全文获取类型
收费全文 | 1719篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
化学 | 1039篇 |
晶体学 | 4篇 |
力学 | 14篇 |
数学 | 370篇 |
物理学 | 335篇 |
出版年
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2016年 | 18篇 |
2015年 | 21篇 |
2014年 | 37篇 |
2013年 | 63篇 |
2012年 | 36篇 |
2011年 | 66篇 |
2010年 | 48篇 |
2009年 | 34篇 |
2008年 | 47篇 |
2007年 | 55篇 |
2006年 | 52篇 |
2005年 | 44篇 |
2004年 | 33篇 |
2003年 | 37篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 19篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 27篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1975年 | 13篇 |
1974年 | 17篇 |
1973年 | 21篇 |
1971年 | 12篇 |
1970年 | 18篇 |
1969年 | 17篇 |
1968年 | 15篇 |
1966年 | 20篇 |
1923年 | 15篇 |
1885年 | 11篇 |
排序方式: 共有1762条查询结果,搜索用时 468 毫秒
91.
C12H10N2O2; monoclinic, space group P1 21/c 1 (Z = 2), 826 observed independent reflexions, R = 0.043; lattice dimensions at 25 °C, a = 975.8(3) pm, b = 466.8(1) pm, c = 1186.8(2) pm, β = 108.51(1)°. 相似文献
92.
H. Seliger M. Eppel E. Gldner I. Kittel A. Ludwig R. Schorr 《Macromolecular Symposia》1992,58(1):215-220
Oligomers of defined sequence and structure modelling main chain LC polymers were prepared a) by solution synthesis; b) by a novel liquid phase synthesis using two monomethoxy-poly (ethylene glycol) supports. Benzyl- and tert.butyl-groups were used as orthogonal pair of protecting groups for route a), and also as compatible anchor groups for carriers in route b). Depending on chain structure and end groups, at least ca. 3 mesogenic elements are required to allow for LC phase transitions. The phase behaviour of oligomers with free carboxylic ends can be explained by their association tendency. 相似文献
93.
94.
We report on investigations of spontaneous polarization echoes in the nonmagnetic multicomponent glass BaO-Al2O3-SiO2 in static magnetic fields. While the echo decay is only marginally influenced, the echo amplitude depends strongly on magnetic fields. It seems that the intrinsic magnetic moment of tunneling systems causes dephasing effects which are detected in our echo experiments. In addition we find a strong increase of the echo amplitude with magnetic fields. This result shows that the coupling of the tunneling systems to magnetic fields is surprisingly strong and cannot be understood on the basis of current theories. 相似文献
95.
Conductivity and superconductivity studies of amorphous [Sn1–y
Cu
y–]1–x
H
x
samples in connection with119Sn Mössbauer effect experiments on119Sn1–x
H
x
give strong evidence that the observed increase of the superconducting transition temperatureT
c in the Sn–H-system is caused by the stabilization of an amorphous structure. Thus the Sn–H-system is very similar to the Sn–Cu-system and no H-specific effect is needed to explain the increase ofT
c. 相似文献
96.
Symmetry relations for macroscopic constants are derived. Especially it is shown that the Voigt-symmetry holds for the indices of the elastic constants. This has been doubted several times for lattices of particles with additional degrees of freedom. In the second part a simple model for Br2- and J2-lattices is discussed. The intermolecular forces are assumed to be van-der-Waals-forces. The influence of the internal degrees of freedom on lattice dynamics is calculated especially for the elastic constants. Further the limiting frequencies forq?0 are given and compared with experimental values. 相似文献
97.
Acetylthioacetamides exist as different keto and enol isomers in chloroform solutions. The keto form with intramolecular hydrogen bonding between the NH and the carbonyl group is the dominant keto isomer. On the other hand the enol forms with intramolecular hydrogen bonding between the OH and the thioketo group are the dominant enol isomers in the temperature range 60°C to ?60°C. The thermodynamic data of the keto-enol equilibria were obtained by measuring the intensities of appropriate high resolution proton signals as a function of temperature. At low temperatures all lines characteristic of the enol forms are doubled in the N-phenyl-substituted derivatives because the rotation of the NH? C6H5 group around the C? N bond becomes slow and the chemical shifts characteristic of the E and Z isomers are different. We estimated approximate thermodynamic data of the E/Z equilibrium in some of the compounds. The changes of the line shape as well as the chemical shifts as a function of temperature indicate the presence of various additional exchange processes. In order to obtain further information we performed curve fittings of the chemical shifts of one acetylthioacetanilide and of a series of monothio-β-diketones (studied in another paper) assuming a fast two site exchange process. On the basis of the results obtained a reaction scheme for N-substituted acylthioacetanilides in solution is proposed. 相似文献
98.
99.
Carl Ludwig Siegel 《Mathematische Annalen》1959,137(5):427-432
Ohne Zusammenfassung 相似文献
100.
We studied the conductivity and superconducting transition temperature Tc of SnAr films. The films were prepared by condensing the SnAr mixture on a sapphire substrate held at 5 K. A plot of the conductivity as a function of Sn concentration shows a metal-insulator transition which agrees with a percolation model consisting of Sn clusters embedded in solid Ar. A drop of Tc is observed below the percolation threshold. 相似文献