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61.
Kobayashi S Ohmae M Ochiai H Fujikawa S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(23):5962-5971
Hyaluronidase (HAase) catalyzes multiple enzymatic polymerizations with controlling regio- and stereoselectivity perfectly. This behavior, that is, the single enzyme being effective for multireactions and retaining the enzyme catalytic specificity, is not usual, and hence, HAase is a supercatalyst. Various sugar oxazoline monomers prepared based on the concept "transition-state analogue substrate" were successfully polymerized and copolymerized with HAase catalysis, yielding natural and unnatural glycosaminoglycans. 相似文献
62.
Kawasaki H Uota M Yoshimura T Fujikawa D Sakai G Kijima T 《Journal of colloid and interface science》2006,300(1):149-154
One-dimensional (1-D) self-assemblies of Pt nanoparticles on a graphite surface have been synthesized via a template-directed sintering process of individual nanoparticles, using nonionic/cationic mixed hemicylindrical micelle templates of dodecyldimethylamine oxide surfactant at graphite/solution interfaces. The dimension and morphology of Pt nanoparticles can be widely controlled by the concentration of Pt ions equivalent to the mixing ratio of nonionic and cationic species in the surfactant micelle. This approach could be extended to fabricate a wide range of self-assembling metallic nanostructures on surfaces using various nonionic/cationic mixed micelle-like self-assemblies carrying metal ions at interfaces, while providing a fundamental insight into a 1-D self-assembly from individual nanoparticles. 相似文献
63.
Kohki Fujikawa Tomohiro Nohara Hiromune Ando Hideharu Ishida Makoto Kiso 《Tetrahedron letters》2010,51(7):1126-5815
A cyclic glucosyl ceramide (GlcCer) acceptor has been developed as a versatile building block for the synthesis of complex ganglioside. A macrocyclic GlcCer acceptor, which was the product of intramolecular glycosylation between glucose and ceramide, exhibited high reactivity during the coupling reactions with a variety of complex oligosaccharyl donors, thereby furnishing the corresponding ganglioside frameworks in high yields. 相似文献
64.
65.
Koichi Takakura Koichiro Hayashi Seizo Okamura 《Journal of polymer science. Part A, Polymer chemistry》1966,4(7):1731-1745
Cyclic ethers such as trioxane and 3,3-bis(chloromethyl)oxetane have been polymerized easily in the presence of maleic anhydride by the irradiation of γ-rays and ultraviolet light. The polymer formed is a homopolymer of cyclic ether. The rate of polymerization is accelerated by suitable amounts of oxygen which is required to form some active species at the initiation step. The polymerization is inhibited by the addition of a small amount of radical scavenger, thus suggesting a radical initiating mechanism. In addition, the polymerization is easily initiated by benzoyl peroxide even in vacuo at or above 50°C. Diaroyl and diacyl peroxides are also effective, and polymerization also proceeds in the presence of chloromaleic anhydride, exactly in the same manner as in maleic anhydride. On the other hand, it is well known that polymerization of these cyclic monomers rarely occurs with radical catalysts and easily with cationic catalysts in the absence of maleic anhydride. From these results, it may be concluded that the polymerization is brought about by means of a radical–cationic species. 相似文献
66.
A new theoretical method to calculate the photoionization cross sections of complex molecules and solids is derived in the framework of the dynamical theory by using the Green's function method. The approximations applicable to treat the photoionization by x-rays are also discussed. 相似文献
67.
