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排序方式: 共有208条查询结果,搜索用时 15 毫秒
161.
First, the carbon-carbon (C-C) bond-forming reaction of aldehydes with bicyclo[m.n.0]-1-oxonium ylides was studied as the ylide was transiently formed in the Rh(II)-catalyzed reaction of a nonenolizable diazoketone, namely, 2-(3-diazo-1,1-dimethyl-2-oxopropyl)-2-methyldioxolane (1). The reaction of 1 with benzaldehyde in the presence of ClTi(Oi-Pr)3 gave the three-carbon, ring-enlarged, and C-C-bonded product 2a (53%). Second, enolizable diazoketone 5 bearing no methyl substituents at the alpha-position was studied under similar catalytic conditions, and the ring-enlarged and C-C-bonded products 19a and 20a were also formed (87%) when titanium compound ClTi(Oi-Pr)3 or Ti(Oi-Pr)4 was used. Similar reactions of diazoketones 27, 29, and 31 bearing a cyclic acetal ring and a longer tethering chain than 5 gave C-C-bonded products 28 (74%), 30 (8%), and 32 and 33 (overall 48%), respectively, albeit 28 and 30 possessed a spiro bisacetal structure. Thus, the hitherto unclarified C-C bond formation of ethereal oxonium ylides with carbonyl electrophiles was realized with the use of an appropriate Lewis acid, for example, ClTi(Oi-Pr)3. 相似文献
162.
Tuyet TM Harada T Hashimoto K Hatsuda M Oku A 《The Journal of organic chemistry》2000,65(5):1335-1343
Sequential etherification of 2,2',6,6'-tetrahydroxybiphenyl (1) with 1,4-di-O-benzyl-L-threitol under Mitsunobu conditions gives desymmetrized biphenyldiol 9 of S-axial chirality exclusively. Cyclization of 9 with 1,omega-dibromoalkanes followed by removal of the chiral auxiliary yields (S)-2,2'-biphenyldiols 14 with alkylenedioxy bridges at the 6 and 6' positions. (S)-6,6'-Dialkyl- and -diphenyldiols 20 are obtained in an efficient manner via Pd(0)-catalyzed cross-coupling of bis(triflate) derivative 17 with organozinc reagents. Bis(triflate) 17 also serves as an intermediate for asymmetric synthesis of axially chiral biphenyldicarboxylic acid 23, terphenylcarboxylic acid 28, lactone 26, and lactam 30. 相似文献
163.
Yasumasa Hamada Fumiyoshi Matsuura Makoto Oku Keiichiro Hatano Takayuki Shioiri 《Tetrahedron letters》1997,38(52):910-8964
New optically active bidentate phosphines, (S,S)- and (R,R)-2,7-di-tert-butyl-9,9-dimethyl-4,5-bis(methylphenylphosphino)xanthenes ((S,S)-1 and (R,R)-1), were prepared through resolution of the corresponding phosphine oxides using (R,R)-(−)-dibenzoyl-tartaric acid and a preliminary experiment on asymmetric synthesis using an allyl substrate proved the utility of the new bidentate phosphines. 相似文献
164.
Jun Nishimura Tomohisa Okuda Yoshihiko Mukai Hidetoshi Hashiba Akira Oku 《Tetrahedron letters》1984,25(14):1495-1498
1,3-bis(4-vinylnaphthyl)propane and 1-(4-vinylnaphthyl)-3-(-vinylphenyl)propane, were cyclocodimerized with indene to afford indenyl-substituted [3.3](1,4)naphthalenophanes and [3.3]paracyclo(1,4)naphthalenophanes. 相似文献
165.
Oku M Hou Y Xing X Reed B Xu H Chang C Ng CY Nishizawa K Ohshimo K Suzuki T 《The journal of physical chemistry. A》2008,112(11):2293-2310
We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum. 相似文献
166.
Allergy-preventive flavonoids from Xanthorrhoea hastilis 总被引:1,自引:0,他引:1
Allergy-preventive activity was demonstrated for an extract of resins from Xanthorrhoea hastilis R. BR. in a search for allergy-preventive substances from natural sources. By bioassay-directed fractionation of this plant extract, a new flavanone, 3',5'-dihydroxy-7,4'-dimethoxyflavanone (1), and two new chalcones, 3,5,2'-trihydroxy-4,4'-dimethoxychalcone (2) and 5,2'-dihydroxy-3,4,4'-trimethoxychalcone (3), were isolated together with five known compounds, 5'-hydroxy-7,3',4'-trimethoxyflavanone (4), 3'-hydroxy-7,4'-dimethoxyflavanone (5), liquiritigenin 7-methyl ether (6), 4,2'-dihydroxy-4'-methoxychalcone (7) and sakuranetin (8). The structures of 1, 2 and 3 were elucidated by spectroscopic methods. All of these compounds showed allergy-preventive effects. 相似文献
167.
Suzuki K Oku J Izawa K Okabayashi HF Noda I O'Connor CJ 《Journal of colloid and interface science》2008,327(1):21-30
Concentration-resolved 2D correlation gel permeation chromatography (GPC) has been used to examine the intricate details of the HCl-catalyzed polymerization of a polymeric silane-coupling agent (SCA), triethoxysilyl-terminated polystyrene (TESiPS). The concentration-resolved 2D correlation GPC maps directly reflect the marked difference in the aggregate-aggregate interactions of dilute and concentrated monomeric units, which govern the differences in the polymerized products. There is an optimum concentration of SCA for the enhancement of interfacial strength and subsequent polymerization. Thus, the concentration-resolved 2D correlation GPC technique can be used as a powerful tool for elucidation of aggregate-aggregate interactions and reaction mechanisms in a surface- or interface-enhanced reaction system. It has been shown that the yield value of polymerization products can be improved to a marked extent by choosing a high initial monomer concentration, due to the increase in the production of oligomers. Multiple reaction processes are promoted by the self-assembly of the monomeric and oligomeric components. 相似文献
168.
M. Segawa H. Matsue Y. Sekiya S. Yamada T. Shinohara T. Oku H. Sasao J. Suzuki H. M. Shimizu 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(3):647-651
We have constructed a new system which could analyze a position distribution of several elements in a sample with 2 dimensional
prompt γ-ray analysis (2D PGA) system using focused neutron beam at JAEA. We aimed that the system could analyze local information
in a sample with a good signal γ-ray from interested elements to noise of background γ-ray ratio. As a result, this system
could determine the position resolution and spatial resolution within 1 mm. 相似文献
169.
Structural revision of glabramycin B, which is an antibacterial 10-membered lactone isolated from a fermentation broth of Neosartorya glabra, was achieved by enantioselective synthesis of our proposed structure. The correct structure of glabramycin B was presumed on comparison with related compounds, and synthesis of it was succeeded via dianion alkylation, Shiina's lactonization and Stille cross-coupling. By this synthesis, we were able to correct the reported structural misassignment, and to confirm the relative configuration of glabramycin B to be 10S*,11S*,15R*,20S*. 相似文献
170.
通过考察聚甲基丙烯酸甲酯(PMMA)/聚(α-甲基苯乙烯丙烯腈)(α-MSAN)共混体系动态粘弹函数的时温叠加,发现在终端区域时温叠加失效与其相分离有关。相分离使得终端区域的动态储能模量G″(或动态损耗模量G″)与频率的关系[IgG″(IgG″)~Igω]明显偏离经典粘弹模型。随组成的改变,时温叠加的失效呈现温度依赖性,其“失效温度”(Td)可很好地表征LCST类共混物的相分离,而且在用其表征相分离时,IgG″-Igω法比IgG″-IgG″法更优越。 相似文献