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141.
Maspoch D Domingo N Ruiz-Molina D Wurst K Tejada J Rovira C Veciana J 《Journal of the American Chemical Society》2004,126(3):730-731
A new pure organic paramagnetic porous molecular material, which combines hydrophilic windows with large hydrophobic nanocontainers, is shown to be stable even in absence of solvent guest molecules. 相似文献
142.
Two theozymes for the intramolecular aldol reaction of δ‐diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition‐state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 338–347, 2001 相似文献
143.
In this study we describe the set-up of a new passive integrating system to measure simultaneously 222Rn, 222Rn progeny (218Po and 214Po) and 220Rn concentration indoors. It consists of four Makrofol-DE (polycarbonate) circular foils. Two are enclosed within two diffusion chambers—each one with a different filter membrane—to measure 222Rn and 222Rn+220Rn. The other two foils are kept in direct contact with air and are electrochemically etched at different conditions to obtain the 222Rn daughters. Theoretical sensitivities of each Makrofol-DE foil are calculated using Monte-Carlo technique. The calculations are performed taking into account: (1) the Bethe–Bloch's expression for the stopping power of heavy charged particles in a medium, (2) the properties and behaviour of 222Rn, 220Rn and their progeny in the open air and within the diffusion chamber and (3) the etching conditions used to visualise -particles tracks. 相似文献
144.
145.
Ring Contraction of 3‐Hydroxy‐3‐(trifluoromethyl)piperidines: Synthesis of 2‐Substituted 2‐(Trifluoromethyl)pyrrolidines 下载免费PDF全文
Alexandra Feraldi‐Xypolia Dr. Domingo Gomez Pardo Prof. Janine Cossy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(37):12876-12880
A ring contraction of 3‐hydroxy‐3‐(trifluoromethyl)piperidines was achieved via an aziridinium intermediate. This contraction facilitates the synthesis of a series of 2‐substituted 2‐(trifluoromethyl)pyrrolidines incorporating a quaternary center at the C2 position. 相似文献
146.
García Camilo Navarro Freddy Ruíz-León Domingo Beltrán Olimpo García Aguirre María Jesús 《Journal of Solid State Electrochemistry》2017,21(1):243-253
Journal of Solid State Electrochemistry - In this work, a cationic porphyrin, ascribed as [Ttolyl(P-(C6H5)3)4]4+, where Ttolyl = 5,10,15,20 tetrakistolylporphyrin, was... 相似文献
147.
María D. Acosta Julio Becerra Guerrero Domingo García Sun Kwang Kim Manuel Maestre 《Journal of Mathematical Analysis and Applications》2014
We characterize the Banach spaces Y for which certain subspaces of operators from L1(μ) into Y have the Bishop–Phelps–Bollobás property in terms of a geometric property of Y, namely AHSP. This characterization applies to the spaces of compact and weakly compact operators. New examples of Banach spaces Y with AHSP are provided. We also obtain that certain ideals of Asplund operators satisfy the Bishop–Phelps–Bollobás property. 相似文献
148.
Jean Rouchaud Olivier Neus Claude Moulard 《International journal of environmental analytical chemistry》2013,93(1):65-80
Abstract For the analysis of metsulfuron-methyl in the crop soils with a sensitivity limit of 0.3 μg kg?1 dry soil, in the soil extract metsulfuron-methyl was separated from its soil metabolites and the soil impurities by repeated thin-layer chromatographies (TLC). In the cleaned soil extract, diazomethane transformed metsulfuron-methyl 1 into N,N′ -dimethyl metsulfuron-methyl 2 (methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)methylamino]carbonyl]methylamino]sulfonyl]benzoate). In the gas-liquid chromatograph with detection by electron capture (GC-EC) and in the combined gas chromatograph-mass spectrometer (GC-MS), 2 was transformed into 1-dioxy-2-N-methyl-3-keto-1,2-benzisothiazole 3 which was measured by GC-EC with confirmation by GC-MS. The metsulfuron-methyl soil metabolites 2-sulfonamido-methylbenzoate 6, 1-dioxy-3-keto-1,2-benzisothiazole (saccharin) 7 and 2-sulfonamidobenzoic acid 8 were analyzed in the soil of winter wheat crops by a procedure similar to the one for metsulfuron-methyl. After their separation and purification in the soil extracts by TLC, 7 and 8 were methylated, and analyzed as 3 in the GC-EC and GC-MS apparatus where the generated 6 was quantitatively transformed into 3; 6 was analyzed as such with the GC and GC-MS apparatus wherein it was transformed into 3. The sensitivity limit for each metabolite was 0.3 μg of equivalents of metsulfuron-methyl kg?1dry soil. The syntheses of the analysis standards of the metsulfuron-methyl derivatives 2 and 3, and of the metsulfuron-methyl metabolites 6, 7 and 8 are described. The transformation pathways of metsulfuron-methyl and of its derivatives are different from those of the pyridine-pyrimidine sulfonylurea herbicides flupyrsulfuron-methyl and rimsulfuron. The soil analysis of a sulfonylurea -by means of one of its transformation product- needs a previous study of the chemical reactivity of the sulfonylurea. This leads to the analysis procedures for the main soil metabolites of the sulfonylurea. 相似文献
149.
A set of seven non-substituted tri-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions has been studied using the reactivity indices defined within the conceptual DFT at the B3LYP/6-31G(d) level of theory. This series of TACs shows a zwitterionic structure and low reactivity towards ethylene. The general characteristic of these TACs is their high nucleophilic and a low electrophilic behaviour. Activation energies computed at the MPWB1K/6-311G(d) level in dichloromethane point to that non-substituted TACs react quickly toward dicyanoethylene showing their ability to react towards electron-deficient ethylenes. However, when the TACs are electrophilically activated by an appropriate substitution there seems to be insufficient activation to react toward electron-rich ethylenes. The electrophilic activation of the TAC moiety for nucleophilic attacks was only determined by the coordination with a Lewis acid. All 32CA reactions studied in this work presented high regioselectivity. The polar character of these 32CA reactions is associated with the global charge transfer found at the TS, which is in agreement with a zwitterionic-type (zw-type) mechanism. According to our results, the present theoretical study suggests that the substitution is required in both, TACs and the ethylene species, in order to experimentally perform these zw-type 32CA reactions under mild conditions. 相似文献
150.