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991.
The stereoselective total synthesis of myriocin 1 from D-mannose is described; the carbon framework with three contiguous chiral centers including a tetra-substituted carbon with nitrogen was effectively constructed using Overman rearrangement as the key reaction. 相似文献
992.
993.
994.
Yoshio Kato Shiro Kido Tsutomu Hashimoto 《Journal of Polymer Science.Polymer Physics》1973,11(12):2329-2337
The resolution attainable in gel-permeation chromatography (GPC) was investigated by using columns packed with polystyrene gel particles of about 5 μ diameter and mixtures of two monodisperse poly-α-methylstyrene samples studied previously. The resolution of GPC was found comparable to that of the sedimentation velocity method and slightly better than that of precipitation chromatography. Standard polystyrene samples obtained from Pressure Chemical Co. also were measured with the same columns. It was found that weight-average to number-average molecular weight ratios (M?w/M?n) of these samples with molecular weight in the range 97,000–411,000 are smaller than 1.006. For samples with molecular weight of 10,000–51,000 and 498,000–860,000, M?w/M?n is larger than 1.006, and the width of molecular weight distributions of these samples differed. In particular, molecular weight distributions of samples with molecular weights 19,800 and 51,000 were shown to be bimodal. It is therefore concluded that GPC is useful for samples of very narrow molecular weight distribution if high-resolution columns are used. 相似文献
995.
Tomihiko Ohsawa Takeshi Oishi 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):185-194
Toluene radical anion, generated by dissolving potassium metal in toluene by the assistance of dicyclohexano-18-crown-6, has been proved to be especially effective for reductive removal of fluorine atom from unactivated alkyl fluorides that resist common reduction conditions. Stereochemical and mechanistic aspects of the present method is discussed. In connection with the preparation of substrates the effect of dipolar aprotic solvents on the nucleophilic fluorination with potassium fluoride/dicyclohexano-18-crown-6 system was also examined, and sulfolane or N,N-dimethyl formamide was shown to be a solvent of choice.T. Ohsawa, T. Takagaki, A. Haneda and T. Oishi,Tetrahedron
Lett.,1981, 2583. 相似文献
996.
Nakamura I Bajracharya GB Wu H Oishi K Mizushima Y Gridnev ID Yamamoto Y 《Journal of the American Chemical Society》2004,126(47):15423-15430
A general protocol for the synthesis of functionalized indenes from o-alkynylbenzaldehyde acetals and thioacetals has been elaborated. Acetals uniformly give cyclization products having the alkyl group from the starting acetylene migrated to the alpha-position, whereas the cyclization of the corresponding thioacetals proceeds without alkyl migration. Optimization of the catalytic system for the cyclization of o-alkynylbenzaldehyde acetals revealed an unknown activation effect: PtCl(2) was found to be a better catalyst for the cyclization of acetals in the presence of olefins than without. A similar catalytic system (PtCl(2)/benzoquinone) has been found to be appropriate for the cyclization of cyclic acetals, whereas the optimal catalyst for the reaction of thioacetals is PdI(2). NMR monitoring of two reactions, acetal 3a + Pd(CH(3)CN)Cl(2) in CD(3)CN and thioacetal 5j + PdI(2) in CD(2)Cl(2), revealed that in both reactions similar cationic species are formed at the early stage of the transformation. Computational data (B3LYP/SDD level of theory) suggest that the difference in the reaction pathways for acetals and thioacetals can be rationalized by taking into account the relative stabilities of the corresponding vinylpalladium intermediates (22 vs 20 and 19 vs 21), which suggests a reversible thermodynamically controlled alkyl migration in the intermediate vinylcationic species. 相似文献
997.
Yamada M Suzuki T Kanaori K Tajima K Sakamoto S Kodaki T Makino K 《Organic letters》2003,5(18):3173-3176
[reaction: see text] A gas mixture of NO and O(2) was bubbled into 2'-deoxyguanosine solution at neutral pH and 37 degrees C. A novel nitrated nucleoside was generated in the reaction mixture in addition to 8-nitroguanine, 8-nitroxanthine, 2'-deoxyxanthosine, xanthine, and guanine. The novel nucleoside was identified as N(2)-nitro-2'-deoxyguanosine by spectrometric data. 相似文献
998.
Using gauge transformations on electron bond operators, we derive exact duality relations between various order parameters for correlated electron systems. Applying these transformations, we find two duality relations in the generalized two-leg Hubbard ladder at arbitrary filling. The relations show that unconventional density-wave orders such as staggered flux or circulating spin current are dual to conventional density-wave orders and there are direct mappings between dual phases. Several exact results on the phase diagram are also concluded. 相似文献
999.
Yoshihiko Shoji Takao Asaka Hideki Dewa Hirohumi Hanaki Yoshinori Hisaoka Toshiaki Kobayashi Takahiro Matsubara Takayuki Mitsui Akihiko Mizuno Shinsuke Suzuki Tsutomu Taniuchi Hiromitsu Tomizawa Kenichi Yanagida 《Infrared Physics & Technology》2008,51(5):394-396
We have demonstrated the idea of circulating a short, intense linac bunch for some tens of turns in an isochronous ring. We compressed a bunch from the SPring-8 linac to a few picoseconds rms by means of an energy compression system and a beam transport line from the linac to NewSUBARU. The NewSUBARU storage ring was set to a quasi-isochronous condition and the bunch circulated for about 50 turns after injection while maintaining the short bunch length. At the same time, a pulse train of strong coherent synchrotron oscillation from the short bunch was observed. 相似文献
1000.
A catalytic photometric detection system based on the chromotropic acid—bromate reaction is adapted to a flow injection system for the rapid, simple and sensitive determination of vanadium. Vanadium in the range 0.3–4.8 ng (10–160 ppb) can be determined at a rate of ca. 60 samples per hour. 相似文献