全文获取类型
收费全文 | 1466篇 |
免费 | 81篇 |
国内免费 | 85篇 |
专业分类
化学 | 214篇 |
晶体学 | 3篇 |
力学 | 662篇 |
综合类 | 8篇 |
数学 | 163篇 |
物理学 | 582篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 44篇 |
2019年 | 26篇 |
2018年 | 29篇 |
2017年 | 24篇 |
2016年 | 41篇 |
2015年 | 49篇 |
2014年 | 60篇 |
2013年 | 92篇 |
2012年 | 62篇 |
2011年 | 82篇 |
2010年 | 78篇 |
2009年 | 107篇 |
2008年 | 109篇 |
2007年 | 93篇 |
2006年 | 106篇 |
2005年 | 96篇 |
2004年 | 73篇 |
2003年 | 45篇 |
2002年 | 49篇 |
2001年 | 35篇 |
2000年 | 28篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 28篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1973年 | 4篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1632条查询结果,搜索用时 609 毫秒
61.
62.
The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64-172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the 14N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters. 相似文献
63.
A ghost fluid Lattice Boltzmann method (GF‐LBM) is developed in this study to represent complex boundaries in Lattice Boltzmann simulations of fluid flows. Velocity and density values at the ghost points are extrapolated from the fluid interior and domain boundary via obtaining image points along the boundary normal inside the fluid domain. A general bilinear interpolation algorithm is used to obtain values at image points which are then extrapolated to ghost nodes thus satisfying hydrodynamic boundary conditions. The method ensures no‐penetration and no‐slip conditions at the boundaries. Equilibrium distribution functions at the ghost points are computed using the extrapolated values of the hydrodynamic variables, while non‐equilibrium distribution functions are extrapolated from the interior nodes. The method developed is general, and is capable of prescribing Dirichlet as well as Neumann boundary conditions for pressure and velocity. Consistency and second‐order accuracy of the method are established by running three test problems including cylindrical Couette flow, flow between eccentric rotating cylinders and flow over a cylinder in a confined channel. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
64.
《Physics and Chemistry of Liquids》2012,50(2-3):131-134
Abstract Thermal Conductivity of CuSbSe2 and CuBiSe2 have been studied in the solid and liquid state in a wide range of temperatures. Measurements of thermal conductivity were carried out using the concentric cylinder method which is based on the flow of heat through a cylindrical wall. 相似文献
65.
R. Bjørk C.R.H. Bahl A. Smith N. Pryds 《Journal of magnetism and magnetic materials》2010,322(22):3664-3671
A permanent magnet assembly in which the flux density can be altered by a mechanical operation is often significantly smaller than comparable electromagnets and also requires no electrical power to operate. In this paper five permanent magnet designs in which the magnetic flux density can be altered are analyzed using numerical simulations, and compared based on the generated magnetic flux density in a sample volume and the amount of magnet material used. The designs are the concentric Halbach cylinder, the two half Halbach cylinders, the two linear Halbach arrays and the four and six rod mangle. The concentric Halbach cylinder design is found to be the best performing design, i.e. the design that provides the most magnetic flux density using the least amount of magnet material. A concentric Halbach cylinder has been constructed and the magnetic flux density, the homogeneity and the direction of the magnetic field are measured and compared with numerical simulation and a good agrement is found. 相似文献
66.
67.
G. Guillon T. Stoecklin A. Voronin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):83-87
We compare the cross sections for the transitions changing the projection of
the total angular momentum of N2
+(2Σ) in collisions
with 3He and 4He at very low collision energy. The fundamental
states of the two nuclear spin isomers of N2
+ are considered as
well as the two fine structure levels of the first excited para level N=2.
It is shown that the two fundamental states of the two nuclear spin isomers
behave differently. For the fundamental para level N=0 of N2
+, the
projection changing cross section is always negligible compared to the
elastic one for both He isotopes. For the fundamental ortho level N=1 of
N2
+, the spin-rotation interaction couples the different spin
levels directly so the spin relaxation becomes a first order process. The
associated resonances increase the projection changing cross section which
remains smaller but becomes comparable with the elastic one. This is in
contrast with the excited rotational levels of N2
+, which for the
rotational deactivation and elastic channels are found to be equal around
the resonances for the collisions involving 3He. These two channels are
always larger than the projection changing one. We also find that, for
transitions involving the fundamental rotational state, the domain of
validity of the threshold laws discussed by Krems and Dalgarno [Phys. Rev. A 67, 050704 (2003)] for a potential decreasing faster than
1/r2 is shortened, due to the long range charge induced dipole potential.
This effect is illustrated for the collisions of 3He with the
fundamental para state of N2
+. 相似文献
68.
During the design process of Blu-ray disc optical pick-up (BD OPU), the optical system and the collimator lens design is especially important. This paper designs an optical system and some lenses for the BD OPU, including collimator lens, beam shaping lens for laser beam shaping, and cylinder lens for signal detecting. In this OPU, we use a triplet lens to collimate the laser beam. At the same time, we build a series of assembly jigs to make sure that each lens can be put into the OPU basement properly. At last, we get the reading spot image and S-curve photo of OPU, which can be used to read Blu-ray disc (BD). 相似文献
69.
Let T be a monad over a category A. Then a homotopy structure for A, defined by a cocylinder P : A A, or path-endofunctor, can be lifted to the category A
T
of Eilenberg–Moore algebras over T, provided that P is consistent with T in a natural sense, i.e. equipped with a natural transformation : T P P T satisfying some obvious axioms. In this way, homotopy can be lifted from well-known, basic situations to various categories of algebras for instance, from topological spaces to topological semigroups, or spaces over a fixed space (fibrewise homotopy), or actions of a fixed topological group (equivariant homotopy); from categories to strict monoidal categories; from chain complexes to associative chain algebras. The interest is given by the possibility of lifting the homotopy operations (as faces, degeneracy, connections, reversion, interchange, vertical composition, etc.) and their axioms from A to A
T
, just by verifying the consistency between these operations and : T P P T. When this holds, the structure we obtain on our category of algebras is sufficiently powerful to ensure the main general properties of homotopy. 相似文献
70.
Oseen’ approximations are used to study the slow motion of a viscous, incompressible, electrically conducting fluid past a
circular cylinder in the presence of a uniform aligned magnetic field. Using series truncation method, the analytical solutions
for the first three terms in the Fourier sine series expansion of the stream function are obtained. Numerical values of the
tangential drag for different values of magnetic interaction parameter and viscous Reynolds number are calculated. 相似文献