全文获取类型
收费全文 | 1363224篇 |
免费 | 29650篇 |
国内免费 | 7733篇 |
专业分类
化学 | 684184篇 |
晶体学 | 20438篇 |
力学 | 75079篇 |
综合类 | 110篇 |
数学 | 242887篇 |
物理学 | 377909篇 |
出版年
2021年 | 13539篇 |
2020年 | 15972篇 |
2019年 | 16120篇 |
2018年 | 13310篇 |
2016年 | 28247篇 |
2015年 | 20928篇 |
2014年 | 30554篇 |
2013年 | 74492篇 |
2012年 | 39114篇 |
2011年 | 36856篇 |
2010年 | 37694篇 |
2009年 | 39893篇 |
2008年 | 35752篇 |
2007年 | 31622篇 |
2006年 | 37180篇 |
2005年 | 29845篇 |
2004年 | 30972篇 |
2003年 | 29165篇 |
2002年 | 29950篇 |
2001年 | 30038篇 |
2000年 | 25770篇 |
1999年 | 22954篇 |
1998年 | 21173篇 |
1997年 | 21138篇 |
1996年 | 21214篇 |
1995年 | 19263篇 |
1994年 | 18721篇 |
1993年 | 18253篇 |
1992年 | 18527篇 |
1991年 | 18776篇 |
1990年 | 18007篇 |
1989年 | 18017篇 |
1988年 | 17622篇 |
1987年 | 17570篇 |
1986年 | 16500篇 |
1985年 | 22865篇 |
1984年 | 24036篇 |
1983年 | 20139篇 |
1982年 | 21765篇 |
1981年 | 20977篇 |
1980年 | 20318篇 |
1979年 | 20635篇 |
1978年 | 21844篇 |
1977年 | 21528篇 |
1976年 | 21209篇 |
1975年 | 19930篇 |
1974年 | 19538篇 |
1973年 | 19992篇 |
1972年 | 14491篇 |
1967年 | 12689篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
912.
The acoustic field inside a shell excited by a spatially inhomogeneous harmonic pressure field is studied. The shell is assumed
to have a finite length, a set of orthogonal stiffening ribs, two ends bounding the acoustic volume, and a sound-insulating
structure, which includes layers of sound-insulating material, resonant elements, and an interior panel. The shell is considered
to be orthotropic with boundary conditions corresponding to a free support. For the acoustic field in the closed volume, analytical
expressions are derived with allowance for the elastoacoustic interaction of the shell with the sound-insulating layers and
with the medium both inside the shell (with arbitrary impedance values at the ends) and outside it. These expressions are
used to investigate the effect of different types of resonant systems on the sound field inside the shell. 相似文献
913.
The first enantiospecific synthesis of allopupukeanones has been accomplished starting from 6-methylcarvone. A biogenetically patterned rearrangement of a pupukeanane to allopupukeanane was employed as the key step. 相似文献
914.
An efficient synthesis of isothiazolidines in good yields is described. 相似文献
915.
916.
917.
918.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
919.
D. Yu. Gladilov S. Yu. Nekhaevskii A. V. Ochkin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(12):1934-1939
Various methods for describing the distribution of water in the H2O-tributyl phosphate (TBP) system were considered. An equation for describing the deviations from the Henry law was proposed. A three-parameter equation for calculating the distribution of water in H2O-TBP-solvent systems was derived. It is based on the additive solubility model and allows for the dependence of the activity coefficients on the TBP concentration. Based on the published data, the parameters of the equation for a number of systems were calculated. 相似文献
920.
J.R. Cooper 《Journal of Molecular Spectroscopy》2006,239(1):51-58
The ν9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν9 + ν4 − ν4 band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν3 fundamental and the ν4, 2ν4 − ν4, and 3ν4 torsional transitions. The first is restricted to −5 ? KΔK ? 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν9 torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν3 fundamental and the gs. Hot band lines with KΔK < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔK < −10, which has been attributed to an interaction with the ν12 fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented. 相似文献