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41.
The Na[Cr(PDA)2] · 2H2O complex (PDA1 = dipicolinic acid anion) and its aquation product, [Cr(PDA)(H2O)3]+, were prepared and characterized. The electronic spectra demonstrate that the bis(dipicolinato) complex undergoes very fast partial dechelation during dissolution. In acidic media, pH controlled, rapid protolytic and ring opening processes lead to coexistence of complexes with one tridentate (PDA) and the other bi- or mono-dentate (PDA). The kinetics of PDA ligand liberation were followed spectrophotometrically within the 0.1–2.0 M HClO4 range at I = 2.0 M. The observed first-order rate constant depends on [H+] according to the equation: k
obs = A[H+]/(1 + B[H+] + C[H+]2). A reaction course via the uncharged [Cr(PDA)(HPDA)(H2O)2]0 complex is proposed. The observed rate increase, followed by rate retardation with [H+] increase, is attributed to the unreactive [Cr(PDA)(H2PDA)(H2O)2]+ complex. In terms of the proposed mechanism, A, B, C parameters have been defined as: A = k
1
Q
1, B = Q
1, C = Q
1
Q
2 where k
1 is the rate constant of the CrIII-carboxylato oxygen bond-breaking in the monodentate HPDA ligand, Q
1 is a composite value describing protolytic and dechelation processes and Q
2 is the protonation constant of the uncharged [Cr(PDA)(HPDA)(H2O)2]0 complex. 相似文献
42.
43.
Lewiński J Marciniak W Lipkowski J Justyniak I 《Journal of the American Chemical Society》2003,125(42):12698-12699
Studies on the reaction of zinc alkyls with O2 are reported which demonstrate that the selective oxygenation of organozinc compound is viable. The reaction of [EtZn(azol)]n (azol = deprotonated 1-aziridineethanol) with an excess of dry O2 in toluene affords the zinc ethylperoxide [EtOOZn(azol)]2[EtZn(azol)]2, while the analogous reaction between Me2Zn and O2 results in the isolation of the Me6Zn7(OMe)8 cluster in high yield. 相似文献
44.
Konrad Kowalski Anne VessièresSiden Top Gérard Jaouen Janusz Zakrzewski 《Tetrahedron letters》2003,44(13):2749-2751
A synthetic pathway giving access to diphenyl ethylene organometallic derivatives possessing the ferrocifen precursor skeleton modified in the Cp′ ring is described. It relies on reaction of the (η5-propionylcyclopentadienyl) (η6-benzene)iron(II) salt 7 with substituted cyclopentadienyl anions or their heteroanalogs followed by the McMurry coupling reaction with 4,4′-dihydroxybenzophenone. Using this approach pentamethylcyclopentadienyl and 3,4-dimethylphospholyl analogs of ferrocifen precursor (10 and 11) have been synthesized. Even with the presence of the bulky and containing phosphorus η5-ligands these compounds are still recognized by the two subtypes of estrogen receptor(ERα and ERβ). 相似文献
45.
Alicja Boryło Bogdan Skwarzec Grzegorz Romańczyk Janusz Siebert 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(3):1685-1691
The determination of polonium 210Po in human blood samples is presented and discussed in this paper. The human blood samples were collected from patients of Medical University of Gdańsk with ischaemic heart disease (morbus ischaemicus cordis, MIC). The polonium concentrations in analyzed human blood samples are very differentiated. 210Po is of particular interest in public health and although is present in the environment in extremely low amounts, it is easily bioaccumulated to the human body. The study shows that the amount of 210Po that is incorporated into the human body depends on the food habits and some difference in its levels could be observed between smokers and non-smokers. 相似文献
46.
Mangeney C Ferrage F Aujard I Marchi-Artzner V Jullien L Ouari O Rékaï el D Laschewsky A Vikholm I Sadowski JW 《Journal of the American Chemical Society》2002,124(20):5811-5821
Citrate-capped gold nanoparticles as well as planar gold surfaces can be efficiently grafted with a covalently attached polymer monolayer a few nanometers thick, by simple contact of the metal surface with dilute aqueous solutions of hydrophilic polymers that are end-capped with disulfide moieties, as shown by UV/vis absorption, dynamic light scattering, and surface plasmon resonance studies. The hydrophilic polymer-coated gold colloids can be freeze-dried and stored as powders that can be subsequently dissolved to yield stable aqueous dispersions, even at very large concentrations. They allow for applying filtrations, gel permeation chromatography, or centrifugation. They do not suffer from undesirable nonspecific adsorption of proteins while allowing the diffusion of small species within the hydrogel surface coating. In addition, specific properties of the original hydrophilic polymers are retained such as a lower critical solution temperature. The latter feature could be useful to enhance optical responses of functionalized gold surfaces toward interaction with various substrates. 相似文献
47.
