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91.
We developed a compact three-stage Ti:sapphire amplifier laser system that produced peak power in excess of 100 TW for a pulse duration of less than 19 fs and an average power of 19 W at a 10-Hz repetition rate. A final 40-mm-diameter Ti:sapphire amplifier is pumped by a Nd:YAG master-oscillator-power-amplifier system that produces ~7-J output of 532-nm radiation. The spatial beam quality is approximately 2 times diffraction limited for the full amplified compressed output pulse. With f/3 optics, this system should therefore be capable of producing a focused intensity of ~3x10(20) W/cm(2) . 相似文献
92.
Diamanti SJ Khanna V Hotta A Yamakawa D Shimizu F Kramer EJ Fredrickson GH Bazan GC 《Journal of the American Chemical Society》2004,126(34):10528-10529
Block copolymerization of ethylene with 5-norbornen-2-yl acetate (1) by the nickel catalyst system [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide]Ni(eta1-CH2Ph)(PMe3) (2) and Ni(COD)2 (bis(1,4-cyclooctadiene)nickel) (3) produces a variety of block copolymer structures that demonstrate microphase separation. Typical block copolymerizations were carried out in an autoclave charged with a solution of the catalyst mixture and 1 (0.15 M) in toluene. The autoclave was sealed and exposed to PC2H4 = 50 psi for a period of time (T1). A pressure jump to PC2H4 = 1100 psi was then applied and the reaction allowed to proceed for another predetermined interval (T2). Independent experiments were performed to isolate and examine the molecular weight and comonomer composition of the first block. Narrow molecular weight distributions and the increase of polymer molecular weight with increases in T1 or T2 are consistent with a product in which an initial block is formed at low ethylene pressures and quantitatively converted to a block copolymer by the jump to high pressure. Transmission electron microscopy confirms that the materials are microphase separated. 相似文献
93.
Koji Yamakawa Tsuyoshi Satoh Nobuyiki Ohba Reiji Sakaguchi Satoshi Takita Nobuhiko Tamura 《Tetrahedron》1981,37(3):473-479
Introduction of an OH group to the tertiary carbon of simple ketones (1, 2 and 6), furanoeremophilane-type ketones (12–19), and tricyclic ketones (20–22) by the use of benzeneseleninic anhydride is described. 10β-Hydroxy compounds were obtained in the case of 12–14 and 20–22. 10α-Hydroxy compounds were obtained in the case of 15 and 16. In the hydroxylation reaction of polycyclic ketones using benzeneseleninic anhydride, the results suggest that the thermodynamically more stable product was usually produced as the major product. 相似文献
94.
Tanaka Y Kasai Y Mochizuki S Wakisaka A Morita EH Kojima C Toyozawa A Kondo Y Taki M Takagi Y Inoue A Yamasaki K Taira K 《Journal of the American Chemical Society》2004,126(3):744-752
We have studied the interaction between metal ions and the metal ion-binding motif in hammerhead ribozymes, as well as the functions of the metal ion at the motif, with heteronuclear NMR spectroscopy. In this study, we employed model RNA systems which mimic the metal ion-binding motif and the altered motif. In Co(NH3)6(III) titrations, we observed large 1H and 31P chemical shift perturbations for the motif and found that outer-sphere complexation of Co(NH3)6(III) is possible for this motif. From the reinvestigation of our previous 15N chemical shift data for Cd(II) binding, in comparison with those of organometallic compounds, we conclude that Cd(II) can form an inner-sphere complex with the nucleobase in the motif. Therefore, the A9/G10.1 site was found to accept both inner-sphere and outer-sphere complexations. The Mg(II) titration for a slightly different motif from the A9/G10.1 site (G10.1-C11.1 to A10.1-U11.1) revealed that its affinity to Mg(II) was drastically reduced, although the ribozyme with this altered motif is known to retain enzymatic activities. This observation suggests that the metal ion at these motifs is not a catalytic center of hammerhead ribozymes. 相似文献
95.
Hirobumi Takahashi Takehiro Fukami Hisaki Kojima Takeru Yamakawa Hiroyuki Takahashi Toshihiro Sakamoto Teruyuki Nishimura Masayuki Nakamura Takashi Yosizumi Kenji Niiyama Norikazu Ohtake Takashi Hayama 《Tetrahedron》2005,61(14):3473-3481
A robust synthetic method for 2-alkylamino-6-carboxy-5,7-diarylcyclopenteno[1,2-b]pyridines via acylamination at the alpha position of the functionalized pyridine system has been developed. The key step in this method was achieved by treatment of the corresponding pyridine N-oxides with 2.5 equiv of imidoyl chlorides in the presence of triethylamine, thus producing the desired 2-acylaminopyridines in good yields (74-96%). 相似文献
96.
Yoshitaka Yamakawa Mitsuru Ueda Kazuhiko Takeuchi Michihiko Asai 《Journal of polymer science. Part A, Polymer chemistry》1999,37(18):3638-3645
Dendritic polyamides with polydispersity of 1.1–1.4 have been successfully prepared from trimesic acid, 5-aminoisophthalic acid, and 4-aminophenylpropionic acid as a core molecule, a dendron, and a spacer unit, respectively, with a one-pot procedure. This procedure involves successive activation of end carboxyl groups with the condensing agent diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate (DBOP), followed by condensation of active amide with 5-aminoisopthalic acid or 4-aminophenylpropionic acid and, finally, capping of the end carboxyl groups with p-anisidine. The structure of dendritic polyamides was investigated by 1H-NMR spectroscopy, and it was found that the polymers obtained contained approximately 10% defects. Furthermore, the model reaction was studied to demonstrate the feasibility of dendritic polyamides. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3638–3645, 1999 相似文献
97.
98.
Masumi Asakawa PeterR. Ashton Vincenzo Balzani Alberto Credi Christoph Hamers Gunter Mattersteig Marco Montalti AndrewN. Shipway Neil Spencer J.Fraser Stoddart MalcolmS. Tolley Margherita Venturi AndrewJ.P. White DavidJ. Williams 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1998,110(3):357-361
99.
100.