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101.
Ronsein GE de Oliveira MC de Medeiros MH Di Mascio P 《Journal of the American Society for Mass Spectrometry》2009,20(2):188-197
The fragmentation mechanisms of singlet oxygen [O(2) ((1)Delta(g))]-derived oxidation products of tryptophan (W) were analyzed using collision-induced dissociation coupled with (18)O-isotopic labeling experiments and accurate mass measurements. The five identified oxidized products, namely two isomeric alcohols (trans and cis WOH), two isomeric hydroperoxides (trans and cis WOOH), and N-formylkynurenine (FMK), were shown to share some common fragment ions and losses of small neutral molecules. Conversely, each oxidation product has its own fragmentation mechanism and intermediates, which were confirmed by (18)O-labeling studies. Isomeric WOH lost mainly H(2)O + CO, while WOOH showed preferential elimination of C(2)H(5)NO(3) by two distinct mechanisms. Differences in the spatial arrangement of the two isomeric WOHs led to differences in the intensities of the fragment ions. The same behavior was also found for trans and cis WOOH. FMK was shown to dissociate by a diverse range of mechanisms, with the loss of ammonia the most favored route. MS/MS analyses, (18)O-labeling, and H(2)(18)O experiments demonstrated the ability of FMK to exchange its oxygen atoms with water. Moreover, this approach also revealed that the carbonyl group has more pronounced oxygen exchange ability compared with the formyl group. The understanding of fragmentation mechanisms involved in O(2) ((1)Delta(g))-mediated oxidation of W provides a useful step toward the structural characterization of oxidized peptides and proteins. 相似文献
102.
103.
Alexandre Salles da Cunha Nelson Maculan Mauricio G.C. Resende 《Discrete Applied Mathematics》2009,157(6):1198-1217
Given an undirected graph G with penalties associated with its vertices and costs associated with its edges, a Prize Collecting Steiner (PCS) tree is either an isolated vertex of G or else any tree of G, be it spanning or not. The weight of a PCS tree equals the sum of the costs for its edges plus the sum of the penalties for the vertices of G not spanned by the PCS tree. Accordingly, the Prize Collecting Steiner Problem in Graphs (PCSPG) is to find a PCS tree with the lowest weight. In this paper, after reformulating and re-interpreting a given PCSPG formulation, we use a Lagrangian Non Delayed Relax and Cut (NDRC) algorithm to generate primal and dual bounds to the problem. The algorithm is capable of adequately dealing with the exponentially many candidate inequalities to dualize. It incorporates ingredients such as a new PCSPG reduction test, an effective Lagrangian heuristic and a modification in the NDRC framework that allows duality gaps to be further reduced. The Lagrangian heuristic suggested here dominates their PCSPG counterparts in the literature. The NDRC PCSPG lower bounds, most of the time, nearly matched the corresponding Linear Programming relaxation bounds. 相似文献
104.
Alexandre X. Martins Mauricio C. de Souza Marcone J. F. Souza Túlio A. M. Toffolo 《Journal of Heuristics》2009,15(2):133-151
We propose a GRASP using an hybrid heuristic-subproblem optimization approach for the Multi-Level Capacitated Minimum Spanning
Tree (MLCMST) problem. The motivation behind such approach is that to evaluate moves rearranging the configuration of a subset
of nodes may require to solve a smaller-sized MLCMST instance. We thus use heuristic rules to define, in both the construction
and the local search phases, subproblems which are in turn solved exactly by employing an integer programming model. We report
numerical results obtained on benchmark instances from the literature, showing the approach to be competitive in terms of
solution quality. The proposed GRASP have in fact improved the best known upper bounds for almost all of the considered instances. 相似文献
105.
The compound Ru(bpy)2(dppz-R)(PF6)2, where bpy is 2,2'-bipyridine and dppz-R is 11-(diethoxyphosphorylmethyl)dipyrido[3,2-a:2',3'-c]phenazine, was prepared and anchored to mesoporous nanocrystalline (anatase) TiO2 thin films as a probe of the effects of interfacial water on excited-state charge transfer processes at semiconductor interfaces. In nitrogen-saturated fluid acetonitrile, the Ru(bpy)2(dppz-R)(PF6)2 compound was found to be highly photoluminescent. Water was found to quench the excited state by a mechanism adequately described by the Perrin model, from which the radius of quenching was abstracted, 75 +/- 2 A. The Ru(bpy)2(dppz-R)(PF6)2 compounds were found to bind to the TiO2 thin films in high surface coverages, 5 x 10(-8) mol cm(-2). When these films were immersed in acetonitrile, long-lived excited states (tau = 825 ns) that were quenched by the addition of water were observed. About 30% of the excited states could not be quenched by water. Efficient electron injection, phi(inj) = 0.8, was observed after light excitation of Ru(bpy)2(dppz-R)/TiO2 in a 0.1 M LiClO4/acetonitrile solution. The addition of large concentrations of water, >0.5 M, was found to decrease the injection yield to phi(inj) = 0.3. 相似文献
106.
