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161.
162.
A ditopic hydrazone ligand (ioap) synthesized from the condensation of 4-methyl-5-imidazole carboxylic acid hydrazide with the iminoester of 2-pyridinecarbonitrile formed targeted [2 x 2] M(4)L(4) (M = Cu(II), Ni(II); L = ioap) grids, and a mixed oxidation state dinuclear cobalt complex. An 'incomplete' trinuclear M(3)L(4) (M = Mn(II)) grid, based on a [2 x 2] grid architecture, resulting from steric congestion of the imidazole methyl-substituent, was also produced. These results lead to the suggestion of one possible route to the self-assembly pathway of the [2 x 2] grids. The Mn(II), Ni(II) and Cu(II) complexes have hydrazone oxygen bridges between metal centres, which lead to antiferromagnetic exchange in the Mn(II)(3) and Ni(II)(4) cases, but, due to the presence of orthogonal bridging connections, to ferromagnetic exchange for the Cu(II)(4) example. Structural and magnetic properties are discussed based on the bridging connections. 相似文献
163.
Serge Ello Laurence Pirault-Roy Attila Wootsch Zoltán Paál 《Reaction Kinetics and Catalysis Letters》2008,94(2):301-310
Platinum-germanium catalysts supported on a non-acidic Al2O3 have been prepared by adding Ge in amounts corresponding nominally to 1/8 (PtGe1/8/Al2O3); 1/2 (PtGe1/2/Al2O3); 1 (PtGe1/Al2O3) and 2 (PtGe2/Al2O3) monolayers by controlled surface reaction of Ge(n-C4H9)4 to Pt/Al2O3. These catalysts were characterized by electron microscopy (TEM), FTIR of CO adsorption and H2 chemisorption. The ring opening of ethylcyclopentane (ECP) was studied as a test reaction between 543 and 633 K. PtGe1/8/Al2O3 catalyst produced the most ring opening products (ROP) in the whole temperature range. A good agreement with statistical
values of ROP was observed at low temperature, but at higher temperature, the opening became selective, producing mostly heptane.
Bimetallic catalysts PtGe1/Al2O3 and PtGe2/Al2O3 led to a nonselective hydrogenolysis, similar to the monometallic platinum catalyst Pt/Al2O3. The catalysts PtGe1/Al2O3 and PtGe2/Al2O3 produced ROP with the lowest selectivity; instead, much aromatics and fragments were formed, in increasing amounts above
600 K. 相似文献
164.
Turowski M Gronowski M Boyé-Péronne S Douin S Monéron L Crépin C Kołos R 《The Journal of chemical physics》2008,128(16):164304
The 193 nm laser irradiation of cyanoacetylene (HCCCN) that was isolated in rare gas solids led to a long-lived luminescence (origin at 3.58 eV), which was assigned to the a (3)Sigma(+)-X (1)Sigma(+) system of cyanoacetylide (CCCN(-)). The identification, which involved (15)N and (2)H isotopic substitution studies, is based on vibronic spacings in the phosphorescence spectrum (compared to previous infrared absorption measurements and to theoretical results regarding CCCN(-) vibrational frequencies), as well as on a BD(T)/cc-pVTZ prediction for the singlet-triplet energy gap in this anion (3.61 eV). The same emission was also generated from KrHC(3)N mixtures subjected to a glow electric discharge immediately before the solidification (cold-window-radial-discharge technique). 相似文献
165.
Sánchez-Paz V Pastoriza-Gallego MJ Losada-Barreiro S Bravo-Díaz C Gunaseelan K Romsted LS 《Journal of colloid and interface science》2008,320(1):1-8
Until recently, determining the distribution of antioxidants, AOs, between the oil, interfacial and aqueous regions of opaque emulsions has not worked well because the concentrations of AOs in interfacial regions cannot be determined separately from their concentrations in the oil and water phases. However, our novel kinetic method based on the reaction between an arenediazonium ion and vitamin E, or alpha-tocopherol, provides the first good estimates for the two partition constants that describe alpha-tocopherol distribution between the oil/interfacial and water/interfacial regions of tributyrin/Brij 30/water emulsions without physical isolation of any phase. The reaction is monitored by a new derivatization method based on trapping unreacted arenediazonium ion as an azo dye and confirmed by linear sweep voltammetry, LSV. The results by both derivatization and LSV methods are in good agreement and show that alpha-tocopherol distributes strongly in favor of the interfacial region when the oil is tributyrin, e.g., ca. 90% when the surfactant volume fraction is Phi I=0.01. The second-order rate constant for reaction in the interfacial region is also obtained from the results. Our kinetic method provides a robust approach for determining antioxidant distributions in emulsions and should help develop a quantitative interpretation of antioxidant efficiency in emulsions. 相似文献
166.
