全文获取类型
收费全文 | 1039篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 655篇 |
晶体学 | 10篇 |
力学 | 17篇 |
数学 | 141篇 |
物理学 | 240篇 |
出版年
2023年 | 3篇 |
2022年 | 27篇 |
2021年 | 18篇 |
2020年 | 16篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 23篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 56篇 |
2012年 | 53篇 |
2011年 | 73篇 |
2010年 | 44篇 |
2009年 | 39篇 |
2008年 | 60篇 |
2007年 | 48篇 |
2006年 | 46篇 |
2005年 | 48篇 |
2004年 | 46篇 |
2003年 | 36篇 |
2002年 | 32篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 3篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1963年 | 3篇 |
排序方式: 共有1063条查询结果,搜索用时 15 毫秒
141.
Doménech A García-España E Navarro P Miranda C 《Dalton transactions (Cambridge, England : 2003)》2006,(41):4926-4935
The voltammetric behaviour of bi- and mono-nuclear complexes formed in solution by Cu(2+) with three polyazacyclophanes containing pyrazole units in aqueous solution is described. Cyclic and square wave voltammetric responses at glassy carbon electrodes indicate that the reduction of copper-macrocycle complexes in solution takes place in two successive one-electron per Cu transfer processes coupled with preorganization and protonation reactions that mimic the behaviour of superoxide dismutase. The electrochemistry of ternary Cu(2+)-receptor-dopamine complexes exhibits significant differences with respect to the protection of the neurotransmitter from post-electron transfer cyclization reactions. 相似文献
142.
Aldegunde J Alvariño JM Kendrick BK Sáez Rábanos V de Miranda MP Aoiz FJ 《Physical chemistry chemical physics : PCCP》2006,8(42):4881-4896
The effect of reactant polarisation on the dynamics of the title reaction at collision energies up to 1.6 eV is analysed in depth. The analysis takes advantage of two novel theoretical concepts: intrinsic reaction properties and stereodynamical portraits. Exact quantum methods are used to determine the polarisation moments that quantify the intrinsic reactant polarisation at various levels of detail, including or not product state and/or scattering angle resolution. The data is then examined with the aid of stereodynamical portraits, which facilitate the rationalisation of the stereochemical effects that are relevant for the reaction dynamics. This allows for detailed characterisations of the so-called direct and delayed reaction mechanisms. 相似文献
143.
Nanosecond laser flash photolysis (lambdaexc = 355 nm) of neutral aqueous solutions of lomefloxacin (LFX, a 8-fluorinated 7-amino-4-quinolone-3-carboxylic acid derivative) produces a detectable transient species, which shows an absorption maximum at 490 nm and can be assigned to an aryl cation. This intermediate has a lifetime of ca. 200 ns in net water, reacts with Br- and Cl- with rate constants of 3.6 x 10(9) M(-1) s(-1) and 4.1 x 10(8) M(-1) s(-1), respectively, and shows a lack of reactivity toward molecular oxygen. From the photolysis of BAY y3118 (BAY, a 8-chlorinated analogue), an aryl cation is also generated, showing absorption maximum at 480 nm (lifetime of ca. 1 micros in net water) and a reaction rate constant of 9 x 10(9) M(-1) s(-1) with Br(-). The existence of these highly reactive species arising from direct photolysis of LFX and BAY can justify the photogenotoxic properties associated with these antibacterial drugs likely due to direct reaction of their cations with DNA. 相似文献
144.
de Sousa M de Castro B Abad S Miranda MA Pischel U 《Chemical communications (Cambridge, England)》2006,(19):2051-2053
A simple set of five components was used to design molecular logic gates based on phthalimide-sensitised Tb(III) luminescence, including the first report of an enabled NOR (EnNOR) gate. 相似文献
145.
