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51.
In this paper, we present a unified finite volume method preserving discrete maximum principle (DMP) for the conjugate heat transfer problems with general interface conditions. We prove the existence of the numerical solution and the DMP-preserving property. Numerical experiments show that the nonlinear iteration numbers of the scheme in [24] increase rapidly when the interfacial coefficients decrease to zero. In contrast, the nonlinear iteration numbers of the unified scheme do not increase when the interfacial coefficients decrease to zero, which reveals that the unified scheme is more robust than the scheme in [24]. The accuracy and DMP-preserving property of the scheme are also veried in the numerical experiments. 相似文献
52.
The paper shows that representing structures, beams and frames by mathematical models based on graph theory enables to provide new perspective on known conjugate structure theorems in mechanics. It is shown that the latter theorems can be derived from the graph theoretical duality principle applied upon the graph representations of the structures. The results reported indicate upon theoretical value of the approach, as the established mathematical foundation can be employed in a variety of mechanical disciplines. 相似文献
53.
设计合成了4种对称的以不同供/吸电子基团为共轭桥、两端连接meso位苯或噻吩取代的新型氟化硼二吡咯甲川(BODIPY)衍生物;通过1H NMR,13C NMR和MS等手段对其进行了结构表征;并采用紫外吸收光谱、荧光发射光谱及循环伏安(CV)等方法研究了其光电性能.紫外光谱数据表明,BODIPY结构具有明显的特征吸收,中间的桥联基团无论是强供电子的苯并二噻吩(BDT)还是强吸电子的苯并噻二唑(BT)均不能使整个分子产生明显的分子内电子迁移(ICT).另一方面,meso位的取代基可与BODIPY核产生微弱的ICT,且meso位噻吩取代的分子比meso位苯环取代的分子表现出更强的ICT.紫外光谱数据和电化学测试结果表明,meso位噻吩取代的分子比meso位苯环取代的分子具有更低的氧化电位和更窄的能隙. 相似文献
54.
In this article, we propose the Gauss-Newton methods via conjugate gradient path for solving nonlinear systems. By constructing and solving a linearized model of the nonlinear systems, we obtain the iterative direction by employing the conjugate gradient path. In successive iterations, the approximate Jacobian of the nonlinear systems is updated by a Broyden formula to construct the conjugate path. The global convergence and local superlinear convergence rate of the proposed algorithms are established under some reasonable conditions. Finally, the numerical results are reported to show the effectiveness of the proposed algorithms. 相似文献
55.
In this Note we describe a preconditionner for iteratively solving the linear system arising from the discretization of a general nonseparable elliptic problem by spectral element method. This preconditionner is constructed from approximating the original problem with the closest (in some sense) separable elliptic problem. A direct method is then used to invert the preconditionner. To cite this article: M. Azaïez et al., C. R. Mecanique 331 (2003). 相似文献
56.
Shin-ichi Matsuoka Shintaro ShimakawaKoji Takagi Masato Suzuki 《Tetrahedron letters》2011,52(50):6835-6838
The head-to-tail dimerization of methacrolein via the conjugate addition of methanol is catalyzed by various organic bases, such as an amine, phosphine, and N-heterocyclic carbene, to give 2,4-dimethyl-2-methoxymethylpentane-1,5-dial in moderate yields. Based on the interpretation of the key intermediates by electrospray ionization mass spectrometry, we propose a reaction mechanism involving the initial conjugate addition of the organic bases to methacrolein to generate a zwitterionic base followed by the activation of methanol. 相似文献
57.
Cu-catalyzed enantioselective 1,4-conjugate addition of β,γ-unsaturated α-keto ester compound was carried out to afford chiral γ-substituted γ-aryl α-keto ester, which could be conveniently converted to the potential skeleton of new Pril drugs. Up to 81% ee and 99% yield were afforded for the 1,4-conjugate addition using D2-symmetric biphenyl phosphoramidite ligand. 相似文献
58.
Stephen G. Davies James A. LeePaul M. Roberts James E. ThomsonJingda Yin 《Tetrahedron》2011,67(34):6382-6403
The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure α,β-unsaturated esters [derived from Corey’s 8-phenylmenthol chiral auxiliary] and enantiopure α,β-unsaturated hydroxamates [derived from our ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine] has been used as a mechanistic probe to determine the reactive conformations of these acceptors. 相似文献
59.
Hideaki Iiduka 《Applied mathematics and computation》2011,217(13):6315-6327
Many constrained sets in problems such as signal processing and optimal control can be represented as a fixed point set of a certain nonexpansive mapping, and a number of iterative algorithms have been presented for solving a convex optimization problem over a fixed point set. This paper presents a novel gradient method with a three-term conjugate gradient direction that is used to accelerate conjugate gradient methods for solving unconstrained optimization problems. It is guaranteed that the algorithm strongly converges to the solution to the problem under the standard assumptions. Numerical comparisons with the existing gradient methods demonstrate the effectiveness and fast convergence of this algorithm. 相似文献
60.
In this paper, we make a modification to the Liu-Storey (LS) conjugate gradient method and propose a descent LS method. The method can generate sufficient descent directions for the objective function. This property is independent of the line search used. We prove that the modified LS method is globally convergent with the strong Wolfe line search. The numerical results show that the proposed descent LS method is efficient for the unconstrained problems in the CUTEr library. 相似文献