全文获取类型
收费全文 | 278786篇 |
免费 | 2278篇 |
国内免费 | 963篇 |
专业分类
化学 | 125254篇 |
晶体学 | 4061篇 |
力学 | 15850篇 |
综合类 | 5篇 |
数学 | 53492篇 |
物理学 | 83365篇 |
出版年
2021年 | 1656篇 |
2020年 | 1797篇 |
2019年 | 1998篇 |
2018年 | 12861篇 |
2017年 | 12570篇 |
2016年 | 9667篇 |
2015年 | 3119篇 |
2014年 | 3879篇 |
2013年 | 9342篇 |
2012年 | 10835篇 |
2011年 | 18794篇 |
2010年 | 11461篇 |
2009年 | 11729篇 |
2008年 | 14241篇 |
2007年 | 16457篇 |
2006年 | 7896篇 |
2005年 | 8107篇 |
2004年 | 7878篇 |
2003年 | 7535篇 |
2002年 | 6456篇 |
2001年 | 6643篇 |
2000年 | 5193篇 |
1999年 | 3918篇 |
1998年 | 3206篇 |
1997年 | 3172篇 |
1996年 | 2981篇 |
1995年 | 2724篇 |
1994年 | 2538篇 |
1993年 | 2426篇 |
1992年 | 2741篇 |
1991年 | 2731篇 |
1990年 | 2648篇 |
1989年 | 2453篇 |
1988年 | 2506篇 |
1987年 | 2505篇 |
1986年 | 2335篇 |
1985年 | 3005篇 |
1984年 | 3256篇 |
1983年 | 2667篇 |
1982年 | 2840篇 |
1981年 | 2808篇 |
1980年 | 2683篇 |
1979年 | 2771篇 |
1978年 | 2853篇 |
1977年 | 2837篇 |
1976年 | 2901篇 |
1975年 | 2685篇 |
1974年 | 2655篇 |
1973年 | 2801篇 |
1972年 | 1780篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
A noncooperative game governed by a distributed-parameter predator-prey system is considered, assuming that two players control
initial conditions for predator and prey, respectively. Existence of a Nash equilibrium is shown under the condition that
the desired population profiles and the environmental carrying capacity for the prey are sufficiently small. A conceptual
approximation algorithm is proposed and analyzed. Finally, numerical simulations are performed, too. 相似文献
872.
Ji-pu Ma Tseng Yaun Rong Functional Analysis Research Center Harbin Normal University Harbin China 《中国科学A辑(英文版)》2007,50(9):1233-1239
Let E, F be two Banach spaces, and B(E, F), Φ(E, F), SΦ(E, F) and R(E,F) be the bounded linear, Fredholm, semi-Frdholm and finite rank operators from E into F, respectively. In this paper, using the continuity characteristics of generalized inverses of operators under small perturbations, we prove the following result Let ∑ be any one of the following sets {T ∈ Φ(E, F) IndexT =const, and dim N(T) = const.}, {T ∈ SΦ(E, F) either dim N(T) = const. < ∞ or codim R(T) = const.< ∞} and {T ∈ R(E, F) RankT =const.<∞}. Then ∑ is a smooth submanifold of B(E, F) with the tangent space TA∑ = {B ∈ B(E,F) BN(A) (∪) R(A)} for any A ∈ ∑. The result is available for the further application to Thom's famous results on the transversility and the study of the infinite dimensional geometry. 相似文献
873.
Elie Leopold 《Numerical Algorithms》2007,44(4):347-366
In this paper, we give some new explicit relations between two families of polynomials defined by recurrence relations of
all order. These relations allow us to analyze, even in the Sobolev case, how some properties of a family of orthogonal polynomials
are affected when the coefficients of the recurrence relation and the order are perturbed. In a paper we have already given
a method which allows us to study the polynomials defined by a three-term recurrence relation. Also here some generalizations
are given. 相似文献
874.
875.
The charge distribution of fragments originatingfrom the fission of the 236U compound nucleus is calculated within a stochastic approach based on Langevin equations. The elongation coordinate, the neck-thickness coordinate, and the charge-asymmetry coordinate are chosen as collective variables. The friction parameter of the charge mode is calculated on the basis of two nuclear-viscosity mechanisms, that of one-body and that of two-body dissipation. It is shown that the Langevin approach is applicable to studying isobaric distributions. In addition, the charge distribution in question is studied as a function of the excitation energy of the compound nucleus and as a function of the coefficient of two-body viscosity. 相似文献
876.
Chris Quigg 《EPJ direct》2002,4(1):1-15
We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ− in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ− are promising. 相似文献
877.
The adsorption of nonionic surfactant Triton X-100 on quartz sand and methylated quartz sand from water and toluene was investigated by means of spectrophotometry, the radiotracer technique, and wetting angle measurements. 相似文献
878.
Y. D. Kolekar S. B. Kulkarni Keka Chakraborty A. Das S. K. Paranjpe P. B. Joshi 《Pramana》2004,63(2):189-197
Nd2Sn2O7 pyrochlores with the substitution of Zr4+ were prepared by conventional ceramic double sintering technique. The single-phase formation was confirmed by X-ray diffraction
and neutron diffraction techniques. Relative intensity calculations for X-ray diffraction analysis were performed for oxygen
positional parametersx = 0.331 and 0.375, while Rietveld refinements were employed for neutron diffraction data. The neutron diffraction study revealed
that there are only two anion sites with 48f and 8b positions. This indicates that the 8a site, i.e. O(3) sublattice, is completely
vacant and the structure is a perfect cubic pyrochlore with space group Fd3m (O
h
7
). From the conductivity measurements, it is observed that the electronic conductivity dominates from room temperature up
to about 525 K and forT > 525 K, the oxygen ion conduction dominates the charge transport in these compositions. Complex impedance spectroscopy indicates
the existence of grain and grain boundary as two separate elements. 相似文献
879.
We study algebraic geometric codes obtained from rational normal scrolls. We determine the complete weight hierarchy and spectrum
of these codes.
相似文献
880.
We introduce new classes of 2-weight cyclic codes which are direct sums of 1-weight irreducible cyclic codes
相似文献