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排序方式: 共有293条查询结果,搜索用时 46 毫秒
71.
Yasumoto K Nishigami A Kasai F Kusumi T Ooi T 《Chemical & pharmaceutical bulletin》2006,54(2):271-274
2,6-Dimethylheptyl sulfate (1) and 6-methyloctyl sulfate (3) were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). The absolute stereochemistry at C2 of 1 was determined by (1)H-NMR analysis of the (R)-MTPA ester of alcohol 2. The absolute configuration at C6 of 3 was determined by Ohrui's method applied to alcohol 4. 相似文献
72.
Alternating-current (ac) magnetic susceptibility measurements for tris(dipicolinato) complexes with a trivalent heavy lanthanide ion, [N(C2H5)4]3[Ln(dipic)(3)] x nH2O (dipic = pyridine-2,6-dicarboxylate; Ln = Tb, Dy, Ho, Er, Tm, or Yb) are reported. While none of the six complexes showed a magnetization lag from the ac magnetic field of 10-10(3) Hz above 1.8 K, the Dy, Er, and Yb complexes with odd numbers of 4f electrons exhibited the magnetization lag in a static magnetic field. This phenomenon is explained to be caused by the elimination of a fast relaxation path, which is only effective for the Kramers doublet ground states in near zero field. At higher static fields, the remaining paths such as Orbach and/or direct processes govern the dynamics of the two-level systems comprised of spin-up and spin-down states. The non-Kramers complexes were found to have a nondegenerate ground state with large energy gaps from higher states, which is consistent with their fast magnetization relaxation. 相似文献
73.
74.
Nishiwaki N Nishida D Ohnishi T Hidaka F Shimizu S Tamura M Hori K Tohda Y Ariga M 《The Journal of organic chemistry》2003,68(22):8650-8656
The acyl group of an alpha-aryl-beta-keto ester was readily transferred to N-, O-, and S-nucleophiles. The transacylation from arylated diethyl 3-oxoglutarate to amines led to unsymmetrical malonic acid amide esters in high yields. The present reaction proceeded under mild conditions without formation of detectable byproducts. Only simple experimental manipulations were required. This reaction was also found to be sensitive to steric factors, which enabled the chemoselective monoacylation of diamines and amino alcohols without any modifications such as protection. 相似文献
75.
Fumie Sato Hiroaki Ishikawa Yoshihiko Takahashi Masatoshi Miura Masao Sato 《Tetrahedron letters》1979,20(39):3745-3748
SiO2-supported titanium chloride () and polystyrene-supported titanocene dichloride () and () were synthesized. These heterogenized titanium compounds are excellent catalysts for hydroalumination of olefins. 相似文献
76.
1,3-Butadiene-2-carboxylates were treated with a titanium(II) alkoxide reagent, Ti(O-i-Pr)4/2i-PrMgCl, to generate diene-titanium alkoxide complexes, the presence of which was verified by hydrolysis and deuteriolysis to give the corresponding monoolefins or their bis-deuterated counterpart. These diene complexes underwent successive addition to an aldehyde (as the first electrophile) and iodine (as the second one) in a highly regio- and stereoselective manner to give the corresponding iodo alcohol. Optically active 1,3-butadiene-2-carboxylates afforded the same adducts of high asymmetric induction. Besides these electron-deficient dienes, electron-rich 2-siloxy-1,3-butadienes also participated in the formation of the titanium complex, which led to the preparation of functionalized enol silyl ethers through regio- and stereoselective coupling with carbonyl compounds and hydrolytic workup. 相似文献
77.
Kiyotaka Koyama Masahiro Ishino Takashi Sugita Kunio Takahashi 《Tetrahedron letters》2004,45(37):6947-6948
Phomactin H (1), a diterpene has been isolated from cultures of an unidentified marine-derived fungus. The structure and relative stereochemistry of phomactin H (1) was determined by X-ray diffraction analysis. Phomactin H (1), having an oxepane moiety, is a new phomactin with a novel skeleton. 相似文献
78.
Tadashi Yamaguchi Fumie Yamazaki Tasuku Ito 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(4):m213-m214
(1,4,7‐Trithiacyclononane)silver trifluoromethanesulfonate crystallizes in a tetrameric form from nitromethane, to give the title compound, [Ag4(C6H12S3)4](CF3SO3)4·2CH3NO2. The complex cation consists of four [AgL]+ units (L is 1,4,7‐trithiacyclononane), with four Ag—S—Ag bridges forming a cyclic tetramer. The almost planar Ag4S4 ring takes an octagonal form. 相似文献
79.
Kageyama G Kawano S Kanagawa S Kondo S Sugita M Nakanishi T Shimizu A Kumagai S 《Rapid communications in mass spectrometry : RCM》2004,18(9):995-1000
A novel allele of transporters associated with the antigen-processing (TAP) 2 gene, TAP2*Bky2 (Val(577)), is significantly increased in Japanese patients with Sj?gren's syndrome (SS), and has a strong association with SS-A/Ro autoantibody production in SS and autoantibody including anti-SS-A/Ro and anti-U1 RNP antibody in systemic lupus erythematosus (SLE). To determine the influence of this natural mutated TAP on peptides loaded onto MHC class I, we analyzed the repertoire of peptides loaded onto MHC class I on transfectants with TAP1 and TAP2 or mutated TAP2 by electrospray ionization tandem mass spectrometry (ESI-MS/MS). After comparison of the peptide profiles we identified three peptides from only mutated TAP transfectants. Moreover, one of these peptides is derived from snRNP A, which is a target for anti-U1 RNP antibody. To our knowledge this is the first report to show that the natural mutation of TAP2 changes the peptide profile loaded onto MHC class I molecules. 相似文献
80.