Kanae Hayashi Michinori Tachibana Seizo Okamura 《Journal of polymer science. Part A, Polymer chemistry》1980,18(12):3381-3391
Radiation-induced polymerization of isoprene in bulk state was studied at 25°C in a wide dose rate range. Variations of the rate of polymerization and molecular weight of the products were essentially the same as those observed in the monomers which were capable of both radical and cationic polymerizations. At low dose rate, 7.0-230 rad/sec, radical polymerization took place. At high dose rate, 8.8 × 103-2.2 × 105 rad/sec, radical and cationic polymerizations took place concurrently. The average molecular weight of the high-dose-rate product was about 850, independent of dose rate. The microstructure of the products at high dose rate consisted mainly of trans- 1,4 units with only about 7% of cis- 1,4 and 10% of 3,4-vinyl units. The residual unsaturation in the high-dose-rate products was 90%. Decreases in cis units and residual unsaturation at high dose rate were accounted for by the change in predominant mechanism of polymerization with dose rate. 相似文献
68.
Copolymerization of methyl vinyl ketone (MVK) with styrene was carried out at 50°C in the presence of cobalt(II) nitrate. The resulting monomer reactivity ratios decreased with an increasing concentration of the cobalt salt. This finding suggests that the metal salt participates in the propagation step of the copolymerization. Absolute copolymerization parameters were determined by assuming a three-component system as free MVK (M1), MVK complexed with cobalt(II) nitrate (M2), and styrene (M3): k11/k12 = 0.184, k11/k13 = 0.235, k22/k21 = 7.18 × 10−2, k22/k23 = 6.79 × 10−4, k33/k31 = 0.380, and k33/k32 = 2.77 × 10−3, and Q2 = 19.65 and e2 = 2.83. The complexed MVK monomer is more reactive to the polymer radical with the terminal styrene unit than the free MVK. Very small values for the monomer reactivity ratios, k22/k23 and k33/k32, show the marked alternating tendency for the copolymerization of the complexed monomer with styrene. In practice, however, alternating copolymer could not be obtained because of the poor solubility of cobalt(II) nitrate. 相似文献
69.
Masashi Ohmae Shun-Ichi Fujikawa Hirofumi Ochiai Shiro Kobayashi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(17):5014-5027
Synthesis of natural and unnatural polysaccharide was achieved via “enzymatic polymerization” by utilizing a glycoside hydrolase as catalyst. Particularly, hyaluronan, chondroitin, and their derivatives belonging to glycosaminoglycans have been prepared using sugar oxazoline monomers designed on the basis of the concept “transition-state analogue substrate”. The oxazoline derivatives of N-acetylhyalobiuronate [GlcAβ(1→3)GlcNAc] and N-acetylchondrosine [GlcAβ(1→3)GalNAc], which have the repeating disaccharide structures of hyaluronan and chondroitin, respectively, were successfully polymerized by the catalysis of hyaluronidase, giving rise to synthetic hyaluronan and chondroitin. Their 2-substituted oxazoline derivatives were also polymerized to the corresponding N-acylated hyaluronan and chondroitin derivatives. Furthermore, N-acetylchondrosine oxazoline derivatives sulfated at the C4, the C6, and both the C4 and C6 of the GalNAc unit were catalyzed by hyaluronidase; the monomer sulfated at the C4 was polymerized to chondroitin 4-sulfate with well-defined structure, whereas the other two monomers were exclusively hydrolyzed to the corresponding disaccharides. These different kinds of natural and unnatural polysaccharides having relatively high molecular weights were produced in all cases by the catalysis of hyaluronidase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5014–5027, 2006 相似文献
70.
Y. Watanabe N. Yamamoto S. Bhunia T. Kawamura S. Fujikawa 《Physica E: Low-dimensional Systems and Nanostructures》2004,23(3-4):305
Vertically aligned InP nanowires were successfully grown by metalorganic vapor phase epitaxy under metal-catalyzed vapor–liquid–solid growth processes. Au nanoparticles with a nominal diameter of 20 nm were used as the seed to control the diameter of the nanowires. Scanning and transmission electron microscopic studies showed highly dense nanowires with uniform diameters along the length direction, and the zinc-blende structure of the nanowires with 1 1 1 growth direction, respectively. Cathodeluminescence measurements showed a significant blueshift in the spectral peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires. 相似文献