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181.
Yoshihisa Kurasawa Ryuichiro Miyashita Atsushi Takada Ho Sik Kim Yoshihisa Okamoto 《Journal of heterocyclic chemistry》1995,32(2):671-674
The p- and m-substituted 3-arylcarbamoylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxalines 3a-o showed the tautomeric equilibria between the enamine C and methylene imine D forms in dimethyl sulfoxide or dimethyl sulfoxide/trifluoroacetic acid media. The linear correlation of the Hammett σp and σm values with the log KT values was observed in the dimethyl sulfoxide/trifluoroacetic acid (2:1) media of compounds 3a-o , wherein KT meaned the tautomeric equilibrium constants ([D]/[C]). 相似文献
182.
Take-aki Mitsudo Yukiatsu Komiya Hideki Boku Yoshihisa Watanabe 《Reaction Kinetics and Catalysis Letters》1985,27(2):399-402
In the Fischer-Tropsch synthesis, potassium tetracarbonylhydridoferrate, KHFe (CO)4, supported on HY-zeolite or silica gel exhibited high selectivity to light olefins without following the Schulz-Flory distribution.
, KHFe(CO)4, HY —, — .相似文献
183.
Poon T Sivaguru J Franz R Jockusch S Martinez C Washington I Adam W Inoue Y Turro NJ 《Journal of the American Chemical Society》2004,126(34):10498-10499
Oxazolidinone-functionalized enecarbamates react stereoselectively with singlet oxygen to give methyldesoxybenzoin (MDB) in moderate to high enantiomeric excess. The stereochemical outcome depends on the E/Z substrate geometry, temperature, and solvent variables. The analysis of the differential activation parameters suggests a large contribution from the entropy term in determining the enantioselectivity. We demonstrate the utility of the temperature and solvent variables in determining the degree of the photochemical kinetic resolution of the enecarbamates; for example, in the photooxygenation at -70 degrees C in methanol, MDB may be obtained in methanol. 相似文献
184.
The hydrolysis and condensation reactions of Si(OC2H5)4 (TEOS) at 80°C in the TEOS---H2O---C2H5OH---HCl solutions with H2O/TEOS molar ratios (r) from 1.0 to 2.0 were followed by gas chromatography (GC) and measurement of molecular weight (
) of the hydrolyzates, in order to explain the viscosity change of the solutions. It has been found that the siloxane oligomers with average polymerization degree (n) from 2 to 7 are formed in the early stage of reaction and undergo condensation to form higher polymers. The n and the number of silanol groups of the oligomers are increased with increasing r. The fact that the solution viscosity increased once rapidly around the so-called gelation point followed by a sluggish increase with the increase of reaction time for an r of 1.7, while it increased rapidly without a break till gelation for an r of 2.0, was attributed to fewer silanol groups and higher steric hindrance as a result of more −OC2H5 groups remaining in the oligomers for an r of 1.7. 相似文献
185.
Motoki Okaniwa Yoshihisa Ohta 《Journal of polymer science. Part A, Polymer chemistry》1997,35(13):2607-2617
The influence of radical initiators upon the emulsion graft copolymerization of styrene and acrylonitrile onto poly(dimethylsiloxane) (PDMS) was studied. As initiators, a series of peroxides and hydroperoxides were coupled with ferrous sulfate, among which the tert-butyl peroxylaurate system gave the highest grafting efficiency (30%). The tert-butyl peroxylaurate initiator fulfills the criteria for efficient radical grafting by generating only the tert-butoxy radical, which is reluctant to form a carbon radical via β-scission, being highly hydrophobic, and not carrying a tertiary hydrogen that may be abstracted by a radical. 13C-NMR analysis of the products showed that the grafting occurred on the silylmethyl groups of PDMS to give 10–25 grafts per polymer and graft ratio in the range 44–140%. The PDMS graft copolymers thus obtained could be used as surface-modifying agents to improve the lubricity and water-repellency of ABS [poly(styrene-co-acrylonitrile)-graft-polybutadiene]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2607–2617, 1997 相似文献
186.
187.
Hikari Morita Kazuho Harada Yoshihisa Okamoto Kaname Takagi 《Journal of heterocyclic chemistry》1999,36(3):767-770
3-Chloro- and 3-bromo-4-methoxycoumarins 1a,b were readily transformed into 4-halo-5-(2-hydroxyphenyl)-3-oxo-2,3-dihydropyrazoles 2a,b with hydrazines. In the reaction of 1a,b with excess hydrazine and phenylhydrazine in boiling ethanol, unexpected 4-hydrazono-3-(2-hydroxyphenyl)-2-pyrazolin-5-ones 3 , 5 were obtained. The structure of 3 was determined by X-ray diffraction analysis. 相似文献
188.
Atsushi Okamoto Hisashi Matsuoka Motoki Saito Yoshihisa Takayama Mototsugu Takamura 《Optical Review》1999,6(3):189-195
We propose a new optical network device photorefractive connection module (PRCM) which operates as optical switch, amplifier and signal distributor controlled by parallel optical signals. Simple optical control bus systems can be realized by cascade connection of PRCMs. PRCM branches off a desired channel from the spatial multiplexed optical bus line by appropriate setting of the control beam pattern. PRCM uses cross polarized four wave mixing (CPFWM) with extraordinary polarized writing beams and an ordinary polarized reading beam to achieve a high connection gain to the next PRCM stage. We analyze the phase matching angle of CPFWM in which the optical paths of two pump beams are slightly different. The phase conjugate reflectivity indicating a branching ratio of optical signal is derived and calculated in consideration of the phase mismatching Δk. The optimum pump ratio and the grating vector orientation for the largest phase conjugate reflectivity and signal amplification factor are discussed for optical design of PRCM. Since the measured signal beam power after passing through the BaTiO3 crystal is three or four times higher than its incident power, PRCM has a sufficient connection gain for optical bus and interconnection systems. 相似文献
189.
190.
A new triterpene and a saponin from Centella asiatica 总被引:1,自引:0,他引:1
Quan Lin Yu Hong Quan Duan Wen Yuan Gao Yoshihisa Takaishi 《中国化学快报》2007,18(1):62-64
A new triterpene and a saponin,named 2α,3β,23-trihydroxyurs-20-en-28-oic acid(1)and 2α,3β,23-trihydroxyurs-20-en-28-oic acid O-α-L-rhamnopyranosyl-(1→4)-O-β-D-glucopyranosyl-(1→6)-O-β-D-glucopyranosyl ester(2),have been isolated from the aerial part of Centella asiatica.Their structures were elucidated by spectral methods,including 2D-NMR spectra. 相似文献