全文获取类型
收费全文 | 11669篇 |
免费 | 313篇 |
国内免费 | 416篇 |
专业分类
化学 | 1108篇 |
晶体学 | 16篇 |
力学 | 683篇 |
综合类 | 49篇 |
数学 | 9473篇 |
物理学 | 1069篇 |
出版年
2024年 | 13篇 |
2023年 | 44篇 |
2022年 | 90篇 |
2021年 | 63篇 |
2020年 | 109篇 |
2019年 | 322篇 |
2018年 | 321篇 |
2017年 | 229篇 |
2016年 | 201篇 |
2015年 | 185篇 |
2014年 | 314篇 |
2013年 | 751篇 |
2012年 | 352篇 |
2011年 | 719篇 |
2010年 | 583篇 |
2009年 | 765篇 |
2008年 | 885篇 |
2007年 | 883篇 |
2006年 | 710篇 |
2005年 | 472篇 |
2004年 | 417篇 |
2003年 | 373篇 |
2002年 | 304篇 |
2001年 | 237篇 |
2000年 | 230篇 |
1999年 | 282篇 |
1998年 | 266篇 |
1997年 | 193篇 |
1996年 | 275篇 |
1995年 | 237篇 |
1994年 | 219篇 |
1993年 | 183篇 |
1992年 | 132篇 |
1991年 | 93篇 |
1990年 | 96篇 |
1989年 | 92篇 |
1988年 | 62篇 |
1987年 | 63篇 |
1986年 | 67篇 |
1985年 | 90篇 |
1984年 | 63篇 |
1983年 | 52篇 |
1982年 | 67篇 |
1981年 | 60篇 |
1980年 | 54篇 |
1979年 | 39篇 |
1978年 | 45篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
Roberto E. Madariaga-Garcia 《Topology and its Applications》2007,154(7):1470-1480
Tkachenko showed in 1990 the existence of a countably compact group topology on the free Abelian group of size c using CH. Koszmider, Tomita and Watson showed in 2000 the existence of a countably compact group topology on the free Abelian group of size c2 using a forcing model in which CH holds.Wallace's question from 1955, asks whether every both-sided cancellative countably compact semigroup is a topological group. A counterexample to Wallace's question has been called a Wallace semigroup. In 1996, Robbie and Svetlichny constructed a Wallace semigroup under CH. In the same year, Tomita constructed a Wallace semigroup from MAcountable.In this note, we show that the examples of Tkachenko, Robbie and Svetlichny, and Koszmider, Tomita and Watson can be obtained using a family of selective ultrafilters. As a corollary, the constructions presented here are compatible with the total failure of Martin's Axiom. 相似文献
42.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
43.
The main results of the paper are as follows: covering characterizations of wQN-spaces, covering characterizations of QN-spaces and a theorem saying that Cp(X) has the Arkhangel'ski?ˇ property (α1) provided that X is a QN-space. The latter statement solves a problem posed by M. Scheepers [M. Scheepers, Cp(X) and Arhangel'ski?ˇ's αi-spaces, Topology Appl. 89 (1998) 265-275] and for Tychonoff spaces was independently proved by M. Sakai [M. Sakai, The sequence selection properties of Cp(X), Preprint, April 25, 2006]. As the most interesting result we consider the equivalence that a normal topological space X is a wQN-space if and only if X has the property S1(Γshr,Γ). Moreover we show that X is a QN-space if and only if Cp(X) has the property (α0), and for perfectly normal spaces, if and only if X has the covering property (β3). 相似文献
44.
This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel.
From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission
electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the
block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant
in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different
values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly
oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical
particle model with a locked aspect ratio. 相似文献
45.
46.
Summary We consider a class of infinite delay equations of neutral type which includes Volterrra type integral und integrodifferential equations. Using abstract approximation results (cf. Trotter-Kato-type) for strongly continuous semigroups we develop an approximation scheme which is based on approximation of the system state by Laguerre (and Legendre) polynomials. Numerical examples demonstrate the feasibility of the scheme and show infinite order convergence for smooth data.Supported in part by the Air Force Office of Scientific Research under Contracts AFORS-84-0398 and AFORS-85-0303 and the National Aeronautics and Space Administration under NASA Grant NAG-1-517 and by NSF under Grant UINT-8521208Supported in part by the Air Force Office of Scientific Research under Contract AFORS-84-0398 and in part by the Fonds zur Förderung der wissenschaftlichen Forschung, Austria, under project No. S3206 相似文献
47.
Risk related to long-term care (LTC) is high for the elderly. Planning for LTC is now regarded as the ‘third leg’ of retirement planning. In this paper, planning for LTC is integrated with saving and investment decisions for an integrated approach to retirement planning. Optimal LTC insurance purchase decisions are obtained by developing a trade-off between post-retirement LTC costs and LTC insurance premiums paid and coverage received. Integrating insurance purchase with wealth evolution, consisting of saving and investment decisions, allows addressing affordability issues.Two-way branching models are used for the stochastic health events and asset returns. The problem, formulated as a nonlinearly constrained mixed-integer optimization problem, is solved using a heuristic. Sensitivity analyses are performed for initial health and wealth status. Some important aspects of an individual’s behavioral preferences are also addressed in this framework to provide more robust decision support. 相似文献
48.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
49.
Piotr Borodulin-Nadzieja 《Topology and its Applications》2007,154(18):3107-3124
We investigate properties of minimally generated Boolean algebras. It is shown that all measures defined on such algebras are separable but not necessarily weakly uniformly regular. On the other hand, there exist Boolean algebras small in terms of measures which are not minimally generated. We prove that under CH a measure on a retractive Boolean algebra can be nonseparable. Some relevant examples are indicated. Also, we give two examples of spaces satisfying some kind of Efimov property. 相似文献
50.
We study the multiplicity of critical points for functionals which are only differentiable along some directions. We extend to this class of functionals the three critical point theorem of Pucci and Serrin and we apply it to a one-parameter family of functionals Jλ, λ∈I⊂R. Under suitable assumptions, we locate an open subinterval of values λ in I for which Jλ possesses at least three critical points. Applications to quasilinear boundary value problems are also given. 相似文献