Kim YJ Wang P Navarro-Villalobos M Rohde BD Derryberry J Gin DY 《Journal of the American Chemical Society》2006,128(36):11906-11915
QS-21 is one of the most promising new adjuvants for immune response potentiation and dose-sparing in vaccine therapy given its exceedingly high level of potency and its favorable toxicity profile. Melanoma, breast cancer, small cell lung cancer, prostate cancer, HIV-1, and malaria are among the numerous maladies targeted in more than 80 recent and ongoing vaccine therapy clinical trials involving QS-21 as a critical adjuvant component for immune response augmentation. QS-21 is a natural product immunostimulatory adjuvant, eliciting both T-cell- and antibody-mediated immune responses with microgram doses. Herein is reported the synthesis of QS-21A(api) in a highly modular strategy, applying novel glycosylation methodologies to a convergent construction of the potent saponin immunostimulant. The chemical synthesis of QS-21 offers unique opportunities to probe its mode of biological action through the preparation of otherwise unattainable nonnatural saponin analogues. 相似文献
107.
Reaction of the tetranuclear complex [PtIMe3]4 with the ligand (S)- and (R)-Ph2P(C6H4)CHNC*H(Ph)Me in a 1:4 molar ratio yields the mononuclear neutral complexes in diastereoisomeric mixtures [PtIMe3{κ2-Ph2P(C6H4)CHNC*H(Ph)Me-P,N}]. Iodide abstraction from mixture with AgBF4 in the presence of pyridine (Py) induces a reductive elimination reaction with loss of ethane, leading to the cationic complex [PtMe(Py){κ2-Ph2P(C6H4)CHNC*H(Ph)Me-P,N}][BF4] [C* = (S)-, 3; (R)-, 4]. When this reaction was carried out in the presence of PPh3 a consecutive orthometallation reaction with loss of methane is produced, forming the cationic complex [Pt(PPh3){κ3-Ph2P(C6H4)CHNC*H(C6H4)Me-C,P,N}][BF4], [(S)-, 5; (R)-, 6]. All species were characterised in solution by 1H and 31P{1H} NMR spectroscopy, elemental analysis and mass spectrometry.The crystal structure of the diastereoisomer (OC-6-44-C)-[PtIMe3{κ2-(R)-Ph2P(C6H4)CHNC*H(Ph)Me-P,N}] has been determined by single-crystal X-ray diffraction. 相似文献
108.
109.
Alan Garbarz Joan La Madrid Mauricio Leston 《The European Physical Journal C - Particles and Fields》2017,77(11):807
We revisit the dynamics of a massive scalar field in a Banados, Teitelboim, and Zanelli background taking into account the lack of global hyperbolicity of the spacetime. We approach this issue using the strategy of Ishibashi and Wald which finds a unique smooth solution as the causal evolution of initial data, each possible evolution corresponding to a positive self-adjoint extension of certain operator in a Hilbert space on the initial surface. Moreover, solutions obtained this way are the most general ones satisfying a few physically sensible requirements. This procedure is intimately related to the choice of boundary conditions and the existence of bound states. We find that the scalar field dynamics in the (effective) mass window \(-3/4\le m_e^2\ell ^2<0\) can be well defined within a one-parametric family of distinct boundary conditions (\(-3/4\) being the conformally coupled case), while for \(m_e^2\ell ^2\ge 0\) the boundary condition is unique (only one self-adjoint extension is possible). It is argued that there is no sensible evolution possible for \(m_e^2\ell ^2<-1\), and also it is shown that in the range \(m_e^2\ell ^2 \in [-1,-3/4)\) there is a U(1) family of allowed boundary conditions, however, the positivity of the self-adjoint extensions is only motivated but not proven. We focus mainly on describing the dynamics of such evolutions given the initial data and all possible boundary conditions, and in particular we show the energy is always positive and conserved. 相似文献
110.
Carmen M. González-Henríquez Claudio A. Terraza Mauricio A. Sarabia Alejandra M. Vera Álvaro E. Aliaga 《光谱学快报》2017,50(1):30-38
Correlation between theoretical and experimental (infrared and Raman spectroscopies) vibrational spectra of two compounds, both with a silyl group present in their main chain and with an optically active structure (L-valine) as side group, was performed. These compounds are based in a chiral dicarboxylic acid monomer and its respective polyamide-imide, oligomer that was previously synthesized by a direct polycondensation. Spectra were recorded in the region comprised between 500 and 4000?cm?1 for infrared and Raman analysis. The Raman spectra were obtained through a 1064?nm laser as excitation source.Theoretical models were carried out in order to find the optimal molecular geometry of the analyzed systems, with a complete assignment of their vibrational spectra. The Raman experimental data obtained with a Nd:YAG laser for this kind of silylated organic compounds, and the comparison between these results with the theoretical data is a useful advance in the polymer synthesis field, which can be used as reference for subsequent studies. 相似文献