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排序方式: 共有206条查询结果,搜索用时 15 毫秒
81.
A procedure for splitting of a lyocell fiber into a multitude of finer fibrils was developed. Crockmeter, usually used for rub-fastness of colored textiles, was modified and used for obtaining required shear force on swollen lyocell fiber. The shear force applied on fibers, and the concentration of NaOH, which affects swelling degree of fiber, were shown to be the leading parameters determining split number of lyocell fiber. While number of shear cycles was found to be of minor relevance for fiber splitting, the applied pressure directly influences the number of splitted fibrils. For example, at a pressure of 34.8 kPa, the average split number of lyocell fiber in 2.5 M NaOH solution was observed as 15, whereas it was observed as 30 for 47 kPa and 41 for 59.3 kPa. Splitting was not observed above 5 M of NaOH solution. Analyses of fiber splitting permit new aspects to study inner structure of lyocell. 相似文献
82.
[reaction: see text] 1,6-Enynes reacted with monoynes to give cyclohexadiene derivatives in the presence of a catalytic amount of [Ir(cod)Cl](2)/ligand. DPPE was most suitable for cycloaddition. Diastereoselective cycloaddition was also possible. In the absence of monoynes, 1,6-enynes cycloisomerized to (Z)-1-alkylidene-2-methylenecyclopentane derivatives. DPPF was most suitable for cycloisomerization. These results are the first examples of highly Z-selective cycloisomerization. 相似文献
83.
Norihiko Misawa Ryoko Nakamura Yukiko Kagiyama Hiroshi Ikenaga Kensuke Furukawa Kazutoshi Shindo 《Tetrahedron》2005,61(1):195-204
Various aromatic molecules, in which heterocycles are linked with a phenyl or benzyl group, were converted to their respective 2,3-diols (catechols) in the benzene ring by growing cell reactions using recombinant Escherichia coli, which expressed the evolved biphenyl dioxygenase [bphA (2072)] genes and the subsequent bacterial dihydrodiol dehydrogenase (bphB) gene. These vicinal diol products showed strong in vitro inhibitory activity against the lipid peroxidation induced by free radicals and strong scavenging activity towards DPPH radicals. The vicinal diols were also synthesized from ionized monocyclic aromatics incorporating an amino or carboxyl group. 相似文献
84.
Miyashita K Ikejiri M Kawasaki H Maemura S Imanishi T 《Journal of the American Chemical Society》2003,125(27):8238-8243
The total synthesis of an antitumor antibiotic, fostriecin (CI-920), via a highly convergent route is described. A characteristic feature of the present total synthesis is that the synthesis was achieved via a coupling procedure of three segments A, B, and C. The unsaturated lactone moiety of fostriecin, corresponding to segment A, was constructed from a known Horner-Emmons reagent, and the stereochemistry of the C-5 position was introduced by asymmetric reduction with (R)-BINAl-H. Segment B having a series of stereogenic centers was synthesized from (R)-malic acid and the stereogenic centers at the C-8 and C-9 positions were prepared by a combination of Wittig reaction and Sharpless asymmetric dihydroxylation reaction. The conjugated Z,Z,E-triene moiety of fostriecin, corresponding to segment C, was eventually constructed by Wittig reaction and Stille coupling reaction. The phosphate moiety, which is known to be essentially important for the antitumor activity, was introduced via two routes: (i) direct phosphorylation of the monohydroxyl derivative in which other hydroxyl groups are protected with silyl groups; (ii) cyclic phosphorylation and selective cleavage of the cyclic phosphate derivative. Although the former route is basically the same as those reported by other groups, the latter route is novel and more effective than the former one. The present total synthesis would serve as a versatile synthetic route to not only fostriecin, but also its various analogues including stereoisomers. 相似文献
85.
Maruyama S Kikuchi K Hirano T Urano Y Nagano T 《Journal of the American Chemical Society》2002,124(36):10650-10651
Zn(2+) plays important roles in various biological systems; as a result, the development of tools that can visualize chelatable Zn(2+) has attracted much attention recently. We report here newly synthesized fluorescent sensors for Zn(2+), ZnAF-Rs, whose excitation maximum is shifted by Zn(2+) under physiological conditions. Thus, these sensors enable ratiometric imaging, which is a technique to reduce artifacts by minimizing the influence of extraneous factors on the fluorescence of a probe. Ratiometric measurement can provide precise data, and some probes allow quantitative detection. ZnAF-Rs are the first ratiometric fluorescent sensors for Zn(2+) that enable quantitative analysis under physiological conditions. ZnAF-Rs also possess suitable K(d) for applications, and high selectivity against other biologically relevant cations, especially Ca(2+). Using these probes, changes of intracellular Zn(2+) concentration in cultured cells were monitored successfully. We believe that these probes will be extremely useful in studies on the biological functions of Zn(2+). 相似文献
86.
A selective anodic oxidation system in which a carbocation intermediate is generated exclusively by use of a temperature-controlled multiphase solution to separate the different stages of the reaction from each other and from the products is described. The formation of a thermomorphic middle layer in an electrolytic solution composed of c-Hex and LPC/MeNO2 results in enhanced interaction between aliphatic alkenes and polar unstable cation. 相似文献
87.
