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1.
Ligands with reactive carbon sites in the periphery of a metal center have emerged as a powerful approach for metal–ligand bond activation. These reactive carbon sites are commonly generated by deprotonation strategies. Carbon–silicon bond cleavage is a potential alternative to access such constructs. Herein, the monodesilylation of bis-silyl-substituted P,N scaffold PNSi2 in the coordination sphere of [RhI(Cl)(CO)( PNSi2 )] ( 1 ) with sodium azide is disclosed. This affords a unique dinucleating anionic κ2-C,N1-P ligand with a carbanionic methine carbon atom directly bound to rhodium as part of a four-membered Rh-N-C-C rhodacycle. This dimer undergoes meta-pyridine C−H activation facilitated by weak bases, which leads to a desymmetrization of the system and provides a σ,π-bridging 3-pyridyl fragment bound to RhI. The facile Si−C cleavage strategy may pave the way to studying the reactivity and functionalization of a variety of κ2-C,N-coordinated pyridine scaffolds for selective transformations.  相似文献   
2.
A cylindrical confined combustor operating under MILD condition is investigated using LES. The combustion and its interaction with turbulence are modeled using two reactor based models, PaSR and EDC. Results show that the Partially Stirred Reactor (PaSR) model yields improved estimation for mean temperature and species mole fractions compared to Eddy Dissipation Concept (EDC). LES data are analysed using advanced post-processing methods such as the chemical Tangential Stretching Rate (TSR), balance analysis and local Principle Component (PCA) analysis. TSR can identify chemical explosive (ignition-like) and contractive (burnt) regions. With the balance analysis of the convective, diffusive and reactive terms in temperature equation, regions with substantial heat release coming from ignition or flame are identified. The local PCA analysis classifies the whole domain into clusters (regions with specific features) and provides the leading species in each cluster. The three analyses correlate well with one another and it is observed that the most chemically active region locates upstream (in the near-field). Also, both autoignition and flame-like structures play equally important roles in MILD combustion.  相似文献   
3.
Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier.  相似文献   
4.
The potential limits of superbasicity achievable with different families of neutral bases by expanding the molecular framework are explored using DFT computations. A number of different core structures of non‐ionic organosuperbases are considered (such as phosphazenes, guanidinophosphazenes, guanidino phosphorus ylides). A simple model for describing the dependence of basicity on the extent of the molecular framework is proposed, validated, and used for quantitatively predicting the ultimate basicities of different compound families and the rates of substituent effect saturation. Some of the considered bases (guanidino phosphorus carbenes) are expected to reach gas‐phase basicity around 370 kcal mol?1, thus being the most basic neutral bases ever reported. Also, the classical substituted alkylphosphazenes were predicted to reach pKa values of around 50 in acetonitrile, which is significantly higher than previously expected.  相似文献   
5.
The metalloradical activation of o-aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)-carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium-sized ring structures. Herein we make use of the intrinsic radical-type reactivity of cobalt(III)-carbene radical intermediates in the [CoII(TPP)]-catalyzed (TPP=tetraphenylporphyrin) synthesis of two types of 8-membered ring compounds; novel dibenzocyclooctenes and unprecedented monobenzocyclooctadienes. The method was successfully applied to afford a variety of 8-membered ring compounds in good yields and with excellent substituent tolerance. Density functional theory (DFT) calculations and experimental results suggest that the reactions proceed via hydrogen atom transfer from the bis-allylic/benzallylic C−H bond to the carbene radical, followed by two divergent processes for ring-closure to the two different types of 8-membered ring products. While the dibenzocyclooctenes are most likely formed by dissociation of o-quinodimethanes (o-QDMs) which undergo a non-catalyzed 8π-cyclization, DFT calculations suggest that ring-closure to the monobenzocyclooctadienes involves a radical-rebound step in the coordination sphere of cobalt. The latter mechanism implies that unprecedented enantioselective ring-closure reactions to chiral monobenzocyclooctadienes should be possible, as was confirmed for reactions mediated by a chiral cobalt-porphyrin catalyst.  相似文献   
6.
Three Pt4L2L′2 heteroleptic rectangles ( 1 – 3 ), containing ditopic redox-active bis-pyridine functionalized perylene bisimide (PBI) ligands PBI-pyr2 ( L ) are reported. Co-ligand L′ is a dicarboxylate spacer of varying length, leading to modified overall size of the assemblies. 1H NMR spectroscopy reveals a trend in the splitting and upfield chemical shift of the PBI-hydrogens in the rectangles with respect to free PBI, most pronounced with the largest strut length ( 3 ) and least with the smallest strut length ( 1 ). This is attributed to increased rotational freedom of the PBI-pyr 2 ligand over its longitudinal axis (Npy-Npy), due to increased distance between the PBI-surfaces, which is corroborated by VT-NMR measurements and DFT calculations. The intramolecular motion entails desymmetrization of the two PBI-ligands, in line with cyclic voltammetry (CV) data. The first (overall two-electron) reduction event and re-oxidation for 1 display a subtle peak-to-peak splitting of 60 mV, whilst increased splitting of this event is observed for 2 and 3 . The binding of pyrene in 1 is probed to establish proof of concept of host-guest chemistry enabled by the two PBI-motifs. Fitting the binding curve obtained by 1H NMR titration with a 1:1 complex formation model led to a binding constant of 964±55 m −1. Pyrene binding is shown to directly influence the redox-chemistry of 1 , resulting in a cathodic and anodic shift of approximately 46 mV on the first and second reduction event, respectively.  相似文献   
7.
Three novel tricyclic diamines (1,7-diazaisoadamantane, 1,5-diazaisoadamantane and 1,6-diazahomobrendane) were prepared. A flexible synthetic strategy was employed which used flat, aromatic azaindoles as the starting materials. The requisite azaindoles were prepared by a tandem Sonogashira coupling/intramolecular cyclization reaction. Ring saturation, appropriate functionalization and intramolecular alkylation provided the three novel tricyclic diamines cores.  相似文献   
8.
Photochemical activation of [(PNNH)Rh(N3)] (PNNH=6‐di‐(tert‐butyl)phosphinomethyl‐2,2′‐bipyridine) complex 2 produced the paramagnetic (S=1/2), [(PNN)Rh?N.‐Rh(PNN)] complex 3 (PNN?=methylene‐deprotonated PNNH), which could be crystallographically characterized. Spectroscopic investigation of 3 indicates a predominant nitridyl radical (.N2?) character, which was confirmed computationally. Complex 3 reacts selectively with CO, producing two equivalents of [(PNN)RhI(CO)] complex 4 , presumably by nitridyl radical N,N‐coupling.  相似文献   
9.
Coordination of a redox‐active pyridine aminophenol ligand to RuII followed by aerobic oxidation generates two diamagnetic RuIII species [ 1 a (cis) and 1 b (trans)] with ligand‐centered radicals. The reaction of 1 a / 1 b with excess NaN3 under inert atmosphere resulted in the formation of a rare bis(nitrido)‐bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru‐N‐Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a / 1 b supports the oxidation of a nitride (N3?) to half an equivalent of N2. The trinuclear omplex is reactive toward TEMPO‐H, tin hydrides, thiols, and dihydrogen.  相似文献   
10.
Synthesis of the previously unreported 1,4-diazaadamantane is described. The overall strategy involves complete saturation of a flat, aromatic heterocycle, appropriate functionalization and intramolecular double alkylation. The alkylation takes place via an iminophosphorane under anhydrous conditions, which produced superior results vs. alkylation of the corresponding primary amine.  相似文献   
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