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61.
This article reports in detail on the discovery that zirconium(IV) salts of secondary amides and lactams are transformed by Cp(2)ZrHCl to N-substituted imines in one step. The method represents the first controlled reduction of amides and lactams to the corresponding imines, a transformation that is otherwise very difficult to achieve because imines are reduced more rapidly than carboxamides by most metal hydride reagents. No products of reductive cleavage of the carboxamides are observed. Efforts to replace 2 mol equiv of Cp(2)ZrHCl with simpler, less costly alternatives led to the finding that a diisobutylaluminum enolate can be substituted for the initial zirconium enolate. Such aluminum amides are smoothly reduced to the corresponding imine using Cp(2)ZrHCl in good yield. Moreover, aluminum amides are also reduced to imines using either low-valent titanium species or triethylsilane. In these alternative procedures, use of Cp(2)ZrHCl is eliminated altogether in the title transformation.  相似文献   
62.
King RB 《Inorganic chemistry》2003,42(26):8755-8761
The bismuth polyhedra in ternary transition metal-centered bismuth cluster halides may form discrete molecules or ions, infinite chains, and/or infinite layers. The chemical bonding in many of these diverse structures is related to that in deltahedral boranes exhibiting three-dimensional aromaticity by replacing the multicenter core bond in the boranes with two-center two-electron (2c-2e) bonds from the central transition metal to the nearest neighbor bismuth vertices. Examples of discrete molecules or ions include octahedral MBi(6)(micro-X)(12)(z)()(-) (X = Br, I; M = Rh, Ir, z = 3; M = Ru, z = 4) with exclusively 2c-2e bonds and pentagonal bipyramidal RhBi(7)Br(8) with a 5c-4e bond in the equatorial pentagonal plane indicative of M?bius aromaticity. The compound Ru(3)Bi(24)Br(20) contains a more complicated discrete bismuth cluster ion Ru(2)Bi(17)(micro-Br)(4)(5+), which can be dissected into a RuBi(5) closo octahedron and a RuBi(8) nido capped square antiprism bridged by a Ru(2)Bi(4)(micro-Br)(4) structural unit. In RuBi(4)X(2) (X = Br, I), the same Ru(2)Bi(4)(micro-Br)(4) structural unit bridges Bi(4) squares similar to those found in the known Zintl ion Bi(4)(2)(-) to give infinite chains of Ru(2)Bi(4) octahedra. The electron counts of the RuBi(5), RuBi(8), and Ru(2)Bi(4) polyhedra in these structures follow the Wade-Mingos rules. A different infinite chain structure is constructed from fused RhBi(7/2)Bi bicapped trigonal prisms in Rh(2)Bi(9)Br(3). This Rh(2)Bi(9)Br(3) structure can alternatively be derived from alternating Rh(2/2)Bi(4) octahedra and Rh(2/)(2)Bi(5) pentagonal bipyramids with electron counts obeying the Wade-Mingos rules. Related chemical bonding principles appear to apply to more complicated layer structures such as Pt(3)Bi(13)I(7) containing Kagomé nets of PtBi(8/2) cubes and Ni(4)Bi(12)X(3) containing linked chains of NiBi(6/3)Bi capped trigonal prisms.  相似文献   
63.
Arsenic (As) is a toxic trace element that occurs naturally in groundwater and soils. Understanding the reactions of arsenite (As(III)) and arsenate (As(V)) with soil and mineral surfaces is critical for predicting the fate and transport of As in the environment and developing better ways to remediate As-contaminated areas. This investigation uses X-ray absorption near edge spectroscopy (XANES) to evaluate the solid phase oxidation state and mineral surface binding sites in three agricultural soil samples from California, USA by fitting linear combinations of XANES spectra derived from several synthetic and well characterized As(III)- and As(V)-treated model compounds (Fe and Al metal hydroxides and aluminosilicate illite clay mineral). The results suggest that As(III) is either partially or completely oxidized to As(V) when reacted with soil in an aqueous, batch reaction. The As(III)-treated Aiken soil was composed of 60% As(III) attached to surfaces similar to lepidocrocite (γ-FeOOH)) and 40% As(V) attached to aluminosilicate (illite). The Fallbrook soil completely oxidized As(III) and the product was As(V) adsorbed on Al hydroxide (gibbsite, γ-Al(OH)3) (62%), illite (16%), and lepidocrocite (γ-FeOOH) (22%). The reaction of As(III) with Wyo soil resulted in 42% As(III) adsorbed on surface similar to goethite and 58% As(V) adsorbed on lepidocrocite. Arsenic(V) adsorption on soil resulted in stable As(V) surface complexes that were well described by XANES spectra from As(V) adsorption complexes on gibbsite, illite, and lepidocrocite.  相似文献   
64.
