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91.
Dr. Hui Ming Ge Han Sun Dr. Nan Jiang Yan Hua Qin Huan Dou Tong Yan Prof. Ya Yi Hou Prof. Christian Griesinger Prof. Ren Xiang Tan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5213-5221
Bioactive natural products offer multiple opportunities for the discovery of novel chemical entities with potential pharmaceutical, nutraceutical and agrochemical applications. Many new organic compounds with novel scaffolds are isolated in small quantities and established methods often fail to determine the structure and bioactivity of such novel natural products. To meet this challenge, we present here a new methodology combining RDC (residual dipolar coupling)‐based NMR spectroscopy in microtubes, with a motif‐inspired biological assessment strategy. Using only one milligram (ca. 1.5 μmol) of sample, the new protocol established the bioactivity as well as the relative and absolute configuration of vatiparol obtained from Vatica parvifolia. Vatiparol is unique in its unprecedented carbon skeleton and selective inhibitory effect on the expression of monocyte chemo‐attractant protein‐1 (MCP‐1, also known as CCL2). The plausible biosynthetic pathway of vatiparol is briefly discussed. The approach introduced here promises to be widely applicable to the determination of the structure and bioactivity of structurally unknown organic samples available in very limited amounts. 相似文献
92.
We introduce the Brauer loop scheme, where • is a certain degeneration of the ordinary matrix product. Its components of top dimension, ⌊N2/2⌋, correspond to involutions π∈SN having one or no fixed points. In the case N even, this scheme contains the upper-upper scheme from [A. Knutson, Some schemes related to the commuting variety, J. Algebraic Geom., in press, math.AG/0306275] as a union of (N/2)! of its components. One of those is a degeneration of the commuting variety of pairs of commuting matrices.The Brauer loop model is an integrable stochastic process studied in [J. de Gier, B. Nienhuis, Brauer loops and the commuting variety, J. Stat. Mech. (2005) P01006, math.AG/0410392], based on earlier related work in [M.J. Martins, B. Nienhuis, R. Rietman, An intersecting loop model as a solvable super spin chain, Phys. Rev. Lett. 81 (1998) 504-507, cond-mat/9709051], and some of the entries of its Perron-Frobenius eigenvector were observed (conjecturally) to equal the degrees of the components of the upper-upper scheme.Our proof of this equality follows the program outlined in [P. Di Francesco, P. Zinn-Justin, Inhomogeneous model of crossing loops and multidegrees of some algebraic varieties, math-ph/0412031]. In that paper, the entries of the Perron-Frobenius eigenvector were generalized from numbers to polynomials, which allowed them to be calculated inductively using divided difference operators. We relate these polynomials to the multidegrees of the components of the Brauer loop scheme, defined using an evident torus action on E. As a consequence, we obtain a formula for the degree of the commuting variety, previously calculated up to 4×4 matrices. 相似文献
93.
Summary An extension of the multiconfigurational SCF approach for the resolution of the vibrational problem is presented; it follows the philosophy of the CASSCF method developed in Quantum Chemistry. The new method allows a more complete treatment of anharmonic mode couplings, converges much faster and gives a clearer physical insight of vibrational interactions. This is exemplified by the calculation of infrared transition moments in the H2O and D2O isotopomers of the water molecule. It is shown how this property varies with the quality of the wave function when vibrational resonances occur. A detailed analysis by means of this new VCASSCF method demonstrates the crucial importance of excited bending oscillators in the intensity of some pure stretching transitions.Boursier F.R.I.A. 相似文献
94.
Klochkov VV Baikeev RF Skirda VD Klochkov AV Muhamadiev FR Baskyr I Berger S 《Magnetic resonance in chemistry : MRC》2009,47(1):57-62
The gated decoupled (13)C NMR spectra of a dipeptide (Glu-Trp) and a tetrapeptide (NAc-Ser-Phe-Val-Gly-OMe) were recorded in D(2)O and in a lyotropic alignment medium (pentaethylene glycol monododecyl ether/n-hexanol). The residual dipolar couplings were extracted as the differences between the observed couplings for the magnetic nuclei dissolved in the latter and former media. Using a computational optimization, the spatial structures of the compounds were calculated starting from their respective low energy conformations obtained on a semiempirical basis. The uniformity of each conformation was confirmed by the solid-state (13)C NMR spectra of powder samples. Differences between the starting structures and final ones, optimized when employing residual dipolar couplings, are discussed. 相似文献
95.
The central elements of the algebra of monodromy matrices associated with the R-matrix are studied. When the crossing parameter w takes a special rational value , where N and n are positive coprime integers, the center is substantially larger than that in the generic case for which the “quantum determinant” provides the center. In the trigonometric limit, the situation corresponds to the quantum group at roots of unity. This is a higher rank generalization of the recent results by Belavin and Jimbo. 相似文献
96.
97.
《Magnetic resonance in chemistry : MRC》2003,41(3):193-201
The oxidation of the trans,cis‐( 2 ) and trans,trans‐epoxides ( 3 ) of differently substituted (Z)‐3‐arylidene‐1‐thioflavan‐4‐ones ( 1 ) with dimethyldioxirane (DMD) yielded the appropriate sulfoxides ( 4, 5 ) and sulfones ( 6, 7 ). The structures were elucidated by the extensive application of one‐ and two‐dimensional 1H, 13C and 17O NMR spectroscopy. The conformational analysis was achieved by the application of 3J(C,H) coupling constants, NOESY responses and ab initio calculations. The preferred ground‐state conformers (twisted envelope‐A, twisted envelope‐B for 6 and twisted envelope‐A, envelope‐B for 7 ) were obtained as global minima of the theoretical ab initio MO study and also the examination of the 17O and 13C chemical shifts, calculated for the global minima structures of the sulfone isomers by the GIAO method. Analogous results, obtained for the sulfoxide isomers ( 4, 5 ), not only led to the preferred conformers but also gave evidence for the trans arrangement of the 2‐Ph group and the oxygen atom of the S?O group. Chemical shift differences between the isomers, sulfoxides and sulfones were corroborated by ab initio calculations of the anisotropic effects of the oxirane ring and the S?O and SO2 groups. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
98.
等谱和非等谱TD族,Lax表示与零曲率表示 总被引:2,自引:0,他引:2
斯仁道尔 《高校应用数学学报(A辑)》1995,(4):375-382
首先,推广文「1」的结果,建立了等谱和非等谱TD族,并给出相应的Lax表示,再用文「2」的方法得到了相应的零曲率表示。 相似文献
99.
The (1)H and (13)C NMR spectra of two stereoisomeric bis-Tr?ger's bases and four stereoisomeric tris-Tr?ger's bases asymmetrically substituted on the external aromatic rings were recorded and the corresponding signals assigned. The relative configuration of the stereogenic units has been unequivocally determined on the basis of homoallylic couplings and NOE experiments. 相似文献
100.