全文获取类型
收费全文 | 18355篇 |
免费 | 1491篇 |
国内免费 | 1250篇 |
专业分类
化学 | 7553篇 |
晶体学 | 122篇 |
力学 | 1326篇 |
综合类 | 272篇 |
数学 | 5446篇 |
物理学 | 6377篇 |
出版年
2023年 | 151篇 |
2022年 | 372篇 |
2021年 | 429篇 |
2020年 | 432篇 |
2019年 | 451篇 |
2018年 | 421篇 |
2017年 | 447篇 |
2016年 | 520篇 |
2015年 | 450篇 |
2014年 | 664篇 |
2013年 | 1274篇 |
2012年 | 779篇 |
2011年 | 797篇 |
2010年 | 698篇 |
2009年 | 1053篇 |
2008年 | 1109篇 |
2007年 | 1134篇 |
2006年 | 1020篇 |
2005年 | 825篇 |
2004年 | 727篇 |
2003年 | 717篇 |
2002年 | 726篇 |
2001年 | 598篇 |
2000年 | 575篇 |
1999年 | 480篇 |
1998年 | 455篇 |
1997年 | 344篇 |
1996年 | 235篇 |
1995年 | 244篇 |
1994年 | 223篇 |
1993年 | 216篇 |
1992年 | 292篇 |
1991年 | 175篇 |
1990年 | 133篇 |
1989年 | 110篇 |
1988年 | 116篇 |
1987年 | 109篇 |
1986年 | 95篇 |
1985年 | 91篇 |
1984年 | 90篇 |
1983年 | 48篇 |
1982年 | 110篇 |
1981年 | 177篇 |
1980年 | 185篇 |
1979年 | 186篇 |
1978年 | 171篇 |
1977年 | 107篇 |
1976年 | 113篇 |
1973年 | 78篇 |
1972年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We prove equivalence of the definitions by the author and by Korevaar and Schoen of the Sobolev classes of mappings of a domain of an arithmetic n-dimensional space to a metric space. 相似文献
102.
103.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献
104.
The authors give the necessary and sufficient conditions for a generalized circle in a Weyl hypersurface to be generalized circle in the enveloping Weyl space. They then obtain the neccessary and sufficient conditions under which a generalized concircular transformation of one Weyl space onto another induces a generalized transformation oil its subspaces. Finally, it is shown that any totally geodesic or totally umbilical hypersurface of a generalized concircularly flat Weyl space is also generalized concircularly flat. 相似文献
105.
§ 1. IntroductionRecently ,thedifferentialequationswithdeviatingargumentswereusuallydiscussed(see[1 ],[4],[5 ]) .In [1 ],AGARWALRPandO’REGANDconsideredequationy″(t) =f(t,y(t) ,y(σ(t) ) ) , a.e .t∈ [0 ,1 ]y(t) =ψ(t) , t∈ [-r ,0 ]y( 1 ) =a ,( )andtheydiscussedtheexistenceofatleastonesolutionforequation ( ) .Inthispaper ,weconsideramoregeneralequation-x″(t) =f(t ,xt) , t∈ [0 ,1 ]x(t) =ψ(t) , t∈ ( -∞ ,0 ]x( 0 ) =x( 1 ) =0 ,( 1 .1 )andsomeexistencetheor… 相似文献
106.
M. I. Gil' 《Proceedings of the American Mathematical Society》2003,131(12):3737-3746
A linear operator in a separable Hilbert space is called a quasinormal one if it is a sum of a normal operator and a compact one. In the paper, bounds for the spectrum of quasinormal operators are established. In addition, the lower estimate for the spectral radius is derived. Under some restrictions, that estimate improves the well-known results. Applications to integral operators and matrices are discussed. Our results are new even in the finite-dimensional case.
107.
G. Kocher-Oberlehner W. Jantsch L. Palmetshofer A. Ulyashin 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):347
Erbium (Er)- and oxygen (O)-doped Cz–Si was additionally doped with hydrogen, using plasma enhanced chemical vapour deposition. Photoluminescence (PL) spectra show a large enhancement especially for samples treated with solid phase epitaxy before hydrogenation and annealing at 900°C later. Secondary ion mass spectroscopy measurements give evidence for an enhanced diffusion of O and Er at this temperature towards the surface. Etching shows that the PL does not stem from the heavily doped surface layer but from a deeper region with lower Er concentration. This conclusion is supported by the appearance of the so-called “cubic” centre with low solubility. Comparing the PL yield of the hydrogenated samples to that of samples with similar Er volume concentration but without hydrogenation still gives a large enhancement. We thus conclude that hydrogen can enhance the solubility of the cubic centre in Si:Er,O. 相似文献
108.
David M. Evans 《组合设计杂志》2004,12(6):459-465
For all ‘reasonable’ finite t, k, and s, we construct a t‐(?0, k, 1) design and a group of automorphisms which is transitive on blocks and has s orbits on points. In particular, there is a 2‐(?0, 4, 1) design with a block‐transitive group of automorphisms having two point orbits. This answers a question of P. J. Cameron and C. E. Praeger. The construction is presented in a purely combinatorial way, but is a by‐product of a new way of looking at a model‐theoretic construction of E. Hrushovski. © 2004 Wiley Periodicals, Inc. 相似文献
109.
110.
In this paper, we exhibit a unified treatment of the mixed initial boundary value problem for second order (in time) parabolic linear differential equations in Banach spaces, whose boundary conditions are of a dynamical nature. Results regarding existence, uniqueness, continuous dependence (on initial data) and regularity of classical and strict solutions are established. Moreover, several examples are given as samples for possible applications.