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排序方式: 共有470条查询结果,搜索用时 15 毫秒
461.
Coggins MK Toledo S Shaffer E Kaminsky W Shearer J Kovacs JA 《Inorganic chemistry》2012,51(12):6633-6644
The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([Mn(II)(S(Me2)N(4)(6-Me-DPEN))](BF(4)) (1), [Mn(II)(S(Me2)N(4)(6-Me-DPPN))](BPh(4))·MeCN (3), [Mn(II)(S(Me2)N(4)(2-QuinoPN))](PF(6))·MeCN·Et(2)O (4), and [Mn(II)(S(Me2)N(4)(6-H-DPEN)(MeOH)](BPh(4)) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally related to recently reported [Mn(II)(S(Me2)N(4)(2-QuinoEN))](PF(6)) (2) (Coggins, M. K.; Kovacs, J. A. J. Am. Chem. Soc.2011, 133, 12470). Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [Mn(III)(S(Me2)N(4)(6-Me-DPEN)](2)-(μ-O)(BF(4))(2)·2MeOH (6), [Mn(III)(S(Me2)N(4)(QuinoEN)](2)-(μ-O)(PF(6))(2)·Et(2)O (7), [Mn(III)(S(Me2)N(4)(6-Me-DPPN)](2)-(μ-O)(BPh(4))(2) (8), [Mn(III)(S(Me2)N(4)(QuinoPN)](2)-(μ-O)(BPh(4))(2) (9), and [Mn(III)(S(Me2)N(4)(6-H-DPEN)](2)-(μ-O)(PF(6))(2)·2MeCN (10). Labeling studies show that the oxo atom is derived from (18)O(2). Ligand modifications, involving either the insertion of a methylene into the backbone or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of μ-oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to μ-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species. 相似文献
462.
Marie R Beech JP Vörös J Tegenfeldt JO Höök F 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10103-10108
By utilizing flow-controlled PLL-g-PEG and PLL-g-PEGbiotin modification of predefined regions of a poly(dimethylsiloxane) (PDMS) micro-fluidic device, with an intentionally chosen large (approximately 1 cm2) internal surface area, we report rapid (10 min), highly localized (6 x 10(-6) cm2), and specific surface-based protein capture from a sample volume (100 microL) containing a low amount of protein (160 attomol in pure buffer and 400 attomol in serum). The design criteria for this surface modification were achieved using QCM-D (quartz crystal microbalance with energy dissipation monitoring) of serum protein adsorption onto PLL-g-PEG-modified oxidized PDMS. Equally good, or almost as good, results were obtained for oxidized SU-8, Topas, and poly(methyl metacrylate) (PMMA), demonstrating the generic potential of PLL-g-PEG for surface modification in various micro-fluidic applications. 相似文献
463.
We have theoretically studied the oxidative addition of HX and X(2) to palladium for X = F, Cl, Br, I and At, using both nonrelativistic and ZORA-relativistic density functional theory at BLYP/QZ4P. The purpose is 3-fold: (i) to obtain a set of consistent potential energy surfaces (PESs) to infer accurate trends in reactivity for simple, archetypal oxidative addition reactions; (ii) to assess how relativistic effects modify these trends along X = F, Cl, Br, I and At; and (iii) to rationalize the trends in reactivity in terms of the reactants' molecular-orbital (MO) electronic structure and the H-X and X-X bond strengths. For the latter, we provide full Dirac-Coulomb CCSD(T) benchmarks. All oxidative additions to Pd are exothermic and have a negative overall barrier, except that of HF which is approximately thermoneutral and has a positive overall barrier. The activation barriers of the HX oxidative additions decrease systematically as X descends in group 17 of the periodic table; those of X(2) first increase, from F to Cl, but then also decrease further down group 17. On the other hand, HX and X(2) show clearly opposite trends regarding the heat of reaction: that of HX becomes more exothermic and that of X(2) less exothermic as X descends in group 17. Relativistic effects can be as large as 15-20 kcal/mol but they do not change the qualitative trends. Interestingly, the influence of relativistic effects on activation barriers and heats of reaction decreases for the heavier halogens due to counteracting relativistic effects in palladium and the halogens. 相似文献
464.
Lugo-Mas P Dey A Xu L Davin SD Benedict J Kaminsky W Hodgson KO Hedman B Solomon EI Kovacs JA 《Journal of the American Chemical Society》2006,128(34):11211-11221
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466.
We present a comparative study of xanthorhodopsin, a proton pump with the carotenoid salinixanthin serving as an antenna, and the closely related bacteriorhodopsin. Upon excitation of retinal, xanthorhodopsin exhibits a wavy transient absorption pattern in the region between 470 and 540 nm. We interpret this signal as due to electrochromic effect of the transient electric field of excited retinal on salinixanthin. The spectral shift decreases during the retinal dynamics through the ultrafast part of the photocycle. Differences in dynamics of bacteriorhodopsin and xanthorhodopsin are discussed. 相似文献
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469.
Attila Kovacs 《ChemInform》2002,33(30):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
470.
Farideh Jalilehvand Mikhail Maliarik Janos Mink Magnus Sandstroem Andrey Ilyukhin Julius Glaser 《ChemInform》2002,33(27):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献