In this article, we describe a series of new complex salts in which electron-rich transition-metal centers are coordinated to three electron-accepting N-methyl/aryl-2,2':4,4' ':4',4' '-quaterpyridinium ligands. These complexes contain either Ru(II) or Fe(II) ions and have been characterized by using various techniques, including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses beta have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d --> pi* metal-to-ligand charge-transfer bands. The latter experiments reveal that these putatively octupolar D(3) chromophores exhibit two substantial components of the beta tensor which are associated with transitions to dipolar excited states. Computations involving time-dependent density-functional theory and the finite field method serve to further illuminate the electronic structures and associated linear and NLO properties of the new chromophoric salts.  相似文献   
65.
Solution redox chemistry of carbon nanotubes   总被引:1,自引:0,他引:1  
UV/vis/NIR absorbance spectra were used to monitor electron transfer between small-molecule redox reagents and carbon nanotubes (CNTs). The oxidation of (6, 5)-enriched nanotubes in water with K(2)Ir(Cl)(6) reveals a valence electron density of 0.2-0.4 e(-)/100 carbon atoms and a reduction potential of approximately 800 mV versus NHE. The reduction potential of CNTs is found to increase with increasing band gap and to decrease with the introduction of an anionic dispersant. In light of this newly revealed redox chemistry of CNTs, we propose that the previously observed bleaching of the CNT absorbance spectrum at low pH is most likely a consequence of the oxidation of the nanotubes by oxygen. These results demonstrate facile oxidation and reduction of CNTs, provide a way to quantify the population of valence electrons, and point to possible applications of CNT in the catalysis of redox reactions.  相似文献   
66.
Ionic flux through a composite membrane structure, containing vertically aligned carbon nanotubes crossing a polystyrene matrix film, was studied as a function of chemical end groups at the entrance to carbon nanotubes' (CNTs) cores. Plasma oxidation during the membrane fabrication process introduced carboxylic acid groups on the CNTs' tips that were modified using carbodiimide mediated coupling between the carboxylic acid and an accessible amine groups of the functional molecule. Functionalization molecules included straight chain alkanes, anionically charged dye molecules, and an aliphatic amine elongated by polypeptide spacers. Functionalization was confirmed by FTIR spectroscopy, and areal functional density was estimated by transmission electron microscopy studies of thiol terminated sites decorated by nanocrystalline gold. The transport through the membrane of two different sized but equally charged molecules (ruthenium bipyridine [Ru-(bipy)3(2+)] and methyl viologen [MV2+]) was quantified in a U-tube permeation cell by UV-vis spectroscopy. Relative selectivity of the permeates varied from 1.7 to 3.6 as a function of tip-functionalization chemistry. Anionic charged functional groups sharply increased the flux of the cationic permeates. This effect was reduced at higher solution ionic strength consistent with shorter Debye screening length. The observed selectivities were consistent with a hindered diffusion model with functionalization at the CNT tip and not along the length of the CNT core.  相似文献   
67.
The structure of a unique bromine-containing ketal, obtusin (1), has been determined by spectral and X-ray crystallographic techniques. Obtusin is a natural component of the Mediteranean red alga Laurenciaobtusa.  相似文献   
68.
Polyacrylamide gel electrophoresis was used to resolve as many as three protein components from incubation mixtures containing the inhibitor, 5-fluoro-2′-deoxyuridylate, the cofactor, 5,10-methylene tetrahydrofolate, and thymidylate synthetase. In a series of mixtures containing excess 5,10-methylenetetrahydrofolate and constant levels of thymidylate synthetase, the relative amounts of the protein components were shown to be dependent on the concentration of the inhibitor. Evidence is presented which suggests that the three protein components correspond to (1) native enzyme, (2) an inhibitor-cofactor-enzyme complex in a 1:1:1 molar ratio, and (3) an inhibitorcofactorenzyme complex in a 2:2:1 molar ratio, respectively. Ternary complexes of thymidylate synthetase are stable to gel filtration and are shown to undergo a relatively slow rate of breakdown on storage at 25 °C.  相似文献   
69.
H2Ru33-S)(CO)9 is deprotonated by K[HBBus3] to give cluster anions which react with [O{Au(PPh3)}3]+ or with AuCl(PPh3)/T1+ to give HRu3Au(μ3-S)(CO)9(PPh3) (1) and Ru3Au23-S)(CO)9(PPh3)2 (3). A similar sequence with HRu33-SBut)(CO)9 leads to Ru3Au(μ3-SBut)(CO)9(PPh3) (2) as the main product although some 1 also forms, indicating SC cleavage competes with deprotonation of HRu33-SBut)(CO)9 by [HBBus3]?. The X-ray crystal structures of 1, 2 and 3 are described; (1) and (2) have “butterfly” AuRu3 cores with markedly different hinge angles of 119 and 148° respectively, while 3 has a trigonal-bipyramidal Au2Ru3 skeleton. All three clusters have the sulphur atom symmetrically bridging the Ru3 triangular face.  相似文献   
70.
The steroechemistry of guggulsterol-1, a component of the exudate of Commiphoramukul, is shown to be 20(R), 22(R)(3).  相似文献   
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