Kentaro Yamane Satoko Hayashi Waro Nakanishi Takahiro Sasamori Norihiro Tokitoh 《Polyhedron》2008,27(18):3557-3566
8-G-1-(p-YC6H4CCSe)C10H6 [2 (G = Cl) and 3 (G = Br): Y = H (a), OMe (b), Me (c), F (d), Cl (e), CN (f) and NO2 (g)] have been prepared and the NMR spectra measured, in addition to 1 (G = H). Structures have been determined by X-ray crystallographic analysis for 2b, 2e and 2g, which are all type B (B), where the Se–Csp bond is placed in the naphthyl plane in B. The type is classified as A if the Se–Csp bond is perpendicular to the naphthyl plane. Structures around the p-YC6H4 (Ar) group are pd (perpendicular) for Y = OMe (2b) and Cl (2e) and pl (planar) for Y = NO2 (2g), where the Se–CNap bond is placed in the aryl plane in pl and perpendicular to the plane in pd. The 1b (A: pd) structure changes dramatically on going to 2b (B: pd) with G = Cl at the 8-position. The effect is called the G-dependence in 2. The G-dependence arises from the energy lowering effect of the np(Cl)σ*(Se–Csp) 3c–4e interaction. Structures are both (B: pd) for 1e and 2e and both (B: pl) for 1g and 2g. One may realize that the structures are unchanged by G = Cl in place of G = H for Y = Cl and NO2 at a first glance. However, the B structures in 2e and 2g must be much more stabilized by the G-dependence of the np(Cl)σ*(Se–Csp) 3c–4e interaction or the GSe–Csp–Csp–Csp2 5c–6e type interaction. The structures of 2 and 3 are examined in solution based on the NMR parameters. The results show that 2 and 3 behave very similarly to each other and the structures are predominantly B, with some equilibrium between pd and pl around the aryl groups in solution. Quantum chemical calculations support the observations. 相似文献
88.
Prakash C. Srivastava Sangeeta Bajpai Roli Lath Rajesh Kumar Vikas Singh Shrinkhala Dwivedi Ray J. Butcher Satoko Hayashi Waro Nakanishi 《Polyhedron》2008
The reaction of organo(heterocyclic)tellurium(IV) derivative: C8H8TeI2(1,3-dihydro-2λ4-benzotellurole-2,2-diyl diiodide) with NH4S2CNC5H10 (ammonium piperidine dithiocarbamate) gives C8H8Te(S2CNC5H10)2 (1) and Te(S2CNC5H10)2 (2) or C8H8TeI(S2CNC5H10) (5) according to the reaction conditions. In such type of metathetical reactions, the formation of 2 is unprecedented and it corresponds to the first Te–C cleaved product. The reaction of 2 with CH3I, yields the oxidative addition product, CH3TeI(S2CNC5H10)2 (8). The formation of 2 is also supported through Quantum Chemical calculations. Another Te–C bond cleaved product TeI2[(C13H10N2S)2] · 4C4H8TeI2 (9) is obtained in the reaction of C4H8TeI2 (1,1,2,3,4,5-hexahydro-1,1-diiodotellurophene) with NH4S2CNHC6H5 (ammonium aniline dithiocarbamate). The reaction of 1,1,2,3,4,5,6-heptahydro-1-iodo-1-(morpholine dithiocarbamato) tellurane [C5H10TeI(S2CNC4H8O)] (10) with 1,10-phenanthroline gives an unusual product C12H8N2 · C4H10INO (11). The structures of the new complexes 2, 8, 9, 10 and 11 have been determined by the X-ray analysis. 相似文献
89.
A set of new delta(Se) parameters is proposed as a standard for the planar (pl) orientational effect of p-YC(6)H(4) (Ar) in ArSeR, employing 9-(arylselanyl)triptycenes (1: p-YC(6)H(4)SeTpc). The Se-C(R) bond in ArSeR is placed on the Ar plane in pl and it is perpendicular to the plane in pd. Large upfield shifts are observed for Y = NMe(2), OMe, and Me (-22 to -6 ppm) and large downfield shifts for Y = COOEt, CN, and NO(2) (19-37 ppm), relative to Y = H, with small upfield and moderate downfield shifts by Y of halogens (-1 ppm for Y = F and 4 ppm for Y = Cl and Br). This must be the result of the p(Se)-pi(C(6)H(4))-p(Y) conjugation in 1 (pl). While the character of delta(Se) in 1 (pl) is very similar to that in 9-(arylselanyl)anthracenes (2 (pl)), it is very different from that of 1-(arylselanyl)anthraquinones (3 (pd)). Sets of delta(Se) of 1 and 2 must serve as the standard for pl and that of 3 does for pd in solutions. Structures of various ArSeR in solutions are determined from the viewpoint of the orientational effect based on the standard delta(Se) of 1-3. While the structure of 2-methyl-1-(arylselanyl)naphthalenes is concluded to be all pl in solutions, those of 8-chloro- and 8-bromo-1-(arylselanyl)naphthalenes are all pd, except for Y = COOEt, CN, and NO(2): The equilibrium between pd and pl contributes to those with Y = COOEt, CN, and NO(2). The structure of 1-(arylselanyl)naphthalenes changes depending on Y. The structures of ArSeMe and ArSeCOPh are shown to be pl and pd, respectively, in solutions. Those of ArSePh and ArSeAr seem to change depending on Y. delta(Se) of 1-3 are demonstrated to serve as the standard to determine the structures in solutions. The rules of thumb derived from the characters in delta(Se) for 1-3 are very useful to determine the structures of ArSeR in solutions, in addition to the analysis based on the plots. 相似文献
90.