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101.
Mehta MA Eddy MT McNeill SA Mills FD Long JR 《Journal of the American Chemical Society》2008,130(7):2202-2212
Several approaches for utilizing dipolar recoupling solid-state NMR (ssNMR) techniques to determine local structure at high resolution in peptides and proteins have been developed. However, many of these techniques measure only one torsion angle or are accurate for only certain classes of secondary structure. Additionally, the efficiency with which these dipolar recoupling experiments suppress the deleterious effects of chemical shift anisotropy (CSA) at high magnetic field strengths varies. Dipolar recoupling with a windowless sequence (DRAWS) has proven to be an effective pulse sequence for exciting double-quantum (DQ) coherences between adjacent carbonyl carbons along the peptide backbone. By allowing this DQ coherence to evolve, it is possible to measure the relative orientations of the CSA tensors and subsequently use this information to determine the Ramachandran torsion angles phi and psi. Here, we explore the accuracies of the assumptions made in interpreting DQ-DRAWS data and demonstrate their fidelity in measuring torsion angles corresponding to a variety of secondary structures irrespective of hydrogen-bonding patterns. It is shown how a simple choice of isotopic labels and experimental conditions allows accurate measurement of backbone secondary structures without any prior knowledge. This approach is considerably more sensitive for determining structure in helices and has comparable accuracy for beta-sheet and extended conformations relative to other methods. We also illustrate the ability of DQ-DRAWS to distinguish between structures in heterogeneous samples. 相似文献
102.
Monot J Petit M Lane SM Guisle I Léger J Tellier C Talham DR Bujoli B 《Journal of the American Chemical Society》2008,130(19):6243-6251
Terminal phosphate groups on double-stranded DNA probes bind strongly to glass substrates coated with a zirconium phosphonate monolayer, and probes immobilized in this way as microarrays can be used to detect protein targets. The sensitivity of the microarray was shown to be enhanced by the use of a polyguanine segment ((G)n , n > or = 5) as a spacer between the phosphate linker and the protein interaction domain. More importantly, the presence of phosphate linkers on both ends of the dsDNA probes leads to significant enhancement of target capture. The relevant characteristics of the different probes when bound to the surface were determined, by the original use of a combination of surface characterization techniques (XPS, AFM, and Sarfus). In this context, the location of the phosphate linkers in the duplex probes was found to result in different probe surface coverage and presentation on the surface, which affect subsequent interactions with the target protein. 相似文献
103.
Audrey Boutonnet Arnaud Morin Pierre Petit Patricia Vicendo Véréna Poinsot François Couderc 《Analytica chimica acta》2016
Pulsed lasers are widely used in capillary electrophoresis (CE) studies to provide laser induced fluorescence (LIF) detection. Unfortunately pulsed lasers do not give linear calibration curves over a wide range of concentrations. While this does not prevent their use in CE/LIF studies, the non-linear behavior must be understood. Using 7-hydroxycoumarin (7-HC) (10–5000 nM), Tamra (10–5000 nM) and tryptophan (1–200 μM) as dyes, we observe that continuous lasers and LEDs result in linear calibration curves, while pulsed lasers give polynomial ones. The effect is seen with both visible light (530 nm) and with UV light (355 nm, 266 nm). In this work we point out the formation of byproducts induced by pulsed laser upon irradiation of 7-HC. Their separation by CE using two Zeta LIF detectors clearly shows that this process is related to the first laser detection. All of these photodegradation products can be identified by an ESI-/MS investigation and correspond to at least two 7HC dimers. By using the photodegradation model proposed by Heywood and Farnsworth (2010) and by taking into account the 7-HC results and the fact that in our system we do not have a constant concentration of fluorophore, it is possible to propose a new photochemical model of fluorescence in LIF detection. The model, like the experiment, shows that it is difficult to obtain linear quantitation curves with pulsed lasers while UV-LEDs used in continuous mode have this advantage. They are a good alternative to UV pulsed lasers. An application involving the separation and linear quantification of oligosaccharides labeled with 2-aminobezoic acid is presented using HILIC and LED (365 nm) induced fluorescence. 相似文献
104.
Functional G-quartet macroscopic membrane films 总被引:1,自引:0,他引:1
Arnal-Hérault C Pasc A Michau M Cot D Petit E Barboiu M 《Angewandte Chemie (International ed. in English)》2007,46(44):8409-8413
105.
106.
