridyl) coumarin exhibited maximum activity. A few have also shown bacteriostatic activity. 相似文献
990.
We discuss the finite representability of a Banach space E in another Banach space F, assuming that F satisfies certain smoothness conditions. We apply these results to develop a classification of superreflexive spaces into isomorphic classes, called k-superreflexive spaces (k = 1, 2,…, ∞); and we derive a strong converse to Dvoretsky's near-sphericity theorem. Further, our main theorem complements an important recent result of Krivine. 相似文献