全文获取类型
收费全文 | 233169篇 |
免费 | 19588篇 |
国内免费 | 14712篇 |
专业分类
化学 | 94360篇 |
晶体学 | 1855篇 |
力学 | 12070篇 |
综合类 | 667篇 |
数学 | 43486篇 |
物理学 | 53561篇 |
综合类 | 61470篇 |
出版年
2024年 | 641篇 |
2023年 | 2693篇 |
2022年 | 4536篇 |
2021年 | 4913篇 |
2020年 | 4837篇 |
2019年 | 4252篇 |
2018年 | 13911篇 |
2017年 | 13532篇 |
2016年 | 11412篇 |
2015年 | 6995篇 |
2014年 | 8347篇 |
2013年 | 9953篇 |
2012年 | 15129篇 |
2011年 | 22034篇 |
2010年 | 14617篇 |
2009年 | 14709篇 |
2008年 | 15972篇 |
2007年 | 17447篇 |
2006年 | 8154篇 |
2005年 | 8351篇 |
2004年 | 6970篇 |
2003年 | 6656篇 |
2002年 | 5514篇 |
2001年 | 4402篇 |
2000年 | 3922篇 |
1999年 | 4860篇 |
1998年 | 4162篇 |
1997年 | 3951篇 |
1996年 | 3856篇 |
1995年 | 3259篇 |
1994年 | 2941篇 |
1993年 | 2439篇 |
1992年 | 2124篇 |
1991年 | 1950篇 |
1990年 | 1599篇 |
1989年 | 1442篇 |
1988年 | 1127篇 |
1987年 | 813篇 |
1986年 | 637篇 |
1985年 | 386篇 |
1984年 | 249篇 |
1983年 | 192篇 |
1982年 | 167篇 |
1981年 | 116篇 |
1980年 | 105篇 |
1979年 | 70篇 |
1978年 | 56篇 |
1973年 | 42篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
951.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate 总被引:1,自引:0,他引:1
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat… 相似文献
952.
953.
Christian-Oliver Ewald 《Communications in Mathematical Physics》2004,250(1):195-213
We define a class of topological spaces ( LCNT spaces ) which come together with a nuclear Fréchet algebra. Like the algebra of smooth functions on a manifold, this algebra carries the differential structure of the object. We compute the Hochschild homology of this algebra and show that it is isomorphic to the space of differential forms. This is a generalization of a result obtained by Alain Connes in the framework of smooth manifolds. 相似文献
954.
955.
Gyula Bene 《Central European Journal of Physics》2003,1(2):332-343
An “almost diagonal” reduced density matrix (in coordinate representation) is usually a result of environment induced decherence
and is considered the sign of classical behavior. We show that the proton of a ground state hydrogen atom can indeed possess
such a density matrix. This example demonstrates that the “almost diagonal” structure may be derived from an interaction with
a low number of degrees of freedom which play the role of the environment. We also show that decoherence effects in our example
can only be observed if the interaction with the measuring device is significantly faster than the interaction with the environment
(the electron). In the opposite case, when the interaction with the environment is significant during the measurement process,
coherence is maintained. Finally, we propose a neutron scattering experiment on cold He atoms to observe decoherence which
shows up as an additional positive contribution to the differential scattering cross section. This contribution is inversely
proportional to the bombarding energy. 相似文献
956.
Supramolecular side chain liquid crystalline polymers (SCLCPs) based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X=100, 76, 60, 41 or 23, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the polymer) and stilbazole derivatives have been obtained through intermolecular hydrogen bonding (H-bonding) interactions between the carboxylic acid and the pyridyl moieties. The formation of H-bonding and self-assembly results in the formation of new mesogenic units, in which H-bonds function as molecular connectors. FTIR shows the existence of H-bonding in the complexes. The polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. The liquid crystalline properties of the supramolecular SCLCPs were studied using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction, and were found to exhibit smectic A phases with focal-conic textures. The thermal stability of the SCLCP increases on increasing the carboxylic acid content in the polysiloxane and the concentration of the stilbazole derivative in the complex. However, the thermal stability decreases on increasing the chain length of the stilbazole derivative. The crystal phase was not formed even on cooling to the glass transition temperature of the polymeric complex. 相似文献
957.
Chunlin Li Yilu Fu Guozhu Bian Tiandou Hu Yaning Xie Jing ZhanDepartment of Chemical Physics University of Science and Technology of China Hefei China Institute of High Energy Physics Chinese Academy of Sciences Beijing China 《天然气化学杂志》2003,12(3)
The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity. 相似文献
958.
959.
The Spectrum of a Linearized 2D Euler Operator 总被引:1,自引:0,他引:1
We study the spectral properties of the linearized Euler operator obtained by linearizing the equations of incompressible two-dimensional fluid at a steady state with the vorticity that contains only two nonzero complex conjugate Fourier modes. We prove that the essential spectrum coincides with the imaginary axis, and give an estimate from above for the number of isolated nonimaginary eigenvalues. In addition, we prove that the spectral mapping theorem holds for the group generated by the linearized 2D Euler operator. 相似文献
960.
Marco Andreatta 《manuscripta mathematica》2003,110(4):505-512
We consider some conditions under which a smooth projective variety X is actually the projective space. We also extend to the case of positive characteristic some results in the theory of vector
bundle adjunction. We use methods and techniques of the so called Mori theory, in particular the study of rational curves
on projective manifolds.
Received: 16 May 2002 / Revised version: 18 November 2002 Published online: 3 March 2003
Mathematics Subject Classification (2000): 14E30, 14J40, 14J45 相似文献