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Takenaka M Kobayashi T Saijo K Tanaka H Iwase N Hashimoto T Takahashi M 《The Journal of chemical physics》2004,121(7):3323-3328
We investigated time evolution of shear moduli in the physical gelation process of 1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol in polystyrene melt. At the gel point, storage and loss shear moduli, G' and G", were described by the power law of frequency omega, G' approximately G" approximately omegan, with the critical exponent n being nearly equal to 2/3, in agreement with the value predicted by the percolation theory. We also investigated the structure factor over two decades in length scale at gel point by using ultra-small-angle X-ray scattering, and small-angle X-ray scattering. We found the power-law behavior in low-q region, indicating that the gel network forms the self-similar structure with mass-fractal dimension. Comparison between the exponent of mass-fractal dimension from structure factor and that from viscoelasticity indicates that hydrodynamic interactions are completely screened out and the excluded volume effects are dominant in the gel. The gel strength was found to increase with the decrease in the lower limit length scale of fractality. 相似文献
24.
A simple and sensitive method for the determination of liquid methanol and ethanol at trace levels by an alkyl nitrite formation reaction has been established. Alcohol was allowed to react with nitrous acid, which was yielded from sulfuric acid and sodium nitrite in the solution, to form the corresponding alkyl nitrite in the hexane organic phase. Alkyl nitrites in hexane were analyzed by a gas chromatograph with an electron capture detector (GC-ECD). The detection limits, which were determined at a signal-to-noise ratio of 3, were 1.1 and 0.7 micrograms/L for methanol and ethanol, respectively, by 1 microL injection. The relative standard deviations for n = 8 were 4.0 and 3.3% for methanol and ethanol, respectively. The method was applied to determine the alcohol concentration in a rice paddy, pond water, tap water, and well water. Those aqueous samples were also spiked with standard alcohols; the average recoveries of spiked methanol and ethanol were 98 and 91% with relative standard deviations of 6.1 and 4.0%, respectively. 相似文献
25.
Vladimir F. Petrov Sofia I. Torgova Ludmila A. Karamysheva Shunsuke Takenaka 《Liquid crystals》1999,26(8):1141-1162
In this review the effect on physico-chemical and electro-optical properties of the introduction of the trans-1,4-cyclohexylene fragment into the molecular core of liquid crystals is discussed, rationalized in terms of existent theories, and compared with the effect of other well-known molecular fragments. 相似文献
26.
Dr. Randa K. Gabr Prof. Dr. Takuji Hatakeyama Prof. Dr. Kazuhiro Takenaka Prof. Dr. Shinobu Takizawa Yoshihiro Okada Prof. Dr. Masaharu Nakamura Prof. Dr. Hiroaki Sasai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9518-9525
The reaction pathway of an enantioselective 5‐endo‐trig‐type cyclization of 3‐alkenoic acids catalyzed by a chiral palladium–spiro‐bis(isoxazoline) complex, Pd–SPRIX, has been studied by density functional theory calculations. The most plausible pathway involves intramolecular nucleophilic attack of the carboxylate moiety on the C?C double bond activated by Pd–SPRIX and β‐H elimination from the resulting organopalladium intermediate. The enantioselectivity was determined in the cyclization step through the formation of a π‐olefin complex, in which one of the two enantiofaces of the olefin moiety was selected. The β‐H elimination occurs via a seven‐membered cyclic structure in which the acetate ligand plays a key role in lowering the activation barrier of the transition state. In the elimination step, the SPRIX ligand was found to behave as a monodentate ligand due to the hemilability of one of the isoxazoline units thereby facilitating the elimination. Natural population analysis of this pathway showed that the more weakly electron‐donating SPRIX ligand, compared with the bis(oxazoline) ligand, BOX, facilitated the formation of the π‐olefin complex intermediate, leading to a smaller overall activation energy and a higher reactivity of the Pd–SPRIX catalyst. 相似文献
27.
Jinshui Chen Dr. Norito Takenaka Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(30):7268-7276
Optically active chiral alkyl chlorides are valuable compounds because of their bioactivity and versatile synthetic utility. Accordingly, the ring opening of epoxides with a chloride nucleophile stands as an important goal in asymmetric catalysis. We describe herein recent advances in the design and development of chiral pyridine N‐oxide catalysts for the enantioselective synthesis of chlorohydrins. 相似文献
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Takenaka S Susuki N Miyamoto H Tanabe E Matsune H Kishida M 《Chemical communications (Cambridge, England)》2010,46(47):8950-8952
Pd cathode catalysts for polymer electrolyte fuel cells have been covered with silica layers a few nanometres thick. The silica-coated Pd catalysts showed high activity and excellent durability for the oxygen reduction under the severe cathode conditions of PEFCs, while Pd catalysts without silica-coating were seriously deactivated under the same conditions. The coverage of Pd metal with silica prevents the diffusion of Pd species out of the silica layers. 相似文献
30.
Katsuhiko Takenaka Natsuyo Shibata Akihiko Oshikiri Masamitsu Miya Hiroki Takeshita Tomoo Shiomi 《Journal of polymer science. Part A, Polymer chemistry》2010,48(17):3714-3721
Anionic polymerizations of three 1,3‐butadiene derivatives containing different N,N‐dialkyl amide functions, N,N‐diisopropylamide (DiPA), piperidineamide (PiA), and cis‐2,6‐dimethylpiperidineamide (DMPA) were performed under various conditions, and their polymerization behavior was compared with that of N,N‐diethylamide analogue (DEA), which was previously reported. When polymerization of DiPA was performed at ?78 °C with potassium counter ion, only trace amounts of oligomers were formed, whereas polymers with a narrow molecular weight distribution were obtained in moderate yield when DiPA was polymerized at 0 °C in the presence of LiCl. Decrease in molecular weight and broadening of molecular weight distribution were observed when polymerization was performed at a higher temperature of 20 °C, presumably because of the effect of ceiling temperature. In the case of DMPA, no polymer was formed at 0 °C and polymers with relatively broad molecular weight distributions (Mw/Mn = 1.2) were obtained at 20 °C. The polymerization rate of PiA was much faster than that of the other monomers, and poly(PiA) was obtained in high yield even at ?78 °C in 24 h. The microstructure of the resulting polymers were exclusively 1,4‐ for poly(DMPA), whereas 20–30% of the 1,2‐structure was contained in poly(DiPA) and poly(PiA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3714–3721, 2010 相似文献