Density functional theory calculations were performed to obtain the structures, vertical electron affinities, and adiabatic affinities of 15 polychlorinated dibenzo-p-dioxins (PCDDs), including several extremely toxic congeners. A three-parameter hybrid density functional, B3LYP, was utilized with two different basis sets, 6-311G(d,p) and 6-311+G(2d,2p). The optimized structures of all PCDDs under consideration were planar, while all corresponding anions attained nonplanar geometries. One of the C-Cl bonds on each PCDD anion was considerably elongated, and the dechlorination of PCDDs occurred as the departing chlorine bent off the aromatic ring plane for effective pi-sigma orbital mixing. The characteristic electron energy-dependent regioselective chloride ion loss channels for 1,2,3,7,8-pentaCDD were elucidated by transition-state theory calculations. The relative low-energy barrier for the dechlorination of 1,2,3,7,8-pentaCDD indicated the high likelihood of obtaining reductive dechlorination (RD) products that are more toxic than the parent species. The calculated vertical electron affinities of PCDDs are consistent with the available experimental attachment energies, and the positive adiabatic electron affinities suggest that PCDDs may act as electron acceptors in living cells. 相似文献
107.
Fuentes-Cabrera M Sumpter BG Sponer JE Sponer J Petit L Wells JC 《The journal of physical chemistry. B》2007,111(4):870-879
M-DNA is a type of metalated DNA that forms at high pH and in the presence of Zn, Ni, and Co, with the metals placed in between each base pair, as in G-Zn-C. Experiments have found that M-DNA could be a promising candidate for a variety of nanotechnological applications, as it is speculated that the metal d-states enhance the conductivity, but controversy still clouds these findings. In this paper, we carry out a comprehensive ab initio study of eight G-Zn-C models in the gas phase to help discern the structure and electronic properties of Zn-DNA. Specifically, we study whether a model prefers to be planar and has electronic properties that correlate with Zn-DNA having a metallic-like conductivity. Out of all the studied models, there is only one which preserves its planarity upon full geometry optimization. Nevertheless, starting from this model, one can deduce a parallel Zn-DNA architecture only. This duplex would contain the imino proton, in contrast to what has been proposed experimentally. Among the nonplanar models, there is one that requires less than 8 kcal/mol to flatten (both in gas and solvent conditions), and we propose that it is a plausible model for building an antiparallel duplex. In this duplex, the imino proton would be replaced by Zn, in accordance with experimental models. Neither planar nor nonplanar models have electronic properties that correlate with Zn-DNA having a metallic-like conductivity due to Zn d-states. To understand whether density functional theory (DFT) can describe appropriately the electronic properties of M-DNAs, we have investigated the electronic properties of G-Co-C base pairs. We have found that when self-interaction corrections (SIC) are not included the HOMO state contains Co d-levels, whereas these levels are moved below the HOMO state when SIC are considered. This result indicates that caution should be exercised when studying the electronic properties of M-DNAs with functionals that do not account for strong electronic correlations. 相似文献
108.
Let G be an abelian group, ε an anti-bicharacter of G and L a G-graded ε Lie algebra (color Lie algebra) over a field of characteristic zero. We prove that for all G-graded, positively filtered A such that the associated graded algebra is isomorphic to the G-graded ε-symmetric algebra S(L), there is a G- graded ε-Lie algebra L and a G-graded scalar two cocycle , such that A is isomorphic to U
ω
(L) the generalized enveloping algebra of L associated with ω. We also prove there is an isomorphism of graded spaces between the Hochschild cohomology of the generalized universal enveloping
algebra U(L) and the generalized cohomology of the color Lie algebra L.
Supported by the EC project Liegrits MCRTN 505078. 相似文献
109.
N. Fraysse H. Thomé L. Petit 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):615-619
Humidity is well-known to significantly affect the mechanical properties, static as well as dynamic, of granular materials.
We present the method of humidification of granular media from an under-saturated vapor that we designed in order to experimentally
quantify such moisture-induced effects under accurately-controlled humidity conditions. We report the quantitative measurements
of the maximum angle of stability of a pile made of small glass beads, as a function of the relative vapor pressure, up to
close to saturation. The results obtained with liquids differing in their wetting properties on glass, namely water and heptane,
are presented. It is shown that the wetting properties of the liquid on the grains have a strong influence on the cohesion
of the non-saturated granular medium.
Received 26 October 1998 and Received in final form 30 March 1999 相似文献
110.
The determination of cadmium in different samples such as coal fly ashes, soils and sediments by Graphite Furnace Atomic
Absorption Spectrometry (GFAAS) was studied. The best analytical conditions and instrumental parameters were deduced. Different
types of matrix modifiers were tested and an optimization of several conditions (pyrolysis and atomization temperatures, heating
rate, use of L’vov platform, etc.) was carried out. A mixture of 2% NH4H2PO4 + 0.4% Mg(NO3)2 in 0.5 mol L–1 HNO3 as matrix modifier provided the highest sensitivity and an efficient behaviour for the three types of samples. A detection
limit of 26 ng g–1 was achieved and other figures of merit are shown. Analytical results obtained by direct calibration using standard samples
prepared in the laboratory and by standard addition method were comparable.
Received: 6 November 1998 / Revised: 4 February 1999 / Accepted: 9 February 1999 相似文献