Ciucanu I Kaykhaii M Montero L Pawliszyn J Szubra J 《Journal of chromatographic science》2002,40(6):350-354
A novel method for the continuous monitoring of thermooxidative degradation products of polystyrene by membrane extraction with sorbent interface (MESI) and gas chromatography (GC) is developed. The results are compared with solid-phase microextraction-GC, which can extract gases, vapors, and aerosols. The volatile and semivolatile degradation products are identified by mass spectrometry. The membrane used in the MESI-GC analysis shows a high permeation for volatile aromatic hydrocarbons; a low permeation for corresponding volatile aldehydes; and no permeation for less volatile alcohols, acids, and degradation products with a high molecular weight, thus reducing significantly the number of compounds detected from MESI-GC. Sensitivity of the method depends on the time of trapping, which is limited by the breakthrough of the trap. By heating the trap at fixed intervals of time, consecutive gas chromatograms are obtained. 相似文献
48.
Dorota Gryko DanielT. Gryko Hanna Sierzputowska‐Gracz Piotr Piatek Janusz Jurczak 《Helvetica chimica acta》2004,87(1):156-166
The efficient synthesis of eight new macrocyclic amides (lactams) via reaction of diesters with diamines under normal dilution conditions is described. The role of intermolecular H‐bond formation and steric hindrance is discussed based on 1H‐ and 15N‐NMR studies of appropriate model compounds. Principles for the optimal choice of esters that can be efficiently transformed into diamides have been developed. 相似文献
49.
Dabkowska I Rak J Gutowski M Nilles JM Stokes ST Bowen KH 《The Journal of chemical physics》2004,120(13):6064-6071
The photoelectron spectrum of the uracil-alanine anionic complex (UA)(-) has been recorded with 2.540 eV photons. This spectrum reveals a broad feature with a maximum between 1.6 and 2.1 eV. The vertical electron detachment energy is too large to be attributed to an (UA)(-) anionic complex in which an intact uracil anion is solvated by alanine, or vice versa. The neutral and anionic complexes of uracil and alanine were studied at the B3LYP and second-order M?ller-Plesset level of theory with 6-31++G(*) (*) basis sets. The neutral complexes form cyclic hydrogen bonds and the three most stable neutral complexes are bound by 0.72, 0.61, and 0.57 eV. The electron hole in complexes of uracil with alanine is localized on uracil, but the formation of a complex with alanine strongly modulates the vertical ionization energy of uracil. The theoretical results indicate that the excess electron in (UA)(-) occupies a pi(*) orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of alanine to the O8 atom of uracil. As a result, the four most stable structures of the uracil-alanine anionic complex can be characterized as a neutral radical of hydrogenated uracil solvated by a deprotonated alanine. Our current results for the anionic complex of uracil with alanine are similar to our previous results for the anion of uracil with glycine, and together they indicate that the BFPT process is not very sensitive to the nature of the amino acid's hydrophobic residual group. The BFPT to the O8 atom of uracil may be relevant to the damage suffered by nucleic acid bases due to exposure to low energy electrons. 相似文献
50.
Bury W Justyniak I Prochowicz D Wróbel Z Lewiński J 《Chemical communications (Cambridge, England)》2012,48(59):7362-7364
Two unique adducts of an oxozinc carboxylate cluster with H(2)O and THF were isolated and structurally characterized, [Zn(4)(μ(4)-O)(O(2)CR)(6)(H(2)O)(THF)]·2(THF) and [Zn(4)(μ(4)-O)(O(2)CR')(6)(THF)(3)] (where R = benzoate and R' = 9-antracenecarboxylate anion). The study shows that the zinc centers of the Zn(4)O core can easily form unique coordination environments without breaking of the Zn-O(carboxylate) bonds. 相似文献