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11.
A new method for silylation of allyl ethers with chlorosilanes has been developed by the use of Cp2TiCl2 as a catalyst. This reaction proceeds efficiently at −20 °C in THF using nBuMgCl. A plausible reaction pathway via allyltitanocene intermediate was proposed. 相似文献
12.
Fuyuki Ito Nobuaki Tanaka Akio Katsuki Akikazu Kakehi Tsuneo Fujii 《Research on Chemical Intermediates》2004,30(3):331-336
Three types of flavylium salts (FVs, yellow, green and red) have been synthesized and the colors depended on recrystallization conditions. The existence of these color states was confirmed by diffuse reflectance spectra. The spectra were almost the same as the absorption spectra in ethanol solution. The molecular state of FVs in crystals will be the same as that in solutions. The crystal colors of the FVs are controlled by the recrystallization conditions. 相似文献
13.
Hiroki Nakamura Jiro Tanaka Nobuaki Nakashima Keitaro Yoshihara 《Chemical physics letters》1981,77(2):419-421
The photoionization of 8-anilino-1-naphthalenesulfonate in polar solvents occurs through a biphotonic process, as proved by nanosecond flash photolysis. A transient absorption of a charge transfer to solvent (CTTS) state is found with ≈10 ns life-time. The state is shown to be an intermediate of the photoionization process. 相似文献
14.
Kô Kaneko Mikako Tanaka Kimiaki Haruki Nobuaki Naruse Hiroshi Mitsuhashi 《Tetrahedron letters》1979,20(39):3737-3740
The 13C-NMR spectra of seven cavanine alkaloids isolated from Veratrum and Fritillaria plants were measured and their signals were assigned, and these results were applicated for structure elucidation of two new cevanine alkaloids, baimonidine and isoverticine, isolated from mature Fritillaria verticillata. 相似文献
15.
Enyo T Arai N Nakane N Nicolaides A Tomioka H 《The Journal of organic chemistry》2005,70(19):7744-7754
[reaction: see text] Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A' states relative to the A' ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br). Attempts to generate and observe the o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, using matrix isolation spectroscopy under conditions similar to those of the successful observation of 2-HN failed. Instead, the observed photoproducts were a mixture of 3-XN and 4-XN. In each case, the major product of the mixture appears to be the thermodynamically more stable one. In the case of X = Br, the observed mixture contains an additional component that is postulated to be Z-6-BrN. o-Phenylenechlorocarbenocarbene is also computed to have a quinoidal singlet biradical ground state and relatively stabilized A' excited states. Attempts to generate the biscarbene under matrix isolation conditions led to the detection of benzochlorocyclobutadiene (3-ClC), small amounts of the ring-open product (dienediyne 4-ClC), and cycloalkyne 5-ClC. Computations suggest that the formation of 5-ClC implies the generation of Z-6-ClC, which is analogous to the formation of Z-6-BrN from 2-BrN. 相似文献
16.
Soh N Imato T Kawamura K Maeda M Katayama Y 《Chemical communications (Cambridge, England)》2002,(22):2650-2651
A novel fluorescent probe, which could be the first example of a ratiometric molecular probe for direct monitoring of NO production, has been developed using a 'spin-exchange' mechanism. 相似文献
17.
Yuichi Yoshimura Tetsuya Kuze Fumiko Komiya Hiromichi Tanaka Kohei Yamada Nobuaki Kaneko 《Tetrahedron letters》2006,47(4):591-594
A practical synthesis of 4′-thioribonucleosides starting from inexpensive l-arabinose is described. 1,4-Anhydro-2,3-O-isopropylidene-4-thioribitol, which was prepared by using a novel reductive ring-contraction reaction, was converted to the 5-O-silylated sulfoxides. The Pummerer-type thioglycosylation of the sulfoxides gave the 4′-thioribonucleosides stereoselectively. 相似文献
18.
Novel vibrational circular dichroism (VCD) studies in the CH region of a series of methyl glycosidic carbohydrates were examined. The specific CH stretching VCD band predicts absolute stereochemistries of their anomeric positions. The C-1 chiral information was extracted to the methoxy substituent as a probe. The concept of the vibrational chirality probe from a single chiral center in the presence of numerous such centers might be useful in determining the absolute configuration, when a multiplicity of chiral centers is present in a molecule such as a carbohydrate. 相似文献
19.
A new method for regioselective carbomagnesation of alkenes and dienes has been developed by the use of a titanocene catalyst. This reaction proceeds efficiently at 0 degrees C in THF in the presence of Cp(2)TiCl(2) by the combined use of organic halides (R-X; R = alkyl, aryl and vinyl) and n-BuMgCl to afford benzyl, alpha-silylalkyl, or allyl Grignard reagents, which were trapped with various electrophiles. The present reaction involves (i) addition of carbon radicals toward alkenes or dienes in the carbon-carbon bond-forming step and (ii) transmetalation on Ti of benzyl-, alpha-silylalkyl-, or allyltitanocene with n-BuMgCl in the carbon-magnesium bond-forming step. The scope and limitations of this reaction have also been examined. 相似文献
20.
Moriya Y Hasegawa T Hayashi K Maruyama M Nakata S Ogawa N 《Analytical and bioanalytical chemistry》2003,376(3):374-378
Visible reflection spectra of diprotonated meso-tetraphenylporphyrin adsorbates spontaneously formed at a dodecane-aqueous sulfuric acid interface have been measured using a home-made device comprising a prism-cell and variable-angle optics. The tilt angle of the pyrrole ring plane was estimated to be 47 degrees from the interface normal by use of an experimentally evaluated molecular density (1.20x10(-10) mol cm(-2)) of the diprotonated molecule in a monolayer form at the liquid-liquid interface. Positive and negative bands have been observed in the p-polarized partial internal reflection (p-PIR) spectra, whose band locations correspond to those in p-polarized external reflection (p-ER) spectra. Nevertheless, the bands in the p-PIR exhibited reversed sign to those of p-ER spectra. These suggest that the surface selection rule of the p-PIR spectrometry has a reversal rule of p-ER and p-PIR can also be used for the analysis of molecular orientation. 相似文献