Production and distribution are two key decisions in supply chain planning. In order to achieve an effective operational performance, it is important for these two decisions to be integrated, especially in supply chains with low inventory levels. In this paper, we propose a mixed integer programming model to integrate production, inventory, distribution and routing decisions in a single framework. The model was inspired by small Brazilian furniture companies and focuses on production and distribution decisions at an operational level. In particular, we consider a scenario in which only one production line and one vehicle, which makes multiple trips over the planning horizon, are available to produce items and deliver final products, respectively. We also take into account some features rarely considered in the literature, but commonly found in real-world applications, such as producing and stocking multiple items, distribution routes extending over one or more periods, multiple time windows and customers’ due dates. Computational tests on a set of randomly generated instances were carried out using a well-known optimization software and six relax-and-fix heuristics, which explore different criteria for partitioning and fixing variables. We also implemented two hybrid heuristics in which an initial solution is first constructed and then fed into the optimization software to improve it. The results showed that one relax-and-fix and the two hybrid heuristics performed better than the solver on the largest instances. 相似文献
146.
Inspired by Arnold’s classification of local Poisson structures [1] in the plane using the hierarchy of singularities of smooth functions, we consider the problem of global classification of Poisson structures on surfaces. Among the wide class of Poisson structures, we consider the class of bm-Poisson structures which can be also visualized using differential forms with singularities as bm-symplectic structures. In this paper we extend the classification scheme in [24] for bm-symplectic surfaces to the equivariant setting. When the compact group is the group of deck-transformations of an orientable covering, this yields the classification of these objects for nonorientable surfaces. The paper also includes recipes to construct bm-symplectic structures on surfaces. The feasibility of such constructions depends on orientability and on the colorability of an associated graph. The desingularization technique in [10] is revisited for surfaces and the compatibility with this classification scheme is analyzed in detail. 相似文献
147.
Alberto Alexandre Assis Miranda Cláudio Leonardo Lucchesi 《Discrete Applied Mathematics》2010,158(12):1275-1278
A matching covered graph is a non-trivial connected graph in which every edge is in some perfect matching. A non-bipartite matching covered graph G is near-bipartite if there are two edges e1 and e2 such that G−e1−e2 is bipartite and matching covered. In 2000, Fischer and Little characterized Pfaffian near-bipartite graphs in terms of forbidden subgraphs [I. Fischer, C.H.C. Little, A characterization of Pfaffian near bipartite graphs, J. Combin. Theory Ser. B 82 (2001) 175-222.]. However, their characterization does not imply a polynomial time algorithm to recognize near-bipartite Pfaffian graphs. In this article, we give such an algorithm.We define a more general class of matching covered graphs, which we call weakly near-bipartite graphs. This class includes the near-bipartite graphs. We give a polynomial algorithm for recognizing weakly near-bipartite Pfaffian graphs. We also show that Fischer and Little’s characterization of near-bipartite Pfaffian graphs extends to this wider class. 相似文献
148.
149.
Mathias Masson Michele Miranda Jr. Fabio Paronetto Mikko Parviainen 《Ricerche di matematica》2013,62(2):279-305
Using purely variational methods, we prove in metric measure spaces local higher integrability for minimal p-weak upper gradients of parabolic quasiminimizers related to the heat equation. We assume the measure to be doubling and the underlying space to be such that a weak Poincaré inequality is supported. We define parabolic quasiminimizers in the general metric measure space context, and prove an energy type estimate. Using the energy estimate and properties of the underlying metric measure space, we prove a reverse Hölder inequality type estimate for minimal $p$ -weak upper gradients of parabolic quasiminimizers. Local higher integrability is then established based on the reverse Hölder inequality, by using a modification of Gehring’s lemma. 相似文献
150.
José Luiz Boldrini Luís H. de Miranda Gabriela Planas 《Journal of Evolution Equations》2013,13(3):535-560
This article considers the issues of existence and regularity of solutions to the following doubly nonlinear differential inclusion $$\omega_t+\alpha (\omega_t)-\Delta \omega-\Delta_p{\omega} \ni f$$ where α is a maximal monotone operator in ${\mathbb{R}^2}$ and Δ p denotes the p-Laplacian with p > 2. The investigation on fractional regularity is based on the Galerkin method combined with a suitable basis for W 1,p , which we exhibit as a preliminary result. This approach also allows the obtaining of estimates in the so-called Nikolskii spaces, since it balances the interplay between the maximal monotone operator with the appearing higher order nonlinear terms. 相似文献