全文获取类型
收费全文 | 550篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 391篇 |
晶体学 | 6篇 |
力学 | 2篇 |
数学 | 69篇 |
物理学 | 104篇 |
出版年
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 4篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 18篇 |
2012年 | 25篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 16篇 |
2008年 | 30篇 |
2007年 | 21篇 |
2006年 | 29篇 |
2005年 | 20篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1968年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有572条查询结果,搜索用时 0 毫秒
51.
Manabu Naito 《Annali di Matematica Pura ed Applicata》1984,136(1):1-13
Summary The equation to be considered is of the form (1) x(n)(t)+p(t)x(g(t))=0 (t>a), where =±1, p(t) > 0 for ta and g(t) as t. It is well- known that a nonoscillatory solution x(t) of (1) satisfies (2) x(t)x(i)(t)>0 (0il), (–1)i–lx(t)x(i)(t)>0 (lin) for some integer l, 0ln, (–1)n–l–1=1. In this paper, for a given l such that 0n–l–1=1, necessary conditions and sufficient conditions are found for (1) to have a solution x(t) which satisfies (2), and a necessary and sufficient condition is established in order that for every >0 the equation x(n)(t)+p(t)x(g(t))=0 (t>a) has a solution x(t) which satisfies (2). Related results are also contained. 相似文献
52.
Michael reaction of 1,7-pctadien-3-one with 2-methylcyclopentane-1,3-dione, followed by intramolecular aldol condensation promoted by L-amino acids produced the optically active (+)-4-(3-butenyl)-7a-methyl-5,6,7,7a-tetrahydroindane-1,5-dione in high chemical and optical yields. The PdCl2-catalyzed oxidation of the terminal double bond gave the methyl ketone, which had 76% optical purity and was made 100% optically pure by recrystallization. Then aldol condensation afforded the tricyclic ketone, which was alkylated with 3-butenyl iodide to afford (?)-3β-t-butoxy-2,3,3a,4,5,7,8,9,9aβ,9bα-decahydro-6-(3-butenyl)-3aβ-methyl-1H-benz[e]inden-7-one. The synthesis of this compound means the total synthesis of (+)-19-nortestosterone. 相似文献
53.
Poly(phenylisopropenylketone (PPIK) and copolymers of PIK and methylmethacrylate (MMA) or styrene (St) were irradiated in benzene solution at 30° with 313 nm light (stationary irradiations) or with 347 nm light (flash photolysis experiments). Homo PPIK undergoes main chain degradation (β-scission) with ø(S) ≈ 0.05. The quantum yield for α-scission is ø(α) = 0.3. For copolymers of MMA and PIK (1 to 15 mol%), ø(S) is 0.04 independent of the copolymer composition. With copolymers of St and PIK, ø(S) was found to increase with decreasing PIK content and to approach 0.15 for very small PIK contents. The flash photolysis experiments showed: (a) the carbonyl triplet decay rate constant kT(6 × 106 sec?1) for CP-MMA-PIK samples is independent of copolymer composition but is lower than for homo PPIK (1 × 107 sec?1). In CP-St-PIK samples kT decreases with decreasing PIK content [from 8 × 106 sec?1 (12 mol% PIK) to 3 × 106 sec?1 (1 mol% PIK)]; (b) the transient spectra of triplet decay products indicate the formation of benzoyl radicals in the cases of PPIK and CP-MMA-PIK, and the formation of various different species in the case of CP-St-PIK.The results are consistent with the following concept. In homo PPIK and CP-MMA-PIK, α-scission (Norrish type I) is the dominant chemical route of triplet deactivation. In CP-St-PIK, however, type II processes become more and more important as the PIK content decreases. 相似文献
54.
Yuka Naito 《Mathematical Methods in the Applied Sciences》2009,32(13):1609-1637
This paper is concerned with the thermoelastic plate equations in a domain Ω: subject to the boundary condition: u|=Dνu|=θ|=0 and initial condition: (u, ut, θ)|t=0=(u0, v0, θ0). Here, Ω is a bounded domain in ?n(n≧2). We assume that the boundary ?Ω of Ω is a C4 hypersurface. We obtain an Lp–Lq maximal regularity theorem. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
55.
Shigeaki Koike Takahiro Kosugi Makoto Naito 《Journal of Mathematical Analysis and Applications》2018,457(1):436-460
The rate of convergence of approximate solutions via penalization for free boundary problems are concerned. A key observation is to obtain global bounds of penalized terms which give necessary estimates on integrations by the nonlinear adjoint method by L.C. Evans. 相似文献
56.
Let X be a Banach space and L the generator of the evolution semigroup associated with the τ -periodic evolutionary process {U(t,s)}t≥s on the space Pτ(X) of all τ-periodic continuous X -valued functions. We give criteria for the existence of periodic solutions to nonlinear systems of the form Lp=−?F(p,?) under the condition that 1 is a normal eigenvalue of the monodromy operator U(τ,0). The proof is based on a new decomposition of the space Pτ(X) by constructing a right inverse of L. 相似文献
57.
We first introduce the notion of positive linear Volterra integral equations. Then, we offer a criterion for positive equations in terms of the resolvent. In particular, equations with nonnegative kernels are positive. Next, we obtain a variant of the Paley-Wiener theorem for equations of this class and its extension to perturbed equations. Furthermore, we get a Perron-Frobenius type theorem for linear Volterra integral equations with nonnegative kernels. Finally, we give a criterion for positivity of the initial function semigroup of linear Volterra integral equations and provide a necessary and sufficient condition for exponential stability of the semigroups. 相似文献
58.
Assuming the existence of the perfect crystal bases of Kirillov-Reshetikhin modules over simply-laced quantum affine algebras,
we construct certain perfect crystals for twisted quantum affine algebras, and also provide compelling evidence that the constructed
crystals are isomorphic to the conjectural crystal bases of Kirillov-Reshetikhin modules over twisted quantum affine algebras. 相似文献
59.
60.