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171.
Hélène Guinadeau Alan J. Freyer Robert D. Minard Maurice Shamma Kemal Hüsnü Can Başer 《Tetrahedron letters》1982,23(25):2523-2526
L. var. Boiss. (Ranunculaceae) has yielded (+)-istanbulamine () which is the first aporphine-benzylisoquinoline formed from one (+)-reticuline-type unit linked to a (+)-N-methylcoclaurine moiety. Other new dimers also present are (+)-bursanine () and (+)-iznikine (). 相似文献
172.
173.
Maurice van Gastel 《Applied magnetic resonance》2010,37(1-4):207-218
The oxidized “unready” Ni-A state [NiFe] hydrogenases has been the subject of recent investigations by spectroscopic and crystallographic techniques. In the Ni-A state, the enzyme is inhibited and cannot turn over molecular hydrogen. Ideally, if the Ni-A state can be avoided, and if the oxidized enzyme exclusively resides in the “ready” Ni-B state, it can be quickly activated, thus increasing its activity of hydrogen production. In this study, recent observations by electron paramagnetic resonance spectroscopy as well as X-ray crystallography are combined and interpreted. Though it remains a mystery as to which differences exist on the geometric and electronic level between the Ni-A and Ni-B states, and in particular about the exact structure of the active site in the Ni-A state, the recent studies when combined do provide important hints. 相似文献
174.
We propose a method for miniaturization of filters based on curved waveguide Bragg gratings, so that long structures can be packed into a small area on a chip. This eliminates the stitching errors introduced in the fabrication process, which compromise the performance of long Bragg gratings. Our approach relies on cascading curved waveguide Bragg gratings with the same radius of curvature. An analytical model for the analysis of these devices was developed, and a filter based on this model was designed and fabricated in a silicon on insulator platform. The filter had a total length of 920μm, occupied an area of 190μm×114μm, and exhibited a stop band of 1.7nm at 1.55μm and an extinction ratio larger than 23dB. 相似文献
175.
Agrawal AG van Gastel M Gärtner W Lubitz W 《The journal of physical chemistry. B》2006,110(15):8142-8150
Pulse electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy have been used to investigate nitrogen coordination of the active site of [NiFe] hydrogenase of Desulfovibrio vulgaris Miyazaki F in its oxidized "ready" state. The obtained (14)N hyperfine (A = [+1.32, +1.32, +2.07] MHz) and nuclear quadrupole (e(2)qQ/h = -1.9 MHz, eta = 0.37) coupling constants were assigned to the N(epsilon) of a highly conserved histidine (His88) by studying a hydrogenase preparation in which the histidines were (15)N labeled. The histidine is hydrogen-bonded via its N(epsilon)-H to the nickel-coordinating sulfur of a cysteine (Cys549) that carries an appreciable amount of spin density. Through the hydrogen bond a small fraction of the spin density ( approximately 1%) is delocalized onto the histidine ring giving rise to an isotropic (14)N hyperfine coupling constant of about 1.6 MHz. These conclusions are supported by density functional calculations. The measured (14)N quadrupole coupling constants are related to the polarization of the N(epsilon)-H bond, and the respective hydrogen bond can be classified as being weak. 相似文献
176.
177.
178.
Maurice J. Dupré James F. Glazebrook Emma Previato 《Complex Analysis and Operator Theory》2013,7(6):1713-1734
Several features of an analytic (infinite-dimensional) Grassmannian of (commensurable) subspaces of a Hilbert space were developed in the context of integrable PDEs (KP hierarchy). We extended some of those features when polarized separable Hilbert spaces are generalized to a class of polarized Hilbert modules and then consider the classical Baker and τ-functions as operator-valued. Following from Part I we produce a pre-determinant structure for a class of τ-functions defined in the setting of the similarity class of projections of a certain Banach *-algebra. This structure is explicitly derived from the transition map of a corresponding principal bundle. The determinant of this map leads to an operator τ-function. We extend to this setting the operator cross-ratio which had previously been used to produce the scalar-valued τ-function, as well as the associated notion of a Schwarzian derivative along curves inside the space of similarity classes of a given projection. We link directly this cross-ratio with Fay’s trisecant identity for the τ-function. By restriction to the image of the Krichever map, we use the Schwarzian to introduce the notion of an operator-valued projective structure on a compact Riemann surface: this allows a deformation inside the Grassmannian (as it varies its complex structure). Lastly, we use our identification of the Jacobian of the Riemann surface in terms of extensions of the Burchnall–Chaundy C*-algebra (Part I) provides a link to the study of the KP hierarchy. 相似文献
179.
Maurice A. de Gosson 《偏微分方程通讯》2013,38(11):2096-2104
180.
In an attempt to crystallize Ce[ReO4]4 · xH2O from aqueous solutions of equimolar amounts of Ce[SO4]2 and Ba[ReO4]2 via salt‐metathesis the serendipitous formation of colorless, transparent, rod‐shaped single crystals of CaNa[ReO4]3 was observed as a result of calcium and sodium impurities within the improperly deionized water used. Structure analysis by X‐ray diffraction lead to the conclusion that the title compound crystallizes in the ThCd[MoO4]3 structure type with the hexagonal space group P63/m and the lattice parameters a = 991.74(6) pm, c = 636.53(4) pm, c/a = 0.642 for Z = 2. The crystal structure contains purely oxygen surrounded and crystallographically unique cations, namely Ca2+ in tricapped trigonal prismatic (d(Ca–O) = 6 × 249 pm + 3 × 254 pm), Na+ in octahedral (d(Na–O) = 6 × 241 pm), and Re7+ in tetrahedral coordination (d(Re–O) = 171–173 pm). Furthermore, it was possible to yield an almost phase‐pure microcrystalline powder of the title compound from a melt of equimolar amounts of Na[ReO4] and Ca[ReO4]2 stemming from aquatically obtained precursors. 相似文献