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排序方式: 共有208条查询结果,搜索用时 15 毫秒
81.
Luo MF Chiang CI Shiu HW Sartale SD Wang TY Chen PL Kuo CC 《The Journal of chemical physics》2006,124(16):164709
We present a scanning tunnel microscopy study of Co clusters grown through vapor deposition on Al(2)O(3) thin films over NiAl(100) at different coverages and temperatures. Formation of Co clusters was observed at 90, 300, 450, and 570 K. At the three lower temperatures, we find narrow cluster size distributions and the mean sizes (with a diameter of 2.6 nm and a height of 0.7 nm) do not change significantly with the coverage and temperature, until the clusters start to coalesce. Even on 3-4-nm-wide crystalline Al(2)O(3) strips where the deposited Co atoms are confined, the same features sustain. Only at 570 K the normal growth mode where the cluster size increases with the deposition coverage is observed, although the data are less conclusive. A simple modeling of kinetic surface processes on a strip confirms the normal growth mode, but fails to show a favored size unless additional energetic constraints are applied on the cluster sizes. Increasing Co coverages to cluster coalescence, a larger preferable size (mean diameter of 3.5 nm and height of 1.4 nm) appears for growth at 450 K. These two sizes are corroborated by morphology evolution of high Co coverages deposited at 300 K and annealed to 750 K, in which the coalescence is eliminated and the two preferable geometries appear and coexist. 相似文献
82.
A general procedure for the synthesis of NG-alkyl, and NG-aryl-L -arginines with relatively high overall yield is reported. The key step involved the coupling of protected L -ornithine 4 with isothiourea 7 to give the fully protected NG-aryl-L -arginine derivative 8 . Subsequent deprotection of 8 in acidic condition provided the final target compound 9 with an overall yield of more than 80%. 相似文献
83.
W. Sierpiski showed that each x in 0<x1 has a representation1/a1...ak is an increasing sequence of positive integers. Weshow that the subset of numbers x for which(ak) is strictlyincreasing is a Cantor set. 相似文献
84.
Thermolysis of (H2CPz′2)M(CO)4 (H2CPz′2 = bis(3,5-dimethylpyrazol-1-yl)methane; M=Mo, W) in 1,2-dimethoxyethane did not give the expected 16-electron complexes, (H2CPz′2)M(CO)3, but gave dinuclear compounds, [(H2CPz′2)M(CO)3]2, probably containing two linear carbonyl bridges and no metal-metal interactions. The dimers reacted with CH3CN to give mononuclear compounds, (H2CPz′2)M(CO)3(NCCH3), identical to the substitution products between (H2CPz′2)M(CO)4 and CH3CN. 相似文献
85.
Deng‐Shiu Yang Ming‐Kuang Wang Chia‐Ming Chang Hwo‐Shuenn Sheu Bing‐Joe Hwang 《中国化学会会志》2003,50(5):985-990
Lithiophorite consists of alternatively stacked MnO6 octahedral sheets and LiAl2(OH)6 octahedral sheets. Its applications in laboratories and industries have been hindered by sophisticated operation procedures, long reaction time, or impurities existing in the final product. We proposed a fast and simple method, mixing birnessite, aluminate and lithium hydroxide together (designated it as the BAL method) in high alkaline conditions (pH > 13), and treating it hydrothermally at 423 K for 6 hours to prepare pure lithiophorite. A specific reaction between lithium cations and aluminate anions plays as a key role in the BAL method. Due to this specific reaction, LixAln(OH)m+z complexed cations can form and penetrate into interlayers of birnessite to replace sodium cations. In high alkaline conditions (pH > 12), LixAln(OH)m+z complexed cations become smaller and are soluble. Thus, the higher alkaline LixAln(OH)m+z complexed cations can penetrate into interlayers of birnessite at a higher rate. Furthermore, impurities, such as lithium intercalated gibbsite (LIG), aluminum oxyhydroxides and aluminum hydroxides are not stable in high alkaline conditions. Consequently, pure lithiophorite can be easily obtained within 6 hours in high alkaline conditions. 相似文献
86.
87.
Wai Chee Shiu Peter Che Bor Lam Fuji Zhang Heping Zhang 《Journal of mathematical chemistry》2002,31(4):405-420
As a general case of molecular graphs of polycyclic alternant hydrocarbons, we consider a plane bipartite graph G with a Kekulé pattern (perfect matching). An edge of G is called nonfixed if it belongs to some, but not all, perfect matchings of G. Several criteria in terms of resonant cells for determining whether G is elementary (i.e., without fixed edges) are reviewed. By applying perfect matching theory developed in plane bipartite graphs, in a unified and simpler way we study the decomposition of plane bipartite graphs with fixed edges into normal components, which is shown useful for resonance theory, in particular, cell and sextet polynomials. Further correspondence between the Kekulé patterns and Clar (resonant) patterns are revealed. 相似文献
88.
Let (x) be the error term associated with the asymptotic formulafor the counting function on the set of numbers that are sumsof three squares. We give a formula for (x) and use it to provethat (x) has average order and normal order 3 1og x/(16 1og2). 相似文献
89.
Chu IK Zhao J Xu M Siu SO Hopkinson AC Siu KW 《Journal of the American Chemical Society》2008,130(25):7862-7872
The mobility of the radical center in three isomeric triglycine radical cations[G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) has been investigated theoretically via density functional theory (DFT) and experimentally via tandem mass spectrometry. These radical cations were generated by collision-induced dissociations (CIDs) of Cu(II)-containing ternary complexes that contain the tripeptides YGG, GYG, and GGY, respectively (G and Y are the glycine and tyrosine residues, respectively). Dissociative electron transfer within the complexes led to observation of [Y(*)GG](+), [GY(*)G](+), and [GGY(*)](+); CID resulted in cleavage of the tyrosine side chain as p-quinomethide, yielding [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+), respectively. Interconversions between these isomeric triglycine radical cations have relatively high barriers (> or = 44.7 kcal/mol), in support of the thesis that isomerically pure [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) can be experimentally produced. This is to be contrasted with barriers < 17 kcal/mol that were encountered in the tautomerism of protonated triglycine [Rodriquez C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006-3012]. The CID spectra of [G(*)GG](+), [GG(*)G](+), and [GGG(*)](+) were substantially different, providing experimental proof that initially these ions have distinct structures. DFT calculations showed that direct dissociations are competitive with interconversions followed by dissociation. 相似文献
90.
The hydrothermal reaction of 2,3‐pyridinedicarboxylic acid (2,3‐H2pda) with a mixture of Cd(NO3)2 and Ni(NO3)2 afforded a coordination polymer, [CdNi(2,3‐pda)2(H2O)3]∞ ( 1 ); in contrast, that with a mixture of Cd(NO3)2 and Zn(NO3)2 surprisingly produced a discrete molecule, trans‐[Cd(3‐pa)2(H2O)4] ( 2 ) (3‐pa? = 3‐pyridinecarboxylate). Since a direct reaction between a single metal salt, Cd(NO3)2 or Zn(NO3)2, and 3‐pyridinecarboxylic acid (3‐Hpa) under similar hydrothermal conditions yielded different coordination polymers containing 3‐pa?, it appears that the apparently thermal decarboxylation from ligated 2,3‐pda2? to 3‐pa? occurs after complexation of both metal cations, Cd(II) and Zn(II). A new coordination mode, formed for 2,3‐pda2? in structure 1 , appears to help formation of microporous channels by piling up the observed 2D hydrogen‐bonded heteropolynuclear layers. Each channel apparently consists of two interpenetrating 63 Cd(II) and Ni(II) nets. 相似文献