Colin J. Thompson Caixia Ding Xiaozhong Qu Zhenzhong Yang Ijeoma F. Uchegbu Laurence Tetley Woei Ping Cheng 《Colloid and polymer science》2008,286(13):1511-1526
Twelve novel poly(allylamine) (PAA)-based, comb-shaped amphiphilic polymers have been developed. Hydrophobic groups of cetyl,
palmitoyl and cholesteryl were randomly grafted to PAA and quaternisation was carried out on some modified polymers. Polymers
were characterised using 1H NMR, elemental analysis and differential scanning calorimetry. All polymers formed nano self-assemblies in the aqueous solution
with a positive zeta potential and were able to encapsulate a hydrophobic agent, methyl orange, in the core. The critical
aggregation concentration (CAC) and the microviscosity were found to be dependent on the polymer hydrophobicity. Being the
most hydrophobic polymer, cholesteryl-grafted PAA had the lowest CAC (0.02 mg mL−1) and the highest microviscosity. They appeared to form dense nanoparticles and were transformed into novel nanostructures
in the presence of free cholesterol. Palmitoyl-grafted polymers formed nanoparticles while cetyl-grafted polymers formed polymeric
micelles. The flexibility of cetyl chains possibly resulted in the formation of multicore polymeric micelles. 相似文献
167.
Hamley IW Krysmann MJ Kelarakis A Castelletto V Noirez L Hule RA Pochan DJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(36):11369-11375
The self-assembly in aqueous solution of a PEG-peptide conjugate is studied by spectroscopy, electron microscopy, rheology and small-angle X-ray and neutron scattering (SAXS and SANS). The peptide fragment, FFKLVFF is based on fragment KLVFF of the amyloid beta-peptide, Abeta(16-20), extended by two hydrophobic phenylalanine units. This is conjugated to PEG which confers water solubility and leads to distinct self-assembled structures. Small-angle scattering reveals the formation of cylindrical fibrils comprising a peptide core and PEG corona. This constrained structure leads to a model parallel beta-sheet self-assembled structure with a radial arrangement of beta sheets. On increasing concentration, successively nematic and hexagonal columnar phases are formed. The flow-induced alignment of both structures was studied in situ by SANS using a Couette cell. Shear-induced alignment is responsible for the shear thinning behaviour observed by dynamic shear rheometry. Incomplete recovery of moduli after cessation of shear is consistent with the observation from SANS of retained orientation in the sample. 相似文献
168.
Tintaru A Benchabane Y Boyer G Humbel S Charles L 《Rapid communications in mass spectrometry : RCM》2008,22(5):687-693
Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) has been used to differentiate two positional isomers of acridine derivatives, N-acridin-4-ylbenzylamide and N-acridin-2-ylbenzylamide. The study revealed that the isomeric ion structures produced by these heterocycles could be distinguished upon collision-induced dissociations (CID). In particular, the loss of a water molecule was shown to be a regiospecific reaction of the protonated N-acridin-4-ylbenzylamide, in which the location of the benzylamide substituent with respect to the acridinic nitrogen greatly assists proton migration by allowing the creation of intramolecular hydrogen bonds. To a lesser extent, the two isomers could also be distinguished by the difference in the abundance of the benzoyl cation in the MS/MS spectra of the [M+H]+ ions, as this ion is produced with a much higher rate from N-acridin-4-ylbenzylamide. Calculations based on quantum-mechanical models have been performed to evaluate the stability of the ion structures and to support mechanisms proposed for these two dissociation reactions. 相似文献
169.
Coupling of liquid chromatography at critical conditions (LCCC) with on-line mass spectrometry (MS) detection was implemented via an electrospray ionization (ESI) interface, using a mobile phase containing the cationizing agent. Critical conditions established for poly(ethylene oxide) were used to characterize a poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) in both MS and MS/MS modes. As co-oligomer molecules were successfully separated according to the PS block size, structural information could be reached from simplified MS spectra. The microstructure of this copolymer, synthesized by nitroxide-mediated polymerization, could further be unambiguously characterized in LCCC/ESI-MS/MS experiments since the PS block size could be reached by both the co-oligomer chromatographic behavior and its MS/MS pattern. 相似文献
170.
Niel V Milway VA Dawe LN Grove H Tandon SS Abedin TS Kelly TL Spencer EC Howard JA Collins JL Miller DO Thompson LK 《Inorganic chemistry》2008,47(1):176-189
"